Anatomy Flashcards
Spinal cord arterial supply from aorta to small vessels
Aorta –> lumbar arteries/intercostal arteries/vertebral arteries –> segmental spinal artery –> dorsal/ventral root artery –> irregular vascular ring, dorsolateral spinal arteries, ventral spinal artery
Irregular vascular ring –> radial arteries
Venral spinal artery –> vertical artery
Inner zone - vertical artery (mostly gray, some white matter); middle zone - vertical and radial arteries; outer zone - radial arteries (white matter)
King
Connective tissue and epithelial cells of the dura, arachnoid and pia
Dura: Dense connective tissue, inner simple squamous epithelial cells
Arachnoid - delicate collagenous connective tissue, inner and outer simple squamous epithelial cells
Pia - outer simple squamous epithelium, inner connective tissue
Between spinal roots: pia + arachnoid are joined and connected to the dura via denticulate ligament
King
What sinuses make up the dorsal system of cranial venous sinuses?
What sinuses make up the ventral system of cranial venous sinuses?
What sinuses make up the connecting sinuses?
Dorsal: dorsal forebrain/deep forebrain –> dorsal cerebral vein and great cerebral vein –> dorsal saggital sinus and straight sinus –> transverse sinus –> SIGMOID SINUS
Ventral: Ventral forebrain –> ventral cerebral vein –> cavernous sinus, petrosal sinus –> SIGMOID SINUS
Connecting: Sigmoid sinus (also called connecting sinus) –> maxillary vein
King’s
Pathway for the superficial and deep cerebral veins
Superficial:
- superficial cerebral veins –> dorsal cerebral veins and ventral cerebral veins
- Dorsal cerebral veins –> dorsal system of cranial venous sinuses –> transverse sinus
- Ventral cerebral veins –> ventral system of cranial venous sinuses –> petrosal sinus
Deep: Deep cerebral veins –> great cerebral vein –> straight sinus –> transverse sinus
King’s
Pathway of spinal cord veins –> systemic venous return
veins of the spinal cord –> ventral spinal vein (w/ ventral spinal artery) or veins on the surface of the spinal cord –> both drain into veins that accompany nerve roots –> vertebral venous sinus –> intervertebral veins (through foramnia, have valves) –> vertebral veins, azygous vein, caudal vena cava
venous blood from the vertebral bodies also drains into the vertebral venous sinus
King’s
When do the epiphysis of the vertebral body appear? When is fusion complete?
How many ossification centers does a vertebrae have?
Appear @ 2-8 weeks
Complete fusion @ 14 mos
Vertebrae has 3 ossification centers: 1 body, 2 laminae
Big Miller’s
What makes up the vertebral arch?
What processes are found on all vertebral arches?
Vertebral arch = 2 pedicles + 2 laminae
- each pedicle has a cranial and caudal vertebral notch - when articulated they form the intervertebral foramen
- each laminae unites dorsally at the spinous process (actually 2 spinous processes that are completely fused)
- processes
- transverse process (junction of pedicle and body)
- cranial and caudal articular processes (junction of pedicle and laminae)
- cranial articular process points craniodorsal/medial
- caudal articular process points caudoventral/lateral
Big Miller’s
What is the transverse foramen of the vertebrae? Where is it absent?
Foramen at the root of the transverse process of the cervical vertebrae EXCEPT C7
- The transverse foramen divides the transverse process into dorsal and ventral components
- The dorsal part is homologous to the transverse process of the other vertebrae
- the ventral part is homologous to the rib
Big Miller’s
The ____ of the atlas unite the dorsal and ventral arch
The _____ of the atlas articulates with the occipital condyles
The _____ of the atlas articulates with the axis
lateral mass
- AKA body of the atlas
- formed by intercentrum I
- The transverse processes (wings) project from the lateral masses
cranial articular fovea (forms the yes joint)
caudal articular fovea
- the dorsal surface of the ventral arch of the atlas contains the fovea of the dens
Big Miller’s
What are the 3 foramen of the atlas
Where is the alar notch located and what runs there?
- Vertebral foramen for the spinal cord
- Alar foramen - short canal passes through the transverse process for the vertebral artery and vein
- Lateral vertebral foramen - canal through the craniodorsal vertebral arch for C1 and vertebral artery
Alar notch - cranial border at the base of the transverse process, vertebral artery runs here
Big Miller’s
What forms centrum 1 of the axis?
Where are the cranial articular processes of the axis?
Where are the caudal articular processes of the axis?
Centrum 1 = dens + cranial articular surface
Cranial articular surfaces of the axis are located laterally on the expanded cranial end of the VERTEBRAL BODY
Caudal articular processes are ventrolateral extensions of the VERTEBRAL ARCH and spinous processes that face ventrally
The dens develops from which 2 ossification centers?
Centrum of the proatlas and centrum 1
- Proatlas (centrum of the proatlas) = transient ossification at the apical tip of the dens, ossified around 42 days post partum and fuses with the dens around 100 days post partum (significant variation)
- Centrum 1 - forms the cranial articular surface of the axis body and the dens
- Ossification first seen at 1-3 weeks
Big Miller’s
What are the 3 ossification centers of the atlas
- Intercentrum 1 = ventral arch
- Pair of neural arches that become the dorsal arch and transverse processes
Big Miller’s
What are the ossification centers of the body of the axis called? (3)
Intercentrum 2
- Fuses with centrum 1 (dens and cranial articular surface) at 7-9 mos
- Narrow ossification center between the ossification centers of centrum 1 and centrum 2
Centrum 2
- Forms the central region of the body of the axis
Caudal epiphyseal ossification center
DeLahunta
Embryology of the vestibular system?
- Derived from ectoderm, contained within mesodermally derived structure
-
Otic placode: proliferation of ectodermal epithelial cells on the surface of the embryo, adjacent to the developing rhombencephalon
- Subsequently invaginates –> otic pit and otic vesicle (otocyst) –> breaks away from its attachment to the surface ectoderm
- Saccular structure undergoes extensive modification of its shape, always retains its fluid filled lumen and surrounding thin epithelial walls as it becomes the membranous labyrinth of the inner ear
- Special modifications of its epithelial surface at predetermined sites form the receptor organs for the vestibular and auditory systems
- Corresponding developmental modifications occur in the surrounding paraxial mesoderm –> provide supporting capsule for the membranous labyrinth
- Fluid-filled ossified structure is the bony labyrinth contained within the developing petrous portion of the temporal bone
(DeLahunta)
What are the 3 components of the bony labyrinth and 4 components of the membranous labyrinth? What kind of fluid is each filled with?
Bony labyrinth of petrous temporal bone (mesodermal origin)
- Vestibule - With vestibular window (stapes inserted here)
- 3 semicircular canals - Each contains a dilation = ampulla
- Cochlea - With cochlear window
- All 3 contain PERILYMPH - Similar to CSF
Membranous labyrinth - ECTODERMAL origin
- Filled with endolymph
- 3 Semicircular ducts with ampullae
- Utriculus + saccule - Within the bony vestibule
- Cochlear duct
Within the membranous labyrinth:
- Semicircular ducts connect with?
- Utriculus connects to saccule by?
- Saccule connects with the cochlear duct by?
Semicircular ducts connect with the utriculus
Utriculus and saccule connect to each other via the endolymphatic duct and sac
Saccule connects with the cochlea via small ductus reuniens
(deLahunta)
What kind of movement do the crista ampullaris semicircular ducts detect? What is the mechanism?
Semicircular ducts detect acceleration and deceleration (especially when the head is rotated)
Rotation of the head to the right: endolymph flows in the right lateral duct –> right cupula is deflected toward the right utriculus –> deviation of the stereocilia toward the kinocilium –> increased activity of the right vestibular neuron
Rotation of the head to the right: Left cupula deflected away from the left utriculus –> deviation of the stereocilia AWAY from the kinocilium –> decreased activity of the left vestibular neurons
Jerk nystagmus to the right
Stereocilia bends towards the kinocilium - does this cause hyperpolarization or depolarization of the vestibular nerve?
Stereocilia + kinocilium bend in the direction of the kinocilium –> opens K+ channels –> influx of K+ and depolarization
Depolarized hair cell –> influx of Ca –> release of glutamate and aspartate –> stimulates vestibular nerve
Where are the macula found? What do they detect and what is the receptor mechanism?
Utriculus
- Oriented horizontally - detects gravity
Saccule
- Oriented vertically - detects deceleration/acceleration
Stereocilia and kinocilium project into the otolithic membrane –> movement of the statoconia AWAY from the hair cells –> bends stereocilia –> impulse in the dendritic zones
What type of neurons make up the vestibular portion of CN 8? Where are the cell bodies located?
Where do the axons of CN 8 enter the CNS?
Once they enter the CNS, what are the 2 possible locations vestibular CN 8 axons will synapse?
Bipolar sensory neurons
Cell bodies are inserted along the course of the axons within the petrous temporal bone = vestibular ganglion
CN 8 enters @ internal acoustic meatus –> lateral surface of the rostral medulla @ the level of the trapezoid body attachment to the caudal cerebellar peduncle
Synapse on:
- Vestibular nuclei
- Caudal cerebellar peduncle –> cerebellum (fastigal nucleus or flocculonodular lobe)
(DeLahunta)
What is the orientation of the 4 vestibular nuclei?
Where does each nucleus project?
Rostral: small, medial
- continues as the medial vestibulospinal tract
Medial: long, medial
- contributes to medial vestibulospinal tract
Lateral: short, lateral
- Continues as the lateral vestibulospinal tract
Caudal: Long, lateral
- continues as the medial vestibulospinal tract
** all are dorsal to the CN VII and CN V GSE neurons/tracts
** Just caudal to the medial and caudal vestibular nuclei is the lateral cuneate nucleus
Lateral vestibulospinal tract
- Where are cell bodies located?
- Travels in which funiculus
- Terminates at?
- Function?
Lateral vestibulospinal tract
- Cell bodies located in the lateral vestibular nucleus
- Courses in the ipsilateral ventral funiculus throughout entire spinal cord
- Axons terminate on INTERNEURONS of the ventral gray columns of all spinal cord segments
- Interneurons are facilitatory to ipsilateral alpha/gamma motor neurons to extensor muscles
- Interneurons are inhibitory to ipsilateral flexor muscles
- Crosses to interneurons that are inhibitory to contralateral alpha/gamma motor neurons of extensors
- Effect of stimulation of the lateral vestibulospinal tract is ipsilateral extensor tonus and inhibition of contralateral extensor tonus
The vestibular nuclei are facilitatory to the vestibulospinal tracts
Medial vestibulospinal tract
- Cell bodies located?
- Travels in which funiculus
- Terminates at?
- Function?
Medial vestibulospinal tract
- Cell bodies in the rostral, medial, and caudal vestibular nuclei
- Ipsilateral ventral funiculus (medial longitudinal fasiculus)
- Terminates on interneurons in the cervical and cranial thoracic spinal cord segments –> alpha and gamma motor neurons
- Controls muscles of the neck (head turn/tilt towards side of vestibular dysfunction)
- The vestibular nuclei are facilitatory to the vestibulospinal tracts
Vesibular nuclei projections within the brainstem (3)
1.
How doo the vestibular nuclei connect with the cerebellum?
Vestibular nuclei and ganglia –> caudal cerebellar peduncle –> cerebellum
- Cortex of the flocculus of the hemisphere
- Nodulus of the vermis
- Fastigal nucleus
** projections from the vestibular nuclei to and from the cerebellum are ipsilateral (this is unique among extrapyramidal centers) –> correlate this with the fact that the vestibulospinal tract does NOT decussate
Postrotary nystagmus: which direction is the fast phase?
Caloric nystagmus - normally induces a jerk nystagmus toward/opposite the ear being stimulated
Quick phase of the nystagmus is directed opposite the direction of rotation
Caloric nystagmus - normally induces a jerk nystagmus to the side opposite the ear being stimulated
How does experimental ablation of the fastigal nucleus affect the vestibular system?
Clinical signs of vestibular system dysfunction can occur if _________________ regions of C1-3 are interrupted
Ablation of the fastigal nucleus –> inhibition of the ipsilateral vestibular nuclei –> vestibular signs
Spinal nerve dorsal roots or dorsal gray matter of the first 3 cervical spinal cord segments interrupted –> ipsilateral vestibular dysfunction
Spinal cord lesions that interrupt the spinovestibular tracts may have the same effect
Between the brain and spinal cord, where does the dura mater start to adhere to the periosteum?
The terminal branches of the vertebral arteries pass through the _____________ to enter the vertebral canal at the atlas, then join the ventral spinal artery to form the basilar artery
Where do the internal carotid arteries enter the skull?
First 1-2 cervical vertebrae, and to the atlantooccipital membrane
The terminal branches of the vertebral arteries pass through the lateral vertebral foramina to enter the vertebral canal at the atlas, then join the ventral spinal artery to form the basilar artery
Internal carotid arteries: enter the carotid canal at the tympanic part of the temporal bone –> foramen lacerum –> tympanooccipital fissure –> through cavernous venous sinus
** between the hypophysis and optic chiasm, the internal carotid artery emerges through the dura –> rostral cerebral, middle cerebral, caudal communicating arteries
Which artery runs between the two frontal lobes?
Rostral cerebral arteries –> course dorsally between the 2 frontal lobes in the longitudinal cerebral fissure –> dorsally over the genu of the corpus callosum to supply the rostral gyri on the medial cerebral hemisphere
** terminal branches anastamose with branches of the middle cerebral artery on the dorsomedial cortex
Where does the middle cerebral artery branch from the arterial circle?
What are the major branches?
Rostral hypophysis: Courses laterally, rostral to the piriform lobe –> dorsolateral over the surface of the cerebral hemisphere –> branches supply the entire lateral hemisphere
- Terminal branches anastamose with those of the rostral and caudal cerebral arteries along the dorsomedial gyri of the cerebral hemisphere
- Rostral choroidal artery - arises at the origin of the middle cerebral artery –> medial surface of the piriform lobe –> ventro-rostral hippocampus –> choroid plexus of the lateral ventricle
- Striate branches - supply the basal nuclei, rostral thalamus, white matter tracts within the cerebral hemisphere (internal capsule)
Where does the caudal cerebral artery leave the cerebral arterial circle?
