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Physiology > Chapter 9 Part 2 > Flashcards

Chapter 9 Part 2 Flashcards

1
Q

What are skeletal muscles stimulated by?

A

Somatic Motor Neurons

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2
Q

What is released at the neuromuscular junction?

A

Acetylcholine

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3
Q

What causes the release of acetylcholine or exocytosis of Ach?

A

The calcium ion entry into the axon terminal of the motor neuron

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4
Q

Where does ACh bind?

A

To receptors on the sarcolemma

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5
Q

What does ACh binding to receptors do?

A

Opens ion channels in the receptors that allow simultaneous passage of Na+ into the muscle fiber and K+ out of the muscle fiber (creates an end plate potential)

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6
Q

How are ACh effects terminated?

A

By its breakdown in the synaptic cleft by acetylcholinesterase (this closes the channel)

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7
Q

What does the neuromuscular junction contain?

A

Axon Terminal
Synaptic cleft
Junctional folds

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8
Q

Where is the neuromuscular junction situated?

A

Midway along length of muscle fiber

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9
Q

What are the axon terminal and muscle fiver separated by?

A

A gel-filled space called the synaptic cleft

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10
Q

What is contained in the synaptic vesicles of axon terminals?

A

Acetylcholine

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11
Q

What do junctional folds of sarcolemma contain?

A

ACh receptors

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12
Q

What events happen at the neuromuscular junction?

A

Nerve impulses arrive at axon terminal and ACh is released into the synaptic cleft
ACh diffuses across cleft and binds with receptors on sarcolemma
Electrical events cause generation of action potential

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13
Q

What does acetylcholinesterase do?

A

It breaks down ACh into acetic acid and choline (this prevents unnecessary muscle fiber contraction so the muscle does not tire)

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14
Q

What charge is the inner membrane when the sarcolemma is polarized?

A

Negative (resting)

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15
Q

What are the 3 steps of generating an action potential in a skeletal muscle fiber?

A

End plate potential
Depolarization
Repolarization

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16
Q

What happens during end plate potential?

A

Local depolarization
ACh binds to open up gated ion channels which causes Na to go in and K to go out of cell
The sarcolemma becomes less negative (more Na is moving in than K moving out)

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17
Q

What happens during depolarization?

A

Generation and propagation of an action potential
The local depolarization spreads across membrane which causes more Na to come into the cell and decrease membrane voltage to reach threshold (unstoppable action potential)

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18
Q

What happens during repolarization?

A

Restoring electrical conditions of resting membrane potential (Na channels close and K channels open to efflux rapidly)

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19
Q

What is the refractory period?

A

The period of time fiber cannot be stimulate until repolarization is complete

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20
Q

What pump restores resting state of membrane?

A

Na+-K+ pump

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21
Q

What is the latent period?

A

Time when E-C coupling events occur

Time between AP initiation and beginning of contraction

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22
Q

What is necessary for contraction?

A

Calcium ions

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23
Q

What channel opens when nerve impulses reach the axon terminal?

A

Voltage-gated calcium channel (causes ACh to be released to synaptic cleft)

24
Q

What channels open and cause end plate potential when ACh binds to its receptors on the sarcolemma?

A

Ligand-gated Na+ and K+ channels

25
Q

What channel opens in order to propagate Action Potential to other parts of sarcolemma?

A

Voltage-gated Na+ channels

26
Q

What causes the Sarcoplasmic reticulum to release Ca2+ to cytosol?

A

The conformational change of voltage-sensitive proteins in T tubules

27
Q

What does contraction produce?

A

Muscle tension

28
Q

What is muscle tension?

A

Force exerted on load or object to be moved

29
Q

True/False: Contraction always shortens muscle.

A

False it may or may not shorten muscle
Isometric contraction-no shortening
Isotonic contraction - muscle shortens

30
Q

What must exceed the load in order for isotonic contraction to occur?

A

The muscle tension (force exerted on load) must exceed load in order for muscles to shorten

31
Q

Each muscle is served by at least one ______ _______.

A

Motor nerve

32
Q

What do motor nerves contain?

A

Axons of up to hundreds of motor neurons

33
Q

What is a motor unit?

A

Motor neuron and all muscle fibers it supplies. (the smaller the number of fibers the finer the control)

34
Q

Why do muscle fibers from motor units spread throughout muscle?

A

So a single motor unit can cause weak contractions of entire muscle

35
Q

Why do motor units usually contract asynchronously?

A

To help prevent fatigue

36
Q

What is a twitch?

A

Motor unit’s response to single action potential of its motor neuron (myogram)

37
Q

What are the three phases of muscle twitch?

A

Latent period
Period of contraction
Period of relaxation
(muscle contracts faster than it relaxes)

38
Q

What happens in the latent period of a muscle twitch?

A

E-C coupling, no muscle tension

39
Q

What happens during the period of contraction during a muscle twitch?

A

Cross bridge formation, tension increases

40
Q

What happens during the period of relaxation for muscle twitch?

A

Calcium ions re enter into the sarcoplasmic reticulum and tension declines to zero

41
Q

What causes differences in strengths and durations of twitches?

A

Variations in metabolic properties and enzymes between muscles

42
Q

What How are muscle responses graded?

A

Changing frequency of stimulation

Changing strength of stimulation

43
Q

What is wave summation?

A

Increased stimulus frequency to where muscle does not completely relax between stimuli (partial relaxation)
If continued at low stimulus, unfused tetanus occurs

44
Q

How does one reach fused tetany results?

A

If stimuli are given quickly enough and the muscle reaches maximal tension

45
Q

What happens at subthreshold stimuli?

A

No observable contraction

46
Q

What happens at threshold stimulus?

A

Stimulus strength is enough to cause first observable muscle contraction

47
Q

What is maximal stimulus?

A

The strongest stimulus that increases contractile force

48
Q

What is contraction force precisely controlled by?

A

Recruitment (activation of more and more muscle fibers)

49
Q

What happens beyond maximal stimulus?

A

No increase in force of contraction

50
Q

Recruitment works on size principle. What is size principle?

A

The motor units with smallest muscle fibers are recruited first and then larger and larger fibers are recruited as stimulus increases
The largest motor neurons are only activated for most powerful contractions

51
Q

What happens during a concentric isotonic contraction?

A

The muscle shortens and does work

52
Q

What happens during eccentric isotonic contractions?

A

The muscle generates force as it lengthens

53
Q

What kind of contraction would occur if you tried to pick up something that was too heavy?

A

Isometric contraction (load is greater than the tension the muscle can develop)

No shortening

54
Q

What is muscle tone?

A

Constant, slightly contracted state of all muscles (postural tone)

55
Q

What causes muscle tone?

A

Spinal reflexes (in response to input from stretch receptors in muscles)

Physiology (17 decks)

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