Central Nervous System Flashcards
Arterial Supply to Spinal Cord
Arterial supply comes from 2 sources:
- longitudinally oriented vessels; descend on the surface of the cord
- feeder arteries that enter the vertebral canal through intervertebral foramina (segmental spinal arteries)
Segmental Spinal Arteries
After entering an intervertebral foramen, the segmental spinal arteries give rise to anterior and posterior radicular arteries which follow and supply the anterior and posterior roots
Spinal Dura Mater
- outermost meningeal membrane, separated from bones by extradural space
- as spinal nerves pass laterally, they are surrounded by a sleeve of dura mater, which merges with and becomes part of the epineurium of the nerves
Longitudinal Spinal Vessels
- anterior spinal artery
- 2 posterior spinal arteries
- arise in cranial cavity
Spinal Arachnoid Mater
- thin delicate membrane against, but not adherent to the dura mater
- separated from pia mater by subarachnoid sace
- ends at S2
- subarachnoid space contains CSF
Spinal Pia Mater
- vascular membrane that firmly adheres to spinal cord surface
- on each sode of the spinal cord, the pia mater has a longitudinally arranged sheath (denticulate ligament). This extends laterally from the cord towards the arachnoid and pia mater
Ascending Tracts
- the pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex. In some texts, ascending tracts are also known as somatosensory pathways or systems
Dorsal Column Medial Lemniscal Pathway
The dorsal column-medial lemniscal pathway (DCML) carries sensory modalities of fine touch (tactile sensation), vibration and proprioception.
Its name arises from the two major structures to comprise the DCML. In the spinal cord, sensation travels via the dorsal columns. In the brainstem, it is transmitted through themedial lemniscus.
First order neurones carry sensory information from touch or proprioceptive receptors to the medulla oblongata. There are two different pathways which the first order neurones take:
Signals from the upper limb travel in thefasciculus cuneatus (the lateral part of the dorsal column). They then synapse in the cuneate nucleus of the medulla oblongata.
Signals from the lower limb travel in thefasciculus gracilis (the medial part of the dorsal column). They then synapse in the gracile nucleus of the medulla oblongata
Second order neurones begin in the cuneate nucleus or gracilis. The fibres receive the information from the preceding neurones, and delivers it to the third order neurones in the thalamus. Within the medulla oblongata, these fibres decussate (cross to the other side of the CNS). They travel in the contralateral medial lemniscus to reach the thalamus.
Third order neurones take the sensory signals from the thalamus to the primary sensory cortex of the brain. They ascend from the ventral posterolateral nucleus of the thalamus, through the internal capsule, terminating at the sensory cortex.
The AnteroLateral System
The anterolateral system consists of two separate tracts:
The anterior spinothalamic tract carries the sensory modalities of crude touch and pressure.
The lateral spinothalamic tract carries the sensory modalities of pain and temperature.
Much like the DCML pathway, both the tracts of the anterolateral system have three groups of neurones:
First order neurones arise from the sensory receptors in the periphery. They enter the spinal cord, ascend 1-2 levels, and terminate at the tip of the dorsal horn (an area known as the substantia gelatinosa).
Second order neurones carry the sensory information from the substantia gelatinosa to the thalamus. Arising from a synapse with the preceding neurones, the neurones decussate (cross to the other side of the CNS). Here, fibres split:
Crude touch and pressure fibres enter the anterior spinothalamic tract.
Pain and temperature fibres enter the lateral spinothalamic tract.
Although they are functionally distinct, these tracts run alongside each other, and they can be considered at a single pathway. The fibres travel in their respective pathways, synapsing in the thalamus.
Third order neurones take the sensory signals from the thalamus to the primary sensory cortex of the brain. They ascend from the ventral posterolateral nucleus of the thalamus, through the internal capsule, terminating at the sensory cortex.
Ascending Tracts- Sensory
Spinocerebellar Tracts- Unconscious
They transmit information from the muscles to the cerebellum.
Within the spinocerebellar tracts, there are four individual pathways:
Posterior spinocerebellar tract – Carries proprioceptive information from the lower limbs to the ipsilateral cerebellum.
Cuneocerebellar tract – Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum.
Anterior spinocerebellar tract – Carries proprioceptive information from the lower limbs. The fibres decussate twice – and so terminate in the ipsilateral cerebellum.
Rostral spinocerebellar tract – Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum
Cerebellum
Anatomical Lobes
There are three anatomical lobes that can be distinguished in the cerebellum; the anterior lobe, the posterior lobe and the flocculonodular lobe. These lobes are divided by two fissures – the primary fissure and posterolateral fissure.
