Descending Motor Systems Flashcards by William Grooms

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

Alpha motor neuron - extrafusal muscle fibers

Gamma motor neuron - intrafusal muscle fibers

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What structures are innervated by lower motor neurons?

Striated muscle

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Name five types of LMN legions

Atonia
Areflexia
Flaccid Paralysis
Fasciculations
Atrophy

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

Lower motor neuron

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

From the cortex, on or near LMN

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Outline UMN lesions

Spastic paralysis - hyperreflexia, hypertonia.

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

-Mild disuse atrophy

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Components of motor neuron

motor neuron and all myofibrils it innervates.

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Neurons controlling axial muscles are _______ to those controlling distal muscles

medial

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Neurons controlling flexors are located _______ to the extensor groups

posterior

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

1 - sustained force, weight bearing

2 - sudden movements, purposeful motion

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

1 - abundant

2 - scant

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

1 - scant

2 - abundant

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

1 - many

2 - few

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

1 - slow twitch

2 - fast twitch

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

1 - slow twitch

2 - fast twitch

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What structure “plans” function of the motor cortex?

Premotor cortex

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

Parallel arrangement

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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?

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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Three structures associated with planning and monitoring movements?

Cerebellum, basal ganglia, association cortex.

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

interneurons

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

Corticospinal (pyramidal) - cortex and spinal cord

Corticobulbar (corticonuclear) - cortex and brainstem

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Four less important tracts in descending motor pathways?

Corticopontine
Rubrospinal
Reticulospinal
Vestibulospinal

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

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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Function of primary motor cortex in this system

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

Primary motor cortex projections go where?

Brainstem/spinal cord.

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

Contralateral muscles

Function of premotor cortex

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

To where does the premotor cortex project

Primary motor area/reticular formation.

Lesion in premotor cortex causes what

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

Function of supplementary motor cortex

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

To where does the supplementary motor cortex project?

Premotor and primary motor areas.

The somatosensory cortex and superior parietal lobule project where?

- 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

What tract controls fine finger movement

CST

Where does dessucation occur in CST?

Spinomedullary junction

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

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

After dessucation, where does synapse from CST occur?

- Cell bodies in anterior horn | - interneurons

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

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

Role of vestibulospinal tract

Control of axial musculature - balance

Role of rubrospinal tract

Control of shoulder and proximal arm musculature

Role of reticulospinal tract

Control of axial musculature - walking

Role of tectospinal tract

-head turning reflexes, visual stimuli response.

Origin of vestibulospinal tract

vestibular nuclei in pons

From where does vestibulospinal tract receive input

Vestibular system and cerebellum

To where do lateral and medial vestibulospinal tracts project?

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

Functions of vestibulospinal tract

Mediate postural adjustments/head movements. Antigravity reflex.

Rubrospinal tract origin

Red nucleus

From where does the rubrospinal tract receive input?

From primary and premotor areas, cerebellum, thalamus

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

Ventral tegmental decussation. Lateral funiculus

To where does rubrospinal tract project?

Contralateral spinal cord.

Function of rubrospinal tract?

Facilitate upper extremity flexor muscle tone.

Medial and lateral reticulospinal tract pathways

M: From pons - ipsilateral - descends near MLF and in anterior funiculus L: From medulla - descends bilaterally in lateral funiculus

Function of reticulospinal tract

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

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

Corticobulbar

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

O: lateral precentral gyrus and insula. | Descends thru internal capsule and thru brainstem. Ipsilateral - bilateral projections to nuclei.

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

VII

How is strength affected by an UMNL vs LMNL

Both decreased

How is muscle tone affected by an UMNL vs LMNL

Upper: increased Lower: decreased

how are stretch reflexes affected by an UMNL vs LMNL

Upper: increased Lower: decreased

How is atrophy affected by an UMNL vs LMNL

Lower: severe Upper: mild