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BMS150 Test 2 > Skeletal Muscle Physiology 1 (Week 8) > Flashcards

Skeletal Muscle Physiology 1 (Week 8) Flashcards

1
Q

Our skeletal muscles are composed of bundles of ___________

A

fascicles

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2
Q

Each fascicle is composed of linearly aligned ______________

A

muscle fibers (myofibres)

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3
Q

a single, multi-nucleated, elongated cell, composed of many sarcomeres that are arranged linearly

A

muscle fibre/myofiber

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4
Q

What the cell membrane of a muscle fibre called?

A

sarcolemma

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5
Q

Sarcomeres are composed of _______________

A

myofibrils

Note: myofibrils are organelles

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6
Q

the connective tissue sheath that surrounds the whole muscle, that extends from the tendons

A

epimysium

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7
Q

the sheath surrounding each fascicle

A

perimysium

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8
Q

the sheath surrounding each individual muscle fibre

A

endomysium

Note: below the endomysium is the sarcolemma (cell membrane of a muscle cell)

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9
Q

Each muscle fibre contains how many myofibrils?

A

1000-2000

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10
Q

Each myofibril is composed of many myofilaments. What is a myofilament composed of?

A
  • contractile proteins (e.g., actin, myosin)
  • regulatory proteins (e.g., tropomyosin, troponin)
  • accessory proteins (e.g., actinin, dystrophin, titin, nebulin)
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11
Q

A sarcomere runs from __________________

A

Z disc to Z disc

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12
Q

the contractile unit of skeletal muscle

A

sarcomere

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13
Q

Thin filaments are made of __________

A

actin

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14
Q

Thick filaments are made of _____________

A

myosin

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15
Q

What gives the striated appearance of skeletal muscle?

A

the overlapping of thick and thin filaments

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16
Q

the center of the sarcomere

A

M-line

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17
Q

True or False: thin filament (actin) attaches to the Z discs and thick filament (myosin) attaches to the M-line

A

True

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18
Q

The A band (darker band) is composed of ___________

A

actin and myosin (they overlap)

Note: However, within the A band, there is a portion that is only myosin = H zone

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19
Q

The I band (lighter band) is composed of ____________

A

actin only

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20
Q

centre of I bands (light bands)

A

Z disc

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21
Q

What part of the sarcomere shortens during contraction?

A

I band

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22
Q

monomer of actin

A

G actin

23
Q

polymer of actin

A

F actin

24
Q

Thin filaments are composed of two strands of _____________ wound together

A

F actin

25
Q

Each G actin (monomer of actin) has a binding site for ____________

A

myosin

26
Q

Each unit of ___________ is composed of a head and tail region

A

myosin

27
Q

Head region of myosin forms _____________ that interact with adjacent actin filaments

A

cross-bridges

28
Q

What are the three important chemical features at the myosin head region?

A

1) ATP activity
2) actin-binding region
3) ATP binding region

Note: ATP is required to change the conformation of the hinge

29
Q

___________ and __________ are regulatory proteins that associates with actin

A

tropomyosin and troponin

30
Q

When a skeletal muscle is in a ______________ (relaxed/contracted) state, tropomyosin molecules cover the myosin-binding site on G-actin monomers

A

relaxed

Note: this prevents cross-bridge formation between actin and myosin

31
Q

Troponin forms a complex of 3 subunits. What are they?

A

1) Troponin C
2) Troponin T
3) Troponin I

32
Q

Troponin C binds to ?

A

calcium

33
Q

Troponin T binds to?

A

tropomyosin

34
Q

Troponin I binds to?

A

actin

35
Q

True or False: When calcium binds to troponin C, the troponin complex undergoes a conformational change and troponin T “pulls” tropomyosin and troponin I off of the myosin-binding site of G actin subunits. This allows cross-bridge formation to occur.

A

True

36
Q

invaginations within the sarcolemma that allows the action potential to be carried deep into the muscle fibre

A

transverse tubules (T tubules)

Note: T tubules are continuous with the extracellular fluid

37
Q

a specialized endoplasmic reticulum containing high concentrations of calcium

A

sarcoplasmic reticulum

38
Q

___________________ are specialized regions of the sarcoplasmic reticulum that associated with the T-tubules

A

terminal cisternae

39
Q

The junction between the T-tubules and the terminal cisternae is called what?

A

muscle triad

(think of T tubule “sandwiched” between terminal cisternae on either side of it)

40
Q

True or False: The concentration of calcium in the ECF (extracellular fluid) and the sarcoplasmic reticulum (SR) is generally low

A

False

The calcium concentration is high in both the ECF and SR (compared to the cytosol). This means that if you open up a calcium channel, it will go right into the cytosol.

41
Q

a motor nerve axon contacts each muscle fiber near the middle of the fiber, forming a synapse called what the ________________

A

neuromuscular junction

42
Q

the region of the sarcolemma in closest contact with the presynaptic nerve terminal is called the _____________

A

motor end plate

43
Q

What neurotransmitter does the motor nerve synapse release onto the muscle fibre’s nicotinic receptors?

A

acetylcholine (Ach)

44
Q

When Ach binds to the nicotinic receptors on the sarcolemma, this activates voltage-gated sodium channels which triggers an ______________, which propagates along the sarcolemma

A

action potential

Note: a skeletal muscle action potential looks very similar to a neuronal action potential but is slightly longer in duration

skeletal muscle AP = 5-10 msec
neuronal AP = 1-2 msec

45
Q

The action potential travels into the T-tubule, bringing depolarization deep into the muscle fiber, signalling/exciting _____________ release from the sarcoplasmic reticulum

A

calcium

46
Q

When the action potential propagates along the T-tubules, it activates _____________ channels in the sarcolemma

A

L-type Ca2+

Note: activation of these channels also triggers activation of Ryanodine receptors on the terminal cisternae… let’s out a ton of calcium out of the sarcoplasmic reticulum (SR)

47
Q

After calcium flows down its concentration gradient (out of the SR and into the cytosol), it then binds to ______________, to expose the binding sites for myosin

A

troponin C

48
Q

True or False: Most of the calcium that activates skeletal muscle comes from the ECF

A

False

Most comes from the sarcoplasmic reticulum (SR)

49
Q

What is the average number of alpha motor neurons that innervate a typical muscle?

A

~100

50
Q

The number of muscle fibers that a motor neuron reaches out to is referred to as what?

A

a motor unit

51
Q

the result of a single action potential from a motor neuron that barely causes any force development in the muscle fibers that it innervates

A

a twitch

52
Q

How do you get smooth, forceful movements?

A

occur when the alpha-motor neuron sends MANY action potentials to the motor unit, at a relatively high frequency

summation of the APs prevent calcium concentrations from dropping (calcium keeps getting released), creating a peak of force

53
Q

True or False: fused tetanus/maximal force generation in skeletal muscle requires a lot of ATP

A

True

54
Q

True or False: Individual “twitch times” vary depending on the role of the muscle

A

True

Example: Your soleus, meant to keep you standing, is a slow muscle. Therefore, one action potential results in a very long twitch (~200msec). Whereas your gastrocnemius helps you more when you’re running to help you push off the ground. This has a faster twitch time (~70msec), because it generates more force. Ocular muscle twitch times are very fast (~25msec)

BMS150 Test 2 (10 decks)

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