Where can it be found?
What does it supply?
Leave the circle at the caudal hypophysis (rostral to the oculomotor nerve)
- Courses caudo-dorso-medially following the optic tract to the longitudinal cerebral fissure
- Continues rostrally on the caudal aspect of the corpus callosum
- Branches anastamose with the rostral and middle cerebral arteries medially
- Supplies the caudal cerebral hemisphere, diencephalon, rostral mesencephalon
Where does the rostral cerebellar artery leave the arterial circle?
Where does it run?
What does it supply?
What are its branches?
Rostral cerebellar artery
- Leaves the caudal communicating artery of the arterial circle caudal to the oculomotor nerve
- Course dorsocaudally along the pons and middle cerebellar peduncle to the cerebellar hemisphere
- Supplies the caudal midbrain and rostral half of the cerebellum
- Branches: medial, lateral, intermediate
Where does the basilar artery anastamose with the caudal communicating branches of the internal carotid artery?
Where does the caudal cerebellar artery leave the basilar artery?
What other branches come off the basilar artery?
At the level of the rostral border of the transverse fibers of the pons
Caudal cerebellar artery
- Branch of the basilar artery near the middle of the medulla
- Courses dorsally to supply the caudal portion of the cerebellum
Labyrinthe artery
- Branches from the basilar artery and follows the vestibulocochlear nerve through the internal acoustic meatus adjacent to the inner ear
Basilar medullary and pontine branches penetrate the adjacent parenchyma
What are the 4 veins that receive blood from the intracranial sinuses?
At its caudal extend, the dorsal sagittal sinus enters the __________ in the occipital bone, then what?
What vessels drain into the dorsal sagittal sinus?
- Maxillary
- internal jugular
- vertebral veins
- Ventral internal vertebral venous plexus
Enteres the foramen for the dorsal sagittal sinus in the occipital bone, then:
- Joins the left and right transverse sinuses at the confluens of the sinuses
The dorsal sagittal sinus receives branches from the dorsal surface of each hemisphere and many of the diploic veins
ROSTRALLY it is formed by the right and left veins of the nasal cavity
What forms the straight sinus, and where does it drain?
Where is the transverse sinus found? What does it divide into?
Great cerebral vein + vein of the corpus callosum forms the straight sinus
It drains into the dorsal sagittal sinus (either before or after the foramen)
Transverse sinus: runs through the transverse canal and sulcus
Divides into a temporal sinus and sigmoid sinus
Where does the temporal sinus leave the cranial vault?
Where does the sigmoid sinus leave the cranial vault?
What do these 2 sinuses have in common?
Temporal sinus - leaves @ the retroarticular foramen within the petrosal bone –> “emissary vein of the retroarticular foramen” –> maxillary vein
Sigmoid sinus - leaves @ jugular foramen, then TOF –> joins ventral petrosal sinus –> vertebral and internal jugular veins
Transverse sinus –> temporal sinus and sigmoid sinus
Where is the vertebral vein found?
Where does the basilar sinus branch from?
Vertebral vein descends the neck in the transverse foramen of the cervical vertebrae
Basilar sinus is a branch of the sigmoid sinus –> condyloid canal –> ventral internal vertebral venous plexus in the vertebral canal
What are the rostral and caudal extents of the cavernous sinus?
What veins drain into the cavernous sinus?
Rostral: orbital fissure. Caudal: petrooccipital canal
Connects with ophthalmic plexus rostrally and maxillary veins laterally
Drains causally to the ventral petrosal sinus –> sigmoid sinus –> basilar sinus
2-3 intercavernous sinuses run between the right and left cavernous sinuses
At each intervertebral foramen, the intervertebral veins connect the ventral internal vertebral venous plexus with the?
Vertebral veins of the neck
Intercostal veins of the thorax –> azygous and costocervical veins
Lumbar veins –> caudal vena cava
The frontal lobe is the portion of each hemisphere rostral to the ______________
Landmarks for the parietal lobe?
Part of the cortex functions as the auditory ad vestibular system cortex
Rostral to the cruciate sulcus
- The precruciate gyrus is part of this lobe - functions in motor cortex
Parietal lobe - caudal to the cruciate sulcus, dorsal to the sylvian gyrus, (no defined caudal boundary, extends causally to the caudal 1/3 of the cerebral hemisphere)
- Postcruciate and rostral suprasylvian gyri found in this lobe
Occipital lobe - caudal 1/3 of cerebral hemispheres
Temporal cortex - sylvian gyri function as the auditory ad vestibular system cortex
What sulcus separates the phylogenetically new cerebrum from the older olfactory cerebrum?
Rhinal sulcus
What embryonic structure becomes the choroid plexus?
Choroid plexus develops where the neural tube neuroepithelium did not proliferate to form neuroparenchyma but remained as a single layer of ependymal neuroepithelial cells = roof plate
The layer of ependymal neuroepithelial cells and the adjacent pia = tela choroidea
Associaed proliferation of capillaries = choroid plexus
Roof plate of the medulla = choroid plexus in the 4th ventricle
Roof plate of the diencephalon = choroid plexus of the 3rd ventricle
Roof plate of the telencephalon = choroid plexus of the lateral ventricles
What comprises the metathalamus?
How does the metathalamus connect to the midbrain?
2 geniculate bodies
- located lateral and dorsocaudal to the thalamus
Lateral geniculate connects to the rostral colliculus via brachium
Medial geniculate connects to the caudal colliculus via brachium
What tract connects the hypothalamus to the habenular nucleus?
Stria habenularis - lies on either side of midline, courses dorsally and caudally from the rostroventral aspect of the hypothalamus over the thalamus to the dorsocaudal aspect of the diencephalon and enters the habenular nucleus
- Considered part of the EPITHALAMUS
There is a thin remnant of the roof plate of the neural tube that extends from one stria habenularis to the other, covered by a thin layer of pia mater
Where is the pineal body found?
Subarachnoid space dorsal to the mesencephalon @ the level of the mesencephalic aqueduct
Single, unpaired
What is the anatomic relationship of the 3 cerebellar peduncles?
Middle cerebellar peduncle = most lateral
Caudal cerebellar peduncle = Medial and caudal
Rostral cerebellar peduncle = most medial and rostral
12: rostral
11: caudal
10 : middle
Where are the habenular nuclei located?
Dorsal aspect of the thalamus, adjacent to the third ventricle, at the level of the interthalamic adhesion and pituitary gland
Where in the nervous system is canabinoid receptor primarily found?
CB1 receptor found in the dorsal horn
- CB1 receptors inhibit voltage-gated calcium channels, decrease excitatory acetylcholine neurotransmitters, increase GABA neurotransmission
CB2 receptors found primarily in immune cells
- Activation of CB2R receptors do not cause the effects on mentation that activation of CB1R produces - has become a target for therapeutic use in human medicine by reducing inflammation, immune suppression, and as chemotherapeutic
(ACVIM 2017)
How does respiration and cardiac function influence ICP?
A pressure fluctuation of 1-2mmH20 is normally associated with arterial pulse in humans
Inspiration –> fall in CSF pressure (the amplitude is extremely variable)
In pathological ICP elevations - these fluctuations in CSF pressure become very marked
If there is a sudden increase in intracranial blood volume, CSF can be momentarily accommodated into the cervical subarachnoid space
(DeTerlizzi)
T/F; hormone releasing factors (TRH, CRH, GHRH, GNRH) are released into the CSF of the third ventricle and carried via CSF to the median eminence
True
The CSF is a vehicle for the intracerebral transport of biologically active substances
Intracerebral transport of opioids and other neuroactive substances from systemic circulation occurs as well
(DeTerlizzi)
What are the 2 regions of the lateral ventricle?
The lateral recesses open into the?
- Rostral horn
- Temporal horn
Subarachnoid space
Also median aperture (obex) opens into subarachnoid space, unclear if this is present in the dog?
(DeTerlizzi)
What are the 3 tissue interfaces of the brain that control the composition of CSF and interstitial fluid??
- Blood brain barrier
- Blood CSF barrier
- CSF brain barrier
(DeTerlizzi)
________________ is at the dorsal surface of the medulla at the caudal end of the 4th ventricle, implicated as a chemoreceptor trigger zone for emesis.
What three characteristics of fluid does it detect?
Area postrema
- Anatomically positioned to detect toxins in the blood and CSF
- Helps monitor and control changes in body fluid compositions such as:
- Plasma osmolality
- Glucose concentration
- Electrolyte concentration
(DeTerlizzi)
Which structure of the inner ear connects with the subarachnoid space?
Cochlear aqueduct, lies between scala tympani and the subarachnoid space
2 components of tight junctions responsible for lack of permeability of the BBB
- Zona occludens associated proteins
- Cingulin
(DeTerlizzi)
BBB and blood CSF barrier are:
- Highly permeable to? (4)
- Slightly permeable to? (3)
- Impermeable to?
- Highly permeable
- Water
- CO2
- Oxygen
- Most lipid-soluble substances (alcohol, anesthetics)
- Slightly permeable
- Sodium
- Chloride
- Potassium
- Impermeable
- Plasma proteins
- Non-lipid soluble large organic molecules
What are the components of the BBB? (4)
- Endothelial cells - nonfenestrated with interendothelial tight junctions
- Pericytes - located in basement membrane sheath
- Perivascular macrophages
- Astrocyte foot processes
(Boron)
How does the neural tube form?
Proliferation of ectodermal epithelial cells called the neuroectoderm
The neural plate is formed from thickened ecroderm
- Invaginates along its axis forming a groove, until the lateral extremities of the plate (also called neural fold) fuse –> neural tube and canal
- As the neural tube forms, it separates from the nonneural ectoderm
Nonneural ectoderm grows over the dorsum of the tube and fuses along midline
(DeLahunta)
Where do the neural crest cells originate?
Arise from the junction of the nonneural and neural ectoderm
As the neural tube forms, it separates from the non-neural ectoderm dorsally
As this separation occurs, a longitudinal column of neural crest cells is left behind in 2 longitudinal columns
The neural crest cells are situated in 2 bilateral columns dorsolateral to the neural tube
(DeLahunta)
How is closure of the neural tube organized?
Progresses rostrally and caudally from the site of development of the rhombencephalon
Closure of the brain portion occurs initially at multiple sites - locations of these sites vary among species of animals
Before complete closure, the most rostral opening = rostral neuropore
(DeLahunta)
The rostral end of the neural tube initially develops into which 3 vesicles?
- Prosencephalon
- Mesencephalon
- Rhombencephalon
Which 2 vesicles grow from the prosencephalon?
- Optic vesicles - grow laterally to contact the overlying skin ectoderm
- Telencephalic vesicles - emerge from rostral prosencephalon, grow out of the neural tube laterally and dorsally
- These vesicles overgrown the original vesicular system, form the cerebral hemispheres
Diencephalon = portion of the prosencephalon that remains at the rostral end of the neural tube
- The optic vesicles remain associated with the diencephalon
(DeLahunta)
The neurohypophysis is a ventral outgrowth of which structure?
Diencephalon
(de Lahunta)
What develops from the dorsal metencephalon? Ventral metencephalon?
What does the caudal rhombencephalon form in to?
What becomes the 4th ventricle?
Dorsal metencephalon = cerebellum
Ventral metencephalon = pons
Caudal rhombencephalon = myelencephalon = medulla oblongata
Lumen of the neural canal in the rhombencephalon –> 4th ventricle
(de Lahunta)
During differentiation of the neural tube, how does the location of the nucleus change as the cell divides?
During interphase, nuclei are located on the external surface of the neural tube
As the nucleus enters mitosis, it migrates through the cytoplasm to the luminal surface of the neural canal
The peripheral portion of the cytoplasm and cell membrane retract to the new luminal position, where cell division is completed
The 2 new daughter cells extend their cytoplasm and cell membranes back to the external surface of the neural tube, and the nuclei migrate back to the periphery again
- Once in this position, the cells may undergo another mitosis or may differentiate
- Because the nucleus is at the EXTERNAL surface during interphase, differentiation occurs at the EXTERNAL surface
(de Lahunta)
What are the 2 basic cell types that form from initial differentiation of neuroepithelial cells in the neural tube?
What are the 3 layers formed by initial differentiation?
- Neuroblasts
- Immature neurons
- They will not divide again
- Grows extensively, forms long processes to become a mature functioning cell
- Spongioblasts
- Form astrocytes and oligodendroglia
As immature neurons and spongioblasts are differentiated and grow, and the neurons produce processes, the neural tube becomes arranged in 3 concentric layers
- Germinal layer
- Mantle layer
- Marginal layer
(de Lahunta)
What occurs in each of the 3 layers of the developing neural tube, and what final structures are formed?
- Germinal layer
- Layer adjacent to the neural tube
- Proliferating neuroepithelial cells - mitotic activity is eventually exhausted, reducing the germinal layer to single layer of ependymal cells
- Mantle layer
- Initially consists of immature neurons and spongioblasts
- Ultimately becomes the gray matter of the spinal cord, brainstem nuclei, cerebellum (nuclei and cortex), and cerebral cortex/basal nuclei
- Marginal layer
- Initially growing axonal processes of the neuronal cell bodies in the mantle layer
- Axons become myelinated by oligodendroglial cells - form the tracts in the white matter
(de Lahunta)
The longitudinal groove of the lateral wall neural canal is called the?
What does this groove divide the neural tube in to?
Sulcus limitans
- Divides the neural tube into dorsal and ventral portions
- Dorsal part = alar plate = sensory
- Ventral part = basal plate = motor
- Floor plate - connects the sides ventrally
_____ arise from neuroepithelial cells, function to guide the developing immature neurons to their sites of destination in the neural tube
After development is completed, where do these cells populate?
Radial glia
- The undergo postnatal differentiation with immature neurons, astrocytes, oligodendrocytes, and ependymal cells
- After development is completed, they populate the:
- Subventricular zone - lateral ventricles of the frontal lobe
- Subgranular zone of the hippocampal dentate gyrus
(de Lahunta)
What region of the brain functions as a source of neuronal stem cells for astrocytes and oligodendrocytes?
