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Anatomy > Descending Motor Systems > Flashcards

Descending Motor Systems Flashcards

1
Q

Name two types of lower motor neurons and their associated muscle fibers

A

Alpha motor neuron - extrafusal muscle fibers

Gamma motor neuron - intrafusal muscle fibers

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2
Q

What structures are innervated by lower motor neurons?

A

Striated muscle

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3
Q

Name five types of LMN legions

A 
Atonia
Areflexia
Flaccid Paralysis
Fasciculations
Atrophy
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4
Q

What’s the last neuron in a descending motor system?

A

Lower motor neuron

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5
Q

In descending motor systems, axons descend from where and synapse where?

A

From the cortex, on or near LMN

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6
Q

Outline UMN lesions

A

Spastic paralysis - hyperreflexia, hypertonia.

Pathological reflexes - Babinski sign - dorsiflection of big toe upon heel stroke.

-Mild disuse atrophy

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7
Q

Components of motor neuron

A

motor neuron and all myofibrils it innervates.

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8
Q

Neurons controlling axial muscles are _______ to those controlling distal muscles

A

medial

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9
Q

Neurons controlling flexors are located _______ to the extensor groups

A

posterior

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10
Q

Outline the actions of type 1 dark and type 2 white muscle fibers respectivley

A

1 - sustained force, weight bearing

2 - sudden movements, purposeful motion

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11
Q

Outline the lipid abundance of type 1 dark and type 2 white muscle fibers respectivley

A

1 - abundant

2 - scant

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12
Q

Outline the glycogen abundance of type 1 dark and type 2 white muscle fibers respectivley

A

1 - scant

2 - abundant

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13
Q

Outline the mitochondria content of type 1 dark and type 2 white muscle fibers respectivley

A

1 - many

2 - few

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14
Q

Outline the physiology of type 1 dark and type 2 white muscle fibers respectivley

A

1 - slow twitch

2 - fast twitch

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15
Q

Outline the physiology of type 1 dark and type 2 white muscle fibers respectivley

A

1 - slow twitch

2 - fast twitch

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16
Q

What structure “plans” function of the motor cortex?

A

Premotor cortex

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17
Q

What term is used to describe the premotor cortex’s direct communication link to LMN?

A

Parallel arrangement

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18
Q

What structures influence cerebral cortical output to cord and brainstem, but have very few outputs to the spinal cord? What are the consequences of this with respect to descending motor systems?

A

Cererbellum and basal ganglia. Because of this, no direct effect on LMN -
info must go to the motor and premotor cortices

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19
Q

Three structures associated with planning and monitoring movements?

A

Cerebellum, basal ganglia, association cortex.

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20
Q

Most action potentials in a descending motor pathways terminate or synapse where?

A

interneurons

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21
Q

Two major tracts in descending motor pathways? What’s another name for each? What structures do they connect?

A

Corticospinal (pyramidal) - cortex and spinal cord

Corticobulbar (corticonuclear) - cortex and brainstem

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22
Q

Four less important tracts in descending motor pathways?

A

Corticopontine
Rubrospinal
Reticulospinal
Vestibulospinal

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23
Q

The pathway for the corticospinal tract begins where primarily? where else

A

Precentral gyrus (area 4) - primary motor cortex (40% of fibers here)

Somatosensory cortex; postcentral gyrus (areas 3, 1 and 2) - 25%

Premotor cortex (area 6) - 20%

Superior parietal lobule (5 and 7) - 5%

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24
Q

Function of primary motor cortex in this system

A

Execution of contralateral voluntary movements, control of fine digital movements.

25
Q

Primary motor cortex projections go where?

A

Brainstem/spinal cord.

26
Q

Lesion in the primary motor cortex results in paralysis of what?

A

Contralateral muscles

27
Q

Function of premotor cortex

A

Plans movements from stimuli. Controls axial musculature. Empathetic facial movements

28
Q

To where does the premotor cortex project

A

Primary motor area/reticular formation.

