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Physiology > Ch 3 - Motor Systems > Flashcards

Ch 3 - Motor Systems Flashcards

1
Q

Posture & Movement depend on a combination of

A
  • Involuntary reflexes coordinated by the spinal cord
  • Voluntary actions controlled by higher brain center
  • It is achieved by contraction & relaxation of various muscle groups
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2
Q

Motor Unit

A

Single motor neuron and the muscle fibers that it innervates

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3
Q

Degree of innervation & level activity of Fine Control

A
  • Few fibers innervated
  • Low threshold & hence fire 1st
  • ex: ocular muscles
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4
Q

Degree of innervation & level activity of Larger movements

A
  • Many fibers innervated
  • High threshold, hence fire last
  • ex: leg muscles
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5
Q

Motor neuron pool

A

Set of motor neurons innervating fibers within the same muscle

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6
Q

Size Principle

A

More motor units = greater tension/contraction

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7
Q

More motor units = greater tension/contraction

A

Size principal

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8
Q

Extrafusal fibers

A
  • Bulk of the muscle
  • Provides the greater force of contraction
  • Innervated by alpha-motor neurons
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9
Q

Intrafusal fibers

A
  • Smaller than & parallel to extrafusal fibers
  • Generate insignificant force compared to extrafusal fibers
  • Form muscle spindles (stretch receptors)
  • Innervated by gamma motor neurons, Ia & II fibers
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10
Q

Muscle Spindles

A
  • Stretch receptors
  • Groups Ia & II afferents which are arranged in parallel to extrafusal fibers
  • Detect changes in muscle length
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11
Q

Group Ia Afferents

A

Detect rate of change in muscle

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12
Q

Detect rate of change in muscle

A

Ia afferents

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13
Q

Group II Afferents

A

Detect actual change in muscle length

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14
Q

Detect actual change in muscle length

A

Group II Afferents

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15
Q

Golgi Tendon Organs

A
  • Group Ib afferents which are arranged in series w/ extrafusal fibers
  • Detects tension
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16
Q

Group Ib afferents that detect tension

A

Golgi Tendon Organs

17
Q

How Does the Spindle Work?

A

Muscle spindle reflexes oppose (correct for) increases in muscle length (stretch). When a muscle is stretched, both extrafusal & intrafusal fibers are lengthened due to parallel arrangement. Increase in length of the intrafusal fibers is detected by the sensory afferent fibers innervating them. Group Ia afferents detects rate of change via nuclear bag & chain. Group II afferents detects change in length of fiber via nuclear chain. Group Ia & II fibers sends sensory info to the spinal cord, synapsing w/ the alpha motor neurons, which then innervate the extrafusal fibers to contract/shorten & return to normal length. Gamma motor neurons are coactivated w/ the alpha motor neurons. Ensures the muscle spindle will remain sensitive to changes in muscle length even during the contraction.

18
Q

Gamma motor neurons

A

Ensures that the muscle spindle will remain sensitive to changes in muscle length even during the contraction

19
Q

Stretch Reflex

A
  • Monosynaptic
  • aka myotatic reflex
  • Muscle is stretched
  • Innervated by group Ia & II fibers afferents
  • Simultaneously, group Ia & II fibers synapses w/ alpha motor neuron causes contraction of synergistic muscle & synapses w/ interneuron causing relaxation of antagonistic muscle. The synergistic muscle returns to normal length. Firing rate of the group Ia afferents returns to baseline
  • Ex: Knee-jerk reflex; tapping the patellar tendon, causing the quadriceps muscle to stretch
20
Q

Stretch Reflex has how many synapses?

A

Monosynaptic

21
Q

Golgi Tendon Reflex

A
  • Dysynaptic
  • Inverse of myotatic reflex
  • Innervated by group Ib afferent fibers
  • Group Ib afferents stimulate the inhibitory interneurons in spinal cord. Inhibition of alpha motor neurons results in relaxation of synergistic muscle
  • Simultaneously, the antagonistic muscle contracts
  • Ex: clasp-knife reflex = This reflex is abnormal and occurs when there is an increase in muscle tone
22
Q

Flexor-Withdrawal Reflex

A
  • Always for withdrawal from dangerous situations
  • Polysynaptic
  • Innervated by group II, III, IV afferents
  • Ipsilateral flexion = relaxation of extensors & contraction of flexors
  • Contralateral extension = contraction of extensors & relaxation of flexors
  • After discharge. A persistent neural discharge. Contracted muscles remain contracted for a period of time after the reflex is activated
23
Q

Extrafusal fibers are innervated by

A

Alpha-motor neurons

24
Q

Intrafusal fibers are innervated by

A

Gamma, Ia & II motor neurons

25
Q

Golgi tendon organs are innervated by

A

Group Ib neurons

26
Q

Function of gamma motor neurons

A

Ensures the muscle spindle will remain sensitive to changes in muscle length even during the contraction

27
Q

Golgi tendon reflex is innervated by

A

Group Ib

28
Q

Is golgi tendon reflex mono-, dy, or poly snaptic?

A

Dysynaptic

29
Q

The Flexor-Withdrawal Reflex is mono-, dy, or poly synaptic?

A

Polysnaptic

30
Q

Flexor-Withdrawal Reflex is innervated by

A

Group II, III, & IV

Physiology (13 decks)

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