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LIFESCI 7C > Muscle & Skeletal System > Flashcards

Muscle & Skeletal System Flashcards

1
Q

Muscles are made of ____, which are made of ____, which are made of ____.

A

muscle bundles
muscle fibers
myofibrils

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2
Q

What are filaments?

A

long, narrow bundles of contractile proteins that interact with one another to cause muscle fibers to shorten

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3
Q

What two filaments make up the sarcomere?

A

actin (thin filament)
myosin (thick filament)

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4
Q

What is the sarcomere?

A

the functional unit of muscle

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5
Q

What is the role of tropomyosin in the sarcomere?

A

blocks myosin binding sites between actin and myosin

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6
Q

What is the role of troponin in the sarcomere?

A

moves tropomyosin away from mysoin binding sites, allowing cross bridges to form and muscle to contract

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7
Q

When myofibrils stretch to longer lengths, the actin-myosin overlap ____.

A

decreases

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8
Q

When myofibrils contract to shorter lengths, the actin-myosin overlap ____.

A

increases

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9
Q

longer muscle length –> ____
shorter muscle length –> ____

A

relaxation
contraction

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10
Q

What is the cross-bridge?

A

the binding of the myosin head to actin at a specific site between myosin and actin filaments

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11
Q

What is the energy source of muscle contraction?

A

conversion of chemical energy released by ATP hydrolysis into force and kinetic energy

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12
Q

What is the first stage of the cross-bridge cycle?

A

ATP is hydrolized into ADP and Pi, and myosin head is cocked back.

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13
Q

What is the second stage of the cross-bridge cycle?

A
  • troponin units on actin are bound by Ca2+ following a nerve impulse
  • tropomyosin is moved away, which exposes the myosin-binding sites on actin
  • myosin head releases Pi to bind to actin via myosin-binding sites
  • cross-bridge is formed
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14
Q

What is the third stage of the cross-bridge cycle?

A

the mysoin head and actin filament stimulate a power stroke via the sliding-filament model, and the muscle contracts

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15
Q

What is the fourth stage of the cross-bridge cycle?

A

as the muscle contracts, ADP bound to the myosin head is released

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16
Q

What is the fifth stage of the cross-bridge cycle?

A

ATP binds to the myosin head, which halts the contraction, and the myosin head detaches from actin

17
Q

What happens at the motor neuron in the neuromuscular junction?

A
  1. action potential reaches the axon terminals of the motor neuron
  2. motor neuron is depolarized, which opens its voltage-gated Ca2+ channels
  3. Ca2+ facilitates the release of ACh neurotransmitters into the motor endplate
18
Q

What happens at the motor endplate and muscle cell in the neuromuscular junction?

A
  1. ACh binds to ligand-gated Na+ channels on the muscle cell, which triggers the influx of Na+ ions into the muscle cell
  2. This causes depolarization of the muscle cell
  3. Depolarization causes the voltage-gated Ca2+ channels in the sarcoplasmic reticulum to open, releasing Ca2+ into the filaments
  4. Ca2+ binds to troponin, which then moves away from tropomyosin to expose myosin binding sites
  5. Cross bridge is formed
19
Q

How does muscle return to its relaxed state following a contraction?

A
  1. AChE breaks down ACh
  2. Ca2+ is transported back to the SR
  3. tropomyosin blocks the myosin-binding sites on actin
20
Q

What is a twitch contraction?

A

a single action potential that only exerts one wave of force

21
Q

What is force summation?

A

when a second action potential arrives before the muscle has relaxed, causing a greater force to be produced

22
Q

Where does Ca2+ go during a twitch contraction?

A

muscle pumps Ca2+ back into the SR

23
Q

Where does Ca2+ go during force summation?

A

it remains within the myofibrils to activate more cross-bridges

24
Q

What is tetanus contraction?

A

muscle contraction of sustained force in which muscle force reaches a plateau at sufficiently high frequency

25
Q

What is slow-twitch?

A

found in muscles that contract slowly and consume ATP slowly

i.e. long distance runners

26
Q

What is fast-twitch?

A

generate force quickly, produce rapid movement, and consume ATP more quickly

i.e. sprinters

27
Q

Slow-twitch muscle fibers are the color ____ due to high ____.
Fast-twitch muscle fibers are the color ____ due to low ____.

A

red; myoglobin
white; myoglobin

28
Q

How does botox work?

A

prevents the release of ACh, which prevents muscle contraction and causes stiffness

29
Q

Excitotoxic shock causes the muscles to ____.
Flaccid paralysis causes the muscles to ____.

A

stiffen; relax

LIFESCI 7C (8 decks)

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