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Anatomy II: Exam I > Descending Pathways > Flashcards

Descending Pathways Flashcards

1
Q

lower motor neurons

A
  • innervates striated m
  • directly signals m to contract (only way movement can be initiated)
  • last neuron in chain of neurons
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2
Q

types of lower motor neurons

A
  • alpha: extrafusal m. fibers (actively contract m)

- gamma: intrafusal m. fiber (regulatory)

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3
Q

lesions associated with lower motor neurons

A
  • atonia: loss of muscle tone
  • areflexia: loss of myotonic (knee jerk) reflex
  • flaccid paralysis
  • fasciculations: spont m contractions
  • atrophy: loss of m tone
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4
Q

where are cell bodies of motor units located?

A

anterior horm

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5
Q

upper motor neurons

A
  • axons descend from cortex

- end on or near LMN

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6
Q

lesions associated with upper motor neurons

A

spastic paralysis

  • hypertonia (increased resting tensor): flexors, leg extensors
  • hyperflexia
  • pathoreflexes (neg plantar reflex or Babinski sign)
  • big toe dorsoflexion, other toes fan when heel stroked
  • atrophy not as severe
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7
Q

motor unit

A

1 motor neuron and all myofibers it innervates
-vary in size, related to control we have over the muscle

extraoccular mm: 10 myofibers/motor unit
gastrocnemius mm: 1000 myofibers/motor unit

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8
Q

type I fibers

A
  • slow twitch
  • for sustained force, weight bearing
  • abundant lipids, less glycogen
  • many mitochondria
  • *turkey leg/duck breast m
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9
Q

type II fibers

A
  • fast twitch
  • for sudden movement and purposeful motion
  • few lipids, abundant glycogen
  • few mitochondria
  • turkey breast m
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10
Q

Basal ganglia/cerebellum motor control

A
  • influence cerebral cortical output to SC and BS

- vital in design, choice of monitoring of movement, no direct effect on LMN

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11
Q

lesions in basal ganglia/cerebellum and effect on motor control

A
  • does not mean weakness

- involuntary, incoordination, difficulty initiating movement

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12
Q

higher centers motor control

A

hierarchical bc cortex “decides” what movement should occur

-parallel arrangement as premotor cortex can directly “talk to” LMN

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13
Q

where do descending motor pathways mostly terminate/synapse?

A

interneurons in SC

*but some directly synapse with primary motor neuron (hand and CST)

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14
Q

location of primary motor area of corticospinal tract

A

precentral gyrus (area 4)

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15
Q

location of somatic sensory area of CST

A

post central gyrus (areas 1-3)

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16
Q

location of premotor area of CST

A

lateral surface of cerebrum (area 6)

17
Q

location of supplementary motor area of CST

A

medial surface of cerebrum (area 6)

18
Q

location of superior parietal lobe of CST

A

areas 5 and 7

19
Q

primary motor area of CST

A
  • fncnt: execution of contralat vol movements and control of fine digital movements
  • projects to BS and SC
  • some monosynaptic terminations on SC MN (hand)
  • usually synapse on interneurons
  • lesions = contralat m paralysis
20
Q

fnctn of premotor area of CST

A
  • plans movmements in response to external cues (instructions
  • control of proximal and axial mm (trunk, shoulders, hip)
  • empathetic facial expression
21
Q

projections and lesions of premotor area of CST

A
  • to primary motor area and reticular formation
  • some fibers project to all spinal levels
  • lesions cause moderate weakness of contralat prox mm
  • loss of ability to link learned hand movements to verbal/visual cues
22
Q

supplementary motor area of CST

A
  • fnctn: plans movements while thinking
  • learns new sequences, assemble prev learned sequences, imagines movements

-projects to premotor and primary motor areas

23
Q

parietal lobe and CST

A
  • somatic sensory area and sup parietal lobule
  • project to primary motor area (direct motor patterns in response to sensory input)
  • project to sensory areas of BS and SC (moderate sensory signals)
24
Q

characteristics of CST

A
  • complex: multiple origins and destinations
  • collaterals project to basal ganglia, thalamus, RF, sensory nuclei (dorsal column nuclie), post and intermed horns of SC
  • not all movements depend on CST
25
Q

origin of CST

A

in cerebral cortex, precentral gyrus, and nearby areas

26
Q

descent of CST

A

thru cerebral peduncle, basis pons, medullary pyramid

27
Q

decussation of CST

A
  • at spinomedullary junction

- lat CST: 80% in medulla and descent in lat funiculi

28
Q

lateral striate artery

A

br of lenticulostriate a, which is br of MCA

29
Q

other descending pathways

A
  1. rubrospinal: control of shoulder and prox arm mm
  2. reticulospinal: control of axial mm - walking
  3. vestibulospinal: control of axial mm - balance
  4. tectospinal: imp for turning head reflexes in response to visual stimuli
30
Q

where do most fibers end of corticobulbar tract?

A

on interneurons in RF, but some end directly on motor neurons (XII)

III, IV, VI receive no direct input

31
Q

path of corticobulbar tract

A

leave cerebral cortex, descend to BS (end on sensory and motor nuclei of CN and RF)

32
Q

which nerves receive bilateral input from corticobulbar tract?

A

V, VII, XII, nucleus ambiguus, XI

33
Q

where does corticobulbar tract originate?

A

in face/mouth portions of motor cortex

no decussation exists

34
Q

facial motor nucleus

A
  • exception to typical CBT pattern
  • motor neurons to lower facial mm, mainly innervated by contralat cortex
  • upper mm innervated bilaterally (unilat damage = inability to smile symmetrically, BUT can wrinkle forehead symmetrically

Anatomy II: Exam I (10 decks)

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