Subventricular zone - most evident in association with the lateral ventricle of the frontal lobe
(de Lahunta)
What is the significance of the subgranular zone of the hippocampal dentate gyrus?
Replaces the dentate gyrus granule neurons
(de Lahunta)
What are the 2 signaling centers that are responsible for the development of the spinal cord? What do they secrete?
- Surface ectoderm (adjacent to the ectoderm that formed the neural plate)
- Secretes bone morphogenic protein 4 (BMP4) = cytokine that enters the neural tube and directs the development of the dorsal portion of the neural tube
- Triggers the release of transforming growth factor beta - diffuses ventrally in the neural tube to induce formation of dorsal horn neurons
- Notocord (located ventral to the neural tube)
- Secretes sonic hedgehog signaling molecule
- Diffuses dorsally in the neural tube - induces formation of ventral horn neurons
(de Lahunta)
What causes the formation of the ventral median fissure in the spinal cord?
Where are the GVA/GVE, GSA/GP, and GSE neurons located?
Ventral growth of the 2 basal layers and associated marginal layers beyond the level of the floor plate
GVA/GVE - located adjacent to each other in their respective dorsal and ventral horns on either side of the dorsal plane through the sulcus limitans
GSA and GP neuronal columns - located dorsally in the mantle layer of the alar plate
GSE - located ventrally in the mantle layer of the basal plate
(de Lahunta)
_____________ provide the neurons that form the spinal ganglia at each segment
Neural crest cells
(de Lahunta)
Before becoming spinal ganglia, neural crest cells migrate to form which structures? (11)
- Melanoblasts to the somitic dermatome and adjacent epidermis
- Cell bodies of post-ganglionic axons in the 2 neuron GVE system
- Medullary cells of the adrenal glands
- Glial cells in the wall of the bowel (plus GVE neurons create enteric nervous system)
- Contributes to formation of the bone and cartilage of the skull
- Derivatives of the brachial arches
- Walls of the great vessels at the base of the heart
- Thyroid parafollicular cells
- Odnotoblasts
- Meninges
- Lemmocytes (Schwann cells) that form myelin of PNS
(de Lahunta)
_______ gene signals are expressed in the notochord, prechordal plate, and rostral neural plate and influence the specialization of the brain into its divisions
Hox genes
- Similar to spinal cord, prechordal plate and rostral ventral notochord –> secrete SHH –> influences ventral patterning of the brain
- BMP 4 and 7 secreted by surface ectoderm - control dorsal patterning of the brain
(de Lahunta)
How does the position of the alar and basal plates differ in the medulla vs. spinal cord?
The dorsal roof plate of the neural tube is stretched extensively dorsolaterally instead of being obliterated by the proliferating alar plate and marginal tissue
This displaces the alar and basal plates into a lateral and ventral position and enlarges the lumen of the neural tube to form the 4th ventricle
The 4th ventricle is covered dorsally by a single layer of neuroepithelial cells that become ependymal cells
Sulcus limitans present in the ventrolateral wall of the 4th ventricle provides the plane of division of the medulla into a ventromedial basal plate and dorsolateral alar plate
(de Lahunta)
The GSE cell bodies of which medullary nuclei migrate ventrolaterally in the medulla?
CN VII, IX, X, and XI
The GSE neurons of the facial nerve migrate from their initial formation in the mantle layer –> facial nucleus in a ventrolateral position
- This migration is called neurobiotaxis
- As s result of this migration, the axons leaving this facial nucleus initially course dorsomedially to the floor of the 4th ventricle, before turning to course ventrolaterally to leave the medulla and form the facial nerve
GSE cell bodies of 9, 10 and 11 undergo a migration ventrolaterally - form the nucleus ambiguus
(de Lahunta)
In the medulla, the preganglionic neurons of the parasympathetic portion of the GVE system are located in an interrupted column located where?
Just ventromedial to the sulcus limitans
Their axons leave in cranial nerves 7, 9, 10 and 11
Sensory neurons arise from primitive neurons that originate from what 2 populations of cells?
- Neural crest cells
- Sensory ganglia of 7, 9, and 10 (GVE and SVA functions)
- Brachial arch ectoderm - ectodermal cells that proliferate to form cranial placodes
- Sensory ganglia of 8 (Special proprioception for vestibular, special somatic afferent for auditory)
(de Lahunta)
The leptomeninges arise from what two types of cells?
- Neural crest cells
- Mesodermal cells
(de Lahunta)
What makes up the tela choroidea?
capillaries in the tela choroidea proliferate to form?
The roof plate of ependymal cells and the thin layer of vascularized pia associated with it
Capillaries here proliferate to form 2 longitudinal rows of a dense capillary bed
(de Lahunta)
The lateral apertures develop in the ______________ and allow communication between the lumen of the 4th ventricle and the subarachnoid space
(de Lahunta)
Medullary roof plate
Here, the choroid plexus protrudes from the lumen of the 4th ventricle out through the aperture @ each side of the cerebellomedullary angle
(de Lahunta)
How does the motor nucleus of CN V develop in the pons?
How do sensory neurons of CN V develop?
Motor neurons arise in the basal plate of the mantle layer –> migrate ventrolaterally into the parenchyma of the pons –> small, well-defined motor nucleus
The GSE of CN V innervate the muscles of mastication derived from the somitomeres of brachial arch 1
Dendritic zones of the head/mucosa –> sensory neurons derived from neural crest cells that form the trigeminal ganglion (GSA neurons) –> trigeminal ganglion
GP neurons for the muscles/joints of the head region –> pons
These sensory axons enter the alar plate region –> for the spinal tract of the trigeminal nerve in the pons/medulla/cranial cervical spinal cord –> terminate in telodendria at synapses in the alar plate (forms sensory pontine nucleus of the trigeminal nerve (in the pons) and the nucleus of the spinal tract of the trigeminal nerve (in the medulla and cranial spinal cord))
** caudally the spinal tract and nucleus meet the analogous functional neurons in the first cervical spinal nerves and spinal cord segment
(de Lahunta)
The cerebellum is formed from the proliferation of what embryonal cells?
How does it affect the roof plate in that region?
The germinal epithelial cells of the alar plate (forming the rhombic lip)
This growth dorsolaterally from each site replaces the roof plate of the 4th ventricle, so that the cerebellum forms part of the dorsal boundary of the 4th ventricle in the metencephalon
(de Lahunta)
How do the pontine nuclei and olivary nucleus form?
Ventral migration of alar plate mantle neurons forms both nuclei
Pontine - Axons of these neurons cross midline and course dorsally into the cerebellum = transverse fibers of the pons –> middle cerebellar peduncle
Neurons of CN III and IV are derived from what embryonic layers?
Basal plate mantle layer
GSE of III and IV - cell bodies do not migrate, remain adjacent to the median plate ventral to the mesencephalic aqueduct
The parasympathetic nucleus of CN III is rostral to the GSE nucleus - neurons also derived from basal plate mantle layer
(de Lahunta)
What forms the tectum of the midbrain?
What forms the crus cerebri of the midbrain?
Alar plate proliferates dorsally to form the tectum of the midbrain - divides into paired rostral and caudal colliculi - associated with afferent visual and auditory reflex functions
The crus cerebri results from telecephalic projection neurons growing causally
(de Lahunta)
At which point is the sulcus limitans no longer evident in the neural tube?
The diencephalon and telencephalon are considered developments of the alar or basal plate?
Rostral to the mesenceephalon
Diencephalon + telencephalon - alar plate
(de Lahunta)
How does the choroid plexus of the lateral and third ventricles develop?
Dorsal median plane of the diencephalon, proliferation of the neural tube epithelial cells does not occur, leaves a single cell thick roof plate
- Small choroid plexus develops in 2 parallel lines
- At the interventricular foramina, each of these is continuous with the choroid plexus that develops from the roof plate of each lateral ventricle
(de Lahunta)
How does the pituitary gland form?
Neurohypophysis - forms from the subthalamus
Adenohypophysis - Dorsal extension of adjacent oral ectoderm (hypophyseal-rathke pouch)
What is the definition of a nerve?
Collection of axons outside the CNS that are myelinated by Schwann cells and arise from the NEURAL CREST
CN 2 axons are myelinated by CNS oligodendroglial cells, covered by meninges, and bathed in CSF
(de Lahunta)
What is the rostral boundary of the brainstem/diencephalon?
Lamina terminalis of the diencephalon
This is the rostral boundary of the third ventricle
The optic chiasm is located at the ventral portion of this lamina
The rostral commissure develops (and remains in) this lamina
(de Lahunta)
At the level of the __________ the telencephalic vesicles grow out of the original prosencephalon to form the 2 cerebral hemispheres that comprise the cerebrum
Each telecephalon forms a cerebral hemisphere connected by the ________________
Rostral commissure
The lamina terminalis is located on the median plane between these 2 outgrowths
Each telencephalic vesicle grows out of the prosencephalon a short distance rostrally, and then in a large curve caudally and ventrally
Each telencephalon forms a cerebral hemisphere connected by the corpus callosum
(de Lahunta)
At one aspect of the _____ wall of the telencephalic vesicle, the neuroepithelial layer of the neural tube does not proliferate and remains a single layer of cells that become ependymal cells
What does this single layer of neuroepithelial cells ultimately form?
At one aspect of the medial wall wall of the telencephalic vesicle, the neuroepithelial layer of the neural tube does not proliferate and remains a single layer of cells that become ependymal cells
- Comparable with the roof plate of the myelencephalon (dorsal to the 4th ventricle) and roof plate of the diencephalon (dorsal to the 3rd ventricle)
This telencephalic roof plate will be attached to the crus of the hippocampal fornix on each side of the stria terminalis
The choroid plexus of each lateral ventricle develops here
(de Lahunta)
What are the 3 divisions of the cerebral cortex?
- Paleopallium (olfactory system)
- Olfactory bulbs
- Olfactory peduncles
- Piriform lobe cortex
- Archipallium
- Hippocampus
- Neopallium
- Cerebral surface
(de Lahunta)
What are association vs. projection vs. commissural axons?
- Association: course between cortical areas within 1 cerebral hemisphere
- Projection: leave the cerebral hemisphere where their cell bodies are located and enter the brainstem via the internal capsule
- Commissural: cross from one cerebrum to the other
(de Lahunta)
What are the 3 commissural structures of the telencephalon and where do they originate?
All initially develop in the lamina terminalis
- Rostral commissure - located ventrally in the lamina terminalis
- Course primarily between paleopallial structures (olfactory) and the basal nuclei on each side
- Hippocampal commissure
- Migrated caudodorsally as the telencephalon developed to reach a position dorsal/caudal to each diencephalon
- Courses between each archipallium (hippocampus)
- Corpus callosum
- Expands dorsally as the cerebrum develops so that it is positioned between the other 2 commissures
- Conects neopallial areas of each hemisphere
- Begins in the lamina terminalis, as telencephalic vesicle expands, corpus callosum enlarges and extends causally and dorsal to the diencephalon
- Cingulate gyrus is located dorsal
- Hippocampus and body of the fornix are ventral
- Forms the lateral roof of the lateral ventricle
- Septum pellucidum develops dorsally in the lamina terminalis between the genu of the corpus callosum and rostral body of the fornix
How are the marginal and mantle layers arranged in the final cerebrum?
Mantle and marginal layers reverse their positions
- Axons of the mantle layer migrate while axons grow centrally - results in gray matter on the surface and white matter centrally
- Radial astrocytes participate in this migration - guide neurons to the surface of the neural tube
Except for the basal nuclei - they are formed by neurons that migrate only a short distance from the mantle layer into the developing white matter
The first neurons to migrate to the developing cerebral cortex form which layer?
Layer VI (deepest)
As more neurons arrive, they pass those already there to form the rest of the layers in a reverse sequence
The last neurons to arrive form layer I (mot superficial)
(de Lahunta)
Post natal neurogenesis is a well-recognized event in which 2 regions?
Olfactory system and hippocampus
(de Lahunta)
What is the embryonic origin of meningiomas?
Arachnoid cap cells which arise from neural crest cells
(de Lahunta)
What transporter is responsible for transporting glucose from the capillary into the brain interstitial space?
GLUT 1 - located on luminal side and basolateral side
(Boron)
What are the components of the blood-CSF barrier?
- Vascular endothelium
- Leaky capillaries
- These are OUTSIDE the BBB
- Choroidal epithelium
- Specialized ependymal cells
- Tall columnar epithelial cells with microvilli brush border and cilia
- APICAL TIGHT JUNCTIONS - different than BBB where the endothelium has tight junctions
How does sympathetic input influence CSF production
How does plasma hypoosmolality influence CSF absorption?
How does blood flow reach the choroid plexus of the lateral ventricles?
How does the amount of blood supplied to the choroid plexus compare to the rest of the cerebrum?
Sympathetic input –> decreases CSF production (vasoconstriction?)
Plasma hypoosmolality –> increase CSF formation
Plasma hyperosmolality –> decrease CSF formation
Linear relationship
Blood flow to the choroid plexus is via the anterior/posterior choroidal artery
The blood flow to the choroid plexus is 10x greater than the average cerebral blood flow
(Boron)
How is the median eminence separated from the ventricular system
The extracellular space of the median eminence is exposed to substances in the blood (which can modulate the release of hypothalamic releasing factors)
The ependymal layer over the hypothalamic region of the 3rd ventricle has TIGHT JUNCTIONS that limit the movement of substances between the hypothalamic nuclei and the CSF
(Boron)
What are arachnoid villi vs. granulations?
What are the 2 main routes of CSF absorption?
Villi = microscopic (Very tiny); granulations = up to 1cm (giant)
2 routes of CSF absorption:
- Arachnoid villi
- Lymphatics associated with spinal nerves
- (also drains across the arachnoid at cranial nerves - considerably drainage at CN 1 and 2)
What is the mechanism of CSF absorption into arachnoid villi?
