Motor Systems Flashcards
1
Q
what are the 2 major motor systems?
A
- pyramidal
- extrapyramidal
2
Q
briefly describe pyramidal and extrapyramidal motor systems
A
- pyramidal: corticospinal and corticobulbar pathways
- extrapyramidal: cerebellum and basal ganglia
3
Q
describe motor system hierarchy
A
4
Q
describe hierarchical control of movement: reflexes
A
spinal cord
5
Q
describe hierarchical control of movement: stereotyped, repetitive movements
A
- spinal cord
- brain stem
- cerebellum
- dependent on central pattern generators that produce rhythmic output needed for walking, flying, and breathing
6
Q
describe hierarchical control of movement: goal-directed, voluntary movement
A
- cortex
- basal ganglia
7
Q
what is level 1 of the motor system hierarchy?
A
spinal cord circuits: muscle conraction, reflexes, central pattern generators
8
Q
describe the pyramidal 2 neuron system
A
lower and upper motor neurons
- lower motor neurons (LMN) innervate muscle
- upper motor neurons: cortical neurons that innervate LMNs
- reach LMNs through corticospinal and corticobulbar tracts
9
Q
describe the motor unit
A
- lower motor neuron and the muscle fibers it innervates
- the building block of movement
10
Q
describe the neuromuscular junction (lower motor neurons)
A
- synaptic connection from the nervous system to the muscle
- action potential triggers calcium release
- docking and then release of vesicles containing ACh
11
Q
describe a reflex arc
A
- the simplest sensory-motor circuit
- simultaneous control of muscle contraction and relaxation
- the rest of the CNS exists to modify this reflex
12
Q
describe the stretch reflex
A
- opposes muscle stretch through contraction
- muscle spindle detects muscle length (static response) and rate of change (dynamic response): these signs are relayed to the spinal cord
- within the cord, motor neurons are excited to activate compensatory contraction
13
Q
describe gamma fiber activation of muscle spindles
A
- gamma motor neuron tells us how much stretching is happening
- intra and extrafusal muscle fibers innervated by gamma and alpha motor neurons respectively
14
Q
describe the motor cortex
A
2nd neuron
- primary motor cortex
- brodmann area 4
- premotor cortex
- brodmann’s area 6 and 8
- planning and guidance
- projects directly to spinal cord
- giant pyramidal (betz) motor neurons
- largest CNS neurons
- layer 5
- long projection axons
- synapse on alpha-motor neurons
15
Q
what is somatotopy?
A
brain maps the motor function of the body
16
Q
describe the somatotopic organization of the motor cortex
A
17
Q
what is the internal capsule?
A
- between thalamus and basal ganglia
- continuous with the cerebral peduncle
18
Q
describe descent of the motor tract
A
19
Q
describe the structures of the internal capsule
A
- anterior limb
- frontal functions
- not clinically relevant
- genu
- corticobulbar (face)
- posterior limb
- corticospinal tracts (CST)
- motor deficiencies
20
Q
is somatotopy retained in the internal capsule?
A
yes
21
Q
where does decussation of the corticospinal tract occur?
A
at the pyramids of the medulla
22
Q
the motor cortex controls mostly ___ side
A
contralateral
23
Q
describe pyramidal decussation
A
- >90% contralateral
- ~10% ipsilateral
- 8% anterior
- 2% lateral
24
Q
describe the primary neuron
A
- decussation is at the level of the medulla
- somatotopy is maintained
25
what are 2 important features in the sacral region of the spinal cord?
* conus medullaris
* cauda equina
26
compare upper and lower motor neuron signs
realize that each column is corresponding to signs when either the upper or lower motor neuron is damage/lost
27
describe the corticobulbar tract
* motor cortex to brainstem cranial nerve nuclei
* muscles of face, head, and neck
* tracts stay ipsilateral, but usually innervate ganglia bilaterally
* travel in the genu of the internal capsule
* do _not_ have major decussation at the pyramids
28
corticobulbar innervation is mostly bilateral. describe the exceptions
* facial nerve
* hypoglossal nerve
* if one side is blown out, it cannot be compensated for due to the lack of bilaterality
29
describe the extrapyramidal system
* interact with pyramidal motor systems, but they are distinct
* do not originate in cortex, but respond to cortical over-ride
* includes vestibulospinal, tectospinal, and rubrospinal systems
* also basal ganglia (contralateral control) and cerebellum (ipsilateral control)
30
describe the vestibulospinal tract
* extrapyramidal
* support posture and balance, control head movements
* relays information from the vestibular nuclei (VIII nerve) to spinal cord
31
describe the tectospinal tract
* extrapyramidal
* mediates reflex postural movements of the head from visual input
* originates in midbrain tectum (superior colliculus)
* axon fibers decussate in midbrain
* terminates in spinal cord
32
describe the rubrospinal tract
* extrapyramidal
* cerebellar inputs; perform planned movements (~alternative to corticospinal system)
* originates in red nucleus
* axon fibers decussate in midbrain
33
what is the clinical definition of basal ganglia?
extrapyramidal motor system
34
what does the basal ganglia do?
