Bio 201 Neuromuscular Junction And Muscle Physiology

Front 1

What is a synapse?

Back 1

Point where a nerve fiber meets its target cell

Front 2

At a neuromuscular junction, one nerve fiber stimulates the muscle fiber at ____ points within the NMJ.

Back 2

Several

Front 3

What is the synaptic knob?

Back 3

The swollen end of a nerve fiber

Front 4

The synaptic knob contains synaptic vesicles filled with what?

Back 4

Acetylcholine

Front 5

Synaptic vesicles undergo ____ releasing ACh into synaptic cleft.

Back 5

Exocytosis

Front 6

What is the synaptic cleft?

Back 6

Tiny gap between the synaptic known and the muscle sarcolemma

Front 7

What is the function of a Schwann cell?

Back 7

Envelops and isolates all of the NMJ from surrounding tissue fluid.

Front 8

The NMJ contains 50 million ACh receptor-proteins incorporated into the muscle cell plasma membrane. How is the NMJ able to put this many receptors in such a small space?

Back 8

The sarcolemma contains junctional folds that increase the surface area holding ACh receptors.

Front 9

What can the lack of ACh receptors lead to?

Back 9

Paralysis

Front 10

What is the basal lamina?

Back 10

Thin layer of collagen and glycoprotein that separates Schwann cell and entire muscle cell from surrounding tissues

Front 11

What significant enzyme is contained in the basal lamina?

Back 11

Acetylcholinesterase that breaks down ACh after muscle contraction causing relaxation

Front 12

Some pesticides contain ____ ____ that bind to acetylcholinesterase and prevent it from degrading ACh.

Back 12

Cholinesterase inhibitors

Front 13

What is spastic paralysis?

Back 13

A state of continual contraction of the muscles.

Front 14

A form of spastic paralysis caused by a toxin of Clostridium tetani is called what?

Back 14

Tetanus or lockjaw.

Front 15

____ in the spinal cord normally stops motor neurons from producing unwanted muscle contractions.

Back 15

Glycine

Front 16

The tetanus toxin blocks ____ glycine release and causes overstimulation and spastic paralysis of the muscles.

Back 16

Glycine

Front 17

What is flaccid paralysis?

Back 17

A state in which the muscles are limp and cannot contract

Front 18

This is a plant poison used by South American Natives to poison blowgun darts.

Back 18

Curare

Front 19

What is the mechanism of action of agents that cause flaccid paralysis?

Back 19

They compete with ACh for receptor sites but do not stimulate the muscles.

Front 20

The study of electrical activity of cells is known as what?

Back 20

Electrophysiology

Front 21

What is significant about muscle fibers and neurons?

Back 21

They are electrically excitable

Front 22

In an unstimulated (resting) cell, there are ____ anions on the inside of the plasma membrane than on the outside.

Back 22

More

Front 23

In an unstimulated (resting) cell, the plasma membrane is electrically ____.

Back 23

Polarized or charge

Front 24

In an unstimulated (resting) cell, there are excess ____ ions in the ECF.

Back 24

Sodium

Front 25

In an unstimulated (resting) cell, there are excess ____ ions in the ICF.

Back 25

Potassium

Front 26

The inside of the plasma membrane is ____ charged by comparison to its outer surface.

Back 26

Negatively

Front 27

What is the voltage or electrical potential?

Back 27

Difference in electrical charge from one point to another

Front 28

What is the value of the resting membrane potential of a myofiber?

Back 28

-90 mV

Front 29

What maintains the resting membrane potential maintained by?

Back 29

The sodium potassium pump.

Front 30

What happens during depolarization?

Back 30

The inside of the plasma membrane becomes briefly positive

Front 31

The quick up-and-down voltage shift from the negative RMP to a positive value and then back to the negative value again is known as what?

Back 31

An action potential

Front 32

The process in which nerve action potentials lead to muscle action potentials is known as what?

Back 32

Excitation

Front 33

Events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract is what phase of muscle contraction and relaxation?

Back 33

Excitation-contraction coupling

Front 34

Step in which the muscle fiber develops tension and may shorten is what?

Back 34

Contraction

Front 35

When its work is done, a muscle fiber relaxes and returns to its resting length. This is known as what?

Back 35

Relaxation

Front 36

What results from a nerve signal opening voltage-gated calcium channels in the synaptic knob?

Back 36

Calcium stimulates exocytosis of ACh from synaptic vesicles and ACh is released into the synaptic cleft

Front 37

After ACh is released into the synaptic cleft, what do the ACh molecules do?

Back 37

2 ACh molecules bind to each receptor protein, opening Na+ and K+ channels

Front 38

After an action potential spreads down into T-tubules what happens?

Back 38

Voltage-gated ion channels in T-tubules and calcium channels in the sarcoplasmic reticulum open and calcium enters the cytosol

Front 39

What is the result of calcium entering the cytosol after being released from the sarcoplasmic reticulum?

Back 39

Calcium binds to troponin on thin filaments causing the troponin-tropomyosin complex to change shape and expose the active sites on actin

Front 40

What happens after the troponin-tropomyosin complex changes shape and actin sites are exposed?

