Skeletal Muscles / Muscles

Question 1

What are the different types of muscle?

Answer 1

Skeletal (voluntary contractions)

Cardiac (myogenic)

Smooth (involuntary contractions)

Question 2

What is skeletal muscle and it’s components of a cell?

Answer 2

Occur at the joints in the skeleton as contractions enables joints to move.
They contract quickly and powerfully but fatigue quickly.

Cell membrane -sarcolemma

Cytoplasm - sarcoplasm

Endoplasmic reticulum - sarcoplasmic reticulum

Lots of mitochondria

Question 3

What is cardiac muscle?

Answer 3

Myogenic - can initiate its own rhythmic contraction

Powerful

Does not fatigue

Branched

Has a gap junction

Question 4

What is smooth muscle?

Answer 4

Slower contractions

Slow to tire

Contractions are involuntary

Used to push fluid through vessels and organs

Question 5

What is a neuromuscular junction?

Answer 5

Junction between a synapse and effector cell which is a muscle

Question 6

What happens at a neuromuscular junction?

Answer 6

1. Action potential opens voltage gated calcium channels
2. Calcium ions can diffuse into the axon tip and vesicles fuse to the membrane
   3 acetylcholine is exocytosed into the synaptic cleft and diffuses across the gap to bind to sodium channel receptors.
3. Sodium ion channels open and sodium ions enter the muscle fibre causing a depolarisation
4. Wave of depolarisation passes down the sarcolemma and down the muscle causing it to contract.

Question 7

What is slow twitch fibre and how is it adapted?

Answer 7

Contracts more slowly that fast twitch

Less powerful contractions but contractions occur over a longer period of time

Adapted for aerobic respiration:
Large store of myoglobin (stores oxygen)
Numerous mitochondria
Rich blood vessel supply

Used for maintaining posture

Question 8

What is fast twitch fibre and how is it adapted?

Answer 8

Contracts quickly and more powerfully however contractions last a shorter period of time.

Adapted for anaerobic respiration:
Increased concentration of enzymes involved in anaerobic respiration 
Increased concentration of glycogen
Stores of phosphocreatine (ADP ——> ATP)
Stores of phosphocreatine 

Used for intense movement and exercise

Question 9

What is actin?

Answer 9

A protein filament (myofibril component) which is thinner and consists of two strands twisted around one another

Question 10

What is myosin?

Answer 10

A protein filament (myofibril component) which is thicker and consists of long rod shaped tails with bulbous heads that project to the side

Question 11

What is tropomyosin?

Answer 11

Protein found in muscle which forms a fibrous strand around the action filament and blocks myosin binding sites on the action filaments

Question 12

Explain the process of muscle contraction

Answer 12

1. Depolarisation causes a release of calcium ions from the sarcoplasmic reticulum which diffuse into the myofibrils
2. The calcium ions cause the movement of tropomyosin (by binding to troponin) on the actin filaments.
3. The movement of tropomyosin exposes the myosin binding sites on the action filaments
4. Myosin head binds to the actin filament
5. Hydrolysis of ATP on myosin heads causes the myosin head to be come cocked(bend)
6. The bending pulls the action filaments across contracting this muscle fibre
7. New ARP molecules bind to each myosin head causing them to detach from the actin sites

Question 13

What is the role of phosphocreatine in providing energy during muscle contraction?

Answer 13

Phosphorylates other compounds which enables them to become more reactive
also enables ATP to be produced by donating a phosphate group to ADP.
The phosphocreatine molecules can easily be re-synthesised (ATP is used to reform phosphocreatine)
Phosphocreatine is not lost from cells

Question 14

What is the sliding filament hypothesis?

Answer 14

1. ATP binds to myosin head and the cross bridge between actin and myosin weakens (recovery stroke)
2. Hydrolysis of ATP enables the myosin head to become cocked
3. Myosin head attaches to the actin forming a cross bridge
4. The Pi (generated from hydrolysis of ATP) is released initiating the power stroke (pulling of the actin filament
5. ADP is released and the process repeats

Question 15

In a myofibril, what is the

I band

A band

M line

Z line

Sarcomere?

Answer 15

I band - only the actin filaments

A band - actin and myosin overlap

M line - only myosin filaments

Z line - end of the sarcomere

Sarcomere - length of filament between the two z lines of the actin filaments

Question 16

What happens to the I band when sarcomeres contract?

Answer 16

Shortens

Question 17

What happens to the A band when the sarcomeres contract?

Answer 17

Stays the same length

Question 18

Why is there a high supply of ATP in muscle cells?

Answer 18

To bind to myosin heads to get them in their high energy unstable states (cocked)

To pump calcium ions back into the sarcoplasmic reticulum (otherwise the muscles would be unable to become relaxed)

To form cross bridges between actin and myosin

To detach myosin heads from the actin filaments

Question 19

Which types of fibre is phosphocreatine found in and why?

Answer 19

Fast twitch

Less adapted for aerobic respiration and therefore must produce ATP anaerobically via phosphocreatine.