Skeletal Muscle Structure and Function

Question 1

Are smooth muscles fully under voluntary control?

Answer 1

No.
It lines the inside of hollow organs.

Question 2

Is cardiac muscle fully under voluntary control?

Answer 2

No.
It is muscle that is only located in the heart.

Question 3

Is skeletal muscle fully under voluntary control?

Answer 3

No, but it mostly is.
This type of muscle applies force to bones in order to move and keep structure.

Question 4

What type of cells are muscles made up of?

Answer 4

Fibres, and their primary function is to generate force via contraction

Question 5

What are the jobs of skeletal muscle?

Answer 5

To generate force via contraction, important for movement and posture, support and protection for soft internal organs, provides voluntary control over major openings in the body, converts energy to heat which is used to maintain core temperature.

Question 6

What are the bundles of muscle fibres called?

Answer 6

Fascicles

Question 7

What are bundles of fascicles called/what do these bundles make?

Answer 7

Muscles

Question 8

Fibres, Fascicles and muscles contain many blood vessels, nerves and are sheathed in connective tissue. Why is this?

Answer 8

Blood vessels: bring in nutrients to the muscle and remove waste products from the muscle.
Nerves: connect to brain to control movements (send messages)
Connective tissue: So that the muscle fibres don’t rub against each other and get worn down/frayed

Question 9

Connective tissue is gathered together at the end to form what that connects muscles to bones?

Answer 9

Tendons

Question 10

Why do muscle fibres contain lots of nuclei?

Answer 10

Because lots and lots of tiny cells line up and then fuse together to form the fibres.

Question 11

What are the repeating units that make up the bundles of myofibrils that make up muscle fibre called?

Answer 11

Sarcomeres

Question 12

What are the two types of filaments/contractile proteins called that make up sarcomeres?

Answer 12

Actin (thin filaments)
Myosin (thick filaments)
The organisation of these filaments give the muscle its striated (striped) appearance

Question 13

What is the cell membrane called that lines the muscle fibre?

Answer 13

Sarcolemma

Question 14

What are the tube-like extensions of sarcolemma called?

Answer 14

Transverse Tubules (T-tubules).
Their job is to conduct electrical signals deep into the core of the fibre

Question 15

What is sarcoplasmic reticulum (SR)?

Answer 15

An extensive membrane network associated with the T tubules at regular intervals

Question 16

What is the job of SR (sarcoplasmic reticulum)?

Answer 16

To take up a store of calcium ions (Ca2+) while the muscle is relaxed, and then to release the calcium into the cytoplasm when the muscle contracts.

Question 17

What is Excitation-Contraction coupling?

Answer 17

It is the pairing of a signalling event (excitation of the muscle cell) with a mechanical event (contraction of the muscle cell).

Question 18

What are the three key proteins that participate in excitation (the signalling event)?

Answer 18

The voltage-gated sensor, The ryanodine receptor, The SR Calcium ATPase

Question 19

What does the voltage-gated sensor do?

Answer 19

Receives signals from the t-tubules and interacts with the ryanodine receptors

Question 20

What does the ryanodine receptor do??

Answer 20

It is a passive calcium channel on the SR that can open to allow Ca2+ out into the cell

Question 21

What does the SR calcium ATPase do?

Answer 21

An active calcium pump that used ATP to move Ca2+ back into the SR against its concentration gradient, ending the excitement.

Question 22

When is EC-Coupling initiated?

Answer 22

When a signal is transmitted down the T-tubules.
The signal is coming from the nerves running throughout the muscle.

Question 23

What happens when the excitation signal gets to the cell?

Answer 23

The voltage sensor is activated, interacting with the nearby ryanodine receptors causing them to open. Once it opens calcium rushes out of the SR and into the cell (bc it is a passive channel). It diffuses into the cell and activates the microfilaments, causing a contraction.

Question 24

How does relaxation occur?

Answer 24

Calcium must be removed from the cell and be put back into the SR. This happens by the SR Calcium ATPase pump, which senses a rise in the intracellular calcium. It burns some ATP to produce energy and then uses that energy to pump calcium back into the SR, against the concentration gradient. This stops the signalling event and the muscle relaxes.