Download Brain motor control

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
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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
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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
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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]
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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
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(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
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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:
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saccades (also in REM sleep), smooth pursuit, vergence, drift, and vestibular control