Striated muscle physiology

Question 1

Four major characteristics of muscle

Answer 1

Contractility, excitability, extensibility, and elasticity

Question 2

Three functions of muscle

Answer 2

Motion, postural maintenance, and heat production

Question 3

Fascicles

Answer 3

A group of muscle fibers

Question 4

Myofiber

Answer 4

Muscle fiber = muscle cell

Question 5

Myofibrils

Answer 5

Composed of many repeating sarcomeres

Question 6

Myofilaments

Answer 6

Myosin and actin filaments

Question 7

Endomysium

Answer 7

Surrounds individual fibers, contains capillaries

Question 8

Perimysium

Answer 8

Surrounds each fascicle, contains blood vessels and nerves

Question 9

Epimysium

Answer 9

Surrounds entire muscle

Question 10

What do all the mysiums come together to create?

Answer 10

Tendons

Question 11

Sarcomere

Answer 11

Basic contractile unit

Question 12

Letters of the sarcomere

Answer 12

A-band: dark band (myosin)
H-zone: where only myosin fibers are
I-band: light band (actin only)
M-line: direct middle of the dark band that has proteins to anchor thick filaments together
Z-line: marks the end of the sarcomere; where the actin filaments attach

Question 13

Thick filament structure

Answer 13

Polymer of ~200 myosin molecules

Question 14

Structure of one myosin protein

Answer 14

Two heavy chains and four light chains; coil together to form a rod and two globular heads

Question 15

Two functions of the globular head

Answer 15

Binds actin and has ATPase activity

Question 16

Geometry of light chain heads

Answer 16

Each pair is oriented 120 degrees from the next pair so myosin interacts with the thin filament in 3D

Question 17

F-actin structure

Answer 17

Double-stranded helix composed of many G-actin monomers (approximately 360)

Question 18

Five interacting proteins involved in the thin filament

Answer 18

F-acin
Tropomyosin
Troponin-T
Troponin-I
Troponin-C

Question 19

Ratio of tropomyosin and troponin to actin

Answer 19

1 tropomyosin/troponin complex per 7 actin monomers

Question 20

What does the troponin-tropomyosin complex do?

Answer 20

Typically blocks the myosin binding site on each G-actin while at rest

Question 21

What happens to the T-T complex during muscle activation?

Answer 21

Moves into the “actin groove,” exposing the myosin binding site

Question 22

Transverse tubules

Answer 22

Invaginations of sarcolemma into the muscle fiber, conduct muscle action potential, and are closely apposed to the sarcoplasmic reticulum.

Question 23

Receptor on the T-tubule for voltage sensing

Answer 23

Dihydropyridine receptor

Question 24

Sarcoplasmic reticulum

Answer 24

Special type of smooth endoplasmic reticulum of muscle that stores a high concentration of Ca2+.

Question 25

Receptor on the sarcoplasmic reticulum for Ca2+ release

Answer 25

Ryanodine receptor

Question 26

Muscle triad

Answer 26

Association of one T-tubule with two adjacent "lateral sacs" of SR

Question 27

SERCA

Answer 27

Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase

Question 28

What is the function of SERCA?

Answer 28

Pumps Ca2+ from the cytoplasm back into the SR lumen to restore the Ca2+ gradient

Question 29

The nervous system communicates with muscle through . . .

Answer 29

Neuromuscular junctions, which work very much like a synapse between neurons

Question 30

Neurotransmitter in the neuromuscular junction

Answer 30

Acetylcholine

Question 31

Nature of AChR in the NMJ

Answer 31

Nicotinic; opens as a cationic channel (mainly Na+)

Question 32

How many subunits does the AChR have?

Answer 32

Five: two alpha, one beta, one gamma, and one delta

Question 33

What is the link between excitation and contraction?

Answer 33

Calcium.

Question 34

Excitation-contraction coupling

Answer 34

A process whereby membrane depolarization is transformed into a chemical signal to initiate muscle contraction

Question 35

Six steps in muscle contraction

Answer 35

1. Excitation-contraction coupling 2. Ca2+ binds troponin 3. Troponin/tropomyosin move to actin groove 4. Myosin binds actin 5. Crossbridge cycle/powerstroke 6. Calcium sequestration -> relaxation

Question 36

Steric hindrance model

Answer 36

Myosin usually can't bind because troponin is in the way

Question 37

Sliding filament model

Answer 37

Free energy cleavage of M*ATP induces a bend in the myosin head from 90 to 45 degrees, pulling the Z-lines inward and shortening the muscle fiber

Question 38

Twitch summation

Answer 38

Multiple action potentials can fire during a single muscle twitch, each causing a release of more calcium. This, in turn, will make more available thin filaments

Question 39

Which arrangement of sarcomeres produces more flexibility? | More force?

Answer 39

Series, parallel

Question 40

Force-velocity relationship of muscle contraction

Answer 40

There is maximum contractility with no load, and a negative hyperbolic relationship as the load gets heavier, eventually causing lengthening

Question 41

Power-stress curve

Answer 41

No power is created when there is no force, but there is also no power created when there is no movement. Curve with a peak, skewed right.

Question 42

Concentric contractions

Answer 42

Muscle is actively shortening

Question 43

Eccentric contractions

Answer 43

Muscle actively lengthening, which is physiologically common and associated with injury and soreness. Exercise with eccentric contractions increase muscle strength

Question 44

Isometric contraction

Answer 44

Muscle actively held at a fixed length

Question 45

Passive stretch

Answer 45

Muscle passively lengthening, likely resulting from a giant protein called "titin" within the muscle fiber

Question 46

Serum CK levels

Answer 46

Blood test revealing muscle injury

Question 47

Actomyosin ATPase accounts for ___% of all ATP consumed in contracting muscle

Answer 47

50-70

Question 48

Other ATP consuming processes in contracting muscle

Answer 48

SERCA: 20-30% | Na/K ATPase:

Question 49

Muscle fatigue

Answer 49

Lactate is produced as a by-product of anaerobic respiration, decreasing pH and inhibiting normal enzyme activity

Question 50

Neuromuscular fatigue

Answer 50

Myasthenia gravis, etc (not common in healthy people)

Question 51

Type of neuromuscular fibers

Answer 51

Slow twitch I Fast twitch red IIA Fast twitch white IIB

Question 52

Difference in E-C coupling between skeletal muscle and cardiac muscle

Answer 52

DHPR - physical coupling vs Ca2+ induced Ca2+ release