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Physiology > Chapter 8 Muscle Physiology > Flashcards

Chapter 8 Muscle Physiology Flashcards

1
Q

3 Types of muscle tissues

A

skeletal, smooth, and cardiac

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2
Q

Skeletal muscle is a collection of ____

A

muscle fibers

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3
Q

Myofibrils

A

cylindrical intracellular structured that have the ability to contract

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4
Q

muscle fibers contain

A

myofibrils

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5
Q

each myofibril is made of organized arrangement of thick and thin __________ _______

A

cytoskeleton microfilaments

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6
Q

A-band

A

The region of stacked thick filaments (dark space in the middle)

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7
Q

H zone

A

the middle of the a band where it is lighter due to a lack of thin filaments

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8
Q

M line

A

Center line of the H zone- contains supportive proteins to hold thick filaments together

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9
Q

I band

A

region of stacked thin filaments only

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10
Q

z line

A

flat, cytoskeleton disc in the middle of the I band that connects thin filaments together

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11
Q

Sarcomere

A

the region between adjacent Z lines- smallest functional unit of muscular contraction

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12
Q

Thick filaments

A

bundles of myosin proteins

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13
Q

Thin filaments

A

mostly actin proteins; also tropomyosin and troponin

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14
Q

2 binding sites on the thick filaments (myosin head)

A

an actin binding site and an ATPace

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15
Q

The heads of the myosin proteins can also be called

A

the cross bridge heads

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16
Q

T/F Individual actin molecules are monomers

A

true

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17
Q

Troponin has 3 binding sites which are

A
  1. for tropomyosin
  2. for actin
  3. for Ca+
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18
Q

In the absent of calcium what happens to the myosin binding sites on the thin filament

A

tropomyosin will cover the bonding sites so they can’t work together when there isn’t calcium

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19
Q

Titin

A

elastic protein that helps muscle recoil back to its resting place

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20
Q

Inside there is a very low level of Ca+ which means…

A

tropomyosin blocks cross-bridge binding sites

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21
Q

When there is an increase in Ca+….

A

Ca+ will bind to troponin -> tropomyosin rolls away exposing cross-bridge binding sites

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22
Q

Could you identify from a list the sequence of steps describing how actin and myosin interact during skeletal muscle contraction?

A

1) Binding: Exposure of cross-bridge binding site -> myosin cross bridge bends up at lower neck and binds to site
2) Power stroke: Binding -> upper neck of myosin cross bridge bends back 45°, sliding thick & thin filaments across each other—basis of contraction
3) Detachment: Link between myosin cross bridge and actin breaks -> cross bridge returns to normal position
4) If [Ca2+]i still elevated -> cross-bridge binding sites still exposed -> cycle repeats

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23
Q

Why does the two myosin heads attach to actin at one time?

A

So filaments don’t slip back after detachment

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24
Q

Thin filaments are pulled in toward the M line causing ….

A

The H zone becomes shorter and the whole sarcomere becomes shorter

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25
Q

Where does the energy for the power stroke (myosin bending) come from?

A

ATP

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26
Q

What causes the increase in [Ca2+]i that leads to sarcomere contraction?

A

An action potential

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27
Q

Transverse (T) tubule

A

invagination of plasma membrane into a tube that runs down into the muscle fiber at the junction of A and I bands

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28
Q

Voltage gated Na+ channels in the T tubules allows…

A

action potential to travel down into cell and depolarize

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29
Q

Sarcoplasmic reticulum

A

network of interconnected membrane-enclosed compartments surrounding each myofibril

30
Q

What does the SR store?

A

Calcium

31
Q

Identify from a list the sequence of steps from neurotransmitter release at the neuromuscular junction to release of Ca2+ from the sarcoplasmic reticulum?

A

1) Action potential travels down tranverse tubule and activates voltage-gated receptors (dihydropyridine receptors) in the membrane of tubule
2) Activated dihydropyridine receptors activate abutting Ca2+-release channels in membrane of sarcoplasmic reticulum
3) Activated Ca2+-release channels open and Ca2+ flows from SR into cytosol
4) Ca2+ in cytosol later sequestered back into sarcoplasmic reticulum via an ATPase pump (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase [SERCA] pump)

32
Q

Which events of contraction require ATP (energy) to keep going?

A

1) Power stroke: Energy from ATP split at myosin ATPase site on cross-bridge
2) Maintenance of Ca2+ gradient: SERCA pump uses energy from ATP to pump Ca2+ back into sarcoplasmic reticulum
3) Maintenance of Na+ and K+ gradients: Na+/K+ pump uses energy from ATP to pump Na+ and K+ across plasma membrane

33
Q

3 stages of cellular respiration

A

glycolysis, citric acid cycle, and oxidative phosphorylation

34
Q

What stage of cellular respiration make the most amount of ATP?

A

Oxidative Phosphorylation

35
Q

What stage(s) of cellular respiration use anaerobic exercise

A

Glycolysis (fast bc of fewer chemical reactions)

36
Q

What stage(s) of cellular respiration use aerobic exercise

A

Citric acid cycle and Oxidative Phosphorylation (slow bc of many chemical reactions)

37
Q

How is anaerobic respiration fueled

A

with glucose

38
Q

How is aerobic respiration fueled?

