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Anatomy 2 > Descending Motor > Flashcards

Descending Motor Flashcards

1
Q

Ascending and descending pathways

A

Consist of three general types:

Long, ascending fibers going to thalamus, cerebellum or various brainstem nuclei
Long, descending fibers going from cerebral cortex or various brainstem nuclei to spinal cord gray matter
Short, propriospinal fibers interconnecting different spinal cord levels
These fibers help coordinate flexor reflexes

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2
Q

Pars caudalis

A

pain processed here.

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3
Q

Lower Motor Neuron

A

Innervates striated muscle, directly signals muscle to contract, only way movement can be initiated
Last neuron in chain of neurons

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4
Q

LMN includes

A

Alpha, Gamma motor neuron

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5
Q

Alpha motor neuron

A

extrafusal muscle fibers, directly contract

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6
Q

Gamma motor neuron

A

intrafusal muscle fibers, anterior horn as well. Work with cerebellum to make sure force is precise.

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7
Q

LMN lesion

A

Atonia - loss of muscle tone
Areflexia - loss of myotatic (knee jerk) reflex
Flaccid paralysis
Fasciculations - spontaneous muscle contractions
Atrophy - loss of muscle tissue

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8
Q

Atonia

A

loss of muscle tone

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9
Q

Areflexia

A

loss of myotatic (knee jerk) reflex

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10
Q

Fasciculations

A

spontaneous muscle contractions

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11
Q

Upper Motor Neurons

A

Axons descend from cortex, end on or near LMN

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12
Q

UMN lesions

A 
Spastic paralysis (paresis)
Hyperreflexia
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13
Q

Hypertonia UMN Lesion

A

(increased resting tension)

Arm flexors, leg extensors

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14
Q

Pathologic refluxes UMN Lesion

A

Pathologic reflexes, e.g. negative plantar reflex or Babinski sign
Big toe dorsoflexion with fanning of other toes when side of heal is stroked

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15
Q

Fasiculations are

A

spontaneous contractions of small groups of muscle fibers that can be visible at the skin surface

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16
Q

Fibrillations

A

contractions of individual muscle fibers that can not be seen visually but are detected using electrical monitoring.

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17
Q

Clonus is a rapid

A

series of alternating muscle contractions that occur in response to the sudden stretch of a muscle

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18
Q

Lower motor neurons & motor units

A

Cell bodies in anterior horn

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19
Q

Axons in ventral root LMN+motor units

A

divide into terminal branches widely distributed in target muscle

Each branch ends at one neuromuscular junction

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20
Q

Systematic arrangement of motor neurons - Neurons controlling axial muscles are

A

medial to those controlling distal muscles

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21
Q

Neurons controlling flexors are -Systematic arrangement of motor neurons

A

located posterior to the extensor groups

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22
Q

Motor units

A

1 motor neuron + all myofibers it innervates = motor unit

Extraocular muscle 10 myofibers/ motor unit
Large antigravity muscle like gastrocneumius 100s up to 1000myofibers/ motor unit