Arachnoid villi are projections of arachnoid membrane (deep) into dural venous sinuses (dorsal)
** also found in veins at intervertebral foraminae
- At a villus, cerebrospinal fluid is separated from blood by flattened fibroblasts and endothelial cells
- Each villus functions as a valve, regulating flow CSF into the venous sinus
- CSF pressure exceeds venous pressure –> villi expands and spaces between cell processes increase - more fluid can flow from the subarachnoid space to the venous sinus
- When pressure in the sinus exceeds CSF pressure, villi collapse
- May also involve transcytosis
(de Lahunta)
T/F: The CSF communicates freely with the brain?
What 2 factors most influence rate of CSF production
True - Ependyma and pia are highly permeable
Choroid plexus weight and exchange of Na/HCO3-
What are sources of CSF other than the choroid plexi?
The active transport of what ion is responsible for formation of CSF? What other processes are involved?
- Ependymal lining of the ventricles
- Pia/arachnoid vessels in the subarachnoid space
- Pial-glial membrane
CSF: ultrafiltrate of plasma, then active secretion of SODIUM results in formation
- Active transport of Na into the ventricle
- Na/K ATPase
- Water, Cl, and HCO3 follow by “facilitated transport”
- Carbonic anhydrase involved
How do concentrations of:
- Ca
- Cl
- Mg
- Glucose
- Na
- K+
- Protein
Compare in CSF vs. plasma?
Cl, magnesium, sodium - slightly higher in CSF vs. plasma
Ca, K+, and glucose - slightly lower in CSF vs. plasma
Protein - significantly lower in CSF than plasma
(De Terlizzi)
What are the 2 mechanisms by which glucose enters the CSF?
What 3 factors is it’s concentration dependent on
Enters via:
- Facilitated transport
- Diffusion
Dependent on
- Blood glucose concentration
- If BG is low, glucose is more avidly transported across the CNS capillary via carrier mechanism
- Rate of glucose transport into the CSF
- Metabolic rate of thee CNS
- (NOT dependent on insulin)
(De Terlizzi)
How do carbonic anhydrase inhibitor and vasopressin influence CSF sodium concentration?
Acetazolamide = carbonic anhydrase inhibitor - slows entrance of sodium into the CSF
Vasopresin - enhances movement of sodium from blood to brain
(De Terlizzi)
How does plasma K+ concentration affect the CSF K+ concentration
Plasma concentration has little effect on K+ concentration
Even with very high K+ plasma concentrations, the CSF potassium concentration remains within the normal range
Choroid plexus epithelium has a lower permeability to K+ than to sodium (reverse is true at capillaries)
If K+ is increased in the CSF, it is exchanged for Na to reduce K and increase Na
(De Terlizzi)
How is a low concentration of CNS calcium maintained?
Active transport mechanism at the BBB
Active transport at the vascular endothelium
Active transport at the choroid plexus epithelium
(De Terlizzi)
How is CSF creatine kinase related to the blood CK?
Elevation in CSF AST and CK - what could this indicate?
They are independent
- The CSF brain has its own isozyme of CK
Extensive myelin degradation
Also inflammation of the CSF often associated with increased LDH activity
(De Terlizzi)
How do CSF enzymes change after subarachnoid hemorrhage
Changes in CSF lactate and pyruvate may indicate what kind of CNS disease?
Study demonstrated decreased activity of CSF enzymes after subarachnoid hemorrhage in dogs
Changes in CSF lactate and pyruvate - may indicate mitochondrial disease
(De Terlizzi)
How are CNS GABA vs. glutamate affected in patients with epilepsy?
What is the normal CSF pressure of dogs and cats under anesthesia?
How does vitamin A affect CSF absorption?
GABA - low levels found in CSF of dogs with epilepsy
Glutamate - Elevated in epilepsy (and other diseases)
Dogs < 170 mmH2O; Cats < 100mmH2O
Vitamin A deficiency –> arachnoid vili atrophy –> poor absorption
(De Terlizzi)
What volume of CSF should be submitted for analysis?
Why are CSF cells so fragile?
0.75 - 2mL
CSF has low protein, lipid, and tonicity
(De Terlizzi)
If CSF analysis is delayed > 1 hour, what 3 cellular changes can occur?
At room temp - what is the time frame for cell degeneration?
- Nuclear pyknosis
- Lysis
- Disintegration of the cytoplasmic and nuclear membranes
Neutrophils degenerate within 1 hour, lymphocytes and macrophages after 3 hours
Eosinophils seem most stable
(De Terlizzi)
What 3 items can be added to CSF to aid stability?
Addition of fetal calf serum with a protein concentration of 3.7g/dL to CSF at a concentration of 20% volume
Addition of hetastarch to CSF at a ratio of 1:1
Calf serum appears to stabilize mononuclear cells more effectively than hetastarch
Addition of 1 drop of 15% formalin to 1-2mL CSF may be used to preserve cell concentration and structure for up to 8h after collection
(De Terlizzi)
What bone does the pituitary live in? What is the rostral margin and caudal margin of the hypophyseal fossa?
Basisphenoid bone
Rostral margin = rostral clinoid process
Caudal margin = dorsum sella
(Big Miller)
How is the dura arranged around the pituitary?
Sella turcica is lined by external/endosteal layer of dura
The inner layer of dura forms the diaphragm sellae that attaches to the clinoid process and does not extend fully into the hypophyseal fossa, has a oval slip that the infundibulum passes through
The subarachnoid space does not invest the hypophysis
(Big Miller)
Where does the intercavernous sinus pass in relation to the pituitary?
The cavernous sinuses bind the hypophysis laterally, connected by intercavernous sinuses
Larger intercavernous sinus passes caudal to the hypophysis
Some individuals have a smaller intercavernous sinus that passes rostral to the hypophysis
(Big Miller)
Where is the interpeduncular cistern live?
What is found within it?
Caudal aspect of the hypophysis
Caudal part of the arterial circle is found here
(Big Miller)
What is the hypophyseal cavity?
Large compressed vesicle that is a remnant of the development of the stomodeal adenohypopseal sac
(Big Miller)
What portions of the anterior pituitary are found in the following positions:
- Between the neural lobe and adenohypophysis
- Separated from the pars intermedia by the hypopseal cavity
- Extends as a cuff around the infundibulum to envelop part of the tuber cinereum
Pars intermedia: between the neural lobe and adenohypophysis
Pars distalis: separated from the pars intermedia by the hypophyseal cavity
Pars tuberalis: extends as a cuff around the infundibulum to envelop part of the tuber cinereum
(Big Miller)
What are the 3 cell types of the adenohypophysis pars distalis and what do they produce?
Acidophilic endocrine cells
- Smaller than basophilic cells
- Arranged around sinusoids
- 2 types - cells that produce somatotropin and cells that produce lactotrophin
Basophilic endocrine cells
- Cytoplasmic granules that have moderate affinity for basic component dye
- Granules composed of glycoprotein
- Larger than acidophilic cells
- Produce thyrotropin and gonadotrophins
Chromophobic cells
- Moderate numbers in the central region
- Produce adrenocorticotropin
(Big Miller)
What products are secreted by the pars intermedia adenohypophysis?
Melanocyte-stimulating hormone
Adrenocorticotropin
(Big Miller)
What cells make up the neurohypophysis? What is released?
Neurons with cell bodies in the hypothalamus –> axons pass to the neural lobe via the infundibulum
Glial cells = pituicytes are the cells that support the axons
The axons release vasopressin and oxytocin at their synapse
(Big Miller)
What are the 2 main arterial sources of blood to the pituitary gland?
Main arterial sources: internal cartotid arteries + caudal communicating arteries
There are also branches from the rostral intercarotid artery, and branches from the rostral communicating arteries
These arteries form the “mantle plexus” that is within the meninges
(Big Miller)
What contributes to the primary blood capillary network and secondary blood capillary network of the pituitary gland?
Mantle plexus –> rostral hypophyseal arteries –> capillaries to the tuber cinereum and proximal infundibulum –> primary blood capillary network
** The primary blood capillary network receives neurohormonal secretions called releasing factors from the median eminence –> takes them to the hypophysis
The capillaries of the adenohypophysis form the secondary blood capillary network
Hypophyseal portal vessels = veins that connect the primary and secondary capillary network
(Big Miller)
Where does the caudal hypophyseal artery supply blood to?
Where does blood that runs through the adenohypophysis ultimately drain to?
Neurohypophysis
Cavernous and intercavernous sinuses
(Big Miller)
What 2 axons supply the majority of the axons that enter the neurohypophysis?
What supplies autonomic innervation to the pituitary gland?
Supraoptic nuclei –> supraopticohypophyseal tract
Paraventricular nuclei –> paraventriculohypophyseal tract
They are UNMYELINATED axons
Sympathetic axons from the cranial cervical ganglion pass via tunica externa of the internal carotid artery and its branches to the vessels of the hypophysis
Parasympathetic innervation has not been described
It is believed that the hormonal input from the adenohypophysis is not under direct autonomic control
(Big Miller)
GSE cell bodies located in the medial portion of the ventral gray horn innervate what muscles?
GSE cell bodies located in the lateral portion of the ventral gray horn innervate what muscles?
Medial gray horn –> axial muscles
Lateral gray horn –> appendicular muscles
- The PROXIMAL limb muscles are located in the –> ventrolateral ventral gray horn
- DISTAL limb muscles –> dorsal VGH
(de Lahunta)
Which spinal cord segments form the fibular vs. tibial nerve of the sciatic nerve?
Fibular nerve: L6 and L7
Tibial nerve: L7 and S1
(deLahunta)
Vertebral formula for:
- Ox
- Sheep
- Swine
- Horse
Including location for the end of the spinal cord
All species have 7 cervical vertebrae
Ox: T13, L6, S5 (ends @ L6/S1)
Horse: T18, L6, S5 (ends @ S2)
Sheep: T13, L6-7, S4 (ends @ L6-S1)
Swine: T14-15, L6-7, S4 (ends @ S1-2)
(de Lahunta)
What nerves, spinal cord segments, and level of the vertebral canal is tested for the following nerves reflexes:
- Withdrawal reflex
- Biceps reflex
- Triceps reflex
- Extensor carpi radialis reflex
Withdrawal:
- All thoracic limb nerves
- Spinal cord segments C6-T2 / C5-T1 within the vertebral canal
Biceps:
- Musculocutaneous
- Spinal cord segments C6-8 / C5-7 within the vertebral canal
Triceps:
- Radial nerve
- Spinal cord segments C7-T2 / C6-T1 within the vertebral canal
Extensor carpi radialis:
- Radial nerve
- Spinal cord segments C7-T2 / C6-T1 within the vertebral canal
(de Lahunta)
What nerve, spinal cord segments, and level of the vertebral canal is tested with the following reflexes:
- Withdrawal
- Patellar
- Cranial crural (cranial tibial)
- Gastrocnemius
Withdrawal:
- Sciatic nerve
- Spinal cord segments L6-S1 / located @ L4-5 within the vertebral canal
Patellar
- Femoral nerve
- Spinal cord segments L4-6 / located @ L3-4 within the vertebral canal
Cranial Crural
- Fibular nerve
- Spinal cord segments L6-7 / located @ L4 within the vertebral canal
Gastrocnemius
- Tibial nerve
- Spinal cord segments L7-S1 / located @ L4-5 within the vertebral canal
(de Lahunta)
What is the only component of the quadriceps that contribute to hip flexion?
What provides cutaneous sensation to digits I and V of the pelvic limb?
Rectus femoris
Digit 1 (Medial) - saphenous nerve branch of the femoral nerve
Digit V (Lateral) - sciatic
** as a rule, with a partially compressed nerve, there will be more loss of motor function with some preservation of sensory function
(de Lahunta)
Pathway of the perineal reflex:
Pinch the skin of the perineum/anus (supplied by the superficial perineal nerve, branch of the pudendal nerve) –> S1-3 (located @ L5/6) –>
- Caudal nerves –> ventral caudal plexus –> sacrocaudalis ventralis lateralis (long depressor of the tail) - flexes the tail
- –> caudal rectal nerve –> external anal sphincter
(Big Miller)
Femoral nerve:
- Spinal cord segments
- Muscles innervated
- Action
Femoral nerve:
- L4, 5, 6
- Iliopsoas, quadriceps, sartorius
- Iliopsoas: flex hip (lumbar hypaxial m)
- Quadriceps: extend stifle joint, flex hip (cranial thigh)
- Sartorius - cranial part - hip flexion, caudal part - stifle extension (medial thigh)
(Big Miller)
Obturator nerve:
- Spinal cord segments
- Muscles innervated
- Action
- Where is it at risk for injury?
- L4, 5 (6)
- External obturator, pectineus, gracilis, adductor
- Overall: Adduction of the limb, extension/lateral rotation of the hip joint, flexion of the stifle, extension of the tarsus
- Located caudal thigh region (obturator is considered pelvic muscle)
- Courses on the medial surface of the ilium, is at risk for injury by iliac fractures
- PL will slide out
(Big Miller)
Cranial gluteal nerve:
- Spinal cord segments
- Muscles innervated
- Action
- L6, 7, S1
- Middle gluteal, deep gluteal, tensor fascia lata
- Lateral pelvic muscles
- TFL - flex hip, abduct limb
- Middle/deep gluteal - extend hip, medial rotation of the hip
(Big Miller)
Caudal gluteal
- Spinal cord segments
- Muscles innervated
- Action
Caudal gluteal:
- L7, (S1, 2)
- Superficial gluteal, (middle gluteal)
- Lateral pelvic muscles - Extends the hip
(Big Miller)
Sciatic nerve
- Spinal cord segments
- Muscles innervated
- Action
Sciatic nerve
- L6-S1 (S2)
- Biceps femoris, Semimembranosus, Semitendinosus (caudal muscles of the thigh)
- Action: Hip extension, stifle flexion, tarsus extension
(Big Miller)
Common fibular nerve:
- Spinal cord segments
- Muscles innervated
- Action
Common fibular nerve
- L6, 7
- Fibularis longus, lateral digital extensor, long digital extensor, cranial tibial
- Craniolateral muscles of the crus
- Tarsus flexion, digit extension, rotation of the hind paw medially
(Big Miller)
Tibial nerve
- Spinal cord segments
- Muscles innervated
- Action
Tibial:
- L7, S1
- Muscles: Gastrocnemius, popliteus, superficial digital flexor, deep digital flexor
- Caudal muscles of the crus
- Action: Extends tarsal joint, flexion of stifle joint
Plantigrade –> TIBIAL NERVE
(Big Miller)
Cutaneous trunci reflex:
Sensory stimulus: mild compression of the skin alongside the spinous processes of the vertebrae using forceps
–> Doral roots –> dorsal gray column –> synapses on long interneurons –> fasiculus proprius on both sides –> project in the ipsilateral and contralateral fasiculus proprios on both sides
Interneurons project cranially to C8/T1 –> ventral gray column –> GSE LMN of the lateral thoracic nerve
RE spinal cord anatomy, what is the difference between a septae, sulci, and fissure
- Where is the dorsal median fissure present?
