09c: Motor Physiology

Question 1

The motor unit is:

Answer 1

Alpha motor neuron and all muscle fibers it innervates

Question 2

The (X) is the final common pathway for motor activation.

Answer 2

X = motor unit (via alpha motor neuron)

Question 3

Which characteristic of (X) determines the “delicacy” of the motor act during motor activation?

Answer 3

X = motor unit;

Size

Question 4

Gastrocnemius has a relatively (high/low) ratio of muscle fibers to alpha motor neurons. What’s the approximate ratio?

Answer 4

High; 1000/1

Question 5

Hand muscles have which approximate ratio of muscle fibers to alpha motor neurons?

Answer 5

100/1

Question 6

Extraocular muscles have which ratio of muscle fibers to alpha motor neurons?

Answer 6

5/1

Question 7

T/F: Muscle twitch is miniature mechanical event that’s larger in gastrocnemius than in lateral rectus.

Answer 7

False - same size in all muscles

Question 8

T/F: Muscle twitch is all-or-none.

Answer 8

True

Question 9

Muscle twitches can summate in which way(s) to produce whole-muscle contractions?

Answer 9

1. Temporal summation

2. Spatial summation

Question 10

Contraction of muscle twitch peaks in (X) amount of time. And relaxes in (Y) amount of time.

Answer 10

X = 80 ms
Y = 200 ms

Question 11

Total tension produced by stimulation of motor unit increases as (X) of motor neuron increases.

Answer 11

X = AP frequency

Question 12

T/F: Temporal summation of individual muscle contractions is linear.

Answer 12

False

Question 13

Muscle fiber organization, in (parallel/series), is what allows for (temporal/spatial) summation.

Answer 13

Parallel;

Spatial

Question 14

The twitch:tetanic contraction ratio in temporal summation is about:

Answer 14

8/1

Question 15

White muscle active in (posture/fight or flight). List an example of this muscle type.

Answer 15

Fight or flight; gastrocnemius

Question 16

Red muscle active in (posture/fight or flight). List an example of this muscle type.

Answer 16

Posture; soleus

Question 17

(Red/white) muscle has small muscle unit.

Answer 17

Red

Question 18

(Red/white) muscle has low oxidative rate.

Answer 18

White

Question 19

(Red/white) muscle has fine control.

Answer 19

Red

Question 20

(Red/white) muscle found more in axial musculature. (Red/white) muscle found more in lateral musculature.

Answer 20

Red; white

Question 21

(Red/white) muscle has high levels of mitochondrial ATPase.

Answer 21

Red

Question 22

(Red/white) muscle has low resistance to fatigue.

Answer 22

White

Question 23

(Red/white) muscle has high contraction rate and (low/high) absolute tension.

Answer 23

White; high

Question 24

(Red/white) muscle has high glycogen content and (small/large) blood supply.

Answer 24

White; small

Question 25

Red muscle has (phasic/tonic) nerve activity. What does that mean?

Answer 25

Tonic; state of continuous activity

Question 26

(Red/white) muscle has lowest threshold for neural activation. This means it’s recruited (first/last) at initiation and drops out (first/last) at end of motor activity.

Answer 26

Red;
First;
Last

Question 27

(Muscle spindle/GTO) arranged in parallel with muscle fibers, measuring muscle (length/tension).

Answer 27

Muscle spindles; length

Question 28

(Muscle spindle/GTO) arranged in series with muscle fibers, measuring muscle (length/tension).

Answer 28

GTO; tension

Question 29

Muscle spindles are located (adjacent to/within) muscle and considered (intra/extra)-fusal.

Answer 29

Within; intrafusal

Question 30

Muscle spindle afferent fiber is (X) type of nerve fiber that has cell body in (Y). This afferent fiber synapses onto:

Answer 30

X = 1A
Y = DRG

1. Interneurons (in SC)
2. Alpha motor neurons (back to same muscle)

Question 31

Muscle spindle receives efferent innervation from (X) type of nerve fiber that has cell body in (Y). This afferent fiber synapses onto:

Answer 31

X = gamma;
Y = ventral horn of SC

Contractile (polar) ends of muscle spindle

Question 32

(Muscle spindle/GTO) responsible for stretch reflex.

Answer 32

Muscle spindle

Question 33

(Alpha/gamma) motor neurons are larger.

Answer 33

Alpha

Question 34

T/F: Stretch/myotatic reflex is the only monosynaptic reflex.

Answer 34

True

Question 35

Information regarding state of muscle length is transmitted to CNS when muscle is (fully contracted/fully relaxed).

Answer 35

The info regarding muscle length is ALWAYS transmitted to CNS

Question 36

Compensatory loading is a phenomenon that’s possible due to (X) and functions to:

Answer 36

X = gamma motor neurons

1. Keep stretch receptors in check
2. Allow 1A afferents to support alpha motor neuron discharge

Question 37

GTO sends afferent innervation via (X) type of nerve fiber that has cell body in (Y). This afferent fiber synapses onto:

Answer 37

X = 1B 
Y = DRG

Inhibitory interneuron (in SC)

Question 38

1B afferent fiber of (muscle spindle/GTO) synapses onto (X), which (activates/inhibits) (Y).

Answer 38

GTO;
X = inhibitory interneuron (in SC)
Inhibits;
Y = alpha motor neuron of same muscle

Question 39

Inverse myotatic reflex via (muscle spindle/GTO) is (mono/di)-synaptic.

Answer 39

GTO; disynaptic

Question 40

Inverse myotatic reflex tends to (increase/decrease/maintain) muscle’s (X).

Answer 40

Maintain;

X = tension

Question 41

“Facilitation” is the term describing overlap of (X) and results in response (smaller/larger/equal) than/to algebraic sum of two rootlets stimulated alone.

Answer 41

X = Subliminal fringes;

Larger

Question 42

“Occlusion” is the term describing overlap of (X) and results in response (smaller/larger/equal) than/to algebraic sum of two rootlets stimulated alone.

Answer 42

X = firing zones;

Smaller

Question 43

(Smaller/larger) cells with (lower/higher) thresholds constitute the subliminal fringe.

Answer 43

Larger; higher