Neuroanatomy Exam 1 Flashcards
Two Basic Divisions of the Nervous System
PNS and CNS
PNS
Spinal nerves and cranial nerves that convey messages to and from the CNS
CNS
Brain and Spinal Cord
Subdivisions of the Brain
1) Cerebrum
- cerebral hemispheres (separated by longitudinal fissure) and Diencephalon
2) Cerebellum
3) Brainstem
Neuron
-structural and functional unit of the nervous system
-receives and transmits bioelectrical signals across synapses
Made of: cell body, neurites (dentrites and axons)
what are the different types of neurons?
multipolar, bipolar and unipolar
what is the most common pathway for a neurotransmitter?
axon to dendrite
Axons in the central nervous system are called
Tract, Lemniscus and Peduncle
Axons in the peripheral nervous system are called
nerves
ipsalateral
same side of
contralateral
opposite side of
ex. the lesion is on the opposite side of the deficet
bilateral
both sides
decussation
pyramidal decussation –> connects dissimilar places
commissure
corpus callosum –> connects similar places in the right and left brain
Sagittal/parasagittal plane
midline/ parallel to midline
coronal/frontal plane
parallel to the long axis of the body
transverse/horizontal plane
perpendicular to the long axis of the body
Cerebral surface
- heavily convoluted
- increases surface area
- we have 2.5 squared feet of cortex (most of which in sulcal walls
functional subdivisions of the cerebral hemisphere (lobes)
Frontal, parietal, occipital, temporal and limbic
Precentral gyrus function
frontal lobe
primary motor cortex, origin of descending motor pathway and initiates voluntary movements
premotor and supplemental motor area location
frontal lobe
part of the precentral, nearby portions of superior and middle frontal gyri
Brocas Area function
frontal lobe
inferior frontal gyrus of one hemisphere (usually left) for the production of spoken and written language
prefrontal cortex function and location
frontal lobe
rest of the frontal lobe, executive functions (personality, foresight and insight)
Frontal Lobe Landmarks
precentral gyrus and sulcus, frontal gyri (superior, middle and inferior), orbital surface, orbital/orbitofrontal gyri, gyrus rectus, olfactory sulcus with tract and bulb
Parietal Lobe, Lateral surface landmarks
postcentral gyrus, superior parietal lobule and inferior parietal lobule
Parietal Lobe, Medial surface landmarks
precuneus, paracentral lobule
postcentral gyrus function
parietal lobe
primary somatosensory cortex, concerned with initial processing of tactile and and proprioceptive information
inferior parietal lobule function
parietal lobe
one hemisphere only (usually left) involved with language comprehension
Rest of the parietal cortex functions
complex aspects of spatial orientation and directing attention
Temporal lobe, lateral surface landmarks
superior, middle and inferior temporal gyri
Temporal lobe, inferior surface landmarks
occipitotemporal (fusiform) gyrus
primary auditory cortex location
superior surface of the temporal lobe, part of the superior temporal gyrus
Wernike’s area
posterior aspect of one temporal hemisphere (usually left)
language comprehension
A lot of the temporal lobes function
higher order visual processing
medial temporal lobe function
learning and memory
“technically part of the limbic lobe, but referred to as the medial temporal structures
occipital lobe, lateral surface landmarks
variable configuration, termed lateral occipital gyri
occipital lobe, medial surface landmarks
cuneus and lingual gyrus
occipital lobe functions
exclusively visual function
primary visual cortex is in the banks of the calcarine sulcus
rest of the lobe consists of visual association cortex involved in higher order visual processing
Limbic lobe surface landmarks
mostly cingulate and parahippocampal gyri
Limbic system function
important in emotional responses, drive-related behaviors and memory
Insula
- not included in the 5 lobes
- buried deep in the lateral sulcus
- covered by frontal, parietal and temporal opercula
- overlies site where telencephalon and diencephalon fuse during development
Diencephalon Divisions
Thalamus, Hypothalamus, Epithalamus and Subthalamus
Thalamus
- ovid gray matter
- massa intermedia of intrathalamic adhesion, area of thalamic fusion across midline, not functional (not seen on all brains)
- borders the third ventricle, line of ventricular attachment marked by stria medullaris
Thalamus Function
- significant and central importance to CNS functions
- NO sensory information EXCEPT olfactory reaches the cortex without hitting the thalamus first
- involved in motor system neural circuits, which are loops that involve the cerebellum and basal ganglion
- Limbic system projections to cortex also stop in the thalamus first
Hypothalamus
- separated from the thalamus from the hypothalamic sulcus
- inferior surface visible on the base of the brain (as mammillary bodies)
- infundibular stalk connects the hypothalamus to the pituitary
- major visceral control center
- limbic functions
- key autonomic ganglion
Brainstem subdivisions
midbrain, pons and medulla
Brainstem function
- convey information to and from the cerebrum
- cranial nerves
Cranial nerve I
olfactory nerve
consists of a bundle of axons that terminate in the olfactory bulb at the anterior end of the olfactory tract
Cranial nerve II
optic nerve
join to form optic chiasm where half of the fibers cross the midline giving rise to the optic tract
the optic tract ends in the thalamus
embryogically part of the diencephalon so part of the CNS
CN III
occulomotor nerve
emerges from the interpeduncular fossa in rostral midbrain
CN IV
trochlear nerve
Found in caudal midbrain. The nerve leaves the dorsal aspect of the brainstem (the only one that does this) just below the inferior colliculus Innervates the superior oblique muscle.
CN V
trigeminal n.
Enters at midpontine level thru middle cerebellar peduncle.
CN VI
abducens n.
Exits brainstem at the pontomedullary junction near midline, near edge of pyramid as it emerges from the pons.
CN VII
facial n.
Exists lateral the abducens at the pontomedullary junction. Has two parts: motor root that is larger and more medial than the sensory root. Sometime the sensory root is known as the intermediate nerve.
CN VIII
vestibulocochlear n.
Exists lateral the facial nerve at the pontomedullary junction. Has two parts: a medially situated vestibular division and a more laterally situated cochlear division.
