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Neuroscience > Muscle Spindles > Flashcards

Muscle Spindles Flashcards

1
Q

How many spindles are in a muscle?

A

40 - 60.

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2
Q

How long are the muscle spindles?

A

4 - 10 mm.

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3
Q

What are intrafusal fibers?

A
  • Skeletal muscle fibers innervated by gamma motor neurons within a sheet of collagen (collagen is fusal shaped)
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4
Q

What are the 2 general types of intrafusal fibers?

A
  • Nuclear bag

- Nuclear chain

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5
Q

Which general type of intrafusal muscle fiber is larger?

A
  • Nuclear bag is twice the length and diameter of chains
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6
Q

How long is each general type of intrafusal muscle fiber>

A
  • Bag 8mm

- Chain 4mm

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7
Q

What are extrafusal muscle fibers?

A

Normal skeletal muscle

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8
Q

To which type of muscle fiber does more than half the innervation go to?

A

Intrafusal.

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9
Q

How are the muscle spindle fibers oriented?

A

In parallel to extrafusal

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10
Q

Which portion of the intrafusal fibers is the receptor portion of the spindle? Which is the muscular portion?

A
  • Middle is receptor

- Outer portions are muscle

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11
Q

Why are nuclear bag fibers termed as such?

A

The collection of nuclei in the middle make the fiber bulge outwards.

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12
Q

What is the term for the afferent nerve fiber that wraps around the nuclear portion of the intrafusal muscle fibers?

A
  • Anulospiral ending
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13
Q

What is the name of afferent nerve fiber that innervates the outer/ muscular portion of the muscle spindle?

A
  • Flower spray fiber
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14
Q

What type of sensory information do the anulospiral endings collect?

A
  • Muscle length

- Rate of muscle length change

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15
Q

What type of sensory information do the flower spray fibers collect?

A
  • Tonic/ muscle length information
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16
Q

What are the 2 types of nuclear bag fibers?

A
  • Dynamic bag

- Static bag

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17
Q

What is the difference between the dynamic and static nuclear bag fibers?

A
  • Dynamic bag responds to rapid changes in muscle length

- Static bag and chains respond to slow stead changes in muscle length

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18
Q

Are chain fibers tonic or phasic?

A

Tonic.

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19
Q

What efferent innervation is there to the dynamic nuclear bag fiber?

A
  • Dynamic beta and gamma fibers
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20
Q

What efferent innervation is there to the static nuclear bag fiber?

A
  • Static gamma
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21
Q

What is the function of the efferent fibers to the muscle spindle?

A

To change the length of the muscle spindle and take up, or let loose slack in the spindle.

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22
Q

Do type II sensory afferents have tonic or phasic components?

A

Only tonic

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23
Q

Do type Ia sensory afferents have tonic or phasic components?

A

Both.

24
Q

Do Ia or II respond more readily to changes in muscle length?

A

Ia

25
Q

Do Ia or II better register muscle length alone?

A

II

26
Q

Which type of afferent fiber is more active during a static stretch of a muscle?

A

II

27
Q

What type of fibers fire off when a muscle spindle/ muscle is in a shortened state for an extended period of time?

A

Gamma fibers

28
Q

What is the adjustment of the length of the muscle spindle in response to muscle length change called?

A

“Re-biasing” the spindle

29
Q

How do afferent responses from the muscle spindle change during dynamic fusimotor stimulation?

A

Afferent responses to phasic length changes are increased.

30
Q

Which nuclear bag is more affected by dynamic gamma motor neurons?

A
  • The dynamic bag/ Nuclear Bag 1
31
Q

What are muscle spindles in the 2nd nuclear bag more sensitive to when static fusimotor stimulation occurs ?

A
  • Increased response to static extension
32
Q

Which spindle fibers are innervated by static gamma/ fusimotor neurons?