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23
Q

MU size

A

Vary in size, related to control we have over the muscle

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24
Q

Darker

A

more mito

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25
Q

Three types of muscle fibers

A

Standing, running, jumping

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26
Q

Standing

A

contract weakly for long periods

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27
Q

Running

A

contract strongly for short/long periods

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28
Q

Jump

A

contract very strongly for very short periods

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29
Q

Each muscle fiber type populates

A

one motor unit, no mixing

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30
Q

Type 1 muscle fiber - Action

A

Sustained force

weight bearing

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31
Q

Type 1 muscle fiber- Lipids

A

Abundant

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32
Q

Type 1 muscle fiber - Glycogen

A

Scant

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33
Q

Type 1 muscle fiber - Ultrastructure

A

Many mito

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34
Q

Type 1 muscle fiber- physio

A

Slow twitch

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35
Q

Type 1 muscle fiber- prototype

A

Turkey leg/ duck breast muscle

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36
Q

Type 2 muscle fiber - action

A

Sudden movements

purposeful motion

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37
Q

Type 2 muscle fiber - lipids

A

scant

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38
Q

Type 2 muscle fiber- glycogen

A

Abundant

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39
Q

Type 2 muscle fiber - ultrastructure

A

few mito

40
Q

Type 2 muscle fiber - physio

A

Fast twitch

41
Q

Type 2 muscle fiber- prototype

A

Turkey breast muscle

42
Q

S

A

slow-twitch; small amounts of force over long time

43
Q

FR

A

fast twitch, fatigue resistant

44
Q

FF

A

fast twitch, fast fatigue, large amount of force, for brief period

45
Q

Motor control

A

Basal ganglia & cerebellum

46
Q

Basal ganglia & cerebellum influence

A

cerebral cortical output to cord and brainstem

47
Q

Basal ganglia, cerebellum and association cortex are

A

vital in design, choice and monitoring of movement, but have no direct effect on LMN

48
Q

Cortex initiates

A

movement, BG and cerebellum refine it.

49
Q

Damage to these areas does not cause weakness may have: (basal ganglia, cerebellum)

A

involuntary movements,
incoordination,
difficulty initiating movement

50
Q

Hierarchical - motor control

A

in that cortex “decides” what movement should occur

Premotor cortex plans and tells motor cortex and then the LMN what to do

51
Q

Parallel - motor control

A

arrangement as premotor cortex can directly “talk to” LMN

52
Q

Basal ganglia and cerebellum involved in planning and monitoring movements, have

A

no (few) outputs to spinal cord most go to motor & premotor cortices

53
Q

Descending Motor Pathways - mostly terminate or synapse on

A

Interneurons in spinal cord, but some directly synapse with primary motor neuron (hand and CST)

54
Q

Descending Motor Pathways - mostly terminate or synapse on

A

Interneurons in spinal cord, but some directly synapse with primary motor neuron (hand and CST)

55
Q

Corticospinal tract (pyramidal tract)

A

Cortex to spinal cord (classic upper motor neuron)

56
Q

Corticobulbar (corticonuclear) tract

A

Cortex to brainstem

57
Q

Corticopontine tract

A

Cortex to basilar pons

58
Q

Corticospinal Tract - motor

A

Primary motor area; precentral gyrus (Area 4) ~ 40% of fibers

59
Q

CST Somatic sensory area

A

postcentral gyrus (Areas 3, 1, & 2) ~ 25%

60
Q

CST Premotor area (Area 6)

A

lateral surface of cerebrum ~ 20%

61
Q

CST Supplementary motor area (Area 6)

A

medial surface of cerebrum ~ 10%

62
Q

Primary Motor Area function

A

Execution of contralateral voluntary movements

Control of fine digital movements

63
Q

Primary motor area projections

A

Projects to brainstem & spinal cord – some monosynaptic terminations on spinal cord motor neurons (hand)

Synapse to interneurons, then to lower motor neurons (hence fine digital movements).

64
Q

Primary motor area lesion

A

results in paralysis of contralateral muscles

65
Q

Premotor Area

A

area 6

66
Q

Premotor Area function

A

Plans movements in response to external cues (e.g., instructions)
Control of proximal and axial musculature (trunk, shoulder, hip)
May assemble empathetic facial movements

67
Q

Premotor area Projects to

A

primary motor area and reticular formation

Some fibers project to all spinal cord levels

68
Q

Premotor area lesions

A

Moderate weakness of contralateral proximal muscles

Loss of ability to associate learned hand movements to verbal or visual cues

69
Q

Supplementary Motor Area (SMA) Function

A

Plans movements while thinking (internally paced)
Assembles (learns) new sequence (playing new music)
Assembles previously learned sequence (music scale)
“Imagines” movements

70
Q

SMA projection

A

Projects to premotor and primary motor areas

71
Q

Parietal Lobe

A

Somatic sensory area and superior parietal lobule

72
Q

Parietal lobe projection

A

Project to primary motor area
Direct motor patterns in response to sensory input
Project to sensory areas of brainstem and spinal cord
Modulate sensory signals

73
Q

CST COLLATERALS

A

project to: Basal ganglia, thalamus, reticular formation, various sensory nuclei (dorsal column nuclei), posterior & intermediate horns of spinal cord