CN that emerge off the medulla
CN IX (glossopharyngeal) CN X (vagus) -emerges from postolivary sulcus CN XI (Accessory) -from the upper cervical spinal cord, ascends into the skull and reverses back and goes into the neck CN XII (hypoglossal) -emerges from anterolateral sulcus
Basal Ganglia
involved in movement control
separated from the thalamus by the internal capsule
caudate, putamen and globus pallidus are the major components
internal capsule
a fiber bundle interconnecting cortex and deep structures
Dorsal striatum
caudate and putamen
lenticular nucleus
putamen and globus pallidus
Where can you find the amygdala?
beneath the uncus in the temporal lobe
Ventricles
- cavity of embryologic neural tube, filled with CSF made in the choroid plexus
- suspends brain, regulates extracellular fluid composition and route by which certain chemical messengers are distributed in the CNS
What are the 4 ventricles and their path
CSF is produced mainly by a structure called the choroid plexus in the lateral, third and fourth ventricles. CSF flows from the lateral ventricle to the third ventricle through the interventricular foramen (also called the foramen of Monro). The third ventricle and fourth ventricle are connected to each other by the cerebral aqueduct (also called the Aqueduct of Sylvius). CSF then flows into the subarachnoid space through the foramina of Luschka (there are two of these) and the foramen of Magendie (only one of these).
subarachnoid cisterns
- areas within the subarachnoid space where the pia mater and arachnoid membrane are not in close approximation. The subarachnoid tissue is not as abundant here as in the normal subarachnoid space and cerebrospinal fluid (CSF) gathers to form pools or cisterns
- arachnoid attached to the inner dural layer
Largest subarachnoid cistern?
Cisterna Magna
cerebellomedullary cistern
Reabsoprtion of CSF
Absorption of the CSF into the blood stream takes place in the superior sagittal sinus through structures called arachnoid villi . When the CSF pressure is greater than the venous pressure, CSF will flow into the blood stream. However, the arachnoid villi act as “one way valves”…if the CSF pressure is less than the venous pressure, the arachnoid villi will NOT let blood pass into the ventricular system
Herniations
Dural reflections are rigid and firmly attached to the skull
when blood pressure starts occupying the space that the brain once had, intracranial pressure increases and results in a subdural hematoma
Functions of the CNS coverings
(for the skull and vertebral column)
- the brain and cord are suspended by membranous coverings called meninges
- they allow the brain to turn with the head
- CSF in the meninges (and ventricles) allow for buoyancy and support of the brain
Three meningeal layers
- Dura mater (outermost, toughest)
- Arachnoid mater
- Pia mater (outermost, attached to the CNS)
What “meningeal layer” contains the CSF?
subarachnoid space btwn the arachnoid and pia mater
leptomeninges
the innermost layers that surround the CNS
arachnoid and pia mater
Two Dural Layers
periosteum (near the skull) and meningeal (inner layer)
potential spaces that can develop
epidural - between dura and calvaria
subdural - in the innermost dural layer, near dura-arachnoid interface
Actual spaces
epidural hematoma - tear of the meningeal arteries btwn the skull and dura
subdural hematoma - tearing of the bridging veins in the subdural space
Dural reflection/dural septum
when dural fold on itself and forms intracranial compartments
the inner meningeal layer forms two main reflections - falx cerebri and tentorium cerebelli
Tentorium cerebelli
- supratentorial compartment contains cerebrum
- infratentorial compartment contains the cerebellum and brainstem (posterior structures)
tentorial notch/incisure
space in the tentorium where the brainstem passes through
Dural Venous sinuses
at the edges of the fused dura (periosteal and meningeal) the 2 layers are not fused and allow for venous flow
these pathways are lined by endothelium
superior sagittal sinus location
along the edge of the falx
transverse sinus location
Left and right found along the posterior attachment of the tentorium
straight sinus location
along attachment of the falx and tentorium
Flow of the venous sinuses
the superior sagittal sinus, both transverse sinuses and straight sinus drains into the confluence of sinuses near the occipital protuberance, then the sigmoid sinuses into the jugular vein
inferior sagittal sinus
at the lower edge of the falx, empties into the straight sinus
occipital sinus
drains into the confluence
superior petrosal sinus
in the edge of the tentorium attached to the petrous temporal bone, carries blood from the cavernous sinus to the transverse sinus
inferior petrosal sinus
follows a groove between the temporal and occipital bones and carries blood from the cavernous sinus to the jugular vein
What two arteries supply the CNS?
vertebral and internal carotid arteries
Branches of the ICA?
the ICA ascends the neck and traverses the petrous temporal bone, and goes through the cavernous sinus
the opthalamic artery branches off of the IC in the subarachnoid space
-both the anterior choroidal and Posterior communicating artery branch off the IC
-the IC bifurcates into the Middle cerebral and anterior cerebral artery along the optic chiasm
Anterior choroidal artery
- long and thin
- clinical significance in strokes
- supplies optic tract, choroid plexus in lateral ventricles, deep structures (internal capsule, thalamus and hippocampus) sometimes cerebral peduncle
posterior communicating artery
- passes posterior to the optic tract to join the posterior cerebral artery
- since the PCA is part of the vertebral artery supply, the posterior communicating artery connects the supplies
anterior cerebral artery
- runs medially in the longitudinal fissure, arches posteriorly and follows the corpus callosum
- supplies the medial frontal and parietal lobes
- the two anterior cerebral arteries are connected by the anterior communicating artery
Middle Cerebral artery
runs laterally into the lateral sulcus, divides into many branches and supplies most of the lateral cerebral hemisphere
perforating arteries
- arise from all arteries at the base of the brain
- numerous around the optic chiasm, btwn the cerebral peduncles, and contain both ant. and post. parts
- involved in strokes and neurological deficits out of proportion to size
- supplies the basal ganglion, thalamus and internal capsule
perforating arteries from the Middle Cerebral artery are called?
Lenticulostriate arteries
Vertebral-Basilar system
- supplies brainstem and cerebellum
- vertebral a. run laterally along the medulla, fuse to the basilar a. at the pons
Prior to forming the basilar a., what does the vertebral a. give rise to?
- posterior spinal artery (supplies post. 1/3 spinal cord)
- anterior spinal artery (join together to make one a. to supply ant. 2/3 spinal cord)
- PICA (supplies inf. cerebellum and lateral medulla)
What does the Basilar a. give rise to?
