Muscle Structure and Contraction

Question 1

Sarcomere

Answer 1

A subunit that goes from Z-line to Z-line, including actin and myosin myofilaments

Question 2

Actin

Answer 2

Thin and light, looks like beads

Question 3

Mysoin

Answer 3

Thick and dark, its heads look like butts

Question 4

What happens in a sarcomere when a muscle contracts?

Answer 4

The actin and myosin slide past each other and the sarcomere length gets shorter. However, actin and myosin stay the same length. Also, cross-bridges are formed.

Question 5

Cross-bridge

Answer 5

When myosin heads are attached to actin binding sites, this will only happen when calcium is released from the sarcoplasmic reticulum and tropomyosin is removed from blocking the actin binding sites

Question 6

Go through steps of muscle contraction

Answer 6

neurotransmitter is released from axon terminal(synaptic vesicles) of a neuron

Neurotransmitter crosses the synaptic cleft and attaches onto the receptors of the post-synaptic cell

An action potential has now been created with Na+ and it will travel down the sarcolemma, T-tubules, and throughout the muscle cell.

This action potential will trigger Ca2+ to leak from the sarcoplasmic reticulum and it will be let out into the sarcoplasm

Then the Ca2+ will bind to the troponin on the actin and tropomyosin will move off of the actin binding sites

Then the myosin will release p then grab the actin and form cross-bridges by latching onto its binding sites

Then the myosin pulls the actin aka a power stroke and then it releases ADP

Next, the myosin will have ATP binding to it which will release the actin and reset it for the next power stroke. They are reset by separating ATP into ADP and P again and the energy becomes stored in the myosin head for the next power stroke. This is when ATP is used up and if there is still calcium in the sarcoplasm then the muscle will continue contracting. If not, it will relax.

Question 7

Practice labeling a muscle cell

Answer 7

Muscle cell
Nucleus
Myofibrils
Sarcomeres
SR
T-tubules

Question 8

Practice labeling sarcomere

Answer 8

Sarcomere
Actin
Myosin
Titin
Z-line
Troponin
Tropomyosin
Calcium
ADP/P
ATP

Question 9

Titin

Answer 9

Holds myosin in position; is the reason that myosin and actin don’t touch

Question 10

What does the SR store?

Answer 10

Calcium

Question 11

Which neurotransmitter is released from the nerve to activate muscle cells?

Answer 11

Acetylcholine

Question 12

What happens to the muscle cell once AcH is bound to the outside?

Answer 12

Na+ goes into the muscle and creates an action potential

Question 13

What causes muscles to contract (where does the movement come from)?

Answer 13

Myosin heads pivot pulling actin inward

Question 14

What must happen first for a muscle to relax?

Answer 14

ACh is removed from muscle cell membrane

Question 15

Which enzyme is responsible to aiding the relaxation of the muscle by its actions in the synapse?

Answer 15

Acetylcholinerase