Structure of Skeletal Muscle and Sliding Filament Theory

Question 1

List the 6 structures of a skeletal muscle.

Answer 1

1. Epimysium.
2. Fascicle.
3. Perimysium.
4. Muscle Fibre.
5. Endomysium.
6. Myofibril.

Question 2

What is the epimysium?

Answer 2

A connective tissue sheath that surrounds each muscle.

Question 3

What is the Fascicle?

Answer 3

A bundle of skeletal muscle fibres surrounded by the perimysium.

Question 4

What is the perimysium?

Answer 4

Connective tissue which surrounds each bundle of muscle fibres.

Question 5

What is the muscle fibre?

Answer 5

Surrounded by a plasma membrane that contains sarcoplasm. Muscle fibre is composed of many fibrils, which give the cell its striated appearance.

Question 6

What is the endomysium?

Answer 6

Connective tissue which surrounds each muscle fibre.

Question 7

What is the myofibril?

Answer 7

Small thread-like strands that run through each muscle fibre.

Question 8

Outline the 5 steps of the sliding filament theory.

Answer 8

1. A neurochemical stimulation, causes calcium ions to be released from the sarcoplasmic reticulum into the sarcomere prompting a reaction in each muscle fibre between the myosin and actin filaments.
2. The binding sites are revealed for myosin to attach to actin via myosin heads which create cross-bridges. These cross bridges attach and reattach at different times along the actin pulling on them to create movement and maintain tension. The breakdown of ATP releases energy to stimulate cross bridges.
3. This causes the actin to move into the centre of the sarcomere, shortening the myofibril and causing the actin and myosin filaments to be almost fully overlapped when in a fully contracted position. The H zone and I band disappear.
4. As each sarcomere shortens so does the total length of each muscle fibre.
5. When the contraction finishes, the myosin and actin filaments return to a relaxed position. ATP releases energy causing myosin to detach from the actin and the cross bridge is broken. Calcium is reabsorbed.

Question 9

What is the H zone?

Answer 9

The distance between actin filaments.

Question 10

What is the A band?

Answer 10

The length of the myosin filament.

Question 11

What is the I band?

Answer 11

The distance from the edge of myosin to the z-line.

Question 12

What is the z-line?

Answer 12

Edge of the sarcomere.