- AICA (supplies ant.,inf. cerebellum (flocculus) and caudal pons)
- SCA (superior cerebellum, caudal midbrain and rostral pons)
- bifurcates at midbrain into 2 PCAS
posterior cerebral artery
- branches supply medial and inferior surfaces of the temporal and occipital lobes
- branches also go to rostral midbrain and posterior diencephalon
Circle of Willis
- connects the vertebral-basilar and IC a. systems via the posterior communicating artery
- the anterior communicating artery connects the Right and Left sides
- little blood flow through
- if major vessel in the circle or proximal to the circle is occluded, the communicating arteries will do anastomoses
Cerebral blood flow
autoregulation: vessels are stretch sensitive, so they constrict when decreased pressure and dilate when increased pressure
collaboration: of the brain and vessels with increased activity
autonomics: more important at extremes
WORKS TO MAKE UNIFORM BLOOD FLOW
Blood brain Barrier
-refers to the anatomic and physio barrier that controls movement of materials from the extracellular fluid of the body to the brain
how does the blood brain barrier work?
- the tight endothelial junctions in the arachnoid layer and lack of pinocytic vesicles organize this
- lipid soluble substances go through
- glucose crosses by facilitated diffusion (but not other molecules of similar solubility and size)
- other substances are active transport
Circumventricular organs
- areas with “leaky capillaries” that allow open communication with the brain and extracellular fluid
- located near the 3rd and 4th ventricle
- sensory function: monitor CSF composition (ependymal cells called tancytes that overly the ventricular surface)
- release hormones from neuronal endings into the blood
Venous drainage
through a system of cerebral veins that empty into dural sinuses to go to the IJV and basilar venous plexus that communicate with the epidural venous plexus of the spinal cord
-a lot of anastomoses
Where do a lot of superficial veins drain in the cerebrum?
superior sagittal sinus
where do a lot of deep internal veins drain in the cerebrum?
straight sinus
What is the principal component of the PNS?
spinal nerve
Where do visceral efferent cell bodies lie in the spinal nerve?
in the lateral horn
where do somatic efferent cell bodies lie in the spinal nerve?
in the anterior horn
where to somatic and visceral efferent cell bodies lie in the spinal nerve?
in the posterior root ganglion
what is motor synonymous with?
efferent
what is sensory synonymous with?
afferent
What are the 3 layers around peripheral nerves?
Epineurium, perineurium and endoneurium
Epineurium
-continuous with the dura mater from the CNS
-most prominent around the trunks of nerves
-provides tensile strength
(outermost)
Perineurium
- continuous with the arachnoid mater from the CNS
- wraps around fascicles (bundle of axons)
- blood-nerve barrier
Endoneurium
surrounds each individual nerve fiber
Where are the blood vessels in peripheral nerves?
btwn the epineurium and and perineurium
what is saltatory conduction?
“jumping from myelin sheath to myelin sheath”
- membrane depolarizes at nodes
- conduction proceeds in either direction
Where is the CNS-PNS junction for glial cells
- highly variable in spinal and cranial nerves
- near foramen
- on vestibular cochlear n. tumors will form at the junction
What does the caliber of the axon relate to?
the amplitude of the action potential
what does the myelin and amount relate to?
action potential conduction velocity
Fibers in the PNS that are heavily myelinated and have a large axon
- lower motor neurons that move the skeletal mm. (alpha)
- type 1a (muscle spindle endings), 1b (golgi tendons) and lower motor neurons
Fibers in the PNS that are unmyelinated and small axon
- postganglionic autonomic
- slow pain, heat, itch and touch
- type C
what is an adequate stimulus?
each receptor has a stimulus that is is most receptive to and will convey to the CNS about
-not always perfect b/c pressure on the eye will lead to depolarization of photoreceptors
chemoreceptor
taste, smell, pH and metabolite concentrations
photoreceptor
retinal visual receptors
thermoreceptor
temperature
mechanoreceptor
most diverse
physical deformation, touch, mm. length and tension, auditory and vestibular receptors
Nociceptors
pain
All receptors have..
- receptive area (may be specialized)
- synaptic area where message is sent to the CNS
- all of them turn an physical stimulus into an electrical signal that the nervous system can understand (receptor potential)
receptor potential
- can encode the intensity and duration of a stimulus
- some receptor systems are more sensitive than others, so this is reflected by identification of the system (CNS can choose to ignore stimulus)
receptive field
- conveys information about location of the receptor
- the “wiring” pattern in ascending sensory pathways to cortex preserve location and nature of the information
- receptive field much smaller on the pinky than in part of the forearm, also a more sensitive area may have more receptors
Adaption of sensory receptors
-receptors become less sensitive to the stimulus if the stimulus is maintained
EXCEPTION: nociceptors
slow adapting - adapt only a little, detect static position, muscle spindle
rapidly adapting - adapt a lot, pacinian corpuscles or hair follicles
**Adaption is at the receptor level, but CNS can regulate receptor sensitivity
muscle spindle receptors
-detect mm. length, in all skeletal mm.
-intrafusal mm. fibers within a capsule are attached to extrafusal (regular) mm. fibers, so that when the mm. stretches, so does the intrafusal fibers
-central area has sensory endings that convey to the CNS
(and gamma fibers help with this)
free nerve endings on mm.
- detect mm. pain if you workout too much
- chemoreceptors that respond to pH and make mm. ache after a workout
golgi tendon receptors
found in mm. tendon junctions detects mm. TENSION
- collagen bundles surrounded by a capsule and sensory fibers form a weave btwn the collagen
- mm. contraction distorts the capsule, stimulating sensory fibers
Muscle spindle and golgi tendon receptors working together
Spindle and GTO have different functions
- If a muscle contracts isometrically, tension generated across tendons and GTOs are stimulated, but spindles won’t be activated as muscle size has not changed.
- A relaxed muscle can be easily stretched and the spindles will be activated, but the GTOs will experience little tension and remain inactive.