- Where can a dorsal intermediate sulcus be seen?
Septum = thin barrier, formed principally by astrocytes in white matter
Sulcus is a shallow grove on the spinal cord surface
Fissure = midline cleft typically lined by pia mater
From large to small: Fissure > sulcus > septum
Dorsal median fissure - absent in cervical and thoracic segments (there is a sulcus and septum instead), present in lumbar
Dorsal intermediate sulcus: cervical spinal cord
(Big Miller)
1cm caudal to the last segment of the spinal cord, the spinal cord is reduced to a uniform strand of glial and ependymal cells called the _______________. Encased in a layer of ___________.
1cm caudal to the last segment of the spinal cord, the spinal cord is reduced to a uniform strand of glial and ependymal cells called the filum terminale. Encased in a layer of pia mater.
- A caudal extension of dura mater that envelops the filum terminale is called the spinal dura mater filament - extends causally in the vertebral canal and attaches to a sacral or caudal vertebrae
- A dura-arachnoid sac enclosing subarachnoid space and CSF in a lumbar cistern, extends approximately 2cm caudal to the end of the spinal cord neuroparenchyma
(Big Miller)
What are the 3 types of GSE LMN neurons of the spinal cord:
- Alpha motor neurons
- Innervate typical muscle fibers responsible for producing muscle tension
- Gamma motor neurons
- Aka fusimotor neurons
- Innervate intrafusal muscle fibers within muscle spindles
- Beta motor neurons
- “A few somatic efferent neurons called beta motor neurons innervate both intrafusal and extrafusal muscle fibers”
(Big Miller)
3 spinal cord tracts that carry nociceptive information
- Spinocervicothalamic tract (mainly skin)
- Spinothalamic tract (visceral and somatic)
- Dorsal column postsynaptic tract (skin)
(Big Miller)
1 spinal cord tract that carries information RE temperature
Spinothalamic tract (visceral and somatic)
(Big Miller)
3 spinal cord tracts that carry information RE tactile stimuli and pressure
- Dorsal column postsynaptic tract (skin)
- Spinocervicothalamic tract (skin)
- Spinothalamic tract (visceral and somatic)
(Big Miller)
2 spinal cord tracts that carry information RE discriminative touch
- Fasiculus cuneatus (mannus)
- Fasiculus gracilis (pes)
2 spinal cord tracts that carry information RE kinesthesia/proprioception
- Fasiculus cuneatus (thoracic limb)
- Spinomedullary tract to nucleus Z (pelvic limb)
(Big Miller)
Trace the pathway of myotactic reflex:
- Receptors = annulospiral endings –> type Ia (largest/fastest/myelinated fibers) sensory fiber –>
- DRG –> dorsal funiculus –> bifurcate into cranial and caudal branches
- Collaterals of these branches go to the ventral horn and excite nearly all the alpha motor neurons that innervate the muscle being stretched
- Collateral branches synapse motor neurons of synergist muscles
- Collaterals synapse on interneurons –> inhibit motor neurons of antagonist muscles
(Big Miller)
Trace the pathway of the withdrawal reflex:
Free nerve endings associated with small myelinated fibers and nonmyelinated axons –> DRG –> enter dorsolateral fasiculus and bifurcate into cranial and caudal branches
Cranial and caudal branches extend over several segments –> collateral branches that enter gray matter to synapse on interneurons and projection neurons
Interneurons excite all flexors of the limb and inhibit reciprocal muscles
(Big Miller)
Where in the spinal cord are the following morphologies observed:
- Ratio of white matter to gray mater is the greatest
- spinal cord perimeter oval in transverse segments
- Spinal cord perimeter appears circular
- Dorsal intermediate sulcus ad septum evident
- Dorsal median fissure
- Apex of the dorsal gray horn pointed
- Apex of the dorsal horn blunted
- Apex of the dorsal horn rectangular
- Lateral gray horn evident
- Ratio of white matter to gray mater is the greatest - cervical segments
- spinal cord perimeter oval in transverse segments - cranial cervical region
- Spinal cord perimeter appears circular - thoracic segments (between intumescence)
- Dorsal intermediate sulcus ad septum evident - cranial half of the spinal cord
- Dorsal median fissure - lumbar and sacral segments
- Apex of the dorsal gray horn pointed - cervical
- Apex of the dorsal horn blunted - thoracic region
- Apex of the dorsal horn rectangular - lumbosacral region
- Lateral gray horn evident - thoracic and cranial lumbar segment
(Big Miller)
Where is the GSE oculomotor nuclei located?
Where is the GVE oculomotor nucleus located?
GSE:
- Mesencephalon at the level of the rostral colliculi
- Adjacent to the mesencephalic aqueduct
- Within the ventral portion of the central gray substance that surrounds the aqueduct
GVE:
- Rostral to the GSE nucleus
- Caudal to the pretectal nucleus
- Similar position in relation to mesencephalic aqueduct
(Big Miller)
What is the pathway of the CN III axons after leaving their nuclei?
GSE axons:
- Pass ventrally through the reticular formation of the tegmentum, remain medial
- Emerge on the lateral side of the interpeduncular fossa
- Form the oculomotor nerve on the medial side of the crus cerebri
- Course rostrally in the middle cranial fossa (lateral to the pituitary gland, adjacent to the cavernous sinus)
- Leaves cranial cavity through the orbital fissure
- Within the periorbita courses laterally with CN II shortly
- Branches to supply:
- Medial, dorsal, and ventral rectus muscle
- Ventral oblique muscle
- Levator palpebrae superioris muscle
GVE axons:
- GVE axons are located superficially in CN III
- At point of branching to muscular branches - CILIARY GANGLION
- Telodendrons of GVE preganglionic neurons synapse on the dendritic zones of the cell bodies of the ganglionic neurons
- Ganglionic axons pass via short ciliary nerves along the surface of the optic nerve –> eyeball –> smooth muscle of the ciliary muscle and sphincter of the pupil
(de Lahunta)
Where are the cell bodies of CN IV, what is the path of the nerve:
Nucleus:
- Located in the caudal mesencephalon, level of the caudal colliculi
- Adjacent to the mesencephalic aqueduct
Axons:
- Courses lateral, dorsal, and caudal –> enter rostral medullary velum –> cross to opposite side and emerge caudal to the caudal colliculus
- Continue rostrally and ventrally on the side of the mesencephalon –> floor of the middle cranial fossa
- Continue rostrally, lateral to the pituitary gland, adjacent to cavernous sinus
- Leave cranial cavity through orbital fissure
- (horses - sometimes leaves through trochlear foramen)
- Within periorbita:
- Innervates contralateral dorsal oblique muscle (pulls dorsal part of the eye medially)
CN VI - where is the nucleus located? Where do the axons pass?
Nucleus:
- Located in the motor nucleus of the abducent nerve in the rostral medulla at the level of the caudal cerebellar peduncle
- Close to midline, adjacent to 4th ventricle
- GSE axons of the genu of the facial nerve pass over this nucleus
Axons:
- Ventrally through the reticular formation of the medulla
- Pass through trapezoid body
- Emerge just lateral to the pyramid
- Course on the floor of the middle cranial fossa, beside the pituitary, adjacent to the cavernous sinus
- Leaves the cranial cavity through the orbital fissure
- Within the periorbita, branches to innervate the lateral rectus and retractor bulbi muscles
(Big Miller)
How can a vestibular ventrolateral strabismus be differentiated from an oculomotor ventrolateral strabismus?
Oculomotor nerve strabismus - present in all head positions
Vestibular nerve strabismus - only present with certain head positions
(de Lahunta)
GSE of CN V - where are the cell bodies located, where do the axons course?
Nucleus:
- Motor nucleus of the trigeminal nerve
- Located in the pons @ level of the middle and rostral cerebellar peduncles
- Medial to the pontine sensory nucleus
- Dorsolateral within the pons
Axons:
- Leave pons ventrolaterally, go through middle cerebellar peduncle –> join sensory neurons entering the pons
- As they emerge from the pons, may be seen as a separate motor nerve root on the medial aspect of the incoming sensory fibers –> leaves in the canal for the trigeminal nerve (petrosal temporal bone)
- Within the canal for the trigeminal nerve, motor neurons pass through the large trigeminal ganglion without synapsing
- Mandibular nerve leaves through the OVAL foramen –> muscles of mastication
(Uemura/de Lahunta)
CN VII GSE - where are the cell bodies located? Where do the axons course?
CN VII GSE nucleus:
- Facial nucleus in the rostral medulla, located ventrolateral
- Medial is the pyramid, lateral is the spinal nucleus of the trigeminal nerve, rostral is the trapezoid body
- @ the level of attachment of the caudal cerebellar peduncle to the cerebellum
Axons:
- Course dorsorostrally toward the 4th ventricle, pass rostrally over the motor nucleus of the abducent nerve forming the genu of the facial nerve
- Emerge from the medulla through the trapezoid body, ventral to the incoming CN VIII
- Leaves through internal acoustic meatus alongside CN 8 –> enters the facial canal within the temporal bone –> stylomastoid foramen
- @ facial canal - separated from the tympanic cavity by a thin layer of connective tissue
- Branches of the facial nerve:
- Stapedius nerve (branches within the facial canal) –> stapedius muscle
- Caudal auricular nerve –> retroauricular muscle
- Digastric nerve –> caudal digastricus
- Auriculopalpebral –> rostral auricular muscles, orbicularis oculi muscles
- Dorsal buccal –> maxillonasolabialis muscle
- Ventral buccal nerves –> ventral orbicularis oris muscle
(de Lahunta, Uemura)
CN 9 GSE LMN - where are the cell bodies located? Where do the axons course?
CN IX
- Cell bodies located in the rostral portion of the nucleus ambiguus (motor nucleus of the glossopharyngeal nerve)
- Nucleus ambiguus - ill defined column of neuronal cell bodies ventrolateral medulla
Axons
- Axons go dorsally, then ventrolaterally –> emerge along lateral medulla w/ GVE preganglionic axons of CN IX
- Just caudal to CN VIII
- Enters jugular foramen, exits tympanooccipital fissure
- Gives rise to (GSE branches)
- Pharyngeal beach - forms pharyngeal plexus w/ pharyngeal branches of CN X and sympathetic fibers of cranial cervical ganglion –> innervates pharyngeal muscles
(GSE component of CN IX is whimpy in comparison to GVE and GSA)
(de Lahunta)
CN X GSE - Where are the cell bodies located? Where do the axons course?
CN X
- Cell bodies in the middle portion of the nucleus ambiguus = motor portion of the vagus nerve
Axons:
- Similar intramedullary course with CN IX GSE axons - course dorsally then ventrolaterally –> emerge on the lateral aspect of the medulla, just rostral to the internal branch of the accessory nerve
- Joined by preganglionic GVE CN X axons = motor portion of vagus nerve
- Leaves through jugular foramen –> GSE of internal branch of accessory nerve join –> leaves tympanooccipital fissure
- Pharyngeal branch –> pharyngeal plexus with CN IX –> striated muscle of the palate, pharynx, and cervical esophagus
- Cranial laryngeal branch –> cricothyroid muscle
- Recurrent laryngeal (contains GSE of internal accessory branch) –> caudal laryngeal nerve –> all other intrinsic muscles of the larynx
- Recurrent laryngeal nerve innervates the cervical and cranial thoracic esophagus
- Small branches from vagus nerve –> directly to esophagus
(de Lahunta)
CN XI - Where do the GSE cell bodies live? Where do the axons course?
CN XI
- Internal branch: cell bodies located in the caudal nucleus ambiguus
- External branch: cel bodies located in the motor nucleus of CN XI - lateral gray horn of C 1-8
Axons pass:
- Internal branch: course dorsally then ventrolaterally within the medulla –> emerge on the lateral aspect of the medulla as the cranial roots of CN XI –> jugular foramen –> join CN X GSE and GVE –> tympanooccipital fissure
- Innervate:
- Intrinsic muscles of the larynx
- Cervical and cranial thoracic esophagus (via recurrent laryngeal)
- Innervate:
- External branch: axons emerge from the lateral cervical spinal cord as the spinal roots of the accessory nerve –> form external branch of the accessory nerve –> courses cranially just dorsal to the denticulate ligament between the dorsal and ventral rootlets –> foramen magnum –> joins the internal branch of CN XI for a few mm –> jugular foramen –> internal branch joins vagus nerve
- Emerges from TOF (accessory nerve that emerges from TOF contains only GSE neurons from the external branch
- Innervates:
- Trapezius
- Sternocephalicus
- Cleidocephalicus
(de Lahunta)
CN XII - where are the GSE cell bodies located, where do the axons course?
CN XII
- GSE neuronal cell bodies located in the motor nucleus of the hypoglossal nerve in the medulla
- Adjacent to the median plane and to the floor of the 4th ventricle
- Long nucleus
Axons pass:
- Directly ventral and lateral from the nucleus through the reticular formation –> emerge lateral to the pyramid as a longitudinal series of small roots
- Row of hypoglossal roots merges at the small hypoglossal canal –> hypoglossal canal
- Innervate:
- Extrinsic tongue muscles
- Intrinsic tongue muscles
- geniohyoideus
- The nerve is much smaller inside the cranial cavity than outside the skull - this is the result of increase in myelination and connective tissue that occurs after the nerve merges from the hypoglossal canal
(de Lahunta)
During the resting stage of neuronal action potential, what is the state of:
- Voltage-gated Na channel
- Voltage-gated K+ channel
- Conductance for K+ compared to Na
Voltage-gated Na channel: Activation gait is closed, inactivation gate open
Voltage-gated K+ channel: gate closed
Conductance for K+ is 50 - 100x greater than conductance for Na+
This is due to leakage of K+ through leak channels
(Guyton)
During the depolarization stage of the neuron action potential, what is the state of:
- Voltage-gated Na channel
- Voltage-gated K channel
- Conductance of K+ ions compared to Na ions?
