Contraction of Skeletal Muscle

Question 1

Define Motor Neuron

Answer 1

nerve cell that controls muscle contraction

Question 2

Define Neuromuscular junction

Answer 2

synapse between motor neuron and muscle cell

Question 3

Action potentials are initiated in response to CNS and travel

Answer 3

through motor neuron and arrive at synaptic terminal

Question 4

ACh is released from a motor neuron terminal in response to

Answer 4

an action potential in the motor neuron

Question 5

When ACh is released following an action potential

Answer 5

ACh diffuses across synaptic gap
ACh binds to receptors on chemically gated sodium channels
Sodium ions flow in
Muscle cell membrane depolarizes

Question 6

When do Chemically regulated channels close?

Answer 6

When ACh is no longer present

Question 7

What is AChE

Answer 7

Acetylcholine Esterase
Located in synaptic gap
Rapidly breaks down Acetylcholine

Question 8

Action potentials in the muscle cell membrane are conducted into the interior of the muscle via ____ and cause Ca 2+ ions to be released from the ____

Answer 8

Transverse Tubules

SR

Question 9

Action potential along T-tubule causes release of calcium to initiate contraction cycle:

Answer 9

1. Ca2+ binds to troponin and moves tropomyosin
2. Myosin head attaches to actin
3. Myosin head pivots and pulls on actin
4. Myosin head detaches with binding of ATP, breaking cross brdige

Question 10

When does the contraction cycle stop?

Answer 10

When calcium ion concentration falls to resting level

Question 11

What happens when AP depolarization ends and voltage gated Ca 2+ channels close?

Answer 11

Calcium ion flow stops

Ca2+ actively pumped out of sarcoplasm

Question 12

What does the duration of contraction depend on?

Answer 12

Duration of stimulation at nerve-muscle synapse
Presence of calcium ions in sarcoplasm
Availability of ATP

Question 13

Contraction ends and relaxation occurs when

Answer 13

AP stop in motor neuron
ACh Esterase breaks down ACh
ACh gated channels close
AP stop in sarcolemma and T tubules

Question 14

When do calcium ion levels in sarcoplasm return to resting levels?

Answer 14

Tropomyosin covers actin sites and no new myosin cross bridges can form

Question 15

True or false: Relaxation requires ATP

Answer 15

True

Question 16

Why does relaxation require ATP?

Answer 16

Needed to pump Ca2+ into SR and to disconnect myosin heads from actin

Question 17

What is rigor mortis?

Answer 17

Lack of ATP after death

Question 18

Define botulism

Answer 18

Blockage of release of ACh

Question 19

Define myasthenia gravis

Answer 19

Interference with binding of ACh to receptors

Question 20

Define polio

Answer 20

Loss of motor neuron

Question 21

Define peripheral nerve damage

Answer 21

Loss of motor neuron axon

Question 22

Define MS

Answer 22

Reduction of AP efficiency and damage to myelin

Question 23

Define tetanus

Answer 23

Excessive stimulation of motor neuron

Question 24

If you interfere with ACh Esterase activity, what would happen

Answer 24

Your heart would stop

Question 25

What is tension

Answer 25

Pulling strength

Question 26

Tension in a muscle depends on

Answer 26

• Tension in individual muscle cells during contraction

- Number of muscle cells that contract

Question 27

The amount of shortening of a muscle depends on

Answer 27

Tension and resistance

Question 28

How is tension produced

Answer 28

sarcomeres shorten, muscle cells shorten

Question 29

Tension can vary due to

Answer 29

length-tension relationship
Frequency of stimulation by motor neuron
Amount of cross bridges form

Question 30

What is the length tension relationship?

Answer 30

Idea that depending on how stretched or compressed a muscle might be, it will effect how much tension that muscle will produce

Question 31

What is a motor unit?

Answer 31

Collection of muscle cells that contract together at the same time, because they are all innervated by the same motor neuron

Question 32

Skeletal muscle contracts most forcefully over a

Answer 32

narrow range of resting legnths

Question 33

What is a twitch

Answer 33

cycle of contraction, relaxation produced by a single action potential in a muscle cell

Question 34

What are the 3 phases of a twitch?

Answer 34

1. latent phase
2. contraction phase
3. relaxation phase

Question 35

Describe the latent phase of a twitch

Answer 35

Action potential occurs

No contraction until Ca 2+ released from SR

Question 36

Describe the contraction phase of a twitch

Answer 36

Tension rises to peak
Ca2+ moves tropomyosin off actin sites
Myosin cross bridges form

Question 37

Describe the relaxation phase of a twitch

Answer 37

tension falls to resting levels
Ca2+ pumps back into SR
Actin sites covered by tropomyosin
No cross bridges remain

Question 38

Sustained muscular contractions are produced

Answer 38

by high frequency of action potentials in muscle cell or motor neurons

Question 39

Summation of tension produces

Answer 39

Greater tension

Question 40

Define Complete tetanus

Answer 40

You can hold something that maximum tension with a sustained contraction

Question 41

Define incomplete tetanus

Answer 41

You sustain a contraction without reaching maximum tension

Question 42

Summation occurs when

Answer 42

You have repeated stimulation produced before relaxation phase has been completed (build up of ca2+ ions in sarcoplasm)

Question 43

What is Tetanus disease

Answer 43

Clostridium tetani bacterial toxin causes high frequency of action potentials in motor neurons