Motor Units and Skeletal Muscle

Question 1

What makes the muscle cell unique from the rest of the cells in the body?

Answer 1

Myofibrils

Question 2

What transmits force from the connective tissue to the muscle tendon?

Answer 2

Fascia layers (endomysium, perimysium, epimysium, deep fascia)

Question 3

Myofibrils contain what myofilaments?

Answer 3

Actin & Myosin

Question 4

What is the chemical composition of a muscle fiber?

Answer 4

75% water
20% protein
5% other

Question 5

What makes up the “other” 5% of a muscle fiber?

Answer 5

sodium, potassium, chloride
ATP
Urea
Lactate
Calcium, magnesium, phosphorus
amino acids, fats, carbohydrates

Question 6

Urea is a byproduct of what?

Answer 6

protein metabolism

Question 7

each muscle fiber is innervated by what?

Answer 7

specific motor neuron

Question 8

What is the difference between primary motor neurons and secondary or alpha motor neurons?

Answer 8

• Alpha motor neurons are innervated by primary motor neuron from the cortex, sensory neurons, interneurons
• each alpha motor neuron has ONE axon that branches into a number of axon terminals that terminate on muscle fibers

Question 9

Definition of a motor unit?

Answer 9

the alpha motor neuron and all the muscle fibers it innervates

Question 10

What concept does the size principle relate to?

Answer 10

activate small to large Motor unit size

Question 11

What happens when a motor unit fires?

Answer 11

all the muscle fibers that it innervates contract - all or none principle

Question 12

What allows for multiple alpha motor neurons to activate at one time?

Answer 12

motor neuron pooling - grouping of motor neurons in the ventral horn of the spinal cord

Question 13

What happens to blood flow when the muscle contracts?

Answer 13

muscle contraction decrease blood flow, relaxation increases the blood flow to the muscle fiber

Question 14

Power/high intensity contraction (> 80%) sustained for several seconds will use high energy phosphates and what kind of metabolism for the muscle effort (initial movement)?

Answer 14

glycolytic metabolism (lack of oxygen)

Question 15

Can blood flow to the muscle increase? If so, how?

Answer 15

Yes, vascular growth can happen from stretch and sheer stress

Question 16

Endurance athletes have how many capillaries around each muscle fiber?

Answer 16

5-7 capillaries (40% higher than untrained individuals)

Question 17

Fuel source?

Answer 17

glucose

Question 18

Glucose that goes through glycolysis moves forward into what?

Answer 18

Krebs cycle and electron transport chain

Question 19

Glycerol moves forward into what?

Answer 19

glycolysis

Question 20

Fatty acids must go through what cycle before they enter the Krebs cycle?

Answer 20

beta oxidation cycle

Question 21

what occurs with a greater oxygen demand?

Answer 21

an increase in the number of capillaries needed (training effect)

Question 22

Fiber number is largely fixed by what trimester of fetal development?

Answer 22

second

Question 23

what is the cell membrane of the muscle fiber?

Answer 23

sarcolemma

Question 24

What allows for hypertrophy or enlargement of the muscle fiber itself?

Answer 24

Satellite cells of the basement membrane of the sarcolemma

Question 25

what are the important components of a muscle fiber? (3)

Answer 25

- glycosomes - myoglobin - high energy phosphates

Question 26

What is another word for the cytoplasm of the skeletal muscle?

Answer 26

sarcoplasm

Question 27

what is the oxygen binding protein that helps facilitate uptake and utilization of oxygen during metabolic activity?

Answer 27

myoglobin

Question 28

Function of glycosomes?

Answer 28

allow storage of glycogen for anaerobic activity

Question 29

Functional significance of a sarcomere?

Answer 29

contains myofilaments (actin and myosin) that contract together

Question 30

What protein physically binds actin and myosin of the sarcomere?

Answer 30

Titin

Question 31

What protein keeps passive stiffness of sarcomere and limits its ROM?

Answer 31

Titin

Question 32

Is the electrical signal from a motor neuron sent directly to the actin and myosin in the muscle cell to achieve a muscle contraction?

Answer 32

No, action potentials get sent down the sarcolemma and the t-tubules that stimulate the release of calcium by the sarcoplasmic reticulum and allow binding of calcium on the actin filaments.

Question 33

What is the large sac or vesicle called that surrounds each myofibril?

Answer 33

Sarcoplasmic reticulum

Question 34

What unique structure have special extensions of the sarcolemma or cell membrane of the muscle fiber?

Answer 34

T-tubules

Question 35

What do t-tubules stimulate the release of to allow for binding of the myosin and actin myofilaments?

Answer 35

Calcium

Question 36

What conducts nerve-initiated AP deep into fiber to myofibril?

Answer 36

T-tubules

Question 37

Motor neurons that are selectively activated in prolonged and lower intensity aerobic activities

Answer 37

Slow oxidative

Question 38

Motor neurons that are activated during fast shortening but also longer duration intense activity

Answer 38

Fast oxidative glycolytic

Question 39

Motor neurons activated during rapid shortening velocity (typically type II fibers)

Answer 39

Fast glycolytic