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EXB 101 > 14-15. Motor Units & Recruitment > Flashcards

14-15. Motor Units & Recruitment Flashcards

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1
Q

Define the motor unit. What does it consist of?

A
  • Functional unit of the neuromuscular system

- Alpha motor neuron + muscle fibers innervated

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2
Q

Where are motoneurons located?

A

Ventral horn of spinal gray matter

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3
Q

From where does the alpha motor neuron cell body receive info? What kind of info does it receive?

A
  • Receive input from neurons in the motor cortex and brainstem
  • Receive additional excitatory and inhibitory input from spinal cord interneurons and muscle afferents
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4
Q

When is an action potential produced in the cell body?

A

When the membrane potential exceeds threshold potential

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5
Q

What is a motor pool? How many motor pools does a muscle have?

A
  • Motoneurons innervating a specific muscle

- Every muscle has one motor pool

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6
Q

What is the innervation ratio?

A

Number of muscle fibers innervated by a single motor neuron

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7
Q

What is the relationship between innervation ratio and motor unit type?

A

Higher innervation ratio = larger alpha, beta, gamma

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8
Q

What are the 2 properties used to classify motor units? Based on these properties, what are the classifications of motor units?

A
  • Fiber size and conduction velocity
  • Alpha = largest, fastest
  • Beta = next largest, fastest
  • Gamma = smallest, slowest
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9
Q

What is the basic function of sensory receptors?

A

Provide info to the system on its own state and that of its surrounding

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10
Q

What is feedback?

A

The flow of info from sensory receptors to the CNS

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11
Q

Afferent vs. Efferent neurons

A
  • Afferent provide feedback info to CNS

- Efferent involved in activating muscle

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12
Q

What are muscle spindles? Location?

A
  • Intrafusal fiber = collection of miniature muscle fibers enclosed in a connective tissue capsule
  • Located in parallel w/ extrafusal fibers of skeletal muscle
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13
Q

What do muscle spindles primarily sense?

A

Muscle length and rate of change of muscle length

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14
Q

What is the Ia afferent fiber? Function? Which sensory fiber is Ia afferent?

A
  • Monosynaptic connection to alpha-motoneurons
  • Increases excitability of alpha motoneurons w/ muscle from which it originates
  • Muscle spindle
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15
Q

What is reciprocal-inhibition?

A

When a motoneuron excites muscle from which it came & inhibits antagonistic muscle

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16
Q

What are the parts of the reflex arc during the stretch reflex.

A
  • Receptor = muscle spindle
  • Afferent pathway = Ia sensory axons
  • Integrating center = spinal cord (interneurons, motoneurons)
  • Efferent pathway = alpha motor axons
  • Effector organ = muscle
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17
Q

Which sensory receptor is Ib afferent?

A

Golgi tendon organ

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18
Q

What does the golgi tendon organ primarily sense?

A

Muscle tension

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19
Q

Where are golgi tendon organs located?

A

Primarily at musculotendinous junctions in series w/ muscle fibers

20
Q

What is the function of golgi tendon organs?

A

Reduce the excitability of alpha and gamma motoneurons

21
Q

What is the function of golgi tendon organs?

A

Reduce the excitability of alpha and gamma motoneurons

22
Q

What reflex do muscle spindles respond to?

A

Stretch reflex

23
Q

What reflex do golgi tendon organs respond to?

A

Disynaptic reflex

24
Q

What are joint receptors? Function?

A
  • Mechanoreceptors

- Provide info on position, displacement, velocity, acceleration of movement, noxious stimuli

25
Q

What do cutaneous receptors sense?

A

Pressure and stretch of the skin

26
Q

What do free nerve endings innervate? Function?

A
  • Innervate almost all structures w/in the muscle belly

- Detect noxious stimuli (pressure, temp, chemicals)

27
Q

What do free nerve endings innervate? Function?

A
  • Innervate almost all structures w/in the muscle belly

- Detect noxious stimuli (pressure, temp, chemicals)

28
Q

What are ERGO receptors? Location?

A
  • Mechanoreceptors and metaboreceptors that provide rapid input (feed forward) from muscles to CNS
  • In skeletal muscle
29
Q

What do ERGO receptors sense?

A
  • Tension
  • Rate of tension development
  • Metabolic rate
30
Q

What variables do ERGO receptors influence?

A

HR, BP, rate of breathing (Ve)

31
Q

How fast do mechanoreceptors respond? What do they respond to?

A

W/in about 200 msec from onset of contraction

32
Q

How fast do metaboreceptors respond? What do they respond to?

A
  • In about 4-5 secs

- Highly sensitive to metabolic rate

33
Q

What are ERGO receptors? Location?

A
  • Mechanoreceptors and metaboreceptors that provide rapid input (feed forward) from muscles to CNS (cardiovascular & respiratory centers)
  • In skeletal muscle
34
Q

How fast do metaboreceptors respond? What do they respond to?

A
  • In about 4-5 secs

- Highly sensitive to metabolic rate

35
Q

What is the equation for Fatigue Index

A

FI = force after 2 mins / initial force

36
Q

What are the 3 classifications of motor units?

A
  • S = slow
  • FR = fast fatigue resistant
  • FF = fast fatiguable
37
Q

What is the fatigue index of slow motor units?

A

1.0

38
Q

What is the fatigue index of FR motor units?

A

> 0.75

39
Q

What are the 2 properties used to classify motor units? Based on these properties, what are the classifications of motor units?

A
  • Fiber size and conduction velocity
  • Alpha = largest, fastest
  • Beta = next largest, fastest
  • Gamma = smallest, slowest
40
Q

What is the fatigue index of FF motor units?

A
41
Q

What 3 properties control the maximum tension that can be produced by a motor unit?

A
  • Innervation ratio
  • Fiber CSA
  • Specific tension
42
Q

What property is the best predictor of the max tension of a motor unit?

A

Innervation ratio

43
Q

What is the size principle?

A

Force development w/ increased motor unit recruitment is nonlinear

44
Q

According to the size principle, in what order are motor units recruited?

A
  • Smaller motor units that generate low force are recruited first
  • Larger motor units that generate greater force are recruited later
45
Q

What are the factors affecting total muscle tension development?

A
  • Number of motor units recruited (as shown by total CSA of muscle that is active)
  • Frequency of motor neuron firing
  • Optimization of muscle fiber length
46
Q

Why do FF units produce greater max tension than S units?

A
  • Larger

- Innervate more muscle fibers

47
Q

What is the relationship between motor unit types and muscle fiber types?

A
  • Alpha = FF = FG = type IIx
  • Beta = FR = FOG = type IIa
  • Gamma = S = S = type I

EXB 101 (7 decks)

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