**A muscle uses spindles and GTOs to monitor length and tension simultaneously.
Where is the dorsal root ganglion?
next to the intervertebral foramen where the spinal nerve exits
what space is in the vertebral canal that is not present in the brain?
epidural space
b/c no more periosteial dura to put right next to the bone
spinal cord segments
-organized according to nerve roots
31 total
8 cervical, 12 thoracic, 5 lumbar and 1 coccygeal
**functional rather than anatomic
where do the dorsal rootlets enter the SC?
posterolateral sulcus
where do the ventral rootlets leave the SC?
anterolateral sulcus
path of spinal cord
rootlets to roots to spinal cord
** all dorsal roots have a dorsal root ganglion as well
dermatomes
each spinal nerve innervates a section of skin
-helpful in diagnosis to find the highest level of sensory deficiency to deduce the cord lesion
What spinal nerve does not innervate a dermatome?
C1
Why are there enlargements in the spinal cord?
because there is a large anterior horn in the SC for motor neurons
Where is the cervical enlargement?
C5-T1
for controlling the upper limb movement
Where is the Lumbar enlargement?
L2-S3
for controlling the lower extremity movement
Explain the SC landmarks from rostral to caudal
starts at the brainstem and travels caudally to the conus medullaris, then the filum terminale (part of the pia wrapped in dura), the filum terminale terminates in the dura which anchors to the cocyx
Posterior median sulcus
in the SC
glial septum
separates the white matter, no real function
Anterior median fissure
distinct cleft for the anterior spinal a.
posterolateral sulcus
for the dorsal root entry (into gray matter)
Anterolateral sulcus
for ventral horn to send out (not clearly seen)
Where does the posterior intermediate sulcus terminate?
T6
(partially divides the posterior funiculi)
divides fasciculus cuneatus and fasciculus gracilis
Anterior white commissure
at the end of the anterior median fissure, allows communication through both sides of the cord
white matter organization in the spinal cord
posterior funiculi - in the back of the H
lateral funiculi - large, ends where the ant. horn fibers leave
anterior funiculi
**at all SC levels
where is the substantia gelatinosa and what does it convey?
in the posterior horn, spinal cord lamina II
pain and temperature
**huge at the lumbar level
the posterior horn of the gray matter in the SC consists mostly of?
interneurons that ..
processes remain in the cord and projection neurons whose axons go up the sensory pathways
the anterior horn of the gray matter in the SC consists of?
motor neurons that control skeletal mm. (lower motor neurons or alpha neurons)
- only means to move a muscle, will become limp, weak, atrophy or undergo paralysis if not working
- groups of clusters (axial is medial clusters and limb muscles are more lateral)
- gamma motor neurons innervate the spindle (length)
What are the 2 specialized columns in the anterior horn of the gray matter?
spinal accessory nucleus (caudal medulla to C5) for the accessory nerve
phrenic nucleus (C3-5) innervates the diaphragm
-cervical cord injuries–> patient cannot breathe
What level is the intermedolateral horn in the gray matter of the SC and what does it carry?
levels T1-L3, preganglionic symp neurons
(axons leave through the ventral roots)
**if you see a distinct projection in the horn then you are in the thoracic level
What else can be found in the lateral part of the gray matter of the SC that you cannot see?
sacral parasympathetic nucleus (S2-4) BUT no distinct horn is formed
-axons leave to supply the pelvic viscera
Clarkes nucleus
collection of neurons at medial surface of the intermediate gray matter (T1-L2)
- relays info to cerebellum about proprioceptive info from the legs
- part of the posterior horn b/c sensory info??
visual differences in the levels of the SC?
cervical - oblong, a lot of white matter, big anterior horn
thoracic - circle, intermediolateral horn, clarks nucleus
lumbar - less white matter, large ant. horn, large substansia gelatinosa
where does the spinal cord terminate?
L1/2
what is the cauda equina and why do we have it?
long dorsal and ventral roots that extend from the SC in the lumbar cistern because the vertebral column grows past the spinal cord so the roots must extend out
what do longitudinal grooves in the SC represent?
nerve fibers
what are denticulate ligaments?
extensions of pia-arachnoid mater than laterally anchor the SC to the dura mater
The Rexed lamina I and V do what?
relay sensory signals
other than the denticulate ligaments, what else helps to laterally anchor the SC
the spinal nerves
what do all reflexes involve?
receptor associated with an afferent neuron with cell body in the DRG and an efferent neuron with cell body in the CNS
-all have interneurons except stretch reflex!!
Stretch reflex
- simplest “Deep Tendon reflex”
- monosynaptic (1 synapse, 2 neurons)
- important during movement and maintaining posture
The role of interneurons
- hit golgi tendon fibers, which then synapse with interneurons that when activated can be inhibitory or activate the efferent fibers
- thought to contribute to fine adjustment in force of muscle contraction during muscle activity
What controls the blood supply to the spinal cord?
anterior spinal artery anterior 2/3 spinal cord (off vertebral)
posterior spinal artery post 1/3 SC (off vertebral or PICA)
What are radicular arteries?
they come off intercostal arteries to form a spinal branch that once past the intervertebral foramen will branch to form both an anterior and posterior radicular artery to help the anterior spinal artery supply the SC
Artery of Adamkiewicz
the great vertebral radicular artery
-comes off the left at about T12
what separates the sensory and motor portions of the SC and brainstem?
Sulcus limitans (develops in the neural tube)
what column in the brainstem are CN III, IV and VI?
somatic motor column
what type of nucleus do all CN III, IV and VI have?
somatic efferent nucleus
What occulomotor CN has a nucleus other than somatic efferent?
CN III, afferent nucleus (E-W nucleus)
What mm. does CN III control?
occulomotor nn.
superior, inferior, medial recti, inferior oblique and levator palpebrae superioris
papillary sphincter and ciliary mm.
What mm. does CN IV control?
trochlear nerve
superior oblique
What mm. does CN VI control?
Abducens nerve
Lateral rectus
where do all of the extrinsic ocular mm. insert?
into the sclera of the eye
What are the three broad functions of the brainstem?
- conduit - info goes to the cortex and SC thru the brainstem, white matter tracts
- cranial nerves (like spinal nerves for the head) that control special functions like taste and eye mm.
