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What level is the abducens nucleus (CN VI)?
pons
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What level is the trochlear nucleus (CN IV)?
(caudal) midbrain
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What level is the oculomotor nucleus (CN III)?
(rostral) midbrain
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What are the four tracts that originate in the brainstem and descend to the spinal cord to influence movement?
- tectospinal
- rubrospinal
- reticulospinal
- vestibulospinal
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What types of input does the superior colliculus receive?
- SNc
- somatosensory
- auditory
- retina
- visual cortex
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What is the function of the tectospinal tract?
- not well understood
- controlling movement orientation of head
- influence interneurons in cervical spinal cord associated with head and shoulder postural reflex, esp. in association with visual stimuli
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Where does the tectospinal tract originate, where does it cross the midline, and where does it synapse?
- originate: superior colliculus (tectum)
- crosses midline: (at origin) dorsal tegmental decussation (caudal midbrain)
- (pons: pontine tegmentum, near midline)
- (incorporates into medial longitudinal fasciculus)
- (spinal cord: anterior funiculus)
- synapse: (contralateral) anterior spinal grey (horn) (cervical cord only)
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Where does the rubrospinal tract originate, where does it cross the midline, and where does it synapse?
- originate: red nucleus
- crosses midline: (at origin) ventral tegmental decussation (midbrain)
- (pons: central tegmental tract)
- (rostal medulla: dorsal to inferior olive nucleus; collaterals: facial nucleus, lateral reticular nucleus)
- (spinal cord: lateral funiculus)
- synapse: (contralateral) anterior spinal grey (horn)
- (--> proximal flexors of upper extremities)
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What are the ultimate influences of the reticulospinal tracts?
They have a complex and widespread influence on voluntary and reflex movements, on muscle tone, and on the central transmission of sensory inputs.
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Which tracts run through the anterior funiculus?
- reticulospinal
- tectospinal
- vestibulospinal
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Where does the (pontine and medullary) reticulospinal tract originate, where does it cross the midline, and where does it synapse?
- originate: reticular formation (pons: rostral and caudal nuclei; medulla: both sides)
- crosses midline: rostral medulla (medullary only); some do not (pontine and medullary)(i.e. bilateral representation fo medullary nuclei)
- (lateral to pontine reticulospinal tract)
- (spinal cord: anterior funiculus)
- synapse: (ipsilateral & contralateral) anterior spinal grey (horn)
- (--> extensors of paravertebral and proximal limb)
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What are the inputs into the vestibular nuclei?
- vestibular part of CN VIII
- cerebellum (fastigial nucleus)
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Where does the vestibulospinal tract originate, where does it cross the midline, and where does it synapse?
- originate: vestibular nuclei (descending: lateral, medial)
- crosses midline: brainstem (medial); some does not (lateral & medial) (i.e. bilateral representation of medial nuclei)
- (spinal cord: anterior funiculus)
- synapse: (ipsilateral & contralateral) anterior spinal grey (horn) (medial only goes to cervical; lateral extends to lumbar)
- (--> extensors of paravertebral and proximal limb)
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From where does the red nucleus receive input?
- cerebellum
- cerebral cortex
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At what level is the medial geniculate nucleus seen?
(rostral) midbrain
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At what level are descending fibers seen?
pons
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At what level is the trigeminal nucleus (CN V)?
pons
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Where is the superior olive nucleus?
- level of pons
- lateral to central tegmental tract
- inferior to trigeminal nucleus
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In which cross-section do you see the middle cerebellar peduncle?
caudal pons
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In which cross-section do you see the inferior cerebellar peduncle?
rostral medulla
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At what level is the solitary tract?
pons; rostral medulla
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Where is the spinothalamic tract seen?
- at the level of the caudal pons
- in between the medial and lateral lemniscus
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Which tracts run through the lateral funiculus?
- rubrospinal
- corticospinal
- hypothalamo-spinal
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What types of neurons for which muscle groups does the rubrospinal tract utlimately influence?
interneurons for the control of tone in flexor muscles
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What are some of the nuclei and connections contained within the reticular formation?
- nuclei:
- cerebral cortex input
- rostral and caudal nuclei for pontine reticulospinal tract
- connections:
- rostral parts: consciousness
- reflex connections (CV, resp, other ANS fxns)
- corticoreticular fibers
- pontine reticulospinal tract
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Which vestibular nuclei give rise to descending tracts?
lateral and medial vestibular nuclei
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Which tracts run through the medial lemniscus?
- reticulospinal
- vestibulospinal
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Which tracts run through the medial longitudinal fasciculus?
- (medial) vestibulospinal (CN VIII)
- tectospinal
- cranial nerve nuclei: CN III, IV, VI
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What are the 3 types of fiber bundles found in the brain and what are their respective functions?
- association: interconnect cortical regions within one hemisphere
- commissural: interconnect homotypical points in the left and right cortices
- projection: project from cortex to brainstem and spinal cord
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What are the 3 types of fibers bundles in the brain and what are examples of each?
- association: superior longitudinal fasciculus, arcuate fasciculus, superior occipitofrontal fasciculus, cingulum, inferior longitudinal fasciculus, inferior occipitofrontal fasciculus
- commissural: corpus callosum, anterior commissure, posterior commissure
- projection: external capsule, internal capsule, extreme capsule, thalamic radiations, optic radiation
- (fibers of cortical origin = pyramidal cell axons)
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What structures do the anterior and posterior commissures connect?
- anterior commissure: olfactory stria; rostral/antrior cortical regions of temporal lobe
- posterior commissure: pretectum
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What types of fibers make up the external and internal capsules? What are their connections?
- projection fibers
- external capsule: cortical projection fibers to putamen and globus pallidus (i.e. lentiform nucleus)
- internal capsule: projection fibers interconnecting cortex with subcortical structures (e.g. striatum) ; continuous with corona radiata and crus cerebri
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What makes up the extreme capsule?
- extreme capsule: association fibers between claustrum and insula
- (i.e. interconnects the insular cortex and nearby temporal and frontal opercular cortices)
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With what structure is the corona radiata continuous with?
internal capsule --> crus cerebri
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Where do the fibers of the internal capsule terminate?
- thalamus
- brainstem
- spinal cord
- basal ganglia
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Name the structures of the visual pathway in order.
- retinal input cells
- optic nerve
- optic chiasm
- optic tract
- lateral geniculate nucleus (thalamus)
- optic radiations
- primary visual cortex (occipital lobe)
- reciprocal connections from cortex to thalamus
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What are the parts of the internal casule?
- projection fibers: most corticofugal (leaving cortex) and corticopetal (entering cortex) fibers
- five parts:
- anterior limb (between caudate and lentiform nucleus)
- genu (just lateral to interventricular foramen)
- posterior limb (between thalamus, substantia nigra and lentiform nucleus)
- sublenticular (inferior)
- retrolenticular (extends posterior to lentiform nuclei)
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What are the structures connected by each of the parts of the internal capsule?
- anterior limb: anterior & dorsomedial nuclei of thalamus <--> frontal lobe cortex
- genu: VA & VL nuclei of thalamus <--> motor & premotor cortex
- posterior limb: VA & VL nuclei of thalamus <--> motor and premotor cortex
- posterior limb: VP nucleus of thalamus <--> somatosensory cortex, and descending fibers of the corticospinal and corticobulbar tracts
- sublenticular: auditory radiation; part of the optic radiation (contralateral upper visual quadrant)
- retrolenticular: optic radiation (LGN <--> occipital lobe cortex)
- (corticopontine fibers travel through all parts of the internal capsule)
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