3 Types of muscle fibers: - _____ fibers contract weakly for long periods of time. - _____ fibers contract strongly for short & long periods. - _____ fibers contract very strongly for very short times. - There [is/is not] mixing of the different myofibers.

- standing - running - jump - is not

Lecture 5 - Descending Motor Systems Flashcards by Noah Christopher

Upper motor neurons (UMN) originate in the motor region of the _____ ______ or the ________ and synapse on lower motor neurons.

cerebral cortex

- brainstem

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Lower motor neurons (LMN) originate in the ______ ______ gray matter or _____ ____ _____ of the spinal cord and are the last in a chain of neurons.

anterior horn

- anterior nerve roots

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Lower motor neurons (LMN) innervate _______ muscle, and signal muscle ________.

striated

- contraction

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Lower Motor Neurons:

Extrafusal muscle fibers use _____ motor neurons. Intrafusal muscle fibers use ______ motor neurons.

alpha

- gamma

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LMN lesions can result in loss of muscle tone called ______.

atonia

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LMN lesions can result in loss of myotatic (knee jerk) reflex called _______.

areflexia

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LMN lesions can result in inability of muscles to contract called _____ ______.

flaccid paralysis

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LMN lesions can result in spontaneous muscle contractions called ________.

fasciculations

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LMN lesions can result in loss of muscle tissue called _____.

atrophy

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LMN lesions can result in irregular contractions of individual muscle fibers called _______.

fibrillations

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UMN lesions result in _____ _______.

spastic paralysis (paresis)

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UMN lesions resulting in increased resting muscle tension called _____.

hypertonia

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UMN lesions resulting in twitching/spastic reflexes called ________.

hyperreflexia

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UMN lesions may result in a characteristic upward extension of the toes (instead of flexion) upon stimulation of the plantar surface; this is called the _______ sign.

Babinski

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Lesions on LMN result in ______ atrophy, while UMN lesions result in _____ atrophy.

severe

- mild

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As a result of UMN lesions, rapid series of alternate muscle contractions in response to the stretching of a muscle is known as a ______.

clonus

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One LMN axon in the ventral root divides into many terminal _____ to innervate a muscle. Each of these ends at one _____ _____ _____.

branches

- neuromuscular junction (NMJ)

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LMN controlling axial muscles are _____ to those controlling distal muscles. Neurons controlling flexors are ______ to the extensor group.

medial

- posterior

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1 motor neuron + all myofibers it innervates = ____ ____.

motor unit

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TRUE or FALSE:

A larger/less specific muscle has more myofibers per motor unit.

TRUE. More specific/smaller muscles have fewer fibers per motor unit.

Ex: Extraocular = 10 myofibers/unit; Gastrocnemius = 1,000/unit

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3 Types of muscle fibers:

_____ fibers contract weakly for long periods of time.
_____ fibers contract strongly for short & long periods.
_____ fibers contract very strongly for very short times.
There [is/is not] mixing of the different myofibers.

standing
running
jump
is not

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Type ___ muscles are for sustained weight/force bearing, and high in lipids and mitochondria, slow twitch, low glycogen. (duck breast)

Type ___ muscles are for sudden movements, low in lipids/mitochondria, fast twitch, high glycogen. (turkey breast)

I
II
“one (type 1) slow (twitch) fat (lipid-rich) red (appearance) ox (oxidative, mitochondria-rich)”

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Higher energy (such as jump type) motor units are [more/less] prone to fatigue, because [more/less] motor units are used than lower energy (such as stand).

- more

TRUE or FALSE:

Basal ganglia, the cerebellum, and the association cortex play a key role in signaling the LMN for complex motor output.

FALSE. Basal ganglia, cerebellum, and association cortex only signal UMN. The UMN then signal the LMN.

TRUE or FALSE: Damage to UMN's contribute to the muscular weakness and atrophy because the muscle receive inadequate motor impulses.

FALSE. UMN damage only results in incoordination; LMN damage results in muscle weakness.

The premotor cortex plans movement, tells the motor cortex, then LMN what to do. This top-down signaling is ________ control.

hierarchical

Direct communication of the premotor cortex and LMN without the motor cortex is referred to as _____ control.

parallel

The basal ganglia and cerebellum output to the _____ _____ and motor cortex, but NOT the _____ _____.

- premotor cortex | - spinal cord

Descending motor neurons mostly terminate on _____ horn neurons and ________.

- dorsal * - interneurons * double check this... motor neurons should synapse in the anterior horn shouldn't they?

6 Descending Motor Pathways: - Cortex to spinal cord = ________ tract - Cortex to brainstem = _________ tract - Cortex to basilar pons = _______ tract - Red nucleus to contralateral anterior horns = ________ tract - Reticular formation (medulla, pons) to medial anterior horns = ______ tract - Vestibular nucleus to spinal cord = ________ tract

- corticospinal tract (UMN) - corticobulbar - corticopontine - rubrospinal - reticulospinal - vestibulospinal

There are 5 areas in the cerebrum associated with the corticospinal tract. From anterior to posterior, these areas are: - The _______ area in the frontal lobe - The ______ ______ area in the precentral gyrus - The ______ ______ area in the postcentral gyrus - The ______ ______ _______ (most posterior) - The ______ ______ area on the medial frontal lobe

- premotor (area 6) (20% fibers) - primary motor (area 4) (40% fibers) - somatic sensory (areas 1, 2, 3) (25% fibers) - superior parietal lobule (areas 5, 7) (5% fibers) - supplementary motor area (area 6) (10% fibers)

TRUE or FALSE: There are both motor and sensory homunculi, located in the primary motor cortex and somatic sensory cortex, respectively.