- integrative function - complex motor patterns and cardiorespiratory control
what does the midbrain consist of?
the superior and inferior colliculi (posteriorly)
open vs. closed medulla
an open medulla is the part of the medulla that had the 4th ventricle behind it, but since the 4th ventricle does not extend the whole way down the medulla, the closed medulla is the part without the 4th ventricle behind it
what is the obex in the medulla?
medulla
a hole where the 4th ventricle opens to the central canal of the SC
Cuneate and Gracile tubercles
medulla
where the 2 posterior columns of the white matter end
(collection of nuclei)
Why is the olive formed?
medulla
because it is made by the olivary nucleus
what is the pyramid bound by and what does it interupt with its deccusation?
medulla
the anterolateral sulcus and interupts the anterior median fissure
Why does the facial colliculus form?
pons
because CN VII is wrapping around CN VI
Hypoglossal trigone
triangular swelling in floor of 4th ventricle made by underlying hypoglossal nerve nucleus.
Vagal trigone
triangular swelling in floor of 4th ventricle made by underlying dorsal motor nucleus of the vagus nerve
Superior colliculus
Gray matter mass in roof (tectum) of rostral midbrain. Has roles in directing visual attention and controlling eye movements.
Inferior colliculus
Gray matter mass in roof (tectum) of caudal midbrain. It is a major component of the auditory system. It received input from the lateral lemniscus; output goes thru the inferior brachium to the medial geniculate nucleus of the thalamus.
Cerebral peduncles
Large bundle of white matter at the base of the midbrain. It contains tightly packed fibers from the cerebral cortex on their way to the brainstem and spinal cord.
what are the “functionality levels” of the brainstem and why do they form?
tegmentum, tectum and stuff added onto the anterior surface, mainly anterior descending tracts (after development). They form because of the closing of the neural tube and development of the 4th ventricle
Tegmentum
tissue anterior to the ventricle
houses all of the CN nuclei
Tectum
“roof”
tissue posterior to the ventricle ( only really the midbrain level) so the colliculi
What are the main fiber tracts located in the brainstem?
corticospinal (anterior), spinothalamic (anterolateral) and medial lemniscus (variable)
differences between the rostral and caudal medulla
- ventricular space (caudal is central canal and rostral is the fourth ventricle
- the nuclei present (caudal is the gracile and cuneate nuclei and tract and rostral is the inferior olivary nucleus)
- arcuate fibers (in caudal the internal arcuate fibers form the medial lemniscus and in the rostral the internal fibers go from IO to the ICP on the opposite side)
- Pyramids (caudal pyramid decussation and rostral pyramids present)
- also the rostral medulla has CN XI
differences between the rostral and caudal pons
- the peduncles (in the caudal pons the MCP dominates with a little bit of ICP and in the rostral pons the SCP dominates)
- the 4th ventricle (large in the caudal and small in the rostral because going into the cerebral aqueduct)
- medial lemniscus (horizontal with feet out lateral, in the rostral pons the ML approaches the STT)
Caudal vs. rostal midbrain
caudal midbrain has inferior colliculi, CN IV and the decussation of SCP
Rostral midbrain has superior colliculi, CN III, the red nucleus and substantia nigra
what arteries supplies the anterior and medial brainstem?
perforating branches of the vertebral-basilar system
where do the vertebral arteries become the basilar?
at the jxn of the medulla and the pons
what arteries supply the lateral brainstem?
AICA, PICA and SCA on their way back into the cerebellum
what are the 6 types of nerve fibers in the brain stem?
somatic efferent, somatic afferent, visceral efferent, visceral afferent, special sensory and brachial motor from the pharyngeal arches
*** one CN cannot have all 6 types, only combinations
what are the somatic motor fiber CN?
III, IV, VI and XII
what are the special sensory fiber CN?
I, II, and VIII
what are the brachiomeric nerves?
V, VII, IX, X and XI
*also have other components to them
somatosensory receptors
direct mechanical, chemical or thermal changes
- unipolar neurons with cell body in DRG or the cranial nerve ganglion
- process in the CNS
- peripheral process with an ending in the skin, muscle or joint
Lower motor neuron
innervates striated mm., directly signals mm. to contract, only way that the movement can be initiated
-last neuron in the chain of neurons
includes alpha (extrafusal) and gamma (intrafusal) mm. fibers
Lesion in the lower motor neuron leads to
atonia, areflexia, flaccid paralysis, fasciculations, fibrillations and atrophy
Upper motor neuron lesion
- spastic paralysis
- hypertonia (incresed resting tension)
- hyperreflexia
- clonus pathologic reflexes like the babinski sign
- mild disuse atrpohy
where are lower motor neurons located?
cell bodies are in the anterior horn and axons form the ventral root that spread widely. Each branch ends at one neuromuscular junction
Describe the arrangement of motor neurons in the anterior horn of the spinal cord
- neurons that control axial mm. are more medial (distal mm. more lateral
- neurons that control flexors are located more posterior than the extensors
what is a motor unit
1 motor neuron and all of the myofibers it innervates
Type 1 mm. fibers
sustain weight bearing forces, lipid rich, a lot of mitochondria, slow twitch and red in appearance
Type 2 mm. fibers
sudden movement, a lot of glycogen, fast twitch
explain how motor units are recruited
they are recruited in order of size.