Conformational change in the voltage-gated Na channel activation –> open conformation
Voltage gated K+ channel opens but much slower rate than VGNa channel
Na conductance becomes 10x greater than K conductance
(Guyton)
During the repolarization stage of neuronal action potential, what is the state of:
- Voltage-gated Na channel
- Voltage-gated K channel
- Na conductance compared to K conductance
Voltage-gated Na channel - inactivation gate closed.
Voltage-gated K channel open - K+ diffuses out of the cell
Conductance of K is becoming greater than Na again
(Guyton)
(The inactivation gate will not reopen until the membrane potential returns to or near the original resting membrane potential)
How does extracellular concentration of Ca effect nerve excitability?
Deficit of Ca –> nerve is hyperexcitable
Na channels become activated by a small increase of the membrane potential
Ca appears to bind the exterior surface of the Na channel –> alters the voltage-level required to open the gate
(Guyton)
Myelination increases the velocity of nerve transmission by _________x
5-50x
(Guyton)
What makes up sarcolemma?
What are myofibrils composed of?
True cell membrane + an outer coat of polysaccharide material containing collagen fibrils
Myofibrils are composed of actin and myosin
(Guyton)
What are the subunits of myosin filament?
What are the subunits of actin filament?
Myosin filament - 200+ myosin molecule
Each myosin molecule is an ATPase
Actin
- Polymerized g-actin makes up F actin strands which are interlaced with tropomyosin
- Troponin - 3 subunits that are attached to tropomyosin
- Troponin + tropomyosin - inhibit interaction of actin and myosin
(Guyton)
What is an A band vs. I band vs. Z disc of the myofibril?
What is a sarcomere?
I band = light band - actin only
Dark band = A band = actin and myosin
Z disk = structure that attaches actin filaments
Sarcomere is the unit between z disks
(Guyton)
What is the mechanism of G-protein coupled receptor and what are the secondary effects?
- Receptor is activated by neurotransmitter –> receptor undergoes conformational change exposing a binding site for G protein complex
- G protein complex binds –> permits alpha subunit to release GDP and bind GTP while separating from the beta/gamma portions of the complex
- Alpha-GTP complex is free within the cytosol to perform various functions
- Opening specific ion channels through postsynaptic cell membrane
- Activation of cAMP or cGMP –> initiate metabolic shift –> long term excitability can be altered
- Activation of intracellular enzymes
- Activation of gene transcription
(Guyton)
How does input from the retina reach CN 3 GSE and GVE nuclei?
Retina –> optic nerve –> optic chiasm –> optic tracts –> pass over LGN and synapse on pretectal nuclei (rostral midbrain)
- -> axons cross at caudal commissure –> contralateral CN3 nucleus
- -> smaller # axons do not cross –> ipsilateral CN 3 nucleus
(de Lahunta)
How is the pupillary sphincter muscle arranged differently than the dilator muscle?
Pupillary sphincter is circularly arranged
Pupillary dilator muscle is radially arranged
Where are sympathetic trunk ganglia found?
Sympathetic trunk ganglia are paired and line on the ventrolateral surface of the vertebral column EXCEPT in the cervical and cranial thoracic region
- Preganglionic sympathetic fiber cell body in lateral horn –> leaves w. ventral root –> branches off spinal nerve –> communicating branch (ramus communicans) –> joins sympathetic trunk and synapses @ sympathetic trunk ganglia –>
- The sympathetic trunk ganglia caudal to the cranial thoracic region are segmentally related to the adjacent vertebrae
- These ganglia are numbered according to the spinal nerve to which the preganglionic sympathetic fibers join
- The sympathetic trunks extend caudally into the sacral and coccygeal vertebrae
- Paired trunks are sometimes partially fused here
(Uemura)
Where does the middle cervical ganglion receive preganglionic sympathetic axons from, and what structures does it supply sympathetic innervation to?
Anatomic landmark for the middle cervical ganglion?
T1-3 lateral gray horn –> ventral roots –> communicating branch –> sympathetic trunk –> pass through cervicothoracic ganglion w/o synapse –> ansa subclavia –> middle cervical ganglion –> cardiosympathetic fibers to the heart/airways
- Middle cervical ganglion - located just cranial to the ansa subclavian, @ thoracic inlet
(Uemura)
Where does the cervicothoracic ganglion receive preganglionic sympathetic axons from, and what structures does it supply sympathetic innervation to?
Anatomic landmark for the cervicothoracic ganglion?
T1-3/4 lateral gray horn –> ventral roots –> communicating branch –> sympathetic trunk –> cervicothoracic ganglion
- Postganglionic axons –> heart and lungs
- Vertebral nerve –> postganglionic axons distributed with C3-8
Cervicothoracic ganglion: located just medial to the first rib
Describe the parasympathetic innervation to the bladder
S1-3 spinal cord segments lateral gray horn –> ventral roots –> spinal nerve –> ventral branches –> parasympathetic fibers branch off
- Parasympathetic fibers from S1-3 form a single pelvic nerve that runs ventrally on the lateral surface of the rectum
- Ventral to the rectum, they meet hypogastric nerves and form pelvic plexus
- Parasympathetic preganglionic axons can synapse @ the pelvic ganglion –> postganglionic axons travel to the detrusor muscle
- Or parasympathetic preganglionic axons travel through the pelvic plexus w/o synapse –> detrusor muscle and synapse w/ postganglionic axon there
Postganglionic parasympathetic axons in the detrusor synapse on muscarinic cholinergic receptors (M2 and M3) of the smooth muscle of the bladder (aka detrusor)
(de Lahunta)
Describe the sympathetic innervation to the urinary bladder
Preganglionic cell body is in the lateral gray horn of L1-4 or L5 –> axons leave w/ ventral root –> spinal nerve –> axons leave spinal nerve (communicating branch) –> sympathetic trunk –> leave w. lumbar splanchnic nerves –> caudal mesenteric ganglion
- Postganglionic axons form hypogastric nerves –> intermix @ pelvic plexus with pelvic nerve
- Postganglionic axons can synapse/terminate @ pelvic plexus on the dendrite/cell body of postganglionic parasympathetic neurons
- Alpha 2 receptors on parasympathetic nerves –> when stimulated, the parasympathetic neuron is inhibited from generating an impulse –> prevents detrusor contraction
- Postganglionic axons can continue to the neck of the bladder –> smooth muscle of internal urethral sphincter –> alpha 1 receptors
- Postganglionic axons can continue to the detrusor muscle beta 3 receptors
(de Lahunta)
At the base of the modiolus, the cochlea is continuous with what 2 structures?
Vestibule
Cochlear window
(de Lahunta)
Regarding the cochlear duct:
- What fluid does it contain?
- What does the apex connect to?
- What does the base connect to?
- What structure is found dorsal? ventral?
- What structures is it continuous with?
Cochlear duct
- Contains endolymph
- Apex of the triangle attaches medially to the spiral lamina of the modiolus
- Base = stria vascularis, then cochlea
- Ventral = scala tympanum, separated by basilar membrane
- Dorsal = scala vestibuli, separated by vestibular membrane
- Continuous with the saccule via the ductus reuinens
(de Lahunta)
Scala vestibuli:
- Where is it found in relation to the cochlear duct
- What fluid does it contain
- What does it communicate with
- Contains perilymph
- Dorsal to the cochlear duct, separated by the vestibular membrane
- Communicates with the stala tympani @ helicotrema
- Communicates with the vestibule of the bony labyrinth
(de Lahunta)
Scala tympani:
- What fluid does it contain
- Where is it in relation to the cochlear duct
- What is it continuous with?
Scala tympani
- Contains perilymph
- Located ventral to the cochlear window, separated by the basilar membrane
- Continuous with the scala vestibuli @ the helicotrema
- Continuous with the subarachnoid space by the perilymphatic duct
- Ends @ cochlear window
(de Lahunta)
Where is the spiral organ of Corti found?
What are the stereocilia of the hair cells of the organ of corti embedded in?
Spiral organ of Corti:
- Located on the basilar membrane
- Hair cells have stereocilia that are embedded in the tectorial membrane
- The dendrites of CN 8 are in synaptic relationship with the base of the hair cells
(de Lahunta)
How does the length of the basilar membrane change from the base to the apex of the cochlea?
Where do high frequencies affect the basilar membrane?
Where do low frequencies affect the basilar membrane?
the basilar membrane is longest at the base of the cochlear coil, progressively shortens through the coils to the apex
High frequencies –> maximally affect the basal portion of the basilar membrane
Low frequencies –> maximal vibration of the basilar membrane at the apex
What muscle connects to the malleus? What nerve innervates it?
What muscle connects to the stapes? What nerve innervates it?
What ossicle does the chorda tympani contact?
The tensor tympani muscle connects to the malleus. It is innervated by the mandibular nerve
Chorda tympani crosses the medial surface of the malleus, then joins the lingual nerve
The stapedius muscle connects to the stapes. It is innervated by the facial nerve
(Uemura)
Auditory pathway from CN 8 dendrites –> cochlear nuclei
Dendrites of CN 8 cochlear portion are in synaptic contact with hair cells of the spiral organ –> cell bodies within the modiolus –> CN 8 divisions join –> internal acoustic meatus –> cerebellomedullary angle –> dorsal and ventral cochlear nuclei on the lateral side of the medulla
The axons of the cell bodies in the cochlea pass into the medulla via 2 ways:
- Ventrally through the trapezoid body
- Cochlear nuclei –> Ipsilateral nucleus of the trapezoid body, or decussates to contralateral nucleus of the trapezoid body
- Dorsally over the caudal cerebellar peduncle by way of the acoustic stria
- Cochlear nuclei –> axon courses dorsally, decussates, ascends in the lateral lemniscus
(de Lahunta)
Lateral lemniscus:
- Contains fibers originating from what three nuclei?
- Terminates where?
- Where is the nucleus of the lateral lemniscus located?
Contains fibers from the cochlear nuclei, dorsal nucleus of the trapezoid body, ventral nucleus of the trapezoid body
Fibers from ipsilateral and contralateral nuclei
Terminates at the caudal colliculus
The nucleus of the lateral lemniscus is located along the ventromedial aspect of the lateral lemniscus
(de Lahunta)
Auditory information from the cochlear nuclei and nuclei of the trapezoid body that has reached the caudal colliculi can be relayed to what three locations?
- Brainstem nuclei (tectonuclear pathway)
- Cervical spinal cord (tectospinal in the ventral funiculus)
- Thalamus (brachium of the caudal colliculus –> medial geniculate nucleus)
(de Lahunta)
Once at the medial geniculate nucleus, where do axons travel for conscious auditory pathway?
Medial geniculate nucleus –> internal capsule –> neocortex of the temporal lobe
- Primarily Sylvian and ectosylvian gyri
- This rostrally projecting auditory pathway is characterized by diffuseness and a bilateral distribution
- Despite this, at the cortical level, the contralateral cochlear duct is more strongly represented
- Crossing occurs at the level of the trapezoid body, between the nuclei of the lateral lemniscus, at the commissure of the caudal colliculus
(de Lahunta)
Tactile receptor:
____________ are present in the basal layer of the epithelium and are sensitive to touch and pressure
Merkel’s discs are present in the basal layer of the epithelium and are sensitive to touch and pressure
Several cells innervated by the same myelinated nerve fiber (A beta)
Considered a free nerve ending type of receptor
Slowly adapting and remain active as long as the stimulus is present
(Guyton)
Tactile receptor:
___________ are receptors involved with a hair follicle, detect movement of objects on the surface of the body
Hair end organ are receptors involved with a hair follicle, detect movement of objects on the surface of the body
- Considered a free nerve ending, present in the dermis
- Adapt quickly
(Guyton)
Tactile receptor:
________________ are multibranched, encapulated nerve endings that are important for signaling continuous states of deformation of the tissues
Ruffini’s endings are multibranched, encapulated nerve endings that are important for signaling continuous states of deformation of the tissues
- Adapt very slowly
- Also found in joint capsules
- Present in the dermis
- Consist of myelinated axon terminals interspersed with collagen fibers and surrounded by several layers of perineural epithelioid cells
(Guyton)
Tactile receptor:
_________ are stimulated by rapid local compression of the tissue and are the largest sensory receptors
Pacinian corpuscles are stimulated by rapid local compression of the tissue and are the largest sensory receptors
- Located immediately under the skin and deep in the facial tissues of the body
- Also found as proprioceptors in joints
- Adapt quickly
- Made of an axon terminal surrounded by numerous concentric layers of perineural epitheloid cells
(Guyton)
How does the receptive field of a second order sensory neuron neuron compare to a peripheral/primary sensory neuron?
Sensory neurons innervating a given receptor field converge on smaller numbers of postsynaptic neurons
Receptive field covered by a central neuron reflects a combined area monitored by various numbers of sensory neurons
Large receptive fields allow the sensory neuron to detect stimulus applied to a wider area, but results in a less precise perception than small receptive fields
(Uemura)
What is the pathway that GP information takes to reach the cerebrum?
