Muscle

Question 1

What are the 3 types of muscle?

Answer 1

Cardiac muscle.
Smooth muscle.
Skeletal muscle.

Question 2

Which muscle types are involuntary?

Answer 2

Cardiac and smooth

Question 3

How are cardiac muscle fibres specialised?

Answer 3

They are myogenic (excitatory and conductive so contract without nervous stimulation)
Intercalated disks containing gap junctions allowing the passage of ions in depolarisation, letting excitation waves spread quickly through cardiac muscle cells.

Question 4

Does cardiac muscle fatigue?

Answer 4

No

Question 5

How does the micrograph of cardiac muscle appear?

Answer 5

Branched, striated, intercalated disks visible.

Question 6

Where is smooth muscle found?

Answer 6

In internal organs and vessels such as arterioles and the bladder.

Question 7

What shape are smooth muscle cells?

Answer 7

Spindle shaped

Question 8

Does smooth muscle fatigue?

Answer 8

Yes but not nearly as much as skeletal muscle.

Question 9

How does smooth muscle appear under a microscope?

Answer 9

Spindle-shaped cells, non-striated.

Question 10

What is the speed of contraction like in smooth muscle compared to cardiac and skeletal?

Answer 10

Very slow.

Question 11

What are the defining features of skeletal muscle contraction?

Answer 11

Fast and strong contraction.

Question 12

What are the defining features of skeletal muscle cells?

Answer 12

They can be multinucleated.

Contain multiple myofibrils made out of actin and myosin filaments.

Question 13

How does skeletal muscle appear under a microscope?

Answer 13

Tubular shaped cells, all aligned.
Striated cells.
Can be multinucleated

Question 14

What is the name for the plasma membrane of a muscle fibre (cell)?

Answer 14

The sarcolemma

Question 15

What is a sarcomere?

Answer 15

A subsection of a myofibril.

The space from one Z-line to the next.

Question 16

Which muscle fibres are thick and which are thin?

Answer 16

Myosin is thick.

Actin is thin.

Question 17

What happens to the Z-lines during contraction?

Answer 17

They get closer together.

Question 18

What happens to the H-band during contraction?

Answer 18

It gets smaller.

Question 19

What is the A-band?

Answer 19

The dark region of the sarcomere, the length of the thick myosin filaments.

Question 20

What kind of molecule is myosin?

Answer 20

Fibrous protein

Question 21

What kind of molecule is actin?

Answer 21

Globular protein

Question 22

What molecules make up the actin filament?

Answer 22

3 actin chains reinforced by tropomyosin bands with troponin forming the troponin-tropomyosin complex.

Question 23

What is the role of the troponin-tropomyosin complex?

Answer 23

Tropomyosin reinforces the structure.

The complex prevents myosin heads binding to the actin filaments when the muscle is relaxed.

Question 24

What happens when an impulse arrives at the neuromuscular junction?

Answer 24

The action potential causes the uptake of calcium ions into the synaptic bulb.
The intake of Ca2+ ions cause vesicles to fuse with the pre-synaptic membrane releasing acetylcholine into the cleft.

Question 25

What effect does the release of acetylcholine into the cleft of the neuromuscular junction have?

Answer 25

Acetylcholine binds to receptors on the sodium ion channels of the sarcolemma, causing Na+ ions to diffuse into the sarcolemma causing depolarisation.

Question 26

What happens at the neuromuscular junction once the sarcolemma begins to depolarise?

Answer 26

The wave of depolarisation travels down T-tubules into the muscle fibre, stimulating the release of calcium ions from the sarcoplasmic reticulum into the myofibril.

Question 27

What effect do the calcium ions have in the myofibril?

Answer 27

Troponin binds to Ca2+, changing the shape of the troponin-tropomyosin complex, unblocking binding sites on the actin filaments.

Question 28

What happens in the myofibril once the binding sites on actin filaments have been unblocked?

Answer 28

The myosin heads attach forming cross-links and perform a powerstroke, pulling the sarcomere together.

Question 29

Once the myosin heads have performed a powerstroke, what must happen for the cycle to repeat and the sarcomere to contract further?

Answer 29

ATP is hydrolysed, breaking the myosin-actin cross links and causing the myosin head to detach and reattach further along.

Question 30

What happens during muscle relaxation?

Answer 30

Nervous stimulation stops. Ca2+ ions are actively transported back into the sarcoplasmic reticulum. The troponin-tropomyosin complex blocks binding sites on the actin filaments. Acetylcholinesterase breaks down acetylcholine in the cleft of the neuromuscular junction.

Question 31

What is the role of creatine phosphate in muscle contraction?

Answer 31

Creatine phosphate supplies phosphate ions to ADP during muscle contraction, forming ATP. Creatine phosphate is a quick source of ATP for the muscle, and must be phosphorylated in the mitochondria after contraction.

Question 32

What is ATP required for in the contraction of skeletal muscle?

Answer 32

ATP is required to break the cross-links between myosin heads and the binding sites on actin filaments. ATP is required to actively transport Ca2+ ions back into the sarcoplasmic reticulum after muscle contraction has taken place.