A
  • Both bag and static
33
Q

How is afferent input, muscle force, and gain of the stretch reflex affected by static fusiform stimulation of the 2nd nuclear bag?

A
  • Afferent increased
  • Muscle force increased
  • No or little change in stretch reflex
34
Q

What sensitivity is NOT increased by static fusiform stimulation in the 2nd nuclear bag?

A
  • Sensitivity to amplitude or velocity of length change
35
Q

How is the nuclear chain fiber affected static fusimotor stimulation?

A
  • Sensitivity of stretch reflex increased when a muscle is at a constant length
36
Q

What is the function of static fusiform stimulation of the nuclear chain fiber?

A
  • Muscle can support heavier loads
37
Q

Which endings are more affected by intrafusal stimulation?

A

Primary endings

38
Q

Which type of intrafusal stimulation may be a means of suppressing the stretch reflex during voluntary movement? Why?

A
  • Static intrafusal stimulation because it reduces the primary ending’s sensitivity to length chang.
39
Q

What are the 3 aspects of servo assistance of motor command?

A
  • Adjustment of spindle bias during movement
  • Abolition of spindle length sensitivity during movement
  • Modulation of spindle length sensitvity during movement
40
Q

What is meant by an adjustment of spindle bias during movement? What is its function?

A
  • Spindle discharge is maintained following muscle shortening
  • Keeps spindle responsive to unexpected length changes resulting from fatigue, change in or load, or obstruction of movement
41
Q

What is meant by an abolition of spindle length sensitivity during movement? When does it occur?

A
  • Decreased spindle discharge during muscle shortening without the need for modulation based on alpha drive
  • Occurs during low velocity, normal, unobstructed movements
42
Q

What efferent stimulation and which muscle spindle fiber is involved in abolishing spindle length sensitivity during movement?

A
  • Static gamma/ intrafusal stimulation to the chain fibers
43
Q

What is meant by modulation of spindle length sensitivity during movement? What is its function

A
  • High length sensitivity

- Rapidly corrects movements that deviate from a desired trajectory

44
Q

Which intrafusal efferent system is responsible for modulating spindle length sensitivity during movement?

A
  • The dynamic system
45
Q

What 2 static intrafusal systems contribute to muscle tone?

A
  • Low frequency spontaneous activity in static bag-2 fibers increasing Ia discharge causing a reflexive mild contraction
  • Gamma stimulation to chain fibers increases tone via Ia and II afferents.
46
Q

What can result from overactivity of the 2 muscle tone static intrafusal systems?

A
  • Hypertonicity
47
Q

What is muscle tone?

A
  • The sensation of resistance felt as one manipulates a joint through space
48
Q

What are 3 reasons for muscle tone as just defined?

A
  • Limb inertia
  • Mechanical/ elastic properties of muscle and connective tissue
  • Reflexed
49
Q

Which 2 afferents are the primary proprioceptive fibers?

A
  • Ia

- II

50
Q

What 2 messages are required to model planned movements?

A
  • Message to spindle signaling desired trajectory of movement
  • A signal to extrafusal muscle that takes into account any load and fatigue
51
Q

Where are golgi tendon organs found? How are they oriented?

A
  • Found at fibers of tendons at muscle insertions, and along the fascial covering of muscles
  • GTOs are arranged in series
52
Q

What type of force stimulates a GTO?

A
  • Tension/ muscle contraction
53
Q

What is the sensory afferent of the GTO?

A
  • Ib
54
Q

What is the efferent of the GTO?

A

There is no efferent component

55
Q

What does the primary afferent of the GTO synapse on?

A

An interneuron in the spinal cord that inhibits the intrasegmental alpha motor neuron

56
Q

What are the 7 functions of the GTO?

A
  • Regulates muscle force by bringing about changes in muscle tension
  • Proprioception
  • Clasp knife reflex
  • Reciprocal excitation to antagonist
  • Protection
  • Muscle tone
  • Contract - relax

Neuroscience (33 decks)

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