Muscle Contraction

Question 1

What are the four stages of muscle contraction?

Answer 1

1. Excitation
2. Excitation-Contraction Coupling
3. Contraction
4. Relaxation

Question 2

What is Excitation in muscle contraction?

Answer 2

Excitation is the communication between the neuron and muscle cell. This leads to excitation of the muscle cell aka ACTION POTENTIAL

Question 3

What is Excitation-Contraction coupling?

Answer 3

It is the conversion of action potential in muscle cell to activation of proteins in the sarcomere

Question 4

What is Contraction?

Answer 4

Muscles develop tension and may shorten -> SLIDING FILAMENT THEORY

Question 5

What is Relaxation in the muscle?

Answer 5

Relaxation is the return of muscle cells to resting length

Question 6

What occurs DURING excitation?

Answer 6

1. The action potential from motor neurons reaches end of axon
2. Voltage-gated Ca 2+ channels open
3. Ca 2+ enters the neuron and causes synaptic vesicles to release Ach into the synapse
4. Ach binds to chemical-gated ion channel in the motor end plate (CHOLINERGIC RECEPTOR)
5. Sodium (Na +) rushes into the cell, some potassium (K+) –> DEPOLARIZATION

Question 7

What happens after depolarization from EPP?

Answer 7

Muscle cell reaches threshold leading to action potential

Question 8

What OCCURS during Excitation-Contraction coupling?

Answer 8

1. Action potential travels across sarcolemma and DOWN the sarcolemma of T-tubules
2. Action potential triggers VOLTAGE-GATED + channels in T-tubules to open which are connected to MECHANICALLY-GATED Ca+ channels in SR
3. the opening of mech-gated ca+ channels in SR releases Ca+ into sarcoplasm

Question 9

What are the steps of Contraction?

Answer 9

1. Myosin hydrolyzes an ATP molecule which produces ADP + P; this will activate myosin head in an extended position
2. Myosin binds to actin active site and forms a cross-bridge between actin and myosin (ADP + P still bound to myosin)
3. Cross-bridge causes release of ADP + P; myosin head will flex and thin filament will slide past thick
4. Another ATP molecule will bind to myosin breaking this cross bridge; ATO immediately hydrolyzes and goes back to step 1

Question 10

What OCCURS during relaxation?

Answer 10

1. Action potentials in axon cease and no more Ach is released from neuron
2. AchE (Acetylcholinesterase) will break down remaining Ach
3. Calcium pumps use ATP to move calcium back into SR

Question 11

What is a muscle twitch?

Answer 11

Troponin-tropomyosin complex covers active sites and due to lack of calcium myosin wont bind; Sarcomere and Muscle cells will return to resting length

Question 12

At the neuromuscular junction, an electrical signal from the motor neuron is translated to a chemical signal (via the secretion of neurotransmitter) and then back to an electrical signal in the muscle cell. What proteins interact with the released neurotransmitter to cause the electrical signal in the muscle cell?

Answer 12

Cation Chemical-gated channels

Question 13

What processes directly require binding of or the use of ATP?

Answer 13

1. Release of cross-bridge (interaction) between actin and myosin.
2. Movement of calcium ions back into the sarcoplasmic reticulum after contraction ends.
3. Conformation change of myosin from the bent conformation to the extended (activated) conformation.

Question 14

Where are chemically-gated channels found in the process of muscle contraction?

Answer 14

Sarcolemma

Question 15

What would happen if someone stabbed your leg with a syringe full of calcium and injected the calcium directly into the sarcoplasm of your muscle cells?

Answer 15

Cross-bridges would form in the absence of an action potential from a motor neuron.

Question 16

What is the calcium pump?

Answer 16

Active transport protein

Question 17

What does AchE do?

Answer 17

breaks down Ach in synaptic cleft

Question 18

Transverse tubules are extensions of which of the following organelles?

Answer 18

Extensions of the Sarcolemma

Question 19

True or False: If calcium protein channels in the sarcoplasmic reticulum (SR) open in response to an action potential, calcium diffuses out of the sarcoplasm and into the SR.

Answer 19

FALSE; Because the SR has a high Ca+ concentration, calcium will diffuse INTO the sarcoplasm if protein channels are open

Question 20

What proteins directly interact during a “cross-bridge” formation?

Answer 20

Actin and Myosin

Question 21

What proteins hydrolyzes ATP during contraction?

Answer 21

Myosin

Question 22

What two roles does ATP play during the contraction stage?

Answer 22

Release myosin from actin active sites and To cause myosin to change shape to the extended position

Question 23

What event occurs during an end-plate potential?

Answer 23

A net movement of positive charge into the cell (Na+)

Question 24

The presence of T-tubules ensure that ___________ myofribils will contract after excitation occurs compared to a cell with no T-tubules.

Answer 24

More; T-tubules help to propagate the action potential deep into the muscle cell. This causes a sufficient amount of calcium to be released into the muscle cell so maximum myofibrils will contract

Question 25

What structures form the “triad” of skeletal muscle cells

Answer 25

SR and T-tubules

Question 26

The botulism toxin (BOTOX) prevents neurotransmitters from being released at the neuromuscular junction. What is one possible mode of its action?

Answer 26

Blocks calcium from associating with vesicles (paralysis of muscles)

Question 27

What is the role of the sarcoplasmic reticulum?

Answer 27

Stores Ca+

Question 28

True or False: If ACh is unable to bind to ACh receptors at the motor end plate of a muscle cell, that muscle cell will not contract even in the presence of an action potential from the motor neuron.

Answer 28

TRUE