29
Q

Lesion in premotor cortex causes what

A

Contralateral proximal muscle weakness. Loss of ability to associate learned hand movements to verbal or visual cues.

30
Q

Function of supplementary motor cortex

A

Plans movements while thinking. Learns new sequences, assembles previosuly learned sequences.

31
Q

To where does the supplementary motor cortex project?

A

Premotor and primary motor areas.

32
Q

The somatosensory cortex and superior parietal lobule project where?

A
  • to primary motor cortex to direct motor patterns in response to sensory input
  • To sensory areas of brainstem and spinal cord to modulate sensory signals
33
Q

What tract controls fine finger movement

A

CST

34
Q

Where does dessucation occur in CST?

A

Spinomedullary junction

35
Q

CST descends through what structures in the rostral midbrain, rostral pons, and caudal medulla respectively?

A

RMB: Cerebral peduncle
RP: basis pontis
CM: medullary pyramid (decussation after)

36
Q

After dessucation, where does synapse from CST occur?

A
  • Cell bodies in anterior horn

- interneurons

37
Q

Three paths for CST fibers, distribution for each, and path of descent

A

Lateral CST (80% of fibers decussate) - descend in lateral funiculus

Uncrossed lateral CST - 10%

Anterior CST - 10% -descend in anterior funiculus for axial mm. activity

38
Q

Role of vestibulospinal tract

A

Control of axial musculature - balance

39
Q

Role of rubrospinal tract

A

Control of shoulder and proximal arm musculature

40
Q

Role of reticulospinal tract

A

Control of axial musculature - walking

41
Q

Role of tectospinal tract

A

-head turning reflexes, visual stimuli response.

42
Q

Origin of vestibulospinal tract

A

vestibular nuclei in pons

43
Q

From where does vestibulospinal tract receive input

A

Vestibular system and cerebellum

44
Q

To where do lateral and medial vestibulospinal tracts project?

A

L: to ipsilateral spinal cord via lateral funiculus
M: Spinal cord cervical levels bilaterally via anterior funiculus

45
Q

Functions of vestibulospinal tract

A

Mediate postural adjustments/head movements. Antigravity reflex.

46
Q

Rubrospinal tract origin

A

Red nucleus

47
Q

From where does the rubrospinal tract receive input?

A

From primary and premotor areas, cerebellum, thalamus

48
Q

Where does the rubrospinal tract decussate? Where does it go from there?

A

Ventral tegmental decussation. Lateral funiculus

49
Q

To where does rubrospinal tract project?

A

Contralateral spinal cord.

50
Q

Function of rubrospinal tract?

A

Facilitate upper extremity flexor muscle tone.

51
Q

Medial and lateral reticulospinal tract pathways

A

M: From pons - ipsilateral - descends near MLF and in anterior funiculus

L: From medulla - descends bilaterally in lateral funiculus

52
Q

Function of reticulospinal tract

A

Walking. Recovery of motor function via projections to motor neurons controlling arm and hand

53
Q

Any muscle innervated by cranial nerves is regulated by what pathway?

A

Corticobulbar

54
Q

Where does the corticobulbar pathway begin? Where does it go?

A

O: lateral precentral gyrus and insula.

Descends thru internal capsule and thru brainstem. Ipsilateral - bilateral projections to nuclei.

55
Q

With respect to corticobulbar pathway, what CN is exception to rule of bilateral innervation

A

VII

56
Q

How is strength affected by an UMNL vs LMNL

A

Both decreased

57
Q

How is muscle tone affected by an UMNL vs LMNL

A

Upper: increased
Lower: decreased

58
Q

how are stretch reflexes affected by an UMNL vs LMNL

A

Upper: increased
Lower: decreased

59
Q

How is atrophy affected by an UMNL vs LMNL

A

Lower: severe
Upper: mild

Anatomy (11 decks)

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