-the more motor units recruited, the greater the force
corticospinal tract origins
- primary motor (precentral gyrus) area 4
- somatic sensory (postcentral gyrus) area 3,1,2
- premotor area - lateral surface area 6
- supplemental motor - medial surface area 6
- superior parietal lobule - area 5 & 7
primary motor area
area 4 (medial and lateral)
function: execution of contralateral voluntary movements and controls the fine digital movements
- projections to the brainstem and spinal cord, some monosynaptic terminations in the SC motor neurons for the hand
- lesion results in paralysis of contralateral musculature
premotor area
area 6, lateral aspect
function: plans movement from external cues, controls proximal and axial musculature, facial empathetic movements
-projections to primary motor area and reticular formation
(some fibers project to all spinal cord levels)
-lesion leads to moderate weakness of contralateral proximal mm. and loss of ability to associate learned hand movements to verbal or visual clues
Supplementary Motor Area (SMA)
Area 6, medial
function: plans movements while thinking (internally paced), assembles new and learned sequences and “imagines” movement
- projects to premotor and primary motor areas
Parietal Lobe
- somatic sensory area and superior parietal lobule, areas 3-1-2 and 5,7
- project to the primary motor area to direct motor patterns in response to sensory input
- projects to sensory areas of brainstem and spinal cord to modulate sensory signals
Vestibulospinal tract
controls axial musculature (balance)
Origin: vestibular nuclei in the pons
-receives input from the vestibular end organ and cerebellum
Lateral vestibularspinal tract
projects via the the lateral funiculus to ipsalateral spinal cord to facilitate antigravity muscles
medial vestibularspinal tract
projects via the anterior funiculus to spinal cord cervical levels bilaterally to control head movements in response to gravity
Rubrospinal tract
origin: red nucleus of the midbrain so “rubro”
receives input from the the premotor and primary motor areas and the cerebellum
goes through the lateral funiculus and decussation in the ventral tegmentum
-contralateral spinal cord
-facilitates upper extremity flexor mm. tone
Reticulospinal tract
origin: brainstem reticular formation (pons and medulla)
receives input from motor and somatic sensory cortex
-courses through the brainstem in the anterior to medial longitudinal fasciculus (MLF) and the anterior fasciculus in the spinal cord (bilaterally)
-functions in the rhythmic walking motion
-support motor recovery to arm and hand???
what are the 3 main divisions of the autonomic nervous system?
sympathetic, parasympathetic and enteric nervous sytem (IBS problems)
what are the similarities of the autonomic and somatic system?
visceral sensory fibers, ascending pathways, descending pathways that control motor neurons and reflexes
What is the difference between the autonomic and somatic nervous system?
the autonomic nervous system use a two neuron chain to reach their efferents
preganglionic cell body in the CNS and postganglionic neuron in the ganglion
what is the same about the parasympathetic and sympathetic efferent system?
their preganglionic fibers are myelinated and their postganglionic fibers are unmyelinated
What are the neurotransmitters used for para and sym?
in the parasymp Ach is used, but different types
in the symp Ach is the 1st synapse and NE is in the 2nd synapse
Other than the neurotransmitters, what is another difference in the parasymp and symp chain?
for para, the ganglion are near (or in) the innervated organ and for symp, the ganglion are near the CNS
describe the symp system
- preganglionic fibers are from spinal cord segments T1 to L2/3
- The fibers travel in the spinal cord to the symp chain, prevertebral ganglion and the adrenal gland
describe the para system
- preganglionic neurons are in the brainstem and sacral cord, they travel in CN III, VII, IX, X and sacral nerves
- they flow to thoracic, abdominal and pelvic viscera. THey do NOT go to the limbs
what are the cranial nerves for the parasympathetics?
CN III, CN VII, CN IX and CN X
CN III parasympathetics
edinger-westphal nucleus (in the rostral midbrain) sends fibers to the ciliary ganglion which then contricts the pupils and affects the ciliary mm. for accomodation for near vision
CN VII parasym
preganglionic nucleus: superior salivatory nucleus in the tegmentum of the pons
postganglionic nucleus: pterygopalatine gang and goes to nasal and lacrimal glands
submadibular ganglion goes to the submandibular and sublingual salivary glands
** both create watery mucous
CN IX parasym
pregang: inferior salivatory nucleus in the medulla
axons terminate in the otic ganglion, goes to parotid salivatory gland
** watery thin mucous
CN X parasym
pregang (in the medulla) : the dorsal motor nucleus (DNX) and Nucleus ambiguous
DNX mostly GI tract and nucleus ambiguous mostly heart
-go along with other vagal nerve fibers to terminate in the wall of the organ (viscera in thorax to transverse colon)
** no specific post gang fibers because so many go so many places
-reduces heart rate, BP, increases gastric secretion and peristaltic activity
Sacral parasymp outflow
pregang: sacral sc lateral horn S2-4
- exit in the ventral root on splanchnic nerves and terminate in the viscera
- transverse colon to rectum ( bladder, uterus, genitals, gonads..)
where are symp preganglionic fibers located?
In the lateral horn of spinal cord from levels T1 to L2/3
Sympathetic ganglia supplying fibers to pelvic & abdominal viscera are called?
prevertebral (collateral) ganglia
What are the 4 things that preganglionic symp fibers can do after leaving the ventral root?
- synapse in nearest ganglion
- ascend the chain and synapse in SCG or MCG
- descend and synapse in lumbar/sacral ganglia
- traverse the chain and emerge as splanchnic nerves
where is white communicating rami present opposed to gray communicating rami?
only T1 to L2/3 spinal nerve have white communicating rami while gray communicating rami (and postganglionic sympathetic fibers) are present on all spinal nerves.
how do postganglionic symp fibers reach the head??
cervical ganglia and carotid plexus (on the ICA)
what is the difference between paravertebral and prevertebral ganglia?
paravertebral is within the chain ganglia and prevertebral is collateral ganglia
Horner’s syndrome
- loss of sympathetic innervation to the face
symptoms: ptosis (eyelid droop), miosis (small pupil), endophthalaos (apparent sunken eye) and anhydrosis (dry skin) - *superior cervical ganglion destroyed
Congenital Horner Syndrome
-loss of symp innervation to the face
ptosis, miosis, endophthalmos, anhydrosis and heterchroma (if before 2)
referred pain
pain in the viscera perceived as somatic pain
-happens when the viscera is innervated by the same cord level as the surface structure
-mixing of signals at spinal cord and brainstem levels
-viscera is not somatotopic
examples:
heart pain during myocardial infarction, intestinal pain in abdomen wall and labor pains in the sacral and back area
Enteric Nervous system
- autonomic
- provides innervation for the intestinal tract, pancreas and gall bladder
- there is a neural plexus (myenteric plexus of auerbach and submuccous plexus of meissner)
- *provides primary control of motility and secretion
- *if problems the IBS
where is the CNS origination of CN IV
trochlear nucleus
where is the CNS origination of CN VI
abducens nucleus
where is the CNS origination of CN III
occulomotor nucleus
what is the action of the superior oblique mm?
internal rotation
what is the action of the inferior oblique mm?
external rotation
where do the occulomotor nerves enter?
the superior orbital fissure
describe the multiple columns of neurons for occulomotor n.