Back 40

Myosin ATPase in the myosin head hydrolyzes an ATP molecule. This results in the head "cocking" in an extended position and binding to an actin active site forming a myosin actin cross-bridge.

Front 41

What occurs after a myosin-actin cross bridge is formed?

Back 41

The myosin head releases ADP and inorganic phosphate causing a power stroke. Upon binding more ATP, myosin releases actin the the process is repeated.

Front 42

Each myosin head performs ____ power strokes per second.

Back 42

Five

Front 43

How many molecules of ATP does each power stroke utilize?

Back 43

One molecule of ATP

Front 44

What causes the relaxation step?

Back 44

AChE breaks down ACh and fragments are reabsorbed into the synaptic knob

Front 45

During relaxation, calcium is pumped back into the SR by ____ ____. Calcium binds to ____ while in storage in the SR.

Back 45

Active transport; calsequestrin

Front 46

After calcium is removed from troponin and is pumped back into the SR what happens?

Back 46

Tropomyosin reblocks the active sites and the muscle fiber ceases to produce or maintain tension.

Front 47

The hardening of muscles and stiffening of the body beginning 3 to 4 hours after death is what?

Back 47

Rigor Mortis

Front 48

Describe the onset of rigor mortis.

Back 48

A deteriorating SR releases calcium which then enters the cytosol, activating myosin-actin cross-bridging. A muscle then contracts but is unable to relax.

Front 49

Why are muscles unable to relax during rigor mortis.

Back 49

Muscles relaxation requires ATP and no ATP is produced after death.

Front 50

When does rigor mortis peak?

Back 50

12 hours after death then diminishes over the next 48 to 60 hours

Front 51

The amount of tension generated by a muscle and the force of contraction depends on how stretched or contracted it was before it was stimulated. This describes what concept?

Back 51

The length-tension relationship

Front 52

Overly contracted muscles produce a weak contraction because why?

Back 52

Thick filaments are too close to Z discs and can't slide

Front 53

Why do overly stretched muscles produce a weak contraction?

Back 53

Little overlap of thin and thick filaments does not allow for many cross bridges to form.

Front 54

____ ____ ____ produces the greatest force when muscles contract

Back 54

Optimum resting length

Front 55

A chart of timing and strength of a muscle contraction is known as what?

Back 55

A myogram

Front 56

A weak, ____, electrical stimulus causes no contraction.

Back 56

Subthreshold

Front 57

The minimum voltage necessary to generate an action potential in the muscle fiber and produce a contraction is what?

Back 57

The threshold

Front 58

A quick cycle of contraction when stimulus is at the threshold or higher is known as what?

Back 58

Twitch

Front 59

This phase of a twitch contraction is the 2msec delay between the onset of stimulus and onset of twitch response

Back 59

Latent Period

Front 60

The force generated during the latent period when no shortening of the muscle occurs is known as what?

Back 60

Internal tension

Front 61

This is the phase of twitch contraction in which filaments slide and the muscle shortens.

Back 61

Contraction phase

Front 62

This is the phase of a twitch contraction in which the SR quickly reabsorbs calcium, myosin releases the thin filaments and tension declines.

Back 62

Relaxation

Front 63

Do muscle twitches vary in strength?

Back 63

YES!

Front 64

What are six factors affecting twitch strength?

Back 64

Stimulus frequency, calcium concentration in the SR, how stretched a muscle was, temperature of muscles, pH, state of hydration

Front 65

Stimuli arriving closer together do what to a twitch?

Back 65

Produce a stronger twitch

Front 66

How does temperature affect twitch strength?

Back 66

Warmed up muscles contract more strongly

Front 67

A lower than normal pH of the sarcoplasm affects twitch strength how?

Back 67

Weakens the contraction

Front 68

How does the state of hydration of a muscle affect twitch strength?

Back 68

Affects the overlap of thick and thin filaments.

Front 69

The process of bringing more motor units into play is called what?

Back 69

Recruitment or Multiple motor unit summation

Front 70

Stimulating the nerve with higher and higher voltages produces ____ contractions

Back 70

Stronger

Front 71

When stimulus intensity (voltage) remains constant, twitch strength can vary with the what?

Back 71

Stimulus frequency

Front 72

When there are up to 10 stimuli per second what is the result of the twitches?

Back 72

Each stimulus produces identical twitches and full recovery between them

Front 73

When there are 10-20 stimuli per second what occurs?

Back 73

Treppe phenomenon

Front 74

What occurs in the treppe phenomenon?

Back 74

A muscle still recovers fully between twitches but each twitch develops more tension than the one before

Front 75

During treppe, stimulis arrive so rapidly that the SR does not have enough time between stimulis to do what?

Back 75

Absorb all the Ca2+ it released

Front 76

During treppe, Ca2+ concentrations in the cytosol rise higher and higher with each stimulus causing what?

Back 76

What subsequent twitch to be stronger

Front 77

Heat released during treppe causes what?

Back 77

Muscle enzymes such at myosin ATPase to work more efficiently

Front 78

20-40 stimuli per second produces what?