Cerebelar Zones
There are three cerebellar zones. In the midline of the cerebellum is the vermis. Either side of the vermis is the intermediate zone. Lateral to the intermediate zone are the lateral hemispheres. There is no difference in gross structure between the lateral hemispheres and intermediate zones
Functional Divisions of the Cerebellum
The cerebellum can also be divided by function. There are three functional areas of the cerebellum – the cerebrocerebellum, the spinocerebellum and the vestibulocerebellum.
Cerebrocerebellum – the largest division, formed by the lateral hemispheres. It is involved in planning movements and motor learning. It receives inputs from the cerebral cortex and pontine nuclei, and sends outputs to the thalamus and red nucleus. This area also regulates coordination of muscle activation and is important in visually guided movements.
Spinocerebellum – comprised of the vermis and intermediate zone of the cerebellar hemispheres. It is involved in regulating body movements by allowing for error correction. It also receives proprioceptive information.
Vestibulocerebellum – the functional equivalent to the flocculonodular lobe. It is involved in controlling balance and ocular reflexes, mainly fixation on an target. It receives inputs from the vestibular system, and sends outputs back to the vestibular nuclei.
Vasculature to Cerebellum
The cerebellum receives its blood supply from three paired arteries:
Superior cerebellar artery (SCA)
Anterior inferior cerebellar artery (AICA)
Posterior inferior cerebellar artery (PICA)
The SCA and AICA are branches of the basilar artery, which wraps around the anterior aspect of the pons before reaching the cerebellum. The PICA is a branch of the vertebral artery.
Venous drainage of the cerebellum is by the superior and inferior cerebellar veins. These drain into the transverse and sigmoid sinuses.
Nuclei (deep) of Cerebellum
- 3 groups of cerebelar nuclei, embedded in the white matter of each hemisphere:
- dentate nucleus: in centre of corpus medullare
- emboliform and globose (interposed)
- fastigial
Dentate Nucleus
- convex, indented lamina of gray matter with a hilum anteromedially
- interior filled with white matter made of efferent fibres. These form a large part of the superior cerebellar peduncle
- projects axons to the red nucleus and thalamus
Emboliform (interposed)
- lies at the hilum of the dentate nuclei
- medial to them are globose nuclei, comprised of smaller cellular groups
- As a part of the interposed nucleus, the emboliform participates in the spinocerebellum, a system that regulates the precision of limb movements
- Axons leaving the emboliform exit through the superior cerebellar peduncle and reach the red nucleus in the midbrainand several thalamic nuclei which project into areas of the cerebral cortex that control limb movement
Fastigial nucleus
- found close to the midline
- developmentqally the oldest, connected to the vestibular nuclei and reticular formation
- projects efferents to spinal cord, midbrain and diencephalon, as well as inferior olivary complex
Cerebellar Fibre System
- cerebellar cortex receives input from 2 groups of excitatory fibres:
- mossy fibres
- climbimg fibres
Climbing Fibres
- are the terminal fibres of the olivocerebellar tracts. Ascend through the layers of the cortex like a vine on a tree
- each climbing fibre wraps around and makes synaptic contact with up to 10 purkinje neurons. However, a single purkinje cell synapses with only one climbing fibre
- on their way, the latter send collaterals to the cerebellar nuclei and to the interneurons of the cortex- granular, stellate, basket and Golgo cells
Mossy Fibres
- terminal fibres of all other afferent cerebellar tracts
- relatively thick, have thin terminations which form globuar structures around the dendrites - cerebellar glomeruli
- exert a more diffuse excitatory effect
Purkinje Cells
Main functional unit of the cerebellum
Layers of the cerebellum
- 3 layers can be distinguished:
- external - molcular
- middle - purkinje
- internal - granular
Molecular Layer
- Characterised by 2 types of inhibitory neurons: stellate cells and basket cells
Stellate cells
- small interneurons
- projections do not extend beyond the external layer
- axons form inhibitory synapses with dendrites of purkinje cells