TRUE.

The primary motor area is responsible for ______ voluntary movements, and control of fine ______ movements. It projects to both the _____ and _____ ____. Lesions affect _______ musculature.

- contralateral - digital - brainstem - spinal cord - contralateral

The premotor area plans movements in response to external ______. It controls ______ and _____ musculature (trunk, shoulder, hip), and may assemble _______ (responsive feeling) facial movements.

- stimuli - proximal - axial - empathetic

Most premotor cortex fibers project to the ______ motor cortex and _______ ______ of the brainstem.

- primary | - reticular formation

Premotor cortex lesions result in moderate weakness of ________ proximal muscles and inability to associate _____ movements to visual and verbal stimuli.

- contralateral | - hand

The part of the brain that learns new sequences, assembles old sequences, and "imagines" movements is the ________ motor area. It projects to the _____ and _____ motor areas for output.

- supplementary - premotor - primary

In the parietal lobe of the cerebrum, just posterior to the central sulcus is the _____ _____ area responsible for sensory input. Directly posterior to this is the _____ _____ lobule on the superior aspect of the parietal lobe.

- somatic sensory | - superior parietal

In response to sensory input, the _____ _____ area directs motor patterns in the _____ motor area. Input to this region is received from the _____ and _____ _____.

- somatic sensory - primary - brainstem - spinal cord

The corticospinal tract (CST) originates in the ______ _______ area in the ______ _______ of the cerebral cortex. It also has some fibers originating from ____ cells.

- primary motor - precentral gyrus - Betz

CST collaterals project to what 6 areas?

- basal ganglia - thalamus - reticular formation - posterior column nuclei - posterior horn - intermediate horns

CST impairment is associated with _____ paralysis and impairment of fine ____ movement.

- flaccid | - finger

The CST leaves the mesencephalon (midbrain) at the _____ _____. It then travels through the anterior ______ _____ of the pons, the _____ ______ of the medulla, and decussates at the __________ junction.

- * cerebral peduncle - basis pontis - medullary pyramid - spinomedullary * the cerebral peduncle is NOT part of the cerebrum

In the ______ CST, 85% of fibers decussate in the medulla and descend in the ______ funiculus (white matter or spinal cord). In the ______ CST, 15% of fibers do not decussate, and descend in the ______ funiculus.

- lateral - lateral - anterior - anterior

TRUE or FALSE: The CST is somatotopically organized.

TRUE

Clinically, the CST can be damaged by strokes when emboli travel up the internal carotid artery and lodge in the ______ ______ artery.

middle choroidal

The CST is a _____ tract because it travels through the pyramid of the rostral medulla.

pyramidal

Control of shoulder and proximal arm musculature is associated with the _______ tract.

rubrospinal

Control of axial musculature for walking is associated with the ________ tract.

reticulospinal

Control of axial musculature for balance is associated with the _________ tract.

vestibulospinal

Head turning reflexes in response to visual stimuli are associated with the ________ tract.

tectospinal

The vestibulospinal tract receives input from the ______ end organ and _______. The [anterior/lateral] tract travels through the lateral funiculus ipsilaterally for ______ muscle reflexes. The [anterior/lateral] tract travels through the anterior funiculus bilaterally for _____ movements in response to gravity.

- vestibular - cerebellum (balance) - lateral - antigravity - anterior - head

The rubrospinal tract receives input from the _____ and _____ motor cortices, and the ______. It decussates at the ventral ______ area, and travels through the [anterior/lateral] funiculus. Innervation is [contralateral/ipsilateral]. It facilitates muscle tone for shoulder and _____ flexors.

- premotor - primary - cerebellum - tegmental - lateral - contralateral - arm

The reticulospinal tract originates in the ______ ______. It receives input from the _____ _____ and _____ _____ cortices. It courses through the medial longitudinal _______ of the brainstem, then the [anterior/lateral] funiculus of the spinal cord [bilaterally/ipsilaterally]. Its function is the support of ______ motor actions like ______.

- reticular formation - primary motor - somatic sensory (pain associated w/ reticular formation) - fasciculus - anterior - bilaterally - rhythmic - walking

The ________ pathway originates in the face/mouth area of the ______ ______ cortex, and inputs directly on cranial nerves and interneurons in the reicular formation. It ceases to exist after reaching its target nuclei.

- corticobulbar | - somatic sensory

The corticobulbar pathway directly influences cranial nerves ___, ___, ___, ___, and the ______ _____ of the reticular formation.

- CN V - CN VII - CN XI - CN XII - nucleus ambiguus

The corticobulbar pathway contralaterally innervates ______ facial muscles and bilaterally innervates ______ facial muscles through the ______ ______ nucleus. Therefore, unilateral damage inhibits smiling, but doesn't affect forehead movement.

- lower - upper - facial motor