Levator palpebrae superioris, in midline innervates muscle bilaterally
Superior rectus innervated contralaterally
Column supplying medial rectus, inferior oblique, inferior rectus are project to ipsilateral muscles
Edinger-Westphal nucleus, preganglionic parasympathetic projection to ipsilateral ciliary ganglion, innervates pupillary sphincter and ciliary muscle
Injury to CN III
ipsalateral lesion eye deviates laterally (LR unopposed)
- no medial movement
- vertical movement impaired (SR, IR, IO)
- diplopia (double vision because eyes are not focused on the same thing
- levator weak –>ptosis
- mydriasis (dilated eye)
- pupil doesn’t constrict in response to light
- no near vision focus
IV is unique of the cranial nerves because
it is the only one to originate entirely from a contralateral nucleus and it is the only cranial nerve on the dorsal brainstem surface.
CN IV injury
- less noticeable
- hard to read, double vision
- the eye will go upwards instead of down
- tilt head to align visual field
what is the facial colliculus?
VI nucleus and internal genu of CN VII
CN IV description
innervates contralateral superior oblique muscle
-fibers leave the nucleus, turn caudally in the PAG, arch dorsally to decussate and leave the brainstem in the midbrain-pons junction (caudal pons)
what is the occulomotor nuclear complex?
E-W nucleus and the occulomotor nerve
CN VI description
innervates ipsalateral LR mm.
nucleus is in the floor of the 4th ventricle in the caudal pons
-medial to the the nucleus are the MLF and motor fibers of VII
nerve injury to CN VI
medial strabismus
what mm. are needed in lateral gaze
ipsa lateral rectus and contralateral medial rectus
explain CN VI nuclear damage
medial strabismus and lateral gaze paralysis
ipsalateral eye will not abduct past the midposition and contralateral eye will not adduct past the midposition
explain MLF connection to the CN VI
the CN VI contains motor and internuclear neurons that ascend to the MLF
-the MLF allows coordination of the head and eye movement through the connection of III, IV and VI (fast track)
Injury to MLF
-internuclear opthalmoplegia “paralysis due to damage between nuclei”
-damage results in removalof excitatory input to ipsalateral III nucleus
-ipsa eye cannot move past midposition during horizontal gaze
CN VI nuclei fine, so lateral movement intact
pupillary light reflex steps
response to light…
1) afferent limb (CN II)- retinal ganglion cells to pretectal nuclei
2) pretectal nucleus is linked to BOTH EWN and goes to the contralateral one via the posterior commissure
3) preganglionic parasym travel with CN III to the ciliary ganglion
4) postganglionic in short ciliary nerves enters the iris and affects the sphincter (constrictor) pupillae
Explain accomodation (near response)
- at rest, the lens is flat from the suspensory ligaments tension
- when the ciliary mm. contracts, the suspensory ligaments relax, and bulging of the lens occurs to focus the light in the fovea for near vision
- the eye also constricts to focus light on the fovea
- the eyes also converge due to increased tone in the medial rectus mm. to focus the light on the fovea
symp pathway to the eyes
- fibers from the hypothalamus cross the midline to go ipsalateral along the descending fibers in the pons and medulla
- preganglionic fibers emerge off the thoracic ventral root and goes up the symp chain to synapse on the SCG
- goes up the IC and external carotid a. to leave the cavernous sinus, join with Vi and to the ciliary n.
what are the 3 main eye control movements
- Scanning
- high speed movement called saccades - Tracking
- smooth pursuit, follow an object - compensation
- holding gaze while moving head (vestibular system)
how many gaze centers are there?
4 (left, right, up, down)
where are the gaze centers for scanning?
in the brainstem reticular formation
where are the horizontal saccades for scanning
paramedian pontine reticular formation and pulls eyes to their respective sides
where are the upward saccades for scanning?
midbrain, rostral interstitial nuclei of the MLF
where are the downward saccades for scanning
in the midbrain next to the upward center
Pathways involved in voluntary saccade to the left.
- Projection from right frontal eye field activates left paramedian pontine reticular formation (PPRF).
- Some PPRF neurons activate adjacent abducens neurons
- Other PPRF neurons send heavily myelinated (fast) internuclear fibers along the medial longitudinal bundle to activate oculomotor neurons serving medial rectus.
what is the main sensory nerve to the head??
CN V
what branch of CN V has both sensory and motor components
mandibular (V3)
where is the principal sensory nucleus of CN V and where is its origin?
pons, skin and deep tissues of the head and dura
where is the spinal nucleus of CN V and where is its origin?
medulla and blends in wiht the lam1/2 of posterior horn of the SC (pain and temp), skin and deep tissues of the head and dura
where is the mesencephalic nucleus of CN V and where is its origin?
midbrain, Myelinated processes from these pseudounipolar neurons form the mesencephalic tract.
the sensory fibers are from the neuromuscular spindles of mastication mm. and pressure and tension receptors in periodontal ligaments. they project to the trigem motor nucleus and supratrigem nucleus
where is the motor nucleus of CN V and where does it terminate?
in the pons, near the principal sensory nucleus. It goes to the MOM and the tensor twins and efferent jaw jerk reflex
where is the supratrigeminal nucleus of CN V and what is its purpose?
node in the reticular formation above the motor nucleus that coordinates chewing (so close to the MOM motor nucleus)
explain the path from the trigeminal spinal nucleus
from the nucleus, they descend to synapse in the caudal nucleus goes through the internal capsule as the trigeminothalamic tract contralaterally to synapse on the VPM of the thalamus, then to the medial aspect of broadmans areas 3,1,2
what is the homologue for the trigeminal spinal nucleus pathway?
the anterolateral pathway
What is the dorsal trigeminal tract?
the part of the main sensory tract that remains uncrossed and transmits tactile sensation of the oral cavity
what are the three “pars” of the spinal trigeminal nucleus?
oral nucleus, interpolar nucleus, and caudal nucleus
divided histologically
why is the spinal trigeminal tract and nucleus less myelinated than the fasiculus cuneatous and nucleus cuneates??
because it transmits pain and temperature
pars oralis
recieves input from intraoral and perioral structures
pars interpolaris
activation of the trigemino-autonomic zone
caudalis-interpolaris zone
not somatopically organized, responds to pain stimuli, activates pain supression mechanisms???
