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IMSK > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

1
Q

what are 4 purposes of skeletal muscle?

A

voluntary and reflexive movements like
1. maintaining posture
2. respiration
3. communication
4. produce body heat

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2
Q

what is the purpose of smooth muscle?

A

constriction and dilation of organs, vessels, and aperatures

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3
Q

what is the purpose of cardiac muscle?

A

heart constriction and relaxation

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4
Q

what does skeletal muscle require for contraction?

A

MUST be innervated

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5
Q

do cardiac and smooth muscle require innervation to contract?

A

no; they have intrinsic contraction

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6
Q

what is a muscle fiber?

A

single muscle cell

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7
Q

what is a myofibril?

A

organized protein fiber within the muscle cell

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8
Q

what is a sarcomere?

A

the unit of the myofibril that shortens to cause muscle contraction

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9
Q

what are thick filaments made up of?

A

myosin

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10
Q

what are thin filaments made up of?

A

actin; which contains troponin and tropomyosin

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11
Q

what are transverse (T) tubules? function?

A

invaginations of the sarcoplasm into the muscle fiber; important in helping the spread of the action potential

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12
Q

what is the sarcoplasmic reticulum? function?

A

modified endoplasmic reticulum with TONS of calcium; important source of calcium and for rapid release and reuptake of calcium

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13
Q

what is the motor unit?

A

the alpha motor neuron and all the muscle fibers it innervates

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14
Q

what is the neuromuscular junction?

A

the synapse between the neuron and the muscle fiber

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15
Q

what is the purpose of small motor units?

A

fine control, like the muscles in our fingers

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16
Q

what is the purpose of big motor units?

A

support/posture, like the muscles in our quads

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17
Q

what is the most highly developed synapse in the body?

A

the neuromuscular junction

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18
Q

how many neurons innervate each muscle fiber?

A

only one!!

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19
Q

what is the alpha motor neuron important for?

A

the integrity of the muscle fiber

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20
Q

what does loss of innervation result in?

A

rapid muscle atrophy

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21
Q

what is the major neurotransmitter released from the alpha motor neuron?

A

acetylcholine (ACH)

22
Q

what is the primary receptor on the muscle fiber?

A

nicotinic, receives acetylcholine

23
Q

what generates an action potential, in terms of muscle fiber parts

A

the cell membrane (sarcoplasm) of the muscle fibers

24
Q

describe how the action potential moves through parts of the muscle fiber and what is results in

A

AP enters the T tubule system and initiates calcium release from the sarcoplasmic reticulum

25
Q

why is it good to have a channel coupled to a receptor?

A

it always opens when you want!

26
Q

give the 8 steps of an action potential moving through the neuromuscular junction

A
  1. motor neuron fires an action potential
  2. calcium enters its voltage-gated channels
  3. acetylcholine is released
  4. sodium enters the muscle fiber
  5. local current is established between the depolarized end plate and the adjacent muscle plasma membrane
  6. muscle fiber initiates action potential
  7. propagated action potential in muscle plasma membrane
  8. acetylcholine degradation
27
Q

what is acetylcholinesterase and what is its use?

A

allows efficient termination of acetylcholine; allows synapses to only respond when AP is traveling down/through a synapse

28
Q

give the 4 steps of calcium release from the sarcoplasmic reticulum

A
  1. the DHP receptor is voltage sensitive and activated by the passing action potential
  2. the DHP receptor has a calcium channel which allows calcium to enter the muscle cell
  3. activation of the DHP receptor causes calcium release from the sarcoplasmic reticulum
  4. calcium from the sarcoplasmic reticulum will bind to troponin of the thin filament
29
Q

give the 7 steps of the power stroke/cycling of the myosin head

A
  1. calcium bonds to troponin and causes a conformation change in tropomyosin to expose myosin binding sites
  2. the myosin head binds to a site and ADP is released
  3. stored energy is released, causing the myosin head to change conformation resulting in the power stroke and the thin and thick filaments slide past each other
  4. ATP binds to myosin, causing it to release from the actin protein
  5. the ATP os hydrolyzed to ADP + Pi, resulting in the myosin head changing conformation (re-cocking)
  6. if calcium is still binding troponin and the myosin binding site on the actin molecule is still exposed, the cycle repeats
  7. if the action potentials cease, the calcium is rapidly pumped back into sarcoplasmic reticulum
30
Q

how long will the myosin head cycle continue?

A

as long as BOTH ATP and calcium are present

31
Q

how many ATP are used per power stroke?

A

one

32
Q

what happens to a muscle if no ATP is present? why and what is this called?

A

the muscle is locked in its contracted state/AKA rigor mortis; ATP allows relaxation (binds to myosin causing it to release from actin)

33
Q

what happens to skeletal muscle if it loses innervation?

A

rapid muscle atrophy; lose all reflexivity and muscle become flaccid

34
Q

what is muscle associated with and how does this relate to muscle shortening?

A

muscle is associated with lots of connective tissue that must be tightened before muscle shortens

35
Q

what is important in generating some muscle tone?

A

the activity of the alpha motor neurons to the muscle; generates some resting tension/muscle tone plus the myotatic reflex

36
Q

what 2 things are required to get movement from a muscle?

A
  1. contract the desired muscle
    AND
  2. relax its antagonistic muscle
37
Q

what are the 2 actions of muscle? describe

A
  1. static: generation of force with no movement of the joint
  2. dynamic: results in joint movement
38
Q

what are the 2 types of dynamic muscle movement?

A
  1. concentric: shortening of the muscle (more common)
  2. eccentric: lengthening of the muscle
39
Q

does the action potential and generation of tension occur simultaneously? why or why not?

A

action potential first, generation of tension slightly lags after due to calcium release, protein interactions, and tensing of elastic elements that all has to occur

40
Q

how does the length of the sarcomere relate to tension in muscle?

A

the resting length is optimal for max tension generation; if sarcomere is too long, there is minimal interaction between the thin and thick filaments; if too short, too much/too cramped interaction and less tension is generated

41
Q

can you generate tension if you can’t shorten the sarcomere?

A

nope

42
Q

how does the number of muscle fibers relate to strength? why?

A

more fibers results in more strength, usually because more motor units are involved

43
Q

which generates more tension: when motor units fire together or individually?

A

when they fire together

44
Q

what does all muscle have for contraction?

A

actin and myosin

45
Q

describe how calcium is related to contraction in all muscle types?

A

calcium is involved in contraction in all 3 muscle types, but the source of calcium differs between the types

46
Q

is troponin found in smooth muscle?

A

NO!

47
Q

list the 6 steps of the contraction cycle in smooth muscle

A
  1. action potential enters voltage-gated calcium channels
  2. calcium enters smooth muscle cell and activates calmodulin
  3. the calcium-calmodulin activated myosin light chain kinase (MLCK) is formed
  4. MLCK phosphorylates the myosin light chain in the myosin head
  5. this causes the head to bind to the actin protein and elicit a power stroke
  6. the power stroke releases the phosphate and the cycle starts over as long as calcium is present
48
Q

if you gave a calcium channel blocker, would smooth muscle contraction increase or decrease? why? give a practical application

A

decrease because most calcium for smooth muscle comes from extracellular sources (not the sarcoplasmic reticulum like in skeletal muscle); drugs that work this way are used to relax arterioles to decrease blood pressure

49
Q

is smooth muscle organized into sarcomeres?

A

nope!

50
Q

how is smooth muscle organized? contrast contraction motion to skeletal muscle

A

like drawstrings; scrunch/constrict contraction instead of linear

IMSK (17 decks)

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