74
Q

CST

A

many functions

75
Q

3Not all movements are dependent on CST

A

If cut in monkeys, after a period of flaccid paralysis, they move again, fine finger movement lost permanently

76
Q

Corticospinal tract (CST) originates in

A

cerebral cortex, precentral gyrus and nearby areas

77
Q

Corticospinaltract Decussation

A

Lateral CST- 80% of fibers cross in decussation in medulla descend in lateral funiculus
Uncrossed Lateral CST- 10%
Anterior CST- 10% of fibers, uncrossed descend in anterior funiculus
Axial muscle activity, some actually cross in anterior commissure prior to synapsing
Somatotopically organized

78
Q

cerebral peduncle descending fibers

A

Corticospinal, corticobulbar, and corticopontine fibers descend in the cerebral peduncle

The corticospinal fibers descend in the middle third of the cerebral peduncle.

79
Q

In the pons the corticospinal tract is

A

broken up into multiple small bundles on each side.

80
Q

In the pons the corticospinal tract is

A

broken up into multiple small bundles on each side.

81
Q

CST rostral medulla

A

The corticospinal tract goes through the pyramid and for this reason some refer to it as the pyramidal tract

82
Q

Rubrospinal tract

A

Control of shoulder and proximal arm musculature

83
Q

Reticulospinal tract

A

Control of axial musculature - walking

84
Q

Vestibulospinal tract

A

Control of axial musculature - balance

85
Q

Tectospinal tract

A

believed to be important in head turning reflexes in response to visual stimuli, unclear function in humans

86
Q

Vestibulospinal Tract(s)

A

Origin: vestibular nuclei in pons

Receives input from:
Vestibular system and cerebellum (balance)
Lateral vestibulospinal tract
Projects via lateral funiculus to:
Ipsilateral spinal cord, facilitates antigravity muscles
Medial vestibulospinal tract
Projects via anterior funiculus to:
Spinal cord cervical levels bilaterally, controls head movements in response to gravity
Function:
Mediates postural adjustments & head movements
Antigravity reflexes
Righting reflex (cats); righting reflex to head inversion

87
Q

Rubrospinal Tract

A

Origin: red nucleus (“rubro”)
Receives input from:
Primary and premotor areas – shoulder and arm control
Cerebellum
Course:
Ventral tegmental decussation
Lateral funiculus
Projects to contralateral spinal cord
Function: like that of vestibulospinal tract;
Facilitates upper extremity flexor muscle tone
Believed to be small in humans, some question significance

88
Q

RF and movement control

A

Two reticulospinal tracts:
Medial: pons; ipsilateral, descends near MLF & in anterior funiculus
Lateral: medulla, descend bilaterally, in lateral funiculus

89
Q

RF and movement control function

A

Function:
Supports rhythmic motor actions, i.e. walking
May support recovery of motor function via projections to motor neurons controlling arm and hand

90
Q

Corticobulbar pathway

A

Some fibers end directly on motor neurons (XII), but most end on interneurons in the reticular formation
III, IV, VI receive no direct input
Figure shows V, VII, XII, nucleus ambiguus (part of X) & XI

91
Q

V, VII, XII, nucleus ambiguus & XI CBP

A

receive bilateral input

Originate in face/mouth portion of motor cortex and other nearby areas

Descend with CST to level of target nucleus, then splits off so no corticobulbar decussation exists

92
Q

Facial motor nucleus

A

Exception to typical CBP pattern

93
Q

Motor neurons to lower facial muscles mainly innervated by

A

contralateral cortex, but upper facial muscles innervated bilaterally

94
Q

Unilateral damage to CBP (e.g. in cerebral peduncle) result

A

Inability to smile or show teeth symmetrically; but ability to wrinkle forehead is unaffected

95
Q

Atrophic hands

A

both upper and lower neuron involvement issues.

96
Q

Fasciculations

A

classic lower neuron. Sensation is preserved, so dorsal column is probably fine. Anterolateral pathway and PNS are fine. Purely motor.

CST runs through damaged area. Losing upper motor neurons and lower motor neurons. This is ALS. Lou Gherigs.

Anatomy 2 (15 decks)

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