Motor units

Question 1

Basic muscle contraction step by step

Answer 1

Brain sends a message to muscles via the spinal chord and motor neurons
attaching to muscle fibers causing the muscle to contract.

Question 2

Muscle order largest to smallest

Answer 2

Belly
Fascicle
*fiber*
myofibril
sarcomere

Question 3

What is motor unit?

Answer 3

A motor neuron and all the muscle fibers it innovates.
A muscle fiber will only be innovated by one neuron but a neuron can innovate multiple muscle fibers.
Motor neurons innovate different numbers on fibers a large one will have more than a smaller one.

Question 4

Why are motor units important?

Answer 4

They represent the fundamental unity by which the nervous system controls force production within the muscle.

Question 5

What are the 2 major strategies used to increase force production?

Answer 5

1) to increase force, increase the number or size of motor units (atrophy).
2) to increase force, increase the rate of action potential (AP) discharge (rate coding).

Question 6

What are the 3 major types of motor units?

Answer 6

1)
FF
FG
IIB*
2)
FR
FOG
IIA*
3)
S
SO
I*

Question 7

Size of cell body for each type of unit largest to smallest

Answer 7

IIB
IIA
I

Question 8

Amount of fibers innovated for each type of unit most to least

Answer 8

IIB
IIA
I

Question 9

Twitch response of each type of unit highest amp to lowest amplitude response.

Answer 9

IIB
IIA
I
Note type I has a prolonged twitch compared to other type IIA and IIB This is due to being slow twitch muscles.

Question 10

Electromyography action potential firing for both weak and max effort for each type of unit from least to most (most is good).

Answer 10

Weak effort
IIB
IIA (less frequent)
I (frequent firing)
Max effort
IIB, IIA and I working as frequent as each other. But IIB has less Action potentials firing as they get tired quicker than the others.

Question 11

2 types of fiber innovators

Answer 11

Low density of enzymes (mitochondrial enzymes)

Higher density of enzymes (myosin ATP-ase)

Question 12

What are mitochondrial enzymes?

Answer 12

Enzymes that are associated with aerobic metabolism (kind of metabolism that can sustain over long period of time). Muscle fibers with a high density of mitochondrial enzymes they tend to be capable of resisting fatigue for a long period of time. like a marathon long distance low intensity

Question 13

What are myosin ATP-ase

Answer 13

Associated with fast twitch contractions such as sprints
Muscle fibers with a high density of myosin ATP-ase they tend to be capable of producing a lot of force quickly but fatigue quicker than mitochondrial enzymes.

Question 14

Are each type of unit dense in mitochondrial enzymes?

Answer 14

IIB: No
IIA: Yes
I: Yes

Question 15

Are each type of unit dense in myosin ATP-ase?

Answer 15

IIB: Yes
IIA: Yes
I: No