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Flashcards in Motor Systems Deck (56):
1

what are the 2 major motor systems?

  • pyramidal
  • extrapyramidal

2

briefly describe pyramidal and extrapyramidal motor systems

  • pyramidal: corticospinal and corticobulbar pathways
  • extrapyramidal: cerebellum and basal ganglia

3

describe motor system hierarchy

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4

describe hierarchical control of movement: reflexes

spinal cord

5

describe hierarchical control of movement: stereotyped, repetitive movements

  • spinal cord
  • brain stem
  • cerebellum
    • dependent on central pattern generators that produce rhythmic output needed for walking, flying, and breathing

6

describe hierarchical control of movement: goal-directed, voluntary movement

  • cortex
  • basal ganglia

7

what is level 1 of the motor system hierarchy?

spinal cord circuits: muscle conraction, reflexes, central pattern generators

8

describe the pyramidal 2 neuron system

lower and upper motor neurons

  1. lower motor neurons (LMN) innervate muscle
  2. upper motor neurons: cortical neurons that innervate LMNs
    1. reach LMNs through corticospinal and corticobulbar tracts

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9

describe the motor unit

  • lower motor neuron and the muscle fibers it innervates
  • the building block of movement

10

describe the neuromuscular junction (lower motor neurons)

  • synaptic connection from the nervous system to the muscle
  • action potential triggers calcium release
  • docking and then release of vesicles containing ACh

11

describe a reflex arc

  • the simplest sensory-motor circuit
  • simultaneous control of muscle contraction and relaxation
  • the rest of the CNS exists to modify this reflex

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12

describe the stretch reflex

  • 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

describe gamma fiber activation of muscle spindles

  • gamma motor neuron tells us how much stretching is happening
  • intra and extrafusal muscle fibers innervated by gamma and alpha motor neurons respectively

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14

describe the motor cortex

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

what is somatotopy?

brain maps the motor function of the body

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16

describe the somatotopic organization of the motor cortex

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17

what is the internal capsule?

  • between thalamus and basal ganglia
  • continuous with the cerebral peduncle

18

describe descent of the motor tract

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19

describe the structures of the internal capsule

  • anterior limb
    • frontal functions
    • not clinically relevant
  • genu
    • corticobulbar (face)
  • posterior limb
    • corticospinal tracts (CST)
    • motor deficiencies

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20

is somatotopy retained in the internal capsule?

yes

21

where does decussation of the corticospinal tract occur?

at the pyramids of the medulla

22

the motor cortex controls mostly ___ side

contralateral

23

describe pyramidal decussation

  • >90% contralateral
  • ~10% ipsilateral
    • 8% anterior
    • 2% lateral

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24

describe the primary neuron 

  • decussation is at the level of the medulla
  • somatotopy is maintained

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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

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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

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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

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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

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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

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40

what is hemiballism?

  • type of hyperkinesia
  • lesion of subthalamic nucleus (stroke)
  • sudden onset of abnormal movements

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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

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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

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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

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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

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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