Basket Cells
- larger with numerous dendrites
- axon of each basket cell forms basket-like plexuses around the bodies of a group of purkinje cells
Purkinje Cell Layer
Single layer of purkinje cells
Granular Cerebellar Layer
- scarce cytolasm
- numerous granular cells and golgi cells found close to purkinje cells
Folia Cerebelli
Surface of cerebellum indented by numerous parallel fissures, which separate slender parallel ridges: folia cerebelli
Cerebellar Afferent and Efferent Connections
- afferent cerebellar connections terminate in the cerebellar cortex
- inferior cerebellar peduncle transmits:
- posterior spinocerebellar tract
- cuneocerebellar and olivocerebellar
- vestibulocerebellar
- middle cerebellar peduncle:
1. pontocerebellar - suerior cerebellar peduncle:
- spinocerebellar
- reticulocerebellar
- locus coeruleus of pontine tegmentum
Pons
- major relay station between cerebral cortex and cerebellum
- anerior: basal bulging of brainstem, separated from medulla and mesencephalon by deep transverse grooves
- posterior: portion of rhomboid fossa, above stria medullares
- divided into basillar and dorsal
Middle Cerebellar Peduncles
- laterally, basillar part of pons continues to cerebellum, forming middle cerebellar peduncles
- composed of longitudinal and transverse fibres
- majority of longitudinal: corticospinal tact. Frontopontine and occipitopontine tracts reach pontine nucllei
- transverse: pontocerebellar tracts
Nuclei in tegmentum pontis
- CN V, CN VI, CN VII, CN VIII
- other components of dorsal pons: reticular formation, efferent and afferent pathways
- efferent: rubrospinal and tectospinal
- afferent: medial lemniscus, spinotectal and anterior spinocerebellar
Locus Coeruleus
Largest accumulation of adrenergic neurons in the brain. 2 nuclei:
- nucleus coeruleus
- nucleus subcoeruleus
Funicules of White Matter of Spinal Cord
- in each half of the spinal cord, white mater is divided into 3 major bundles, called funiculi
- dorsolateral sulcus marks division between dorsal funiculus and lateral funiculus
- right and left ventral funicului are connected by a ventral white commisure
Midbrain
- contains both white matter tracts and grey matter nuclei. Transversed by cerebral aqueduct (of Sylvius)
- plane passing along the CA divides the midbrain into a pair of cerebral peduncles ventrally and tectum dorsally
- cerebral peduncle: crus cerebri and tegmentum
Tegmentum
- houses nuclei of CN III and CN IV
- occulomotor nucleus lies at level of sup colliculus
- trochlear nucleus situated in central grey, close to the midline, at the level of the inf colliculi
Red Nucleus
- largest and most prominent
- through its connections, takes part in modulation of voluntary movements and belongs to extrapyramidal motor system
- receives afferents: corticorubral from frontal lobe and cerebellorubral (from dentate nucleus)
- efferents project to:
- inf olivary nucleus via central tegmental tract
- spinal cord - rubrospinal tract. Latter cross the midline, thus forming the ventral tegmental decussation of Forrel
- reticular nuclei
Tectum
- dorsal to CA
- plate with 4 elevations: called lamina quadrigemina. Each side has 2 mounds: sup and inf colliculi
- 2 slender ridges originate from colliculi:
- brachium collic sup reaches LGN
- brachium collic inf reaches MGN
Superior Colliculus
- vision reflex centre
- receives input from optic tract and from spinal cord (spinotectal)
- projects fibres:
- to motor nuclei of CN III IV VI
- to LGN
- to spinal medulla tectospinal tract, thus forming posterior tegmental decussation (of Meynert)
- to nuclei of origin in brainstem and to nuclei pontis
- to reticular nuclei
- Afferent pathway for light reflex ends in pretectal nucleus. Projects to Edinger-Westphal nuclei on both sides
Inferior Colliculus
- contains nuclei colliculi infirioris, relay station along the auditory pathway
- majority of fibres of lateral lemniscus relay here, continues to MGN
Substantia Nigra
- 2 parts: pars compacta and pars reticulata
- pars compacta projects to basal ganglia, supplying striatum with dopamine
- pars reticulata serves mainly as a relay station
Diencephalon
- thalamus
- metathalamus
- epithalamus
- hypothalamus
- subthalamus
Thalamus
- relay station of all major sensory systems