* modulates the initiation, termination, and amplitude of intentional movements
* unilateral disease causes contralateral signs
35
describe modulatory cortical loops
* basal ganglia afferents
* robust input from almost all parts of the cortex
* basal ganglia efferents
* ventral thalamic relay to cortex
* somatic motor loop - somatomotor control
* occulomotor loop: eye movements
* frontal loop: cognitive functions
* limbic loop: emotional and visceral functions
36
what are the inputs, outputs, intrinsic, and modulatory characteristics of the basal ganglia?
* input: caudate, putamen
* output: globus pallidus - internal segment; substantia nigra - pars reticulata
* intrinsic: globus pallidus - external segments; subthalamic nucleus
* modulatory: substantia nigra - pars reticulata
37
describe direct and indirect pathways
* direct pathway - facilitates movement; fewer neurons, so it is faster
* indirect pathway - inhibits movement; more neurons, so it is slower
\*red = inhibitory, green = excitatory
38
describe the general difference between hyperkinesia vs. hypokinesia
* hyperkinesia - excessive movements, often with increasing dimentia; ex. Huntington's disease/chorea
* hypokinesia - decreased movements; ex. parkinson's disease
39
describe huntington's disease
* decreased striatal output
* decreased inhibition of GPe
* increased inhibition of subthalamic pathways
* disinhibition of thalamic pathways
* hyperkinesis
\*D1 and D2 refer to dopamine receptors
40
what is hemiballism?
* type of hyperkinesia
* lesion of subthalamic nucleus (stroke)
* sudden onset of abnormal movements
41
describe parkinson's disease
* decreased dopamanergic output from substantia nigra compacta
* decreased inhibition of GPe (indirect) and GPi (direct)
* increased subthalamic nucleus activity
* increased activity of GPi
* decreased thalamic output
* hypokinesis
bottom line: direct pathway becomes less active, indirect pathway becomes more active
42
what are 2 therapies for parkinson's disease?
* levadopa
* ablation or deep brain stimulation
function to re-establish circuit balance
43
describe cerebellum blood supply
vertebral arteries:
* superior cerebellar a.
* anterior inferior cerebellar a.
* posterior inferior cerebellar a.
44
what are the afferents and efferents of the cerebellum?
* afferents: climbing fibers (inf. olive) and mossy fibers (come from pons, most input)
* efferents: purkinje cells to cerebellar nuclei (main) or vestibular nuclei
45
what are the 4 nuclei of the cerebellum?
Fat Guys Eat Donuts
* fastigial nucleus: vestibular
* globose nucleus: muscular tone
* emboliform nucleus: muscle tone
* dentate nucleus: coordination, fine voluntary motor activity)
46
what are the 3 subcomponents of the cerebellar peduncles?
* superior (SCP): midbrain; efferents to thalamus
* middle (MCP): pons; corticopontocerebellar afferents
* inferior (ICP): midbrain; spinocerebellar afferents and efferents to brainstem
cerebellar peduncles are tracts in and out of the cerebellum
47
describe the spinocerebellar tract
1. proprioceptive info comes in via sensory neurons
2. information ascends ipsilaterally through inferior cerebellar peduncle
3. axons synapse in cerebellar nuclei and cerebellar cortex
lesion will cause ipsilateral cerebellar signs
48
describe the cerebellar efferents of the thalamocortical tract
cerebellar efferents
* primary: purkinje cells to dentate nucleus
* secondary: exit to superior CP
* enters middle CP
* END: Cb hemispheres
* note: also sends collaterals to deep cerebellar nuclei
49
describe the cerebellar afferents of the corticopontocerebellar tract
* primary: corticopontine
* secondary: pontocerebellar (decussate in pons)
* enter middle CP
* END: Cb hemispheres
* note: also sends collaterals to deep cerebellar nuclei
50
describe corticopontocerebellar tract signs
in general, upper motor signs mostly obscure cerebellar signs
* lesion A: in internal capsule; upper motor neuron signs
* lesion B: in pons; upper motor neuron signs
* lesion C: in MCP; ipsilateral cerebellar signs
51
what is spinocerebellar ataxia?
* walking, balance, gait problems
* loss of precision and timing of movements
* swallowing, judging distances, spasticity
52
describe alcoholic cerebellar degeneration
* anterior cerebellar lobe degenerates
* gait, trunk, and lower limb ataxia
53
what 3 things can lesions of the vermis cause?
1. truncal ataxia - loss of axial muscle coordination
2. gait ataxia - unsteady gait, tied to anterior lobe syndrome/alcoholism
3. abnormal saccades
54
what 6 things can lesions of the cerebellar hemispheres cause?
1. ataxia - loss of coordination of voluntary movements
2. hypotonia - decreased muscle tone
3. intention tremor - swaying of limb or finger during directed movement
4. dysmetria - over or under shooting a target
5. dysdiadochokinesia - inability to perform rapidly alternating movements
6. speech and cognitive impairments possible
55
what 2 things can lesions of the flocculonodular lobe cause?
1. truncal ataxia - uncoordinated axial muscles result in poor balance
2. nystagmus - uncoordinated and unintended eye movements (dancing eyes)
56
describe pallidotomy
ablation of the globus pallidus internal segment
* usually done in patients with levodopa associated dyskenisis
* bilateral pallidotomy produced severe apathy and often depression
* can also interfere with executive function and language (left side)
* can produce ipsilateral hemiballism