Caudal to T6: Proprioceptors –> DRG –> dorsal funiculus w/o synapse
Join fasiculus gracilis –> nucleus gracilis in the medulla
Cranial to T6: Proprioceptors –> DRG –> dorsal funiculus w/o synapse
Join fasiculus cuneatus (lateral to gracilis) –> medial cuneate nucleus in the medulla
The axons from the nucleus gracilis/medial cuneate nucleus –> decussate in medulla as deep arcuate fibers –> medial lemniscus
Entire spinal cord: Proprioceptors –> DRG –> nucleus proprius (dorsal horn) –> ipsilateral lateral funiculus (as spinocervical tract) –> lateral cervical nucleus (dorsal horn C1-2) –> decussate in caudal medulla –> medial lemniscus
Collaterals of dorsal spinocerebellar tract –> nucleus Z –> internal arcuate fibers –> medial lemniscus
Medial lemniscus –> ventral caudal lateral nucleus of the thalamus –> thalamocortical fibers –> internal capsule, centrum semiovale –> somesthetic cortex of the cerebral hemisphere
(de Lahunta)
What is the pathway for reflex activity associated with general proprioceptive information from the head?
GP receptor organs in the:
- Muscles of mastication
- Facial and extraocular muscles
- Temporomandibular joints
–> GP axons join all 3 branches of the trigeminal nerve –> enter pons w/o synapse –> mesencephalic nucleus of the trigeminal nerve
Axons from mesencephalic nucleus of the trigeminal nerve –>
- GSE alpha-LMN of cranial nerve nuclei
- Pontine sensory nucleus of the trigeminal nerve –> Cranial nerve GSE neuron
(de Lahunta)
What is the conscious pathway for general proprioception from the head?
GP (muscles of mastication, extraocular muscles, TMJ joint, temporal muscles) –> trigeminal nerves –> mesencephalic nucleus of the trigeminal nerve –> pontine sensory nucleus of the trigeminal nerve –> decussate –> join contralateral trigeminal lemniscus (aka quintothalamic tract) –> medial lemniscus –> ventral caudal medial nucleus of the thalamus –> internal capsule –> centrum semiovale –> somesthetic cortex
(de Lahunta)
What is the reflex pathway associated with GSA information?
Temp/nociception/touch –> DRG –> dorsolateral sulcus –> dorsolateral fasiculus
Within the spinal cord, the GSA axon forms relatively short branches that course cranially and caudally on the surface of the dorsal gray column for 2-3 segments (called dorsolateral fasiculus)
Collaterals of dorsolateral fasiculus –> dorsal gray column and synapse on substantia gelatinosa
** S. gelatinosa is located on the apex of the dorsal horn
S. gelatinosa neurons –> middle of the dorsal gray horn –> interneurons –>
- GSE alpha motor neuron in the ventral gray horn
- Axon of interneuron enters fasiculus proprius –> cranially/caudally –> GSE alpha LMN in adjacent spinal cord segments
(de Lahunta)
What is the difference between a dermatome, cutaneous zone, and autonomous zone
Dermatome - area of cutaneous sensation for an individual dorsal root (spinal nerve)
Cutaneous area - area of cutaneous sensation for one named nerve. Considerable overlap
Autonomous zone - area of cutaneous sensation belonging to only one specific named nerve
What is the pathway of the spinothalamic tract
Nociceptors –> DRG –> cell body in dorsal gray horn (Lamina I, II, V) –> crosses to contralateral lateral funiculus (as spinothalamic tract)
Spinothalamic tract ascends as a multisynaptic pathway (axons leave the tract, enter spinal cord gray matter, synapse on a neuronal cell body –> reenters ipsilateral or contralateral spinothalamic tract
@ brainstem –> collaterals synapse in various reticular formation nuclei - activate ARAS
Spinothalamic tract synapses on ventral caudal lateral nucleus of the thalamus –> thalamocortical projection fibers –> internal capsule –> centrum semi ovale –> somesthetic cortex (frontoparietal lobe)
** contralateral pathway predominates
(de Lahunta)
How is GSA information conveyed from the head to the cerebrum?
Nociceptor –> branches of trigeminal nerve –> trigeminal ganglion –> pons –> axons form spinal tract of the trigeminal nerve –>
- synapse on the pontine sensory nucleus of the trigeminal nerve
- synapse nucleus of the spinal tract of the trigeminal nerve
Axons from both of these nuclei –> trigeminal lemniscus/qunitothalamic tract –> medial lemniscus –> ventral caudal medial nucleus of the thalamus –> thalamocortical fibers –> internal capsule –> centrum semi ovale –> somesthetic cerebral cortex
(de Lahunta)
What is the reflex pathway for GSA information of the head
Nociceptors –> branches of CN V –> trigeminal ganglion –> spinal tract of the trigeminal nerve –> pontine sensory nucleus/nucleus of spinal tract of V –>
- Ipsilateral and contralateral facial nucleus GSE LMN (palpebral reflex)
(de Lahunta)
Development of the cerebellum:
Alar plate region of metencephalon –> rhombic lip –> proliferating germinal cells of the rhombic lip follow 1 of 2 pathways –?
- Immature (primitive neurons) or glioblasts
- Migrate to the surface of the rhombic lip
- Give rise to purkinje neurons and neurons of cerebellar nuclei
- Actively dividing germinal layer cells
- Continue to divide as they migrate to the surface of the rhombic lip = superficial layer called the external germinal layer
- As the cerebellar folia develop, these germinal cells will remain on the external surface of these folia
- Continue to divide until they have formed an external germinal layer that is 10-12 cells thick
- The deeper layers stop dividing and differentiate into immature neurons –> migrate deeper past Purkinje cells –> granule cell neurons of the granular layer
- Also creates the stellate (interneurons) of the molecular layer
(de Lahunta)
What are the 3 layers of the cerebellar cortex from superficial to deep? What cells/structures live in each layer?
- Molecular
- Axons and telodendria of granule cell neurons
- Dendritic zones of the Purkinje neurons
- Small population of interneurons and astroctytes
- Purkinje
- Purkinje cell bodies
- Granular
- Granule neuron cell bodies
- Golgi cell (between Purkinje and granular layer)
(de Lahunta)
What is the postnatal development of the cerebellum like in the dog and cat? Calf?
Dog and cat - External germinal layer reaches maximum thickness until 1 week old, decreases in size after 2nd postnatal week
- Poorly populated granule cell neuron layer is present at birth
- Grows rapidly over the first few weeks –> continues to grow for up to 10 weeks
- External germinal layer cells persist for as long as 60-84 days in the kitten, 75 days in the puppy
- When all the cells have migrated into the molecular layer and granular layers, only the leptomeninges remain on the surface of the folia
Calf - External germinal layer reaches maximum thickness at 183 days gestation –> slowly decreases in thickness –> 2 cells thick by 2 mos old gone by 6 mos postnatally
** avoid confusing the external germinal layer in young animal with meningitis!
(de Lahunta)
Picture: 2-day old puppy: 1 – choroid plexus, 2 – cerebellar nucleus; thick external germinal layer covering the developing folia at the top of the image
Cerebellum ventral surface
op = caudal
1-15?
- Right cerebellar hemisphere
- Caudal vermis
- Uvula
- Paramedian lobule
- Uvulonodular fissure
- Ansiform lobule
- Nodulus
- Dorsal paraflocculus
- Ventral paraflocculus
- Flocculonudular peduncle
- Flocculus
- Cerebellar peduncles
- Lingula
- Rostral vermis
- Uvulonodular fissure
(de Lahunta)
What are the components of the archicerebellum?
Aka vestibulocerebellum
Flocculus = small lobule on the ventral aspect of the cerebellar hemisphere
Nodulus = rostral part of the caudal vermis, adjacent to the 4th ventricle
Flocculus and nodulus are connected by the flocculonodular peduncle
Dorsal view of the cerebellum (rostral is to the left)
1-9?
- Ventral paraflocculus
- Dorsal paraflocculus
- Dorsal surface of cerebellum
- Primary fissure
- Vermis of the rostral lobe
- Right cerebellar hemisphere
- Vermis of the caudal lobe
- Ansiform lobule
(de Lahunta)
1-4?
- Stellate cell
- Basket cell
- Golgi cell
- Granule cell
Inhibitory neurons = broken line
Facilitatory neurons = solid line
What is the mechanism by which climbing fibers influence the Purkinje cells?
Cell body in olivary nucleus –> axons enter caudal cerebellar peduncle –> collaterals synapse on cerebellar nuclei –> main axons continue to the white lamina of a folium –> molecular layer
In the molecular layer: excitatory synapse on the dendritic zone of a Purkinje neuron
ASPARTATE is the neurotransmitter released
Where is the olivary nucleus located? Where does it receive fibers from and where does it project to?
Located in the ventrolateral caudal medulla
Rostral margin: facial nucleus, Caudal margin: obex
Ventral margin: Pyramid and medial lemniscus
UMN system, spinal cord afferents –> olivary nucleus –> decussate –> join contralateral caudal cerebellar peduncle
Appearance of 3 fingers oriented obliquely
What makes up the spinocerebellum?
Vermal and paravermal lobule
Receive sensory signals from the spinal cord –> controls posture, locomotion and gaze
- Proprioception from dorsal/ventral spinocerebellar, cuneocerebellar tracts –> paraflocculus –> interposital nucleus –>
- Rostral cerebellar peduncle –> contralateral motor cortex
- Caudal cerebellar peduncle –> red nuleus, olivary nucleus
- The paravermal zone and interposital nucleus influence the motor centers that give rise to the corticospinal and rubrospinal tracts
- Proprioception from dorsal/ventral spinocerebellar, cuneocerebellar tracts –> vermis –> fastigal nucleus –>
- Contralateral cerebral motor cortex
- Reticular formation
- The circuit involving the fastigal nucleus, vermis, cerebral motor cortex, and reticular formation is essential for maintenance of posture and muscle tone
(Uemura)
Where is the cell body of the pyramidal neurons in carnivores? Ungulates?
What are these cell bodies called? What lamina are they located in?
Carnivores: overlaps with sensory area - postcruciate gyrus and rostral syprasylvian gyri
Postcruciate gyrus - neurons –> appendicular musculature
Suprasylvian gyrus –> cervical muscles, muscles of specific areas of the head
Ungulates: medially along the frontal lobe in the region of the precruciate gyrus
These areas may be arranged somatotopically
Neuron cell bodies = giant pyramidal cells or Betz cells
Located in lamina V of the cerebral cortex of the gyri that comprise the motor area
(de Lahunta)
Picture: Topography of the cerebral motor cortex. 1, Postcruciate gyrus: A, pelvic limb; B, thoracic limb. 2, Rostral suprasylvian gyrus: C, ear; D, eyelid; E, masseter, temporal muscles; F, lateral cervical muscles.
What forms the ventral corticospinal tract and where do its axons terminate?
Pyramidal neurons:
- 75% decussate –> lateral corticospinal tract
- 25% do not decussate –> ventral corticospinal tract
- Ventral funiculus, adjacent to the ventral median fissure
- Decussate in the ventral commissure –> terminate in the midthoracic spinal cord segments
- Except in cats - serves the entire spinal cord gray matter
- Synapse on interneurons –> gamma motor neuron OR dorsal horn
** Ungulates - entire pyramidal system is confined primarily to the cervical spinal cord segments
(de Lahunta)
What are the 6 layers of the cerebral cortex
(outer –> inner)
- Molecular layer
- Dendrites of pyramidal cells
- Fibers of stellate cells
- Afferent endings of projection fibers and association fibers
- External granular layer
- Stellate cells (axons confined to the cortex) - ramifying vertically (centripetally and centrifugally) and also horizontal
- Small pyramidal cells - axons may terminate in the cortex
- External pyramidal layer
- Medium-sized pyramidal cells - apices point towards the surface, each giving rise to a thick apical dendrite that extends into the molecular angle
- The lateral range of the pyramidal cells form shorter horizontal dendrites
- Axons of the pyramidal cells are thinner than the main dendrites
- Some of the axons of these pyramidal cells end in the deeper layers of the cortex, others enter the white matter but return to the cortex (association or commissural fibers)
- Internal granular layer
- Stellate cells (axons confined to the cortex) - ramifying vertically (centripetally and centrifugally) and also horizontal
- Internal pyramidal layer (also called Ganglion layer)
- Large-sized pyramidal cells
- Similar morphology to layer III
- Form corticofugal fibers
- These project to the basal nuclei, brainstem nuclei and spinal cord (form corticospinal pathways)
- Others are association fibers which leave the cortex and go to distant cortical regions
- Multiform layer
- Small nerve cells with axons that are distributed chiefly in the more superficial layers of the same or contralateral cortex
What basal nuclei is considered a ventral extension of the rostral end of the caudate nucleus?
Nucleus accumbens
___________ is an extrapyramidal nucleus that is a medioventral extension of the pallidum
Endopeduncular nucleus
Most obvious where it is positioned between the internal capsule and optic tract
What is the extrapyramidal feedback circuit of the neocortex and basal nuclei?
Neocortical extrapyramidal neurons –> caudate nucleus –> pallidum –> ventral rostral nucleus of the thalamus –> neocortex
At the time of cortical initiation of voluntary movement, this circuit provides a modifying control mechanism
The ventral rostral thalamic nucleus is a projection nucleus for the extrapyramidal system
What are the 2 extrapyramidal nuclei of the mesencephalon?
- Substantia nigra
- Red nucleus
Rubrospinal tract: where does it receive axons from, where does it run and where does it terminate?
Function?
Afferent axons from ipsilateral motor area of neocortex –> internal capsule/crus cerebri –> red nucleus in the mesencephalon
Axons of the red nucleus immediately decussate in the tegmentum –> descend caudally as the rubrospinal tract
Found in the lateral funiculus of the spinal cord (closely associated with lateral corticospinal tract), extends the entire length of the spinal cord
Axons terminate on interneurons of the ventral gray column of the spinal cord –> facilitatory to flexor muscles –> functions in the initiation of protraction of the limbs
Also: RUBRONUCLEAR AXONS: leave red nucleus –> decussate –> terminate in CN nuclei with GSE LMN
(de Lahunta)
What is the feedback circuit involving the neocortex, red nucleus, and cerebellum?
Neurons of the neocortex –> ipsilateral pontine nucleus –> decussate transverse fibers of the pons –> middle cerebellar peduncle –> cerebellar cortex –> cerebellar nucleus –> rostral cerebellar peduncle –> decussate in the tegmentum –> red nucleus (ipsilateral to original cortical neurons) –> thalamus (ventral rostral nucleus) –> neocortex
What are the 2 types of intrafusal muscle fibers?