- lateral surface of thalamus separated from the lentiform nucleus by internal capsule
- 3 major groups of thalamic nuclei: lateral, medial and anterior
- thalamus is a relay station along two extrapyramidal motor loops:
- dento-rubro-thalamo-cortico-ponto-cerebellar
- cortico-striato-pallido-thalamo-cortico
Anterior Group of Thalamic Nuclei
- receives from mamillary body: mammillothalamic tract
- finctionally associated with limbic system
Medial Group of Thalamic Nuclei
- dorsomedial = major nucleus. Receives input from lateral thalamic nuclei, the hypothalamus and has a 2 way connection to the pre-frontal cortex
- integrates a variety of sensory info
Lateral Group of Thalamic Nuclei
- subdivided into dorsal and ventral tiers:
- dorsal: lateral dorsal, lateral posterior and pulvinar
- ventral: ventral anterior, ventral lateral, ventral posterolateral and ventral posteromedial
- VA receives from globus pallidus and substantia nigra. its efferent fibres terminate in the primary motor area
Metathalamus
- represented by pair of geniculate bodies: lateral and medial
- LGN: visual relay centre, optic radiation terminates in occipital lobe area 17
- MGN: auditory relay station, efferents form acoustic radiation
Epithalamus
stria medullaris thalami
habenular trigone:
habenular nuclei, medial and lateral
habenula
habenular commissure
pineal gland, corpus pineale (epiphysis)
**posterior commissure** subfornical organ (circumventricular organs)
Hypothalamus
- anatomically includes: optic chiasm, tuber cinereum, infundibulum and mammilary bodies
- mammillary bodies: white matter exterior and 2 grey matte nuclei inside: medial and lateral mamillary nuclei
- tuber cinereum: basal eminence in the midline, behind optic chiasm. Inferiorlly continues into infundibulum
- hypothalamus crossed by 2 white matter tracts and pars tecta of the column of the fornix andf the mamillothalamic tract. Divide the substance of the hypothalamus into media and lateral zones
Nuclei of the Hypothalamus
- Medial group:
- anterior
- paraventricular
- dorsomedial
- ventromedial
- infundibular
- posterior
- Lateral group:
- supraoptic
- lateral
- tuberomamillary
- lateral tuberal
Cranial Dura Mater Structures
sickle-shaped falx cerebri
tentorium cerebelli
falx cerebelli
diaphragma sellae
cavum trigeminale (Meckeli)
Cranial Dural Venous Sinuses
superior sagittal sinus
inferior sagittal sinus
transverse sinuses
sigmoid sinuses
confluence of the sinuses
occipital sinus
straight sinus (sinus rectus)
petrosquamous sinus
superior petrosal sinuses
inferior petrosal sinuses
cavernous sinuses
intercavernous sinuses,
anterior and posterior
Subarachnoid Cisterns
subarachnoid cisterns:
cisterna cerebellomedularis
posterior et lateralis
cisterna pontocerebellaris
cisterna ambiens
cisterna trigeminalis
cisterna cruralis
cisterna interpeduncularis
cisterna carotidis
cisterna chiasmatis
cisterna fossae lateralis cerebri
Cranial Pia Mater
very thin membrane, Latin “tender mother”
neural crest derivative
vascular membrane – nourishing the brain:
superficial epipial layer – sheet of flat cells
inner membranous layer – fibrous tissue,
intima pia
Blood Supply of the Brain
Vertebrobasilar system:
aa. vertebrales a. basilaris
Carotid system:
a. carotis interna
Communication:
circulus arteriosus cerebri
Vertebrobasilar system
Vertebrobasilar system:
vertebral artery:
posterior inferior cerebellar artery
basilar artery:
anterior inferior cerebellar artery
superior cerebellar artery
labyrinthine artery
(internal auditive artery)
pontine arteries
posterior cerebral artery
Carotid system
Carotid system:
internal carotid artery
(cerebral part):
anterior cerebral artery
anterior communicating artery
middle cerebral artery
“a. haemorrhagica” (of Charcot)
Circulus arteriosus cerebri (circle of Willis)
Heptagon of Willis:
anterior communicating artery
anterior cerebral arteries
posterior communicating arteries
posterior cerebral arteries
Venous Drainage of the Brain
superficial cerebral veins:
vv. superficiales cerebri
into dural venous sinuses
- *deep cerebral veins:**
vv. profundi cerebri
v. magna cerebri (Galeni) - *communication:**
vv. emissariae
vv. diploicae - *cerebellar veins**
v. magna cerebri
brainstem veins:
medulla oblongata : sinus occipitalis, sinus petrosus
inferior, v. jugularis int.
