muscles 2

Question 1

Motor Neuron

Answer 1

nerve cell that controls muscle contraction

Question 2

neuromuscular junction

Answer 2

synapse between motor neuron and muscle cell

Question 3

how is action potential initiated?

Answer 3

• travels through motor neuron and arrives at synaptic terminal
• initiated in motor neuron in response to CNS commands

Question 4

Where does control of skeletal muscle activity occur?

Answer 4

neuromuscular junction

Question 5

How does AP in motor neuron cause ACh to be released?

Answer 5

• ACh diffuses across synaptic gap

- ACh binds to receptors on chemically gated sodium channels in muscle membrane

Question 6

what happens before and after sodium ions flow into muscle cell?

Answer 6

Before: ACh binds to receptors on chemically gated sodium channels in muscle membrane
After: depolarizes the muscle cell membrane and starts an action potential in the muscle cell

Question 7

How long do chemically regulated gates stay open?

Answer 7

As long as ACh is present

Question 8

What does Acetylcholine Esterase (AChE) do and where is it located?

Answer 8

located: synaptic gap

rapidly breaks down Acetyl Choline

Question 9

Excitation of muscle cell causes the action potential to spread where?

Answer 9

Across the entire muscle cell membrane including the T tubules

Question 10

Action potential along T-tubule causes what?

Answer 10

release of Ca from citernae of SR

Question 11

List the steps of the contraction cycle

Answer 11

1) Ca binds to troponin, moving tropomyosin
2) attachment of myosin head to actin
3) pivot of myosin head pulls on actin
4) detachment of myosin head w/ binding of ATP

Question 12

How does Ca ion concentration return to resting level?

Answer 12

AP depolarization ends, voltage gated Ca channels in SR close
-Ca ion flow into sarcoplasm stops

Question 13

How is Ca transported out of sarcoplasm?

Answer 13

• across sarcolemma to outside of cell
• across sarcoplasmic reticulum membrane into SR
• requires ATP

Question 14

Duration of contraction depends on?

Answer 14

1) Duration of stimulation at nerve-muscle synapse (neuromuscular junction)=continued release of ACh and multiple AP in muscle fiber
2) Presence of Ca ions in sarcoplasm till Ca returns to resting level
3) Availability of ATP, needed to power myosin head

Question 15

Contraction ends and relaxation occurs when?

Answer 15

• Action potentials stop in motor neuron
• AChE breaks down ACh in neuromuscular synaptic gap
• ACh gated channels close, sodium ion influx stops
• AP stop occurring in sarcolemma and T-tubules

Question 16

Why does relaxation require ATP?

Answer 16

• ATP needed to pump Ca into the SR
• ATP needed to disconnect myosin heads from actin
• Rigor mortis- lack of ATP after death

Question 17

What does Ca ion resting levels do during relaxation?

Answer 17

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

Question 18

botulism

Answer 18

blockage of release of ACh

Question 19

myasthenia gravis

Answer 19

interference w/ binding of ACh to receptors

Question 20

polio

Answer 20

loss of motor neuron

Question 21

peripheral nerve damage

Muscular system disorder

Answer 21

loss of motor neuron axon

Question 22

MS

Answer 22

reduction of AP efficiency, damage to myelin

Question 23

tetanus

Answer 23

excessive stimulation of motor neuron

Question 24

Tension depends on

Answer 24

• tension that develops in individual muscle cells during contraction
• number of muscle cells that contract

Question 25

What causes sarcomere shortening?

Answer 25

The sliding of actin and myosin filaments

Question 26

What causes muscle cells to shorten?

Answer 26

all sarcomeres shortening

Question 27

Amount of shortening depends on?

Answer 27

tension and resistance

Question 28

Tension produced in individual muscle fibers can vary due to?

Answer 28

• length-tension relationship

- frequency of stimulation by motor neuron

Question 29

Tension produced by entire muscle depends on?

Answer 29

• # of muscle cells receiving nerve stimulation, commanding them to contract
• muscle cells are grouped in motor units

Question 30

skeletal muscle contracts most forcefully over?

Answer 30

A narrow ranges of resting lengths

Question 31

Tension and the number of cross bridges formed depends on?

Answer 31

Degree of overlap of actin and myosin filaments

Question 32

What is a twitch?

Answer 32

• cycle of contaction, relaxation produced by a single AP in a muscle cell
• not typical in normal muscle activity

Question 33

Twitch, Latent phase

Answer 33

Action potential occurs

-no contraction until Ca is released from SR

Question 34

Twitch, Contraction phase

Answer 34

Tension rises to peak

• Ca moves tropomyosin off of actin sites
• myosin cross bridges form,actin is pulled

Question 35

Twitch, Relaxation phase

Answer 35

Tension falls to resting levels

• Ca is pumped back into SR
• Actin sites covered by tropomyosin
• No cross bridges remain

Question 36

Sustained muscular contractions are produced by?

Answer 36

• high frequency of action potentials in muscle cell

- produced in response to high frequency of acton potentials in motor neuron (high frequency of stimulation)

Question 37

complete tetanus

Answer 37

maximum tension production in a muscle cell-maximum cross bridge formation

Question 38

“Tetanus” disease

Answer 38

• caused by Clostridium tetani bacteria

- bacterial toxin causes high frequency of action potentials in motor neurons