Muscles

Question 1

What are the 3 types of muscle?

Answer 1

Skeletal, cardiac and smooth

Question 2

Give 3 features of cardiac muscle

Answer 2

-The cells are striated and branched
-Intercalated discs are present (for electrical conduction)
-The cells are uninucleate

Question 3

Give 3 features of smooth muscle and 2 examples of where you would find it

Answer 3

-cells are spindle shaped
-The cells are uninucleate
-The cells have no striations
Smooth muscle is found in the ciliary muscle and iris of the eye, the gut lining and the walls of arteries and veins

Question 4

Give 2 features of skeletal muscle

Answer 4

-cells are striated with banding patterns
-cells are multinucleate (with nuclei at the periphery of the cells)

Question 5

Smooth muscle and cardiac muscle are involuntary, whereas skeletal muscle is voluntary. What does this mean?

Answer 5

Their contractions are not under conscious control, unlike the muscles attached to our skeletons which we consciously control

Question 6

Describe the fine structure of skeletal muscle cells

Answer 6

-skeletal muscle cells are muscle fibres, surrounded by a sarcolemma (which folds inwards to form T-Tubules) under which the many nuclei are formed
-These muscle fibres have many myofibrils running down them lengthwise
-The myofibrils are made up of thick protein filaments called myosin and thinner protein filaments called actin, running lengthwise

Question 7

What is a sarcomere?

Answer 7

The sarcomere is the contractile unit of the myofibrils, running from Z line to Z line (the z line is the join between adjacent actin filaments)

Question 8

What causes striations and banding pattern typical of striated muscle?

Answer 8

The bands are due to the regular alternating pattern of actin and myosin, with the thicker myosin filaments forming darker striations and the thinner actin filaments forming less dense or lighter regions

Question 9

Label this sarcomere

Answer 9

See notes
Should include
-sarcomere
-M line
-H zone
-A band
-I band

Question 10

What is the A band composed of?

Answer 10

The A band is made up from both actin and myosin

Question 11

What is the I band composed of?

Answer 11

The I band is made up from actin filaments only

Question 12

What is the H zone composed of?

Answer 12

The H zone is made from myosin only

Question 13

What is sarcoplasma and sarcoplasmic reticulum?

Answer 13

Sarcoplasma is the cytoplasm of the muscle cells and sarcoplasmic reticulum is a system of membranes surrounding the muscle cells which store and release calcium ions

Question 14

Which bands are A, B and C cross-sections of?

A-small dots
B-smaller and larger dots
C-larger dots

Answer 14

A= I band
B= A band
C= H zone

Question 15

What occurs at the neuromuscular junction when an impulse arrives at the synaptic bulb?

Answer 15

1. An AP arrives at the synaptic bulb of a motor neurone
2. Calcium ions diffuse in, causing synaptic vesicles to move to and fuse with the motor end plate
3. The neurotransmitter, Ach diffuses across the cleft and attaches onto receptor sites on the sarcolemma
4. Positive sodium ions diffuse in via ion channels to cause depolarization
5. If threshold level is reached, an AP is set up in the T-Tubules

Question 16

Describe how contraction of the muscle is brought about via the sliding filament theory

Answer 16

1. The AP transmitted through the T-Tubules causes calcium ions to be released from the SR into the sarcoplasm
2. They bind onto blocking molecules (ancillary protein) on the actin filaments which results in binding sites for myosin being freed
3. The bulbous myosin heads form actomyosin cross-bridges as the attach to the actin binding sites followed by a rotation through 45°
4. This pulls the actin filaments across the actin and towards the centre of the sarcomere
5. ATP attached to the myosin head, hydrolyses, releasing the energy needed to detach the myosin head
6. Cycle of attachment, rotation and release of myosin heads continues in a ratchet-like mechanism until calcium ions run out or nervous stimulation stops
7. As many sarcomeres lying end to end, in many fibres, shorten during contraction, the overall result is that the muscle contracts

Question 17

How is muscle contraction made powerful?

Answer 17

It is powerful due to the fact that many parallel, side by side myofibrils in many muscle fibres all contract at once

Question 18

What factors may influence the strength of contraction?

Answer 18

-Length or time the muscle is stimulated for
-The number of muscle fibres being stimulated
-The frequency of the signals to contract

Question 19

Describe how a sarcomere changes during contraction

Answer 19

-Overall length shortens as distance from z line to z line decreases
-The H zone become shorter
-The I band becomes shorter
-THE A BAND STAYS THE SAME