pons: sinus petrosus superior,
sinus transversus
midbrain: v. magna cerebri
Cerebral Hemispheres
three surfaces:
superolateral (convex)
medial (flat and vertical)
inferior (irregular):
orbital part
tentorial part
six lobes:
frontal lobe
parietal lobe
occipital lobe
temporal lobe
insular lobe
limbic lobe
main sulci:
central sulcus (of Rolando)
lateral sulcus (of Sylvius)
parietooccipital sulcus
cingulate sulcus
collateral sulcus
Gyri and Sulci: External
SuperoLateral surface:
Gyri and Sulci: Internal
Medial Surface
Cortical Cell Types
1. pyramidal cells – 66% of the total neocortical cell population (glutamate- and aspartatergic)
- small-sized (10-15 μm)
- medium-sized (20-40 μm)
- large-sized (50-80 μm)
- giant pyramidal cells of Betz (80-120 μm) – in the precentral gyrus (motor cortex)
2. stellate (granule) cells – 33% of the total neocortical population (Golgi type II cells)
- small in size (8-14 μm) – interneurons (GABA, VIP, SP, CCK, ENK)
- horizontal cells of Cajal – small and fusiform; in the most superficial cortical layer
- fusiform cells – “modified pyramidal cells”; spindle-shaped, in the deepest cortical layer
- cells of Martinotti – small and multipolar; in practically all cortical layers
- basket cells – horizontally extended
- neurogliaform stellate cells – small in size
3. pleomorphic cells – modified pyramidal cells; – large-sized and varying in shape,
in the deepest layer
Cortical Layers (Brodmann)
I. Molecular layer
(plexiform lamina)
II. External granular
lamina
III. External pyramidal
lamina
IV. Internal granular
lamina
V. Internal pyramidal
(ganglionic) lamina
VI. Multiform (fusiform)
lamina
White Matter Fibres
association fibers –
fibrae associationes
telencephali
commissural fibers –
fibrae commissurales
telencephali
projection fibers –
fibrae projectiones
telencephali
Association Fibres
short association fibers:
fibrae arcuatae cerebri (U fibers)
long association fibers:
cingulum
superior longitudinal fasciculus
inferior longitudinal fasciculus
uncinate fasciculus
inferior frontooccipital fasciculus
arcuate fasciculus
vertical occipital
fasciculus
Commisural Fibres
anterior (rostral) commissure
commissure of the fornix
(hippocampal commissure)
commissura magna
(corpus callosum)
Hypothalamic Afferent Connections
corticohypothalamic fibers
limbic system –
hippocampo-hypothalamic afferents
amygdalo-hypothalamic fibers
septal region
piriform lobe
thalamus – periventricular nucleus, zona incerta
brainstem reticular formation –
dorsal longitudinal fasciculus (of Schütz)
mammillary peduncle
Hypothalamic Efferent Connections
medial forebrain bundle
hypothalamo-hypophysial – neurohypophysis
mammillary efferent fibers – fasciculusmammillaris princeps:
fasciculus mammillothalamicus
fasciculus mammillotеgmentalis
descending hypothalamic projections:
n. tractus solitarii, n. dorsalis n. vagi
laminae І and ІІ of the spinal cord
Basal Ganglia
nucleus caudatus
nucleus lentiformis
nucleus subthalamicus
substantia nigra
Reticular Formation Nuclei
- Median column of reticular nuclei – raphe nuclei (serotonergic)
- Medial column
- Lateral column – parvocellular
Median Column of Reticular Nuclei
nucleus raphes obscurus et pallidus in medulla
nucleus raphes magnus in pons
nucleus raphes centralis superior and
nucleus raphes dorsalis in midbrain
Medial Column of RN
medullary gigantocellular (magnocellular) nucleus
pontine gigantocellular nucleus
nucleus tegmenti pontis
nucleus pontis caudalis
nucleus pontis oralis
nucleus cuneiformis
nucleus subcuneiformis
Lateral Column - Parvocellular
nucleus pontis centralis
nuclei parabrachiales
nucleus tegmentalis pedunculopontinus
Reticular Formation Functions
controls ~25 specific behaviors:
sleep
walking
eating
urination & defecation
sexual activity
additional functions:
arousal
attention
cardiac reflexes
motor functions
regulates awareness
relays nerve signals to the cerebral cortex
one of the phylogenetically oldest portions of the brain
Functional Systems in the CNS
Sensory (afferent) systems
Motor (efferent) systems
Limbic system
Reticular system
Central transmitter systems:
Sensory Pathways
general (somatic) sensations:
superficial (exteroceptive) – skin
• pain and temperature