A

With glucose or fatty acids

39
Q

Do you use anaerobic or aerobic respiration for high intensity?

A

Anaerobic

40
Q

What does glycolysis produce?

A

Pyruvate

41
Q

What happens when there’s excess pyruvate that doesn’t enter the citric acid cycle?

A

It converts pyruvate into lactic acid and that’s where muscle soreness during exercise comes from

42
Q

Muscle fibers have an alternate pathway for immediate availability of ATP called…

A

creatine phosphate

43
Q

How is creatine phosphate involved in ATP synthesis? Under what conditions would this
reaction occur and why?

A

Muscle fibers have an alternate pathway for immediate availability of ATPàcreatine phosphate
Increased O2 uptake continues after exercise (heavy breathing) partially due to O2 consumption during oxidative phosphorylation to rebuild creatine phosphate reserves

44
Q

Isometric Contractions

A

Tension produced without muscle changing in length

45
Q

Isotonic Contractions

A

Muscle changes in length

46
Q

2 types of isotonic contractions

A

Concentric and eccentric

47
Q

How does the velocity of muscle shortening change with increased load?

A

As load increases, maximum velocity of shortening decreases.

48
Q

Problem: Muscles can only contract a small distance, but our limbs need to move over a much larger distance

A

Solution: Insert muscle onto bone near joint to make the joint a 3rd-class lever

49
Q

Most energy used by muscles is converted to _______

A

Heat

50
Q

Motor Unit

A

one motor neuron plus all of the muscle fibers it innervates

51
Q

Motor unit recruitment

A

few motor units activated creates weak contraction, while many more units activated creates strong contraction

52
Q

Twitch Summation

A

increased rate of action potentials from motor neuron can lead to summation of muscle fiber tension

53
Q

Twitch summation mostly due to cumulative increase in what?

A

[Ca2+]I

54
Q

What happens when there is more Ca2+?

A

-more exposed cross-bridge binding sites on actin
-more cross-bridge cycling
-more tension

55
Q

Tension on muscle fibers can also be influenced by…

A

-length of fiber at onset of contraction
-extent of fatigue
-thickness of fiber

56
Q

3 types of skeletal muscle fibers

A
  1. Slow-oxidative fibers
  2. Fast-oxidative fibers
  3. Fast-glycolytic fibers
57
Q

Whats the difference between slow and fast muscle fibers?

A

Fast: High myosin ATPace activity
Slow: Low myosin ATPace activity

58
Q

Difference between oxidative and glycolytic fibers

A

Oxidative: More capable of producing ATP via oxidative phosphorylation
Glycolytic: More capable of producing ATP via glycolysis

59
Q

What is muscular hypertrophy, and what causes it?

A

-An increase in size.
-Regular, short bouts of high-intensity, anaerobic exercise can lead to it.

60
Q

How do regular, long bouts of aerobic exercise increase oxidative capacity?

A

Additional mitochondria and capillaries for oxidative fibers -> more efficient use of O2

61
Q

What are the various nervous system inputs onto motor neurons (or the spinal cord interneurons that directly project to motor neurons)?

A

Motor Cortex- voluntary movements
Brainstem- postural adjustments for voluntary movements
Afferent input (proprioceptors, nociceptors, tactile mechanoreceptors)- reflexive movements
Local interneurons in spinal cord- rhythmic movements

62
Q

Muscle Spindle

A

Proprioceptive afferent fiber ending wrapped around a special intramural muscle fiber

63
Q

How is a muscle spindle activated?

A

When muscles lengthen, the spindles are stretched. This stretch activates the muscle spindle which in turn sends an impulse to the spinal cord.

64
Q

Identify the sequence of steps in the stretch reflex?

A

Tap on patellar tendon, muscle spindle is the receptor, afferent nerve, spinal cord, efferent nerve, quads flex

65
Q

Does the withdrawal reflex simply lead to contraction of a muscle, or complementary contraction and relaxation of a set of muscles? In what CNS structure does all of the integration of the withdrawal reflex take place?

A

It inhibits the antagonist muscle and relaxes it and then contracts the agonist to pull the part away. Integration center is the spinal cord.

66
Q

How are thick and thin filaments organized differently in smooth muscle fibers?

A

-Muscle fibers are short and have a tapered shape
-Each smooth muscle fibers only contain one nucleus
-The thick and thin filaments are not stacked instead criss-crossed through cell linked by dense bodies held in place by intermediate cytoskeleton filaments

67
Q

Are contractions in smooth muscle shorter or longer in duration than those of skeletal muscle cells?

A

They can contract half their length much longer than skeletal muscle

68
Q

Although the chemical cascade leading to contraction is different in smooth muscle, what is the ion that triggers it?

A

They do not have troponin so they are always exposed. The cross-bridge binding is prevented by unphosphorylated myosin-light chain.

69
Q

Multiunit smooth muscle is neurogenic meaning

A

it contracts in response to stimulation by autonomic fiber

70
Q

Single-unit smooth muscle is myogenic meaning

A

internal electrical oscillations cause contractions, but can be influenced by autonomic input

Physiology (9 decks)

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