Skeletal Muscle

Question 1

What are the functions of muscles?

Answer 1

Movement (skeletal, intestinal, cardiac).
Static support.
Heat production.

Question 2

What are the three layers of muscle?

Answer 2

Epimysium, perimysium and endomysium.

Question 3

How are parallel muscles organised?

Answer 3

Fascicles all have a common point of attachment and are parallel to one another.

Question 4

How are circular muscles organised?

Answer 4

A ring of muscle that surrounds a bodily opening. It constricts and relaxes to control blood flow.

Question 5

How are pennate muscles organised?

Answer 5

Feather shaped. Fascicles attach at an angle to a central tendon. Can be unipennate, bipennate or multipennate.

Question 6

What are the miscellaneous shapes of muscles?

Answer 6

Fusiform.
Quadrate.
Triangular.
Longitudinal.
Convergent.

Question 7

Define tendon.

Answer 7

Connects muscles to bone.
Tough and round.
Some muscles share a common tendon.

Question 8

Define aponeurosis.

Answer 8

Connects muscles to muscles.
Delicate and flat.

Question 9

What do tendons and aponeuroses have in common?

Answer 9

Made of dense fibrous CT.
They don’t shorten.
They alter force direction.

Question 10

What can myotomes and dermatomes test for?

Answer 10

Lesions of the spinal cord.
Motor or sensory loss can be checked by testing joint movement or an area of skin.

Question 11

Describe skeletal muscle.

Answer 11

Bundles of fibres.
Attached to bones by tendons.
Muscles are arranged in lever systems - amplifies muscle shortening velocity and manoeuvrability.

Question 12

Describe skeletal muscle cells.

Answer 12

Multinucleate (on the periphery).
Formed by mononucleate myoblasts (does not replace cells if damaged).

Question 13

How are they replaced if damaged?

Answer 13

Satellite cells replace muscle cells by differentiation.
Other fibres undergo hypertrophy.
Muscles never fully recover.

Question 14

Only myosin is?
Ends of sarcomere?
Myosin and actin in a sarcomere?
Middle of sarcomere?

Answer 14

H zone.
Z lines.
A band.
M line.

Question 15

How are filaments organised in muscle, and how does this help function?

Answer 15

Myosin - triangles.
Actin - hexagons.
Striations and regular arrangements - very strong, can generate a lot of force.

Question 16

What occurs during muscle shortening?

Answer 16

I band and H zone reduces.

Question 17

Describe the cross-bridge cycle.

Answer 17

1. An increase of [Ca2+] causes myosin to bind with actin.
2. ADP and Pi detach, causing movement.
3. ATP binds to myosin and causes myosin to detach from actin.
4. ATP is hydrolysed and this energises the cross-bridge for the cycle.

Question 18

Describe tropomyosin and troponin.

Answer 18

Tropomyosin - covers the binding site.
Troponin - holds tropomyosin in position.
Ca2+ binds to troponin and alters the shape, causing tropomyosin to pull away.

Question 19

Describe excitation-contraction coupling.

Answer 19

1. An AP in muscle occurs.
2. Ca2+ is released from lateral sacs.
3. Ca2+ binds to troponin and moves tropomyosin.
4. Cross-bridge occurs.
5. Ca2+ is taken up into the SR.
6. Troponin restores tropomyosin position.

Question 20

Where is Ca2+ stored?
Where does depolarisation spread down?

Answer 20

Sarcoplasmic reticulum.
T-tubules.