• vibration, touch and pressure
• stereognosia
deep (proprioceptive)
• joints and tendons
interoceptive (visceroceptive)
• organs and blood vessels
special sensations:
visual system
vestibulocochlear system
gustatory system
olfactory system
PCML Pathway
(lemniscus medialis)
touch, pressure and stereognosia
І neuron – ganglion spinale
ІІ neuron – nucl. gracilis et cuneatus
ІІІ neuron – nucleus ventralis posterolateralis thalami
gyrus postcentralis (upper 2/3)
low touch and pressure
tractus spinothalamicus anterior (ventralis)
Trigeminal Lemniscus
orofacial touch and pressure
І neuron – ganglion trigeminale
ІІ neuron – nucl. pontinus (sensorius principalis)
ІІІ neuron – nucleus ventralis posteromedialis thalami
gyrus postcentralis (lower 1/3)
Ascending nociceptive pathways
(anterolateral system)
pain (nociception) and temperature
І neuron – ganglion spinale
ІІ neuron – spinal laminae І, ІІ and V
tractus spinothalamicus lateralis
lemniscus medialis
ІІІ neuron – nucleus ventralis posterolateralis thalami
gyrus postcentralis (middle and upper 1/3), rostral part of gyrus cinguli, insular cortex (limbic system)
Spinal Pain System
lateral pain system – “rapid pain”
(“neospinothalamic system”)- tractus spinothalamicus lateralis
medial pain system – “slow pain”
(“paleospinoreticulothalamic system”)- tractus spinoreticularis et tractus spinotectalis
tractus spinotectalis- colliculi superiores
Dorsolateral system: laminae ІІІ and ІV, І and V
tractus spinocervicalis- nucleus cervicalis lateralis
tractus spinomesencephalicus- substantia grisea centralis
Head Pain and Temp System
І neuron – ganglion trigeminale
tractus spinalis n. trigemini
ІІ neuron – nucl. spinalis n. trigemini
lemniscus trigeminalis
ІІІ neuron – nucleus ventralis posteromedialis thalami gyrus postcentralis (lower 1/3)
Tractus Spinocerebellaris Posterior
from trunk
to cerebellum
І neuron – ganglion spinale
ІІ neuron – nucl. thoracicus (Clarke-Stilling) - tractus spinocerebellaris posterior (Flechsig) - cortex cerebelli
Tractus Spinocerebellaris Ant
ІІ neuron – nucl. thoracicus (Clarke-Stilling) - tractus spinocerebellaris anterior (Gowers) - rostral part of cortex cerebelli
Tractus Bulbocerebellaris
from the upper limb
І neuron – ganglion spinale
ІІ neuron – nucl. cuneatus accessorius - tractus cuneocerebellaris - cortex cerebelli
Proprioceptive Pathways of the Head
І neuron – nucl. mesencephalicus n. trigemini - tractus mesencephalicus n. trigemini - nucl. motorius n. trigemini
ІІ neuron – nucl. ventralis posteromedialis -gyrus postcentralis
Rhinencephalon
aka olfactory system
- part of the basal forebrain
- mediates olfaction
- includes:
- olfactory bulb and tract
- olfactory striae and trigone
- olfactory tubercle
- primary olfactory cortex:
- piriform area (gyrus ambiens)
- periamygdaloid area (gyrus semilunaris)
- secondary olfactory cortex
- entorhinal area
- cranial part of parahippocampal gyrus
Limbic System
- papez circuit: a route the limbic system communicates between the hippocampus, thalamus, hypothalamus and cortex
- functions: cortical control of long-term memory, learning, emotions
- cortical structures: limbic lobe
- subcortical nuclei:
- hippocampal ormation and fornix
- amygdaloid nuclar complex
- septal nuclei
- hypothalamus, epithalamus
- various thalamic nuclei
- part of the basal ganglia
Hippocampal Formation
- inside medial temporal lobe
- three major regions:
- hippocampus proper
- dentate gyrus
- subiculum transition zone
- hippocampal function:
- behavioral inhibition
- learning and recent memory
- spatial coding
Fornix
means arch
- c shaped bundle of fibres
- sole efferent system
- carries info from hippocampus to mammillary bodies and septal nuclei
- structure:
- crus
- body
- hippocampal commisure
- anterior fibres to septal nuclei and nucleus accumbens
- posterior fibres to mammillary bodies
Amygdala
- deep within medial temporal lobes
- nuclei:
- corticomedial group - basal ganglia
- basolateral group:
- lateral amygd nucleus
- basal amygd nucleus
- accessory basal amygd nucleus
- central nucleus, medial and lateral
- functions:
- fear reactivity and other emotional functions
- feeding
- sexual behaviour
Rhinencephalon Pathway
Olfactory
