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Brain motor control And some model systems Pep-talk: • There are many deficits in motor function and coordination. • After you have learned how much of the brain is dedicated to motor function and coordination, you will appreciate what a gift it is not to be spastic. • Spinal tracts have names like cortico-spinal tract (from -> to). • Above and beyond spinal reflexes, these tracts mediate descending influences on spinal motor neurons. Voluntary • • • • • Corticospinal Pyramidal (75-90% crosses) 10 to the 6th axons goes through pyramids not pyramidal neurons Lateral and ventromedial pathways precentral gyrus -> internal capsule -> cerebral peduncles -> pyramids ->decussate in brain stem > • lateral cortical spinal tract • medial cortical spinal tract) • only primates have monosynaptic pathway Brown Sequard Syndrome • A half spinal cord injury: • contralateral loss of spinothalamic below injury • ipsilateral loss of lemniscal. • motor (ipsilateral impairment) Like somatotopic • The pathway is neatly organized topographically at the levels of • internal capsule, • Cerebral peduncle in midbrain, • Pyramid in medulla Corticobulbar • • • • • • Output for face and upper body via facial nerve Trigeminal Vagus Accessory hypoglossal Upper vs lower face • Interesting in that upper face has bilateral innervation, lower face is only contralateral in its control • The famous Sunday night TV anchorman Ed Sullivan ("We have a really big shew for you tonight") had the lopsided mouth described in Box B for unilateral damage (or stroke). More descending pathways • Superior colliculus (tectospinal) goes down to control head movements • Vestibular control for posture and catching balance • Red nucleus adds control to arm muscles • Rubrospinal tract from red nucleus replaced by corticospinal in evolution Yet another pathway • corticoreticulospinal tract • Reticular formation controls axial muscles and proximal limbs • pontine reticulospinal- help to maintain posture • medullary reticulospinal - liberates antigravity from reflex Precentral gyrus • • • • topographic map like sensory homumculus work by neurosurgeon Penfield, note relative "magnifications” Precentral gyrus = Brodmann area 4 = M1 Basal ganglia • Extrapyramidal (because it lies outside the pyramids) • caudate + putamen = striatum (striated because strands of internal capsule make it look striated) • putamen + globus pallidus = lentiform nucleus [lens shaped] • • • • • To and from basal ganglia In summary: inputs to basal ganglia cortex & substantia nigra & pars compacta outputs from basal ganglia The globus pallidus is a relay nucleus for the caudate and putamen and so is the subthalamus. • To VA/VL complex of thalamus to motor cortex • also to substantia nigra pars reticulata to superior colliculus Parkinson's • (see the neurotransmitter lecture) • Lowered excitatory input from substantia nigra via D1 dopamine receptors leads • (through globus pallidus and thalamus) to decreased excitation at motor cortex, • explaining the hypokinesia of motor cortex. • Also there is another interaction via D2 receptors to subthalamic nucleus Huntington's • • • • • • • (1872) disease (chorea) choreoathetosis Dominant late onset - counseling issues Woodie Guthrie lake Maracaibo degeneration of putamen and caudate short arm of chromosome 4 1983 and since: cloning -CAG repeat (polyglutamine repeat), • 15-34 (normal) -> 42-66 (Huntington's) More • Other trinucleotide repeat diseases: fragile X syndrome, • myotonic dystrophy, • and others • sometimes they get worse from generation to generation (anticipation) Cerebellum • Dysmetria (cannot approach target), ataxia, intentional tremor if cerebellar damage. • Cerebellum highly developed in electric fish. • Cerebellum is involved in rhythmic activity and plasticity. • An additional decussation makes it so that cerebellum controls the ipsilateral side of the body. cerebellum "simple circuit” • excitatory & inhibitory interactions are known • Mossy fibers input to 10-100 billion granule cells to parallel fibers, • many connect to each spectacular Purkinje cell. • Also inpput from climbing fiber makes more 1:1 connection to Purkinje fiber. • Also local circuits from basket cells, Golgi cells, and stellate cells • Purkinje is output Cerebellar mutants • • • • • very interesting mouse mutants, reeler, weaver, leaner, lurcher, staggerer, & nervous, Purkinje cell degeneration (last two interestingly cause blindness too) reeler is cloned, had a defect in protein like extracellular matrix proteins and has defect in migration of cells during development. • weaver is a K+ channel. Wiring (eye movements) • a reminder of muscles and wiring • Abducens (VI) to lateral rectus • Trochlear (IV) to (contralateral) superior oblique • Occulomotor (III) to the rest (and eyelid control and the pupil) Types of eye movements: • • • • • saccades (also in REM sleep), smooth pursuit, vergence, drift, and vestibular control