7. Extrapyramidal sytem Flashcards
The extrapyramidal system contains all the descending motor tracts EXCEPT…
Pyramidal system tracts:
- Lateral corticospinal
- Ventral corticospinal
- Corticonuclear
Importance of extrapyramidal system in domestic species
Dominates over pyramidal system
2 roles of the extrapyramidal system
- Antigravity support
- Spinal reflex recruitment for initiation of movements
What are the command centers of the extrapyramidal system
- Cerebral cortex
- Basal nuclei
- Tegmentum (red nucleus)
- Tectum (caudal and rostral colliculi)
- Reticular centers (pontine, medullary, +- midbrain)
- Vestibular nuclei
Name the extrapyramidal tracts
- (cortico)RUBROspinal tract
- Medial TECTOspinal tract
- Pontine & medullary RETICULOspinal tract
- Lateral & medial VESTIBULOlospinal tract
Cereberal cortex
In the extrapyramidal system, widespread regions of the cerebral cortex send projections where?
Other extrapyramidal command centers (basal nuclei + other brainstem nuclei)
Basal nuclei
Name the 5 and locate (slide 9)
- Nucleus accumbens (1)
- Caudate nucleus (2)
- Putamen (5)
- Globus pallidus (3, 4)
- Claustrum (7)
Basal nuclei
Name the structures on slide 9
- Nucleus accumbens
- Caudate nucleus
- Medial globus pallidus
- Lateral globus pallidus
- Putamen
- Amygdala
- Claustrum
Basal ganglia
Define…
Neostriatum (striatum)
Lentifrom nucleus
Corpus striatum
- NEOSTRIATUM: caudate + putamen
- LENTIFORM NUCLEUS: putamen + globus pallidus
- CORPUS STRIATUM: all basal nuclei + white matter of internal + external capsule
Basal nuclei
Among the basal nuclei, the role of the _ is unknown
Claustrum
Basal ganglia
NUCLEUS ACCUMBENS - Shape & location
- Small
- Ventral extension (nose) of caudate
- Surrounds ventral portion of rostral horn of internal capsule
Basal nuclei
CAUDATE - Shape & location
- Largest
- C-shaped with large head and narrow body
- Lateral to lateral ventricles
- Medial to internal capsule
Basal nuclei
Medial GLOBUS PALLIDUS - Location
- Medial to putamen
- Lateral to internal capsule
Basal nuclei
PUTAMEN - Location
- Lateral to globus pallidus
- Medial to claustrum (separated from claustrum by thin external capsule)
Basal nuclei
CLAUSTRUM - shape & location
- Long thin plate
- Lateral to external capsule
- From head of caudate (rostrally) -> ventral border of 3rd ventricle (caudally)
- BARRIER between external capsule and insula
Basal nuclei
CAUDATE - Afferents vs efferents
- A: Cerebral cortex + substantia nigra
- E: globus pallidus
Basal nuclei
Which is the only basal nuclei that sends efferents OUTSIDE of the basal nuclei (allows communication with rest of CNS)?
Medial globus pallidus
Globe trotter
SUBSTANTIA NIGRA - location, neurons, components (slide 16)
- Tegmentum (midbrain), dorsal to crus
- Cell bodies contain melanin and synthesize dopamine (act on D1/D2-R)
- Pars compacta, pars reticulata
SUBTHALAMIC NUCLEI - Location, afferents, efferents (slide 17)
- Ventral to thalamus
- Ventromedial to internal capsule
- A: Lateral globus pallidus
- E: Medial globus pallidus (loop)
6 keep points of how basal nuclei regulate movement
- Thalamus is always facilitatory
- Thalamus is under tonic inhibition by medial globus pallidus
- Globus pallidus is inhibited by the neostriatum (disinhibition)
- Substantia nigra + subthalamic nuclei always fire in the background, fine-tuning movement
- Substantia nigra has dopaminergic neurons that inhibit (D2R) or activates (D1R) the neostriatum
- Subthalamic nuclei for a loop with lateral and medial globus pallidus (allows communication between two parts of globus pallidus)
Describe pathways of the extrapyramidal system DURING MOVEMENT
- Activation of extrapyramidal neurons of the cereberal cortex –> activates neostriatum –> inhibits globus pallidus –> disinhibits thalamus –> MOVEMENT
- Subsequent activation of the substantia nigra –> further activates neostriatum (D1R) –> further inhibits globus pallidus –> MORE movement
- Feedback inhibition of the substantia nigra by neostriatum helps prevent excessive/constant movement
Describe pathways of the extrapyramidal system DURING ABSENCE OF MOVEMENT
- Substantia nigra sends inhibitory (D2R) outputs to neostriatum –> allows globus pallidus to inhibit thalamus
- Inhibition of the lateral globus pallidus –> activates subthalamic nucleus –> further activates medial globus pallidus –> more inhibition of thalamus
Causes and consequences of NIGROPALLIDAL ENCEPHALOMALACIA (NPE, chewing disease)
- Necrosis of substantia nigra + globus pallidus
- Yellow star thistle (centaurea solstitialis) or Russian knapweed (centaurea repens)
- Spastic paresis of lips, pharyngeal, TMJ, facial muscles. Mouth partly opened, retracted lips, chewing motions
RED NUCLEUS - location, afferents & efferents
- Tegmentum, dorsal to substantia nigra, ventromedial to motor nucleus of CNIII
- A: cortex, basal nuclei, cerebellum
- E: olivary nucleus (loop to cerebellum), spinal cord (RS tract)
olive rouge
Caudal & rostral COLLICULI - Loacation and roles
- Tectum
- Visual (rostral) and auditory (caudal) reflexes
corticoRUBROSPINAL TRACT
- Cortex -> internal capsule -> crus -> red nucleus (ipsi)
- Immediately DECUSSATES in the midbrain->
- Entire SC through LATERAL funiculus
- Facilitatory to FLEXORS (protraction)
Medial TECTOSPINAL TRACT (acoustic startle reflex)
- Auditory info -> cochlear nuclei -> lateral lemniscus -> CAUDAL colliculus -> MNG (thalamus) -> auditory cortex
- Auditory cortex -> ROSTRAL colliculus -> SC through medial tectospinal tract
- Enables orientation of head, eyes, body in respose to sounds
2 RETICULOSPINAL TRACTS
- MEDULLARY: LATERAL funiculus; facilitatory to FLEXORS
- PONTINE: VENTRAL funiculus; facilitatory to EXTENSORS
(unclear if decussations)
MedulLary = Latera, fLexors
2 subtypes of medullary reticulospinal tracts (King)
- Medial: projects to SC
- Lateral: inhibits medial tract
2 VESTIBULOSPINAL TRACTS
- Origin from 4 VN
- Both ipsilateral
- Both travel in VENTRAL funiculus
- Both facilitatory to EXTENSORS
- Lateral v.s.t.: limbs + axial muscles
- Medial v.s.t: neck + shoulders
OLIVARY NUCLEUS - role
Provides feedback loops from extrapyramidal system to cerebellum
OLIVARY NUCLEUS - location
Dorsal to the pyramids (medulla)
Describe loop from olivary nucleus to cerebellum (slide 56)
Cerebral cortex -> red nucleus -> olivary nucleus -> caudal cerebellar peduncle -> cerebellum -> rostral cerebellar peduncle, to either
- red nucleus
- back to cerebral cortex
Describe two loops between extrapyramidal system and cerebellum
- Reticular formation (decussates) + vestibular nuclei (ipsilateral) –> caudal c.p. –> cerebellum –> caudal c.p.
- Tectum (decussates) –> rostral c.p. –> cerebellum –> rostral c.p.