1st order: olfactory mitral and tuft cells
- olfactory bulb
- olfactory tract
- anterior olfactory nucleus - to olfactory striae, medial and lateral as well as to;
- olfactory cortex (piriform, periamygdaloid and hippocampus)
Limbic System Pathway
- hippocampus (subiculum)
- fornix
- precommisure to septal nuclei, ventral striatum, cingulate gyrus
- anterior commisure
- posterior commisure
- hypothalamus (and then to mammilary bodies)
- anterior thalamic nucleus
- cingulate gyrus
Layers of the Hippocampus
alveus
oriens
pyramidale
radiatum
lacunosum
moleculare
Lateral Ventricle
- left ventricle: 1st ventricle
- right ventricle: 2nd
- arch shaped: general shape of hemispheres
- parts:
- anterior horn, trianguar, in frontal lobe- septum pellucidum
- central part, into the parietal lobe- collateral trigone
- posterior horn, into occipital lobe- calcar avis
- inferior horn, into temporal lobe- hippocampus, collateral eminemce
- composition: CSF, produced in choroid plexus:
- no choroid plexus in anterior and posterior horns
- comminication: 3rd ventricle via interventricular foramina (of Monro)
Spinocerebellar Tract
The spinocerebellar tract is a set of axonal fibers originating in the spinal cord and terminating in the ipsilateral cerebellum. This tract conveys information to the cerebellum about limb and joint position (proprioception).
Proprioceptive information is obtained by Golgi tendon organs and muscle spindles:
- Golgi tendon organs consist of a fibrous capsule enclosing tendon fascicles and bare nerve endings that respond to tension in the tendon by causing action potentials in Ib afferent neurons (relatively large, myelinated, quickly conducting).
- Muscle spindles fibers are complicated systems of length monitoring within muscles which result in information being carried via Ia neurons (larger and faster than Ib) (from both nuclear bag fibers and nuclear chain fibers) and II neurons (solely from nuclear chain fibers).
All of these neurons are “first order” or “primary” and are sensory (and thus have their cell bodies in the dorsal root ganglion). They pass through Rexed laminae layers I-VI of thedorsal horn to form synapses with “second order” or “secondary” neurons in the layer just beneath the dorsal horn (layer VII).
SpinoCerebellar Tracts
dorsal (posterior) spinocerebellar:
tract from muscle spindle (primarily) and golgi tendon organs. Ipsilateral Caudal Aspect of the body and legs
ventral (anterior) spinocerebellar tract:
from golgi tendon organs. Ipsilateral Caudal Aspect of the body and legs
cuneocerebellar tract:
from muscle spindle (primarily) and golgi tendon organs. Ipsilateral arm
rostral spinocerebellar tract:
from golgi tendon organs. Ipsilateral arm
Pathway for dorsal and spinocuneocerebellar tracts
The sensory neurons synapse in an area known as Clarke’s nucleus or “Clarke’s column”.
This is a column of relay neuron cell bodies within the medial gray matter within the spinal cord in layer VII (just beneath the dorsal horn), specifically between T1-L3. These neurons then send axons up the spinal cord, and project ipsilaterally to medial zones of the cerebellum through the inferior cerebellar peduncle.
Below L3, relevant neurons pass into the fasciculus gracilis (usually associated with the dorsal column-medial lemniscal system) until L3 where they synapse with Clarke’s nucleus (leading to considerable caudal enlargement).
The neurons in the accessory cuneate nucleus have axons leading to the ipsilateral cerebellum via the inferior cerebellar peduncle.
Pathway for ventral and rostral spinocerebellar tracts
Some neurons of the ventral spinocerebellar tract instead form synapses with neurons in layer VII of L4-S3. Most of these fibers cross over to the contralateral lateral funiculus via the anterior white commissure and through the superior cerebellar peduncle. The fibers then often cross over again within the cerebellum to end on the ipsilateral side. For this reason the tract is sometimes termed the “double-crosser.”
The Rostral Tract synapses at the dorsal horn lamina (intermediate gray zone) of the spinal cord and ascends ipsilaterally to the cerebellum through the inferior cerebellar peduncle.
