Lecture 22 Flashcards Preview

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Flashcards in Lecture 22 Deck (24):
1

What is the difference between alpha and gamma motor neurons?

Both outgoing motor neurons from the ventral horn of the spinal cord
Alpha = big
Gamma = small

2

What is a motor unit?

Alpha motor neuron + all the muscle fibers it innervates
Also "smallest amount of muscle that can be voluntarily activated"

3

What is the innervation ratio? What does a small vs large ratio mean?

Number of muscle fibers innervated by a single motor neuron
Small ratio = fine control movement of muscles

4

Name the three types of muscle fibers.

SO - 1, slow oxidative
FO - 2a, fast oxidative
FF - 2b, fast fatigable

5

Describe contraction speed, fatigue resistance, oxidative capacity, mitochondria, capillaries, glycogen content, and fiber diameter of SLOW OXIDATIVE.

TYPE 1
Contraction speed = slow
Fatigue resistance = high
Oxidative capacity = high
Mitochondria = high
Capillaries = high
Glycogen content = low
Fiber diameter = small

6

Describe contraction speed, fatigue resistance, oxidative capacity, mitochondria, capillaries, glycogen content, and fiber diameter of FAST OXIDATIVE.

Contraction speed = fast
Fatigue resistance = medium
Oxidative capacity = high
Mitochondria = high
Capillaries = high
Glycogen content = medium
Fiber diameter = medium

7

Describe contraction speed, fatigue resistance, oxidative capacity, mitochondria, capillaries, glycogen content, and fiber diameter of FAST GLYCOLYTIC.

Contraction speed = fast
Fatigue resistance = low
Oxidative capacity = low
Mitochondria = low
Capillaries = low (poorly vascularized)
Glycogen content = high
Fiber diameter = large

8

What action is fast glycolytic typically used during?

Jumping

9

What are the 2 methods that muscle increases the force it produces? Which method is used first?

1. Rate modulation = more activity of already firing neurons
2. Recruitment = recruit more motor units, usually seen with high activity

10

What is the size principle?

Muscle fibers are recruited in size order
Slow --> FO --> FF
Slow are easier to excite

11

What is plasticity of muscle fibers?

Ability to change the muscle fiber types through conditioning

12

How does endurance training change muscle types?

↑oxidative properties of the muscle: more mito & oxidative enzymes (tending towards FO)
LITTLE hypertrophy (Think of marathon runners! Their muscles are not big!)

13

What should you expect to see if you reinnervate a group of muscle fibers?

Fibers of motor units are grouped

14

What are intrafusal fibers? How are they innervated?

Muscle spindle in a connective tissue case
Motor innervation via gamma motorneurons

15

What are extrafusal fibers? How are they innervated?

Muscle fibers!
Alpha motor neurons synapse onto these
All-or-none excitation and recruitment - you know this!

16

What are the sensory nerves that carry info from muscle spindles to the spine? What info do each carry?

Ia - (primary) proprioception, info about changes in acceleration and velocity
II - (secondary) motor learning, changes in length

17

What are the 2 types of fibers that make up intrafusal fibers?

Bag = tonic contraction, attached to extrafusal fibers
Chain = twitch contraction, attached to bag fibers

18

What does it mean to say that "secondary codes the muscle length"?

Secondary = II sensory muscle nerves
Its return firing to the spinal cord exactly mirrors amount of stretch

19

How does muscle spindle sensory firing change between stretch vs contraction?

Stretch = lots of firing, telling spine about what is happening
Contraction = no firing

20

How does muscle spindle sensory firing change with stretching?

Stretch = lots of firing, telling spine about what is happening

21

How to muscle spindle motor and sensory innervation change with muscle contraction? What is the term for this phenomena?

Gamma motor neurons signal to contract interfusal fibers at the same time as sensory firing goes silent (spindle unloading)
Gamma contraction "resets" sensory region so the spindle sensory will still be responsive during contraction
FUSIMOTOR SET = adjusting the gain of the spindle to the appropriate behavior via gamma dynamic reset

22

What info does the golgi tendon organ relay?

Proprioceptive about tendons

23

What does stretching do to the GTO? What other muscle information is tendon stretching a signal for?

Increase firing
Stretch is the code for muscle FORCE

24

How does muscle contraction change GTO signaling?

MORE firing
Makes sense because contraction is an even more direct parallel to force!