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Pathophysiology > Chapter 12 - Muscles > Flashcards

Chapter 12 - Muscles Flashcards

1
Q

muscles generate:

A

motion, force, and heat

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2
Q

striated muscles:

A

skeletal and cardiac

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3
Q

cardiac and smooth muscles are controlled by

A

autonomic innervation, paracrine signals, and hormones. some are autorhythmic and contract spontaneously

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4
Q

examples of antagonistic muscle groups

A

flexor-extensor pairs

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5
Q

sarcolemma

A

the cell membrane of a muscle fiber

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6
Q

sarcoplasm

A

the cytoplasm of a muscle fiber

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7
Q

sarcoplasmic reticulum (SR)

A

a form of modified endoplasmic reticulum that wraps around each myofibril. concentrates and sequesters Ca2+ w/ the help of a Ca2+-ATPase. calcium release from the SR creates calcium signals that play a role in muscle contraction

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8
Q

myofibrils

A

the main intracellular structures in striated muscles; highly organized bundles of contractile and elastic proteins that carry out the work of contraction

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9
Q

terminal cisternae

A

longitudinal tubules w/ enlarged end regions in the SR

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10
Q

transverse tubules (t-tubules)

A

invaginations of the muscle fiber membrane, a/w SR. allow action potentials to move rapidly into the interior of the fiber and release calcium from the SR

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11
Q

thick filaments are made of

A

myosin

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12
Q

thin filaments are made mostly of

A

actin

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13
Q

function of titin and nebulin

A

stabilize the position of thick and thin filaments

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14
Q

myosin crossbridges

A

span the space between thick and thin filaments of myofibril. created via binding of actin to myosin

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15
Q

sarcomere

A

contractile unit of a myofibril

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16
Q

Z disks

A

2 z disks and the filaments between them form a sarcomere. zigzag protein structures that serve as the attachment site for thin filaments

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17
Q

I bands

A

the lightest color bands of the sarcomere; represents region occupied only by thin filaments

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18
Q

A band

A

darkest of the sarcomere’s bands; encompasses the entire length of a thick filament

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19
Q

H zone

A

central region of the A band that is lighter than the outer edges of the A band b/c the H zone is occupied by thick filaments only

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20
Q

M line

A

band that represents protein that form the attachment site for thick filaments, equivalent to the Z disk for the thin filaments. each M line divides an A band in half. (think: M = middle)

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21
Q

muscle tension

A

the force created by a contracting muscle

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22
Q

load

A

a weight or force that opposes contraction of a muscle

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23
Q

sliding filament theory of contraction

A

states that during contraction, overlapping thick and thin filaments slide past each other in an energy-dependent manner as a result of actin-myosin crossbridge movement

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24
Q

3 major steps leading up to skeletal muscle contraction

A
  1. events at the neuromuscular junction convert an acetylcholine signal from a somatic motor neuron into an electrical signal in the muscle fiber
  2. excitation-contraction (E-C) coupling - the process in which muscle action potentials initiate calcium signals that in turn activate a contraction-relaxation cycle.
  3. at the molecular level, a contraction-relaxation cycle can be explained by the sliding filament theory of contraction. In intact muscles, one contraction-relaxation cycle is called a muscle twitch
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25
Q

neuromuscular junction

A

the site where a motor neuron excites a skeletal msucle fiber. the junction is a chemical synapse consisting of the points of contact between the axon terminals of a motor neuron and the motor end plate of a skeletal muscle fiber

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26
Q

events at the neuromuscular junction

A

1st major step leading up to skeletal muscle contraction. conversion of acetylcholine signal from a somatic motor neuron into an electrical signal in the muscle fiber

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27
Q

excitation-contraction (E-C) coupling

A

the process in which a somatic motor neuron releases ACh, which initiates a muscle action potential, which initiates calcium signals that in turn activate a contraction-relaxation cycle

28
Q

twitch

A

a single contraction-relaxation cycle

29
Q

in relaxed muscle, ____ partially blocks the myosin-binding site on actin

A

tropomyosin

30
Q

to initiate contraction, ___ binds to ___

A

Ca2+ binds to troponin. this unblocks the myosin-binding sites and allows myosin to complete its power stroke

31
Q

Ca2+-ATPase

A

used by SR during muscle relaxation to pump Ca2+ back into the lumen

32
Q

myosin ATPase

A

hydrolyzes ATP to ADP and Pi, allowing myosin to convert energy from ATP into motion

33
Q

power stroke

A

occurs when myosin releases Pi and the myosin head moves. at the end of the power stroke, myosin releases ADP

34
Q

rigor state

A

end of power stroke cycle in which ADP is released from myosin and myosin is bound tightly to actin

35
Q

the contraction cycle (steps)