Exteroception Pathway
anterior spinothalamic
anterior white funiculus
dorsal root ganglia
substantia gelatinosa
ascend brainstem
VPL nucleus
areas 3, 1, 2
Temperature and Pain (body)
Lateral Spinothalamic
lateral white funiculus
DRG
substantia gelatinosa of Rolando
ascend brainstem
VPL nucleus
3,1,2
Spinocerebellar Proprioception
Ventral
Ventral Spinocerebellar
lateral white funiculus
DRG
marginal cells
ascend brainstem
superior peduncle
anterior lobe of cortex
Spinocerebellar Proprioception
Dorsal
Dorsal Spinocerebellar
lateral white funiculus
DRG
clarke cells
ascend brainstem
inferior peduncle
anterior lobe of cortex
SpinoTectal
AudioVisual
Spinotectal
lateral white funiculus
afferent visual info
chief sensory cells
ascend brainstem
superior colliculus nucleus
SpinoReticular
AudioVisual
Spinoreticular
anterolateral white funiculus
afferent info consciousness
interomediolateral cells
ascend brainstem
lateral reticular nucleus, caudal pontine nucleus, reticular nucleus
Pain Sensory Trigeminal Pathway
touch
proprioception
- trigeminal ganglion (V VII IX X)
- main sensory trigeminal nucleus
decussate into ventral trigem lemniscus
- VPM thalami
3,1,2 via posterior limb of internal capsule
Spinal Trigeminal Pathway
crude touch
pain
temp
- trigeminal ganglia
- spinal trigeminal nucleus
decussate into ventral trigeminal lemniscus
- VPM nucleus and intralaminar nucleus
multiple areas of cortex via possterior limb of internal capsule
Ascending Interoceptive Pathways
- sensitivity from body’s viscera
- predominantly nociceptive, common way with pain and temp pathway
Conventional Visceroceptive Pathway
І neuron – ganglion spinale
ІІ neuron – subst. intermedia medialis- tractus spinothalamicus lateralis
ІІІ neuron – nucleus ventralis posterolateralis thalami- somatosensory cortical areas
Accessory Visceroceptive Pathway
І neuron – nervus vagus
ІІ neuron – nucl. tractus solitarii
ІIІ neuron – nucl. ventralis posterolateralis
Motor Pathways
Efferent
**Pyramidal motor system**– two neuron system: tractus corticospinalis (pyramidalis) tractus corticonuclearis (corticonuclear system)
Extrapyramidal motor system (basal ganglia system)
– multineuronal and polysynaptic
Oculomotor system:
frontal eye area (area 8, parts of 6 and 9 areas)
prefrontal cortex
Pyramidal Deccusation
pyramidal decussation – 85% decussate lateral (crossed) corticospinal tract to the contralateral side in the medulla oblongata
anterior corticospinal tract: 15% uncrossed
to the ipsilateral side in the medulla oblongata
Extrapyramidal Motor Pathways
cortico-rubro-spinal tract – extremities:
tractus frontorubralis. nucleus ruber. tractus rubrospinalis
cerebello-rubro-spinal tract:
cerebellar cortex. deep cerebellar nuclei. tractus. cerebellorubralis. nucleus ruber. tractus rubrospinalis
cortico-reticulo-spinal tract:
fibrae corticoreticulares. nuclei reticulares. fibrae reticulospinales – medial and lateral parts
cerebello-reticulo-spinal tract:
cerebellar cortex. nucleus dentatus. tractus cerebelloreticularis. nuclei reticulares. tractus reticulospinalis
cerebello-vestibulo-spinal tract:
flocculo-nodular cerebellar cortex. nucleus fastigii. tractus cerebellovestibularis. nucleus vestibularis lateralis. tractus vestibulospinalis
Basal Ganglia Pathways
Closed reverberating circuits of the basal ganglia:
striatum is the main acceptor
pallidum is the main effector
Anterior CorticoSpinal Pathway
anterior white funiculus
Betz cells, somatosensory 3,1,2. Premotor area 6
pyramidal deccussation
anterior grey horn
Lateral CorticoSpinal
lateral white funiculus
Betz cells, somatos area 3,1,2. Premotor area 6
pyramidal deccussation, lower medulla
anterior grey horn
CorticoBulbar
CorticoNuclear
primary motor area 4
cranial nerves
V, VI, XI, XII
Medial Longitudinal Fasciculus
- interstitial cells of cajal
- vestibular nucleus
- reticulur nucleus
- superior colliculus
- goes to anterior white funiculus and then anterior motor neurons
Spinal Ganglion
- spindle shaped aggregations on the dorsal roots- dorsal root ganglions
- pseudounipolar neurons, or spherical
- satellite cells (capsular cells, amphicytes)
- Scwann cells and blood vessels
- located in ntervertebral foramina
- functional modalities:
- mechanoreception
- nociception
- proprioception