Pars caudalis
target for fibers mediating pain, crude touch and temperature sensation (superficial and deep structures)
-cause referred pain??
somatotopic organization of pain-temperature afferents from pars caudalis
mand division: dorsal
opthalamic: ventral
- fibers representing the center of the face end near the obex and the fibers representing the back of the face end in the upper cervical cord
syrinx
cavity in the SC that can go up the brainstem
-causes loss of pain and temp to the outside of the face, and if continues up then eventually the whole face will lose pain and temp
Trigeminal Neuralgia
“suicide disease” – brief episodes of excrutiating pain (mainly to mandibular region) brought on by tactile stimulus and compression of a vessel
- responds to medications
- surgeries include cutting the nerve root or ganglion which results in tactile and discrim touch loss, also sectioning the spinal portion of the tract and cutting off the pars caudalis, but high mortality rate because of location next to vessels
- ** MIcrovascular decompression (put a pad between trigem and superior cerebellar artery)
what tract is a homologue of the mesencephalic and main sensory nucleus of CN V?
posterior column (medial lemniscus)
jaw jerk reflex
monosynaptic reflex
-masseter spindle innervated by tap on chin which leads to cell body which leads to motor nucleus which then causes the limb to move
what mm. does that facial nerve innervate?
orbicularis oris and orbicularis oculi (closes the mouth and eyes) and the stapedius mm.
what are the actions of CN VII?
muscles of facial expression, modulate sound volume, anterior 2/3 of tongue taste, skin of the outer ear, palatine tonsils and posterior nasal cavity sensory, salivation and lacrimation
selective weakness of lower facial mm.
- corticobulbar pathway
- motor neurons to the lower face are innervated contralaterally by the cortex, but upper facial mm. are innervated bilaterally
- *unilateral damage to the corticobulbar pathway results in inability to smile symmetrically, but ability to wrinkle forehead
Bells Palsy
unilateral facial paralysis due to dysfunction of CN VII
- inflammatory condition in the facial nerve
- rapid onset, improves with corticosteroids
- paresis above and below eye, irritation of cornea, protect from drying out (lacrimation and salivation decreases, hyperacusis (loud sounds)
corneal blink reflex
-touch cornea and both eyes will blink
afferent limb is V (vi) to the spinal nucleus trct
efferent limb is CN VII elicited by bilateral projection from SpV nucleus (reticular formation)
**clinical test of V, VII and central connections
Jaw opening and closing reflexes
CN V
what is the main visceral sensory nucleus in the brainstem?
solitary nucleus
where do the gustatory afferents go once they are in the solitary tract?
to the solitary nucleus then to either reflex (swallowing and salivation) or uncrossed to the thalamus (VPM) to the gustatory cortex (Insula and medial surface of the frontal operculum)
CN XII
type: somatic motor (lower motor neuron)
origin: hypoglossal nucleus (seen in the rostral medulla)
peripheral termination: Tongue mm.
what protrudes the genioglossus mm.?
hypoglossal nerve
lesion in the hypoglossal nerve
(LMN) deviation towards the side of the lesion when the tongue protrudes ( because tongue on the other side is stronger) fasciltations and atrophy of the mm.
(UMN) small deviation towards the side opposite the lesion because corticobulbar fibers decussate adjacent to the hypoglossal nucleus
CN XI
type: branchial motor
origination: accessory nucleus in cervical spinal cord (caudal medulla to C5)
peripheral site: sternocleidomastoid and trapezius
CN XI lesion
Scapula and clavicle hang due to weak trapezius
Weak shoulder shrug as levator scapulae must work alone
Muscle atrophy leads to scalloped appearance of neck contour
Somatic Sensory CN IX
origin: spinal trigeminal nucleus to superior ganglion of IX (skin of the outer ear)
Visceral Sensory CN IX
1) origin: nucleus of the solitary tract to the inferior ganglion of IX
termination: taste buds on the posterior 1/3 tongue, carotid body and sinus
2) origin: nucleus of the solitary tract to inferior ganglion of IX (spinal trigeminal)
termination: mucosa posterior 1/3 tongue and pharynx and middle ear
visceral motor CN IX
origin: inferior salivatory nucleus to the otic ganglion
terminates: parotid gland
branchial motor CN IX
origin: nucleus ambiguous
termination: pharynx (stylopharyngeous)
glossopharyngeal neuralgia
Similar to trigeminal neuralgia
Rare, but distressing
Sudden burst of pain starts in posterior tongue or wall of pharynx, then radiates to ear
Trigger zone on tongue/ pharynx and attacks precipitated by swallowing or talking
Pharmacologic management or tractotomy of spinal trigeminal tract in caudal medulla
somatic sensory CN X
origin: spinal trigem nucleus to superior ganglion of X
term: skin of the upper ear
visceral sensory CN X
origin: nucleus of the solitary tract to inferior ganglion of CN X
term: taste buds of epiglottis and esophagus
origin: Nucleus of the solitary tract to the inferior ganglion of CN X (spinal trigem nucleus)
term: thoracic and abdominal viscera and pain and temp to the larynx and pharynx
visceral motor CN X
origin: dorsal motor nucleus to nucleus ambiguus
term: thoracic and abdominal viscera (heart and lun
branchial motor CN X
origin: nucleus ambiguos
term: larynx and pharynx
gag reflex
afferent: CN IX
efferent: CN X
touch the side of the pharynx to ellict a bilateral response
(central connection unclear)
tongue thrust reflex
in infants
afferent limb: CN V or IX
efferent limb: CN XII
vasovagal syncope
Vasovagal syncope: response to a trigger, vagus decreases heart rate & blood pressure, decreasing cerebral blood flow, results in fainting and confusion
Vagal nerve stimulator: Stimulate vagal nerve to modulate mood or seizure activity
Jugular Foramen syndrome
CN IX, IX, X, XI, XII nerves & sympathetic nerve (internal carotid nerve) and are at risk of entrapment by a skull base tumor
**sign is constant pain in middle ear and in the ear
