Skeletal muscle

Question 1

What is skeletal muscle

Answer 1

Voluntary - we can control them, regulate body temperature and control posture etc

Converts chemical energy (ATP) into mechanical energy

Question 2

What does the perimysium do?

Answer 2

Coating.
Allows the muscles to slide over each other so less friction when more muscles are being activated

Question 3

What is the muscle fasciculus

Answer 3

A bundle of muscle fibres

Question 4

What is a muscle fibre (myocyte)?

Answer 4

Cylindrical, multinucleated cells composed of many myofibrils

Question 5

What is a myofibril?

Answer 5

The basic rod-like unit of a muscle cell

Question 6

What are myofilaments?

Answer 6

The myofibril’s thick, thin and elastic filaments.

Question 7

What are myosin filaments?

Answer 7

The thick filaments

Question 8

What is the functional unit of contraction called?

Answer 8

Sarcomere

Question 9

what are F-actin filaments

Answer 9

The thin filaments

Question 10

What are Titin filaments

Answer 10

Elastic filaments that run through the core of each myosin filament and anchor it to the Z-line (so myosin filaments don’t move)

Question 11

Light microscope originally revealed ____ bands and ____ bands.
Fine dark lies called _____ bisect the _____ bands

Answer 11

1. light (i bands)
2. dark (A bands, A in dArk)
3. Z-lines
4. light

Question 12

What is the sliding filament theory in terms of muscle contraction?

Answer 12

Describes the mechanism of muscle contraction

The thick and thin filaments slide over one another

Hence neither of the thick or thin filaments shorten

During contraction, the H-zone becomes narrower

The elastic titin filaments keep the thick filament in a central position

Question 13

What function do myosin head groups have?

Answer 13

They bind to the actin (there’s an actin binding site on the head group)

Myosin headgroup has an ATPase site so ATP will be hydrolysed. The energy from hydrolysis of ATP will be used in the contraction process

Question 14

What does Tropomyosin do in the thin filaments?

Answer 14

A protein that binds to and stabilizes actin filaments in cells.

Question 15

What does Tropomyosin do in skeletal and cardiac muscle cells?

Answer 15

It’s released after interacting with troponin and calcium

Facilitates the binding of actin to myosin that causes muscle contraction

Question 16

How do the myosin head group and actin interact if the actin’s myosin binding site is blocked by the tropomyosin?

Answer 16

In the presence of calcium ions

1. Calcium ions bind to troponin which troponin will go through a conformational change.
2. Then tropomyosin will go through a conformational change
3. which will result in exposure of myosin binding sites on the actin molecules.

Question 17

Where does the calcium come from that enables the binding between myosin head group and actin?
(HARD)

Answer 17

skeletal muscle is voluntary muscle therefore contraction requires nervous impulse

1. impulse is transferred from a neuron to the sarcolemma of a muscle cell
2. Impulse travels along sarcolemma and down the T-Tubules. Then, passes to the sarcoplasmic reticulum (SR)
3. As impulse travels down SR the calcium gates in membrane of SR open.
   As a result, calcium ions diffuse out of SR and among the myofilaments.
4. Calcium fills the binding sites in the troponin molecules which alters shape and position of the troponin to then cause movement of the attached tropomyosin molecule.
5. movement of tropomyosin permits the myosin head to bind to the actin

Question 18

When does a sarcomere shorten?

Answer 18

When myosin heads and thick myofilaments form crossbridges with actin molecules and thin myofilaments

Question 19

How does the myosin head become activated before the cross bridge cycle can begin?

Answer 19

When ATP binds to the myosin head and is hydrolysed to ADP and inorganic phosphate.

The energy released from the hydrolysis of ATP activates the myosin head, forcing it into the “cocked” position

Question 20

What is the cross bridge cycle? (HARD)

Answer 20

1. CROSS BRIDGE FORMATION

The activated myosin head binds to actin and forms a cross bridge. Inorganic phosphate is released. The bond between myosin and actin become stronger

2. THE POWER STROKE

ADP is released. The activated myosin head pivots, sliding the thin myofilaments toward the centre of the sarcomere

3. CROSS BRIDGE DETACHMENT

When another ATP binds to the myosin head, the link between myosin and actin weakens. Myosin head detaches.

4. REACTIVATION OF MYOSIN HEAD

ATP is hydrolysed to ADP and inorganic phosphate. The energy released during hydrolysis reactivates the head, returning it to the cocked position

Question 21

When does cross bridge cycling end?

Answer 21

When calcium ions are actively transporter back into the sarcoplasmic reticulum.

Question 22

How much does a single power stroke shorten the muscle?

Answer 22

By approximately 1% of the entire muscle. Therefore, to achieve an overall shortening of up to 35%, the whole process must be repeated many times

Question 23

3 gradations of skeletal muscle contractions. And give their definitions

Answer 23

Twitch = single contraction and relaxation cycle produced by an action potential within the muscle fibre itself

Summation = if a twitch happens and then another twitch happens before the first one relaxes then the power can be added as a summation onto the previous twitch

Tetanus = if summation is done frequently enough then they will all contract to a maximum level

Question 24

What happens when a motor neuron(unit) is stimulated? What’s the all-or-none principle?

Answer 24

Consists of a neuron and all the muscle fibres connected to it

When a neuron is stimulated, all of its fibres will contract completely

This is called the all or none principle

The more motor units stimulated, the stronger the muscle contraction

Question 25

What’s the size principle (motor units)?

Answer 25

A motor neuron with a small number of fibers will have a certain amount of tension.

If want to increase this tension then need to recruit the motor neurons that have larger and more fibers to achieve the desired strength of contraction