A
  1. ATP binds to myosin. myosin releases actin.
  2. myosin hydrolyzes ATP. energy from ATP rotates the myosin heads to the cocked position. myosin binds weakly to actin.
  3. power stroke begins when tropomyosin moves off actin’s myosin binding site in response to troponin-Ca2+ complex.
  4. myosin releases ADP at the end of the power stroke.
36
Q

excitation-contraction coupling and relaxation: initiation of muscle action potential

A
  1. somatic motor neuron releases ACh at meuromuscular junction.
  2. net entry of Na+ through ACh receptor-channel initiates a muscle action potential.
37
Q

excitation-contraction coupling steps

A
  1. action potential in t-tubule alters conformation of DHP (dihydropyridine L-type calcium channel) receptor.
  2. DHP receptor opens RyR (ryanodine receptor-channel) Ca2+ release channels in SR, and Ca2+ enters cytoplasm.
  3. Ca2+ binds to troponin, allowing actin-myosin binding. 4. myosin heads execute power stroke.
  4. actin filament slides toward center of sarcomere.
38
Q

excitation-contraction relaxation phase steps

A
  1. sarcoplasmic Ca2+-ATPase pumps Ca2+ back into SR.
  2. decreases in free cytosolic [Ca2+] causes Ca2+ to unbind from troponin.
  3. tropomyosin re-covers binding site. when myosin heads release, elastic elements pull filaments back into their relaxed position.
39
Q

latent period

A

between the end of the muscle action potential and the beginning of muscle tension development; represents the time required for Ca2+ release and binding to troponin

40
Q

phosphocreatine

A

storage site for energy for muscle fiber contraction

41
Q

anaerobic metabolism of glucose

A

rapid source of ATP but not efficient

42
Q

aerobic metabolism of glucose

A

very efficient source of ATP but requires an adequate supply of oxygen to the muscles

43
Q

creatine kinase (CK)

A

AKA creatine phosphokinase (CPK); enzymes that transfers the phosphate group from phosphocreatine to ADP

44
Q

muscle fatigue

A

a reversible condition in which a muscle is no longer able to generate or sustain the expected power output. has multiple causes

45
Q

fast-twitch fiber

A

muscle fibers that develop tension rapidly

46
Q

fast-twitch oxidative-glycolytic fibers

A

fast muscle fibers that use a combination of aerobic and anaerobic metabolism and therefore do not fatigue as fast as glycolytic fibers

47
Q

fast-twitch glycolytic fibers

A

fast muscle fibers that rely on anaerobic metabolism and therefore fatigue rapidly

48
Q

slow-twitch (oxidative) fibers

A

muscle fibers that develop tension slower than fast-twitch. contractions last longer. use oxidative phosphorylation for production of ATP. do not fatigue as fast as glycolytic fibers.

49
Q

myoglobin

A

an oxygen-binding pigment that transfers oxygen to the interior of the muscle fiber

50
Q

the tension of a skeletal muscle contraction is determined by

A

the length of the sarcomeres before contraction begins

51
Q

tetanus

A

a state of maximal contraction; increasing the stimulus frequency causes summation of twitches w/ an increase of tension.

52
Q

motor unit

A

composed of a group of muscle fibers and the somatic motor neuron that controls them. the number of muscle fibers in a motor unit varies, but all fibers in a single motor unit are of the same fiber type.

53
Q

isotonic contraction

A

creates force as the muscle shortens and moves a load

54
Q

isometric contraction

A

creates force w/o moving a load

55
Q

lengthening contractions

A

create force while the muscle lengthens

56
Q

series elastic elements

A

allow the fibers in isometric contractions to maintain constant length even though the sarcomeres are shortening and creating tension

57
Q

smooth muscle vs. skeletal muscle

A

smooth muscle is slower than skeletal muscle but can sustain contractions for longer w/o fatiguing. skeletal muscle is striated; smooth is not. smooth muscle has less myosin. smooth muscle actin lacks troponin.

58
Q

phasic muscles

A

smooth muscles that are usually relaxed or cycle through contractions

59
Q

tonic smooth muscle

A

smooth muscle that is usually contracted

60
Q

single-unit smooth muscle

A

contracts as a single unit when depolarizations pass from cell to cell through gap junctions

61
Q

multiunit smooth muscle

A

individual muscle fibers are stimulated independently

62
Q

smooth muscle contraction

A

Ca2+ binds to calmodulin and activates myosin light chain kinase (MLCK). MLCK phosphorylates myosin light protein chains, which activates myosin ATPase. this allows crossbridge power strokes.

63
Q

smooth muscle relaxation

A

Ca2+ is pumped out of the cytosol, and myosin light chains are dephosphorylated by myosin phosphatase

64
Q

myogenic contraction

A

stretch on the cell depolarizes it and opens membrane Ca2+ channels

65
Q

pharmacomechanical coupling

A

smooth muscle contraction initiated by chemical signals can take place w/o a significant change in membrane potential

66
Q

cardiac muscle fibers

A

striated, have a single nucleus, and are electrically linked through gap junctions.

Pathophysiology (9 decks)

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