Back 78

Incomplete tetanus

Front 79

In ____ tetanus, each new stimulus arrive before the previous twitch is over. The new twitch piggy backs on the previous one generating higher tension.

Back 79

Incomplete tetanus

Front 80

____ summation results from two stimuli arriving close together

Back 80

Temporal

Front 81

____ summation results from one wave of contraction added to another

Back 81

Wave

Front 82

A state of sustained fluttering contraction is referred to as what?

Back 82

Incomplete tetanus

Front 83

40-50 stimuli per second produces what?

Back 83

Complete tetanus

Front 84

During ____ tetanus, the muscle has no time to relax between stimuli. Twitches fuse to a smooth, prolonged contraction. When one motor unit relaxes, another contracts and takes over so the muscle does not lose tension.

Back 84

Complete

Front 85

In ____ muscle contraction, muscle is producing internal tension while an external resistance causes it to stay the same length or become longer. It can be a prelude to movement when tension is absorbed by elastic component of a muscle. It is important in postural muscle function and antagonistic muscle joint stabilization.

Back 85

Isometric muscle contraction

Front 86

In ____ muscle contraction, the muscle changes in length with no change in tension.

Back 86

Isotonic

Front 87

What happens in concentric contraction?

Back 87

Muscle shortens while maintaining tension

Front 88

What happens in eccentric contraction?

Back 88

Muscle lengthens as it maintains tension

Front 89

All muscle contraction depends on what?

Back 89

ATP

Front 90

ATP supply depends on the availability of what?

Back 90

Oxygen, glucose and fatty acids

Front 91

ATP can be synthesized in what two ways?

Back 91

Aerobic respiration and anaerobic fermentation

Front 92

This method of synthesizing ATP enables cells to produce ATP in the absence of oxygen. It yields little ATP and produces lactic acid.

Back 92

Anaerobic fermentation

Front 93

This method of synthesizing ATP requires a continual supply of oxygen.

Back 93

Aerobic respiration

Front 94

During short, intense exercise, ____ supplies oxygen for a limited amount of aerobic respiration at the onset but is rapidly depleted.

Back 94

Myoglobin

Front 95

What is the function of myokinase?

Back 95

Transfers phosphate from one ADP to another creating ATP

Front 96

What is the function of creatine kinase?

Back 96

Obtains phosphate from phasphate--storage molecules creatine phosphate

Front 97

The ____ system uses ATP and CP collectively. It provides nearly all energy used for short bursts of intense activity.

Back 97

Phosphagen

Front 98

In the absence of oxygen, ____ can generate a net gain of 2 ATP for every glucose molecule consumed and produces lactic acid

Back 98

Glycolysis in anaerobic fermentation

Front 99

The glycogen-lactic acid system produces enough ATP for what?

Back 99

30-40 seconds of maximum activity

Front 100

Aerobic respiration theoretically produces ____ ATP per glucose.

Back 100

36-38

Front 101

The progressive weakness and loss of contractility from prolonged use of the muscles is what?

Back 101

Muscle fatigue

Front 102

Decline of ATP synthesis as glycogen is consumed, slowing down of the sodium-potassium pump, lactic acid lowering the pH of the sarcoplasm, accumulation of extracellular potassium, motor nerve fibers using up their acetylcholine and fatigue of CNS are all causes of what?

Back 102

Muscle fatigue

Front 103

The ability to maintain high-intensity exercise for more than 4 to 5 minutes is what?

Back 103

Endurance

Front 104

One's endurance is determined in large part by one's what/

Back 104

Maximum oxygen uptake

Front 105

The point at which the rate of oxygen consumption reaches a plateau and does not further with an added workload is what?

Back 105

Maximum oxygen uptake

Front 106

The difference betweeb the resting rate of oxygen consumption and the elevated rate following exercise is what?

Back 106

Excess post-exercise oxygen consumption

Front 107

Replacing the oxygen reserves that were depleted in the first minute of exercise, replenishing the phosphagen system, oxidizing lactic acid and serving the elevated metabolic rate are all reasons that the ____ is necessary.

Back 107

Excess post-exercise oxygen consumption

Front 108

____ increases the level of creatine phosphate in muscle tissue and increases speed of ATP generation. It is useful in burst-type exercises in order to beat muscle fatigue

Back 108

Oral Creatine supplement

Front 109

____ ____ packs extra glycogen into muscle cells in order to beat muscle fatigue.

Back 109

Carbohydrate loading

Front 110

These type of muscle fibers are referred to as the dark meat. They have abundant mitochondria, myoglobin and capillaries. They are adapted for aerobic respiration and fatigue resistance.

Back 110

Slow oxidative, slow-twitch or type I fibers

Front 111

This type of muscle fiber is referred to as the white meat. Fibers are well-adapted for quick responses but not for fatigue resistance. They are rich in enzymes of phosphagen and glycogen -lactic acid systems

Back 111

Fast-glycolytic, fast twitch, or type II fibers

Front 112

Muscle size, fascicle arrangement, motor unit size, multiple motor unit summation, temporal summation, length-tension relationship, and fatigue are all determinants of what?

Back 112

Muscle strength