- Nuclear bag - interrupted near its middle by nonstriated dilation containing most of the nuclei
- Nuclear chain - no central dilation, most of its nuclei are accumulated near the middle of the fiber
(de Lahunta)
What is the tonic gamma loop mechanism?
What is the phasic gamma loop mechanism? (aka flexor-reflex gamma loop)
Tonic gamma loop:
Gamma efferent input –> contraction of intrafusal fibers –> stretches nuclear bag region –> stimulates 1a afferent annulospiral ending –> DRG –> (+/- interneuron) –> ventral horn –> alpha motor neuron –> extensor muscle contraction
This is responsible for maintaining normal muscle tone
Phasic gamma loop/flexor reflex gamma loop:
Gamma efferent input –> contraction of intrafusal fibers –> stimulates group II sensory neuron –> DRG –> (+/- interneuron) –> ventral horn –> flexor muscles
Functions with UMN to initiate flexor reflexes in the generation of gait
(de Lahunta)
What are the layers of the retina? (10)
Outer (scleral) to inner (vitreal)
- Pigment epithelium - single layer of cuboidal cells
- Processes of the apical membrane interdigitate with processes of the external segments of the photoreceptors
- Role - regeneration of rhodopsin, removal of degenerate rod membranous lamellae
- Melanin granules fill apical cytoplasm
- Photosensitive layer
- Dendritic zone and cell body of the SSA neuron (photoreceptor cell)
- External segment - parallel lamellae of the rods and cones
- Rods - rhodopsin, cones - idopsin
- External limiting membrane
- Junctional complexes between photoreceptor neurons and supporting radial astrocytes (Muller cells)
- External nuclear layer
- Composed of the nuclei of the cell bodies of the photoreceptors = SSA neurons
- External plexiform layer
- Axons and telodendria of the photoreceptor neurons
- Axons and dendritic zones of the bipolar neurons
- Processes of horizontal neurons (interneurons between photoreceptors)
- Internal nuclear layer
- Nuclei in the small cell bodies of the bipolar neurons
- Bipolar neurons: connect photoreceptor neurons with ganglionic neurons in the visual pathway
- Cell bodies of horizontal interneurons
- Cell bodies of amacrine interneurons
- Nuclei of radial astrocytes
- Internal plexiform layer
- Axons and telodendria of the bipolar neurons
- Axons/dendritic zones of ganglionic neurons
- Processes of amacrins interneurons
- Ganglion layer
- Cell bodies of ganglion neurons
- Nerve fiber layer
- Axons of the ganglionic axons, unmyelinated until they penetrate the sclera at the optic disc (area cribrosa)
- Internal limiting membrane
- Layer of radial astrocytes
- Basmement membrane adjacent to vitreous
What takes place within photoreceptor cell of the retina in the dark?
Dark:
- Photoreceptors have cGMP-gated Na+ channels in the outer segment membrane
- In the dark - cGMP is high within the photoreceptor cell –> binds to Na channels –> opens channel –> depolarization –> release of glutamate on bipolar and horizontal cells
- Rods/cone cells only generate receptor potentials, not action potentials
(Uemura)
What takes place within a photoreceptor cell in light?
- Light stimulates rhodopsin/iopsin –> activation of transducin (GPCR)
- Transducin stimulates cGMP phosphodiesterase –> hydrolyzes cGMP
- Reduced intracellular cGMP –> closes cGMP Na channels –> hyperpolariztaion of photoreceptor cell –> reduced release of glutamate
(Uemura)
Each optic tract contains axons mostly from what part of each retina?
Each optic tract contains axons mostly from the MEDIAL retina of the contralateral eyeball, and the LATERAL side of the ipsilateral eyeball
(deLahunta)
What gyri comprise the cerebral visual cortex?
- Caudal marginal gyri
- Ectomarginal gyri
- Occipital gyri
- Splenial gyri
MNEMONIC: SOME
The visual pathway is somatotopic - specific anatomic portions of the retina are represented in specific anatomic portions of the optic tract, lateral geniculate nucleus, optic radiation, visual cortex
(de Lahunta)
What brainstem tract carries GVA information?
Solitary tract
- Cell bodies in facial ganglion, distal ganglion of CN 9 and 10 –> axon enters the medulla –> courses rostrally in the solitary tract –> synapse in the solitary nucleus
(de Lahunta)
What is the pathway of the lateral olfactory tract?
Cell body: brush and mitral cells of the olfactory bulb –> caudally on the surface of the olfactory peduncle –> continued as lateral olfactory tract –> ipsilateral olfactory cortex (surface of the piriform lobe) –> synapses here with neurons in the cortex of the olfactory peduncle or olfactory tubercle
Olfactory tubercle = nucleus between the medial and lateral olfactory tracts
(de Lahunta)
Figure 16.4
Anatomy of the special visceral afferent olfactory system. A, Amygdala; CLRS, caudal lateral rhinal sulcus; LOT, lateral olfactory tract; MB, mamillary bodies; MOT, medial olfactory tract; OB, olfactory bulb; OP, olfactory peduncle; OT, olfactory tubercle; PHG, parahippocampal gyrus; RLRS, rostral lateral rhinal sulcus; RMRS, rostral medial rhinal sulcus.
How are the functions of the 2 olfactory bulbs coordinated?
Olfactory bulb –> medial olfactory tract –> rostral commissure –> contralateral medial olfactory tract –> contralateral olfactory bulb
Piriform lobe –> commissural axons pass in the rostral commissure –> contralateral piriform lobe
This is the “conscious perception” pathway
(de Lahunta)
Figure 16.4
Anatomy of the special visceral afferent olfactory system. A, Amygdala; CLRS, caudal lateral rhinal sulcus; LOT, lateral olfactory tract; MB, mamillary bodies; MOT, medial olfactory tract; OB, olfactory bulb; OP, olfactory peduncle; OT, olfactory tubercle; PHG, parahippocampal gyrus; RLRS, rostral lateral rhinal sulcus; RMRS, rostral medial rhinal sulcus.
What is the mechanism of receptor transduction of olfactory stimulus?
Olfactory binding protein - protein that is secreted by nasal mucosa. Thought to carry and/or concentrate odorant molecules
The olfactory binding protein carries odorant molecules to the cilia of the olfactory sensory neurons
A receptor odorant complex activates a G-protein –> leads to activation of second messenger systems, opening of Ca2+ channels, and depolarization of the cilia
This depolarization is conducted to the axon hillock of the olfactory sensory neuron, where action potentials are generated
@ the olfactory bulb, olfactory sensory neuron is believed to secrete a peptide neurotransmitter
(Uemura)
Where is the hippocampal commissure located?
Dorsal to the caudal thalamus
At the level of the rostral mesencephalic aqueduct
(de Lahunta)
What are the 3 components of the hippocampal formation?
How are is efferent fibers organized?
Hippocampal formation:
- Hippocampus - long, curved nuclear mass
- Connections to the cingulate gyrus and hypothalamus
- Dentate gyrus - medial to the hippocampus, projects efferents to the hippocampus
- Subiculum - between the lateral edge of the hippocampus and the medial edge of the parahippocampal girus
- The entorhinal cortex of the parahippocampal gyrus is continuous with the subiculum –> continuous with the hippocampus
Efferent fibers:
- Efferent fibers of the dentate gyrus project to the hippocampus
- Efferent fibers of the hippocampus and subiculum form the fornix –> projects to the hypothalamus
- Subicular fibers of the fornix terminate in the hypothalamus and thalamus
- Hippocampal fibers of the fornix terminate primarily in the mammillary nuclei of the hypothalamus
(Uemura)
Regarding the forix:
- The fornix is made of fibers that leave the hippocampus as the ___________
- The 2 crura meet _______(rostral/caudal) to the hippocampal commissure and continue as the _____________
- How is the fornix related to the interventricular foramen?
- The fornix is made of fibers that leave the hippocampus as the fimbria
- The 2 crura meet rostral to the hippocampal commissure and continue as the body of the fornix
- Axons of the fornix body turn ventrally at the rostral commissure –> columns of the fornix
- Small bundle –> rostral to the rostral commissure in the septum pellucidum –> septal area
- (confused if this is actually considered column of fornix)
- Larger bundle –> caudal to the rostral commissure –> thalamus and mamillary body
- Small bundle –> rostral to the rostral commissure in the septum pellucidum –> septal area
- The columns of the fornix form the rostral border of the interventricular foramen on each side
- Caudal border of the interventricular foramen = choroid plexus (leptomeninges associated with choroid plexus here)
(de Lahunta)
What portion of the limbic system serves the following function:
Plays a key role in aggressive behavior
Exerts a general suppressive effect on a variety of visceral functions regulated by the hypothalamus
Cingulate gyrus
- Bound by the genual sulcus and the splenial sulcus
(Uemura)
What are the components of the septal area?
What are the afferent (3) and efferent (1) connections of the septal area?
- Subcallosal area
- Cerebral cortex ventral to the genu of the corpus callosum
- Septal nuclei
- Collection of neuronal cell bodies in the rostral septum pellucidum that bulges into the medial side of the lateral ventricle
- Dosal and just rostral to the bend in the body of the fornix
Afferent:
- Hippocampus (via columns of the fornix)
- Amygdaloid body (via diagonal band and stria terminalis)
- Olfactory bulb –> medial olfactory tract
Efferent
- Median forebrain bundle –> hypothalamus
- Stria habenularis –> habenular nuclei
- Columns of fornix –> hippocampus
(de Lahunta)
What are the diencephalic components of the limbic system?
- Epithalamic habenular nucleus
- Septal area –> stria habenularis –> habenular nucleus
- Connects to the mesencephalon (habenulointercrural tract)
- Rostral thalamic nuclei
- Mamillary body of the hypothalamus –> mammilothalamic tract –> rostral thalamic nucleus
- Rostral thalamic nuclei –> cingulate gyrus and adjacent neopallium
- Hypothalamus (Mamillary body)
- Connects to mesencephalic tectum, visceral motor nuclei in the medulla, mesencephalic intercrural nucleus
(de Lahunta)
What is the Papez circuit?
Made of the
- Cingulate gyrus
- Hippocampal formation
- Mammillary nuclei of the hypothalamus
- Thalamus
Efferents of the neocortex –> cingulate gyrus –> hippocampal formation –> fornix –> mammillary nuclei –> mammilothalamic tract –> thalamus –> cingulate gyrus
Red = Papez Circuit
(Uemura)
What are the cell layers of the hippocampus? What neurons give rise to the axons of the fornix?
- Dentate gyrus
- 3 layered archicortex - molecular cells, granular cells, polymorph cells
- Embedded into the concavity of the hippocampus proper
-
Hippocampus proper
- Gyrus folded concave medially
-
Archicortex is composed of 3 major layers
- Molecular
-
Double pyramidal cells
- These axons run in the fornix
- Join alveus –> continue as fimbria –> crus of fornix, body of fornix, column of fornix (see below)
- Polymorph cell layer
- Divisible into 4 zones: CA1 (at the subiculum) –> CA4 (at the dentate gyrus)
- Subiculum
- Composed of variable layers
- Major source of hippocampal output to the adjacent entorhinal cortex of the piriform lobe and parahippocampal gyrus
What are the 6 groups of thalamic nuclei?
Where are the internal and external medullary lamina of the thalamus?
- Rostral thalamic group (limbic system)
- Medial thalamic (medial dorsal nucleus)
- Lateral thalamic group
- Dorsal
- Dorsolateral nucleus
- Caudolateral nucleus
- Pulvinar nucleus
- Ventral
- Ventral rostral nucleus (extrapyramidal)
- Ventral lateral nucleus (cerebellum)
- Ventral caudal group
- Ventral caudal medial nucleus (cranial nerves)
- Ventral caudal lateral nucleus (spinal nerves)
- Dorsal
- Caudal thalamic group (metatlalamus)
- Medial geniculate nucleus (auditory, vestibular)
- Lateral geniculate nucleus (vision)
- Intralaminar thalamic group
- Central medial nucleus
- Paraventricular nucleus
- Thalamic reticular nucleus (ARAS)
Internal medullary lamina - Divides each side of the thalamus into medial and lateral halves
External medullary lamina - defines the external boundary of the lateral half of the thalamus. It is separated from the internal capsule by the narrow thalamic reticular nucleus
What are the 3 regions of hypothalamic nuclei?
- Rostral region (chiasmic group)
- Supraoptic nucleus
- Suprachiasmic nucleus
- Paraventricular nucleus
- Rostral hypothalamic nucleus
- Preoptic nuclei
- Rostral periventricular nucleus
- Intermediate region (tuberal group)
- Dorsomedial, ventromedial nuclei
- Infundibular nucleus
- Lateral hypothalamic area
- Caudal region, mamillary group
- Premammillary nucleus
- Dorsal and dorsocaudal hypothalamic areas
- Lateral perifornical hypothalamic nuclei
- Periventricular nucleus
- Mamillary nuclei
(de Lahunta)
What 3 gyri comprise the primary somesthetic area?
- Postcruciate gyri
- Rostral suprasylvian gyri
- Rostral ectosylvian gyri
(Uemura)
____________ of the skull is the central surface point on the external occipital protuberance
Inion
_______ of the skull is the junction on the median plane of the right and left frontoparietal sutures, or the point of crossing of the coronal and sagittal sutures
Bregma
(Miller’s)
__________ of the skull is the middle of the ventral margin of the foramen magnum
Basion
(Miller’s)
What structures run through the caudal palatine foramen and sphenopalatine foramen?
Caudal palatine foramen: major palatine artery, vein and nerve
Sphenopalatine foramen: Sphenopalatine artery and vein, caudal nasal nerve
(Little Miller’s)
- Basilar membrane
- Cochlear duct
- Cochlear nerve
- Inner tunnel
- Modiolus
- Organ of Corti
- Osseous spiral lamina
- Scala tympani
- Scala vestibuli
- Spiral ganglion
- Spiral ligament
- Spiral limbus
- Spiral tunnel
- Stria vascularis
- Tectorial membrane
- Temporal bone, petrous part
- Vestibular membrane
(Bacha Histology)
