Muscle Physiology

Question 1

What is the basic contractile unit of skeletal muscle?

Answer 1

motor unit

Question 2

What is the function of a motor unit?

Answer 2

all fibers are innervated by a single motor unit

Question 3

What stimulates a skeletal muscle contraction?

Answer 3

motor neuron

Question 4

What is excitation-coupling?

Answer 4

the series of events from electrical stimulation of the muscle to contraction and force generation

Question 5

What neurotransmitter is released into the neuromuscular junction?

Answer 5

acetylcholine

Question 6

How does the ACh binding to its receptor on the muscle cell lead to the firing of an action potential?

Answer 6

it depolarizes the muscle plasma membrane past the threshold to fire an action potential

Question 7

How is the action potential propagated through the muscle?

Answer 7

it is carried over the surface of the muscle and goes into the T-tubule system

Question 8

What channels open when an action membrane is initiated along a motor neuron?

Answer 8

voltage-gated calcium channels

Question 9

The opening of voltage-gated calcium channels initiates the release of what neurotransmitter?

Answer 9

acetylcholine

Question 10

When the endplate potential reaches threshold, what channels will open?

Answer 10

voltage-gated sodium channels

Question 11

What type of channel serves as a voltage sensor as the action potential propagates along the sarcolemma and t-tubules?

Answer 11

L-type calcium channel

Question 12

A conformational change in what channel results in the calcium release from the sarcoplasmic reticulum?

Answer 12

L-type calcium channel with ryanodine receptor

Question 13

What enzyme pumps calcium back into the sarcoplasmic reticulum?

Answer 13

Ca-ATPases

Question 14

What molecule in the sarcomere does calcium bind to?

Answer 14

troponin-C

Question 15

What are the steps that allow the binding of calcium to troponin C to lead to actin-myosin cross-bridge cycling?

Answer 15

• Calcium binds to troponin-C
• Conformational shift in troponin-T
• Conformational shift in tropomyosin
• Exposes active site on F-actin
• Initiates actin-myosin cross-bridge cycling

Question 16

Binding of what to the myosin head decreases affinity of myosin for actin resulting in
detachment of the head.

Answer 16

ATP

Question 17

What is a twitch?

Answer 17

A single action potential leads to a spike in Ca2+ that

initiates a small contractile force

Question 18

What is tetanus?

Answer 18

Repeated stimulation of muscle before it has time to relax
Leading to sustained increases in
Ca2+ and sustained force generation

Question 19

What is temporal summation?

Answer 19

multiple subthreshold EPSPs from one neuron occur close enough in time to combine and trigger an action potential

Question 20

What is an Isometric contraction?

Answer 20

a contraction that

generates force with no shortening

Question 21

What is a Isotonic contraction?

Answer 21

shortening against

constant force

Question 22

What is the Length-passive force relationship a result of?

Answer 22

elastic nature of cell

membrane and connective tissue

Question 23

What is the Length-active force relationship a result of?

Answer 23

arrangement of actin and myosin

molecules in the sarcomere

Question 24

What is the optimal length of a muscle?

Answer 24

Initial muscle length

that, leads to maximal force generation

Question 25

What is the optimal length of a muscle a result of?

Answer 25

optimal organization of a muscle

Question 26

What influences the force generate during isometric condition of a muscle?

Answer 26

– number of cells stimulated – frequency of stimulation – Length of muscle before stimulation

Question 27

What is the relationship between force and velocity?

Answer 27

Changes in the initial length of the muscle shift the curve and isometric point but do not alter the Vmax

Question 28

What impacts the difference in velocity at any given afterload?

Answer 28

number of crossbridges taking part in contraction

Question 29

What decides the number of crossbridges taking part in contraction?

Answer 29

preload

Question 30

What is Vmax dependent on?

Answer 30

how fast a single | crossbridge can cycle unimpeded

Question 31

What is Vmax a result of?

Answer 31

molecular characteristics | of myosin ATPase

Question 32

What is the relationship between calcium and force?

Answer 32

direct

Question 33

How is force graded in a muscle?

Answer 33

Recruitment of more motor units Alternating stimulation of adjacent motor units

Question 34

How does Poliomyelitis impact muscles?

Answer 34

destruction of motor nerve fibers which leads to atrophy of the affected muscle

Question 35

How do polio patients regain muscle strength and recover from paralysis?

Answer 35

some remaining | fibers will sprout new extensions that innervate other muscle fibers--resulting in larger than normal motor units

Question 36

What are macromotor units?

Answer 36

larger than | normal motor units

Question 37

How do macromotor units impact fine motor control?

Answer 37

results in loss of fine motor control

Question 38

What three characteristics impact muscle size?

Answer 38

- genetics - testosterone - training

Question 39

What is hypertrophy?

Answer 39

increase in muscle fiber diameter

Question 40

How do myofibrils change in hypertrophic muscle??

Answer 40

increased number

Question 41

How do mitochondria change in hypertrophic muscle??

Answer 41

increased number and size

Question 42

How does ATP content change in hypertrophic muscle??

Answer 42

40% increase

Question 43

How does glycogen content change in hypertrophic muscle??

Answer 43

up to 100% increase in storage

Question 44

How does triglyceride content change in hypertrophic muscle??

Answer 44

up to 75% increase in storage

Question 45

How do enzymes change in hypertrophic muscle??

Answer 45

increase

Question 46

How are atrophied muscles treated?

Answer 46

Resistance training Electrical stimulation Selective androgen receptor stimulation

Question 47

How is passive force generated in a muscle?

Answer 47

produced by titin, that spans the half-sarcomere, connecting the A-band to the I-bands

Question 48

If the muscle is lengthened, what force increases?

Answer 48

passive force

Question 49

If the muscle is shortened, what force increases?

Answer 49

active force

Question 50

What is active force and how is it generated?

Answer 50

the rise in force observed on activation of a muscle and is associated with cross-bridge interactions between myosin and actin

Question 51

What are the steps for contracting smooth muscle?

Answer 51

``` • Increased Intracellular Calcium • Calmodulin-calcium binding protein • Myosin Light Chain Kinase • Myosin Phosphatase • Latch State ```

Question 52

How can the Vmax be shifted up or down for smooth or cardiac muscle?

Answer 52

stimulation of the sympathetic and parasympathetic system

Question 53

How many nuclei do skeletal muscle cells have?

Answer 53

multiple near sarcolemma

Question 54

How many nuclei do smooth muscle cells have?

Answer 54

single, centrally located

Question 55

How many nuclei do cardiac muscle cells have?

Answer 55

single, centrally located

Question 56

Where are filaments found in skeletal and cardiac muscle?

Answer 56

in sarcomeres

Question 57

Where are filaments found in smooth muscle?

Answer 57

scattered throughout sarcoplasm

Question 58

What is the energy source of skeletal muscle?

Answer 58

aerobic metabolism usually | glycolysis during peak activity

Question 59

What is the energy source of smooth muscle?

Answer 59

aerobic metabolism

Question 60

What is the energy source of cardiac muscle?

Answer 60

aerobic metabolism | usually lipid or carb substrates

Question 61

What is optimal preload?

Answer 61

initial stretching of the cardiac myocytes (muscle cells) prior to contraction

Question 62

How can changes in optimal length affect velocity of contraction?

Answer 62

force of a muscle contraction declines with increasing velocity