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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
Three types of muscle fibers
Standing, running, jumping
26
Standing
contract weakly for long periods
27
Running
contract strongly for short/long periods
28
Jump
contract very strongly for very short periods
29
Each muscle fiber type populates
one motor unit, no mixing
30
Type 1 muscle fiber - Action
Sustained force | weight bearing
31
Type 1 muscle fiber- Lipids
Abundant
32
Type 1 muscle fiber - Glycogen
Scant
33
Type 1 muscle fiber - Ultrastructure
Many mito
34
Type 1 muscle fiber- physio
Slow twitch
35
Type 1 muscle fiber- prototype
Turkey leg/ duck breast muscle
36
Type 2 muscle fiber - action
Sudden movements | purposeful motion
37
Type 2 muscle fiber - lipids
scant
38
Type 2 muscle fiber- glycogen
Abundant
39
Type 2 muscle fiber - ultrastructure
few mito
40
Type 2 muscle fiber - physio
Fast twitch
41
Type 2 muscle fiber- prototype
Turkey breast muscle
42
S
slow-twitch; small amounts of force over long time
43
FR
fast twitch, fatigue resistant
44
FF
fast twitch, fast fatigue, large amount of force, for brief period
45
Motor control
Basal ganglia & cerebellum
46
Basal ganglia & cerebellum influence
cerebral cortical output to cord and brainstem
47
Basal ganglia, cerebellum and association cortex are
vital in design, choice and monitoring of movement, but have no direct effect on LMN
48
Cortex initiates
movement, BG and cerebellum refine it.
49
Damage to these areas does not cause weakness may have: (basal ganglia, cerebellum)
involuntary movements, incoordination, difficulty initiating movement
50
Hierarchical - motor control
in that cortex “decides” what movement should occur | Premotor cortex plans and tells motor cortex and then the LMN what to do
51
Parallel - motor control
arrangement as premotor cortex can directly “talk to” LMN
52
Basal ganglia and cerebellum involved in planning and monitoring movements, have
no (few) outputs to spinal cord most go to motor & premotor cortices
53
Descending Motor Pathways - mostly terminate or synapse on
Interneurons in spinal cord, but some directly synapse with primary motor neuron (hand and CST)
54
Descending Motor Pathways - mostly terminate or synapse on
Interneurons in spinal cord, but some directly synapse with primary motor neuron (hand and CST)
55
Corticospinal tract (pyramidal tract)
Cortex to spinal cord (classic upper motor neuron)
56
Corticobulbar (corticonuclear) tract
Cortex to brainstem
57
Corticopontine tract
Cortex to basilar pons
58
Corticospinal Tract - motor
Primary motor area; precentral gyrus (Area 4) ~ 40% of fibers
59
CST Somatic sensory area
postcentral gyrus (Areas 3, 1, & 2) ~ 25%
60
CST Premotor area (Area 6)
lateral surface of cerebrum ~ 20%
61
CST Supplementary motor area (Area 6)
medial surface of cerebrum ~ 10%
62
Primary Motor Area function
Execution of contralateral voluntary movements | Control of fine digital movements
63
Primary motor area projections
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
Primary motor area lesion
results in paralysis of contralateral muscles
65
Premotor Area
area 6
66
Premotor Area function
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
Premotor area Projects to
primary motor area and reticular formation | Some fibers project to all spinal cord levels
68
Premotor area lesions
Moderate weakness of contralateral proximal muscles | Loss of ability to associate learned hand movements to verbal or visual cues
69
Supplementary Motor Area (SMA) Function
Plans movements while thinking (internally paced) Assembles (learns) new sequence (playing new music) Assembles previously learned sequence (music scale) “Imagines” movements
70
SMA projection
Projects to premotor and primary motor areas
71
Parietal Lobe
Somatic sensory area and superior parietal lobule
72
Parietal lobe projection
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
CST COLLATERALS
project to: Basal ganglia, thalamus, reticular formation, various sensory nuclei (dorsal column nuclei), posterior & intermediate horns of spinal cord
74
CST
many functions
75
3Not all movements are dependent on CST
If cut in monkeys, after a period of flaccid paralysis, they move again, fine finger movement lost permanently
76
Corticospinal tract (CST) originates in
cerebral cortex, precentral gyrus and nearby areas
77
Corticospinaltract Decussation
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
cerebral peduncle descending fibers
Corticospinal, corticobulbar, and corticopontine fibers descend in the cerebral peduncle The corticospinal fibers descend in the middle third of the cerebral peduncle.
79
In the pons the corticospinal tract is
broken up into multiple small bundles on each side.
80
In the pons the corticospinal tract is
broken up into multiple small bundles on each side.
81
CST rostral medulla
The corticospinal tract goes through the pyramid and for this reason some refer to it as the pyramidal tract
82
Rubrospinal tract
Control of shoulder and proximal arm musculature
83
Reticulospinal tract
Control of axial musculature - walking
84
Vestibulospinal tract
Control of axial musculature - balance
85
Tectospinal tract
believed to be important in head turning reflexes in response to visual stimuli, unclear function in humans
86
Vestibulospinal Tract(s)
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
Rubrospinal Tract
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
RF and movement control
Two reticulospinal tracts: Medial: pons; ipsilateral, descends near MLF & in anterior funiculus Lateral: medulla, descend bilaterally, in lateral funiculus
89
RF and movement control function
Function: Supports rhythmic motor actions, i.e. walking May support recovery of motor function via projections to motor neurons controlling arm and hand
90
Corticobulbar pathway
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
V, VII, XII, nucleus ambiguus & XI CBP
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
Facial motor nucleus
Exception to typical CBP pattern
93
Motor neurons to lower facial muscles mainly innervated by
contralateral cortex, but upper facial muscles innervated bilaterally
94
Unilateral damage to CBP (e.g. in cerebral peduncle) result
Inability to smile or show teeth symmetrically; but ability to wrinkle forehead is unaffected
95
Atrophic hands
both upper and lower neuron involvement issues.
96
Fasciculations
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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