Practice Questions - Week 8 - Muscle

Question 1

In a myofibril, actin binding sites and an ATPase are normally found on the?

a) double helix of actin

b) cross-bridges of thin filaments

c) troponin complex

d) cross-bridges of thick filaments

e) tropomyosin

Answer 1

d)

Question 2

Which of the following statements about the sliding filament mechanism of muscle contraction is FALSE?

a) One cross bridge cycle only decreases the sarcomere length by approximately 20 nm.

b) Shortening of the myofibril is active.

c) A single action potential causes a shortening of around 1 % of the length of the sarcomere.

d) The cross-bridge cycle is repeated many times following just a single action potential.

e) Lengthening of the myofibril is passive.

Answer 2

c)

Question 3

Which of the following statements about thick filaments is/are TRUE?

1. Thick filaments are in the order of 12-18 nm in diameter.
2. Thick filaments are around 1.6 microns in length.
3. Each thick filament is made up of a large number of molecules of the protein MYOSIN all packed together.

a) Only 1

b) 1, 2 & 3

c) Only 3

d) Only 2 & 3

e) Only 2

Answer 3

b)

Question 4

Which of the following is NOT a feature of a muscle fibre at rest?

a) The sarcoplasmic Ca2+ concentration is very low.

b) The myosin cross-bridges have been “primed” by the breakdown of ATP by the ATPase present on the cross bridges.

c) The ADP produced by the hydrolysis of the ATP remains bound to the ATPase on the cross-bridge.

d) The endoplasmic reticulum concentration of Ca2+ is very low.

e) Interactions between the myosin cross-bridges and the actin thin filaments are prevented by the tropomyosin filaments.

Answer 4

d)

Question 5

Acetylcholine release from the axon terminals of motoneurones is initiated by which of the following?

a) Opening of voltage-gated Ca2+ channels.

b) The presence of an action potential in the muscle fibre.

c) Opening of ligand-gated Ca2+ channels. *

d) Endocytosis.

e) The release of Ca2+ from the sarcoplasmic reticulum.

Answer 5

c)

Question 6

The troponin complex contains three polypeptides which have binding sites for which of the following?

1. Tropomyosin.
2. Actin
3. Ca2+

a) 1, 2 & 3

b) Only 2 & 3

c) Only 2

d) Only 3

e) Only 1

Answer 6

a)

Question 7

If a muscle was found to have 90 muscle fibres innervated by each motoneurone it would probably be involved in which of the following types of movement?

a) Lower leg extension during kicking a football.

b) Movement of the thumb whilst writing.

c) Stabilisation of the ear ossicles during hearing.

d) Movement of the eye ball during reading.

e) Upper arm flexion while tossing the caber.

Answer 7

b)

Question 8

Which of the following would you NOT expect to find at the mammalian neuromuscular junction?

a) muscarinic acetylcholine receptors

b) voltage-gated Ca2+ channels

c) Schwann cells

d) acetylcholinesterase

e) synaptic vesicles containing the neurotransmitter acetylcholine

Answer 8

a)

Question 9

Which of the following statements about rigor mortis is TRUE?

a) Rigor mortis typically lasts about 4 hours.

b) Rigor mortis is due to the failure of Ca2+ to bind to the troponin complex and displace the tropomyosin filament.

c) Rigor mortis is thought to be partly due to the absence of ATP which is required to bind to the cross bridges and detach the thick filaments from the thin filaments.

d) Rigor mortis is the stiffness which skeletal muscles begin to exhibit 2-3 days after death.

e) Rigor mortis is thought to be partly due to the leakage of Ca2+ into the endoplasmic reticulum.

Answer 9

c)

Question 10

Which of the following statements about skeletal muscle is/are TRUE?

1. Under the light microscope skeletal muscle appears striated.
2. The alternating dark and light bands are caused by the highly ordered arrangement of the thin and thick filaments within the myofibril.
3. The dark bands are known as I bands, the light bands as A bands and the thin line which is sometimes observed splitting the I bands is known as the Z line.

a) 1 & 2 only

b) 1 only

c) 2 only

d) 2 & 3 only

e) 1, 2 & 3

Answer 10

a)

Question 11

Which of the following statements concerning the structure of a myofibril is/are TRUE?

1. The distance between two I bands is known as the SARCOMERE.
2. The dark bands are caused by the thin filaments and the light bands by the thick filaments.
3. The Z line is caused by the junctions between successive blocks of thick filaments.

a) Only 1

b) Only 2 & 3

c) Only 2

d) 1, 2 & 3

e) Only 1 & 2

Answer 11

a)

Question 12

Which of the following statements is/are TRUE?

1. Thin filaments are in the order of 5-8 nm in diameter.
2. Thin filaments are around 1 micron long.
3. Thin filaments contain two chains of myosin which are twisted around each other to form a double helix.

a) Only 1

b) Only 1 & 2

c) Only 2

d) Only 2 & 3

e) 1, 2 & 3

Answer 12

b)

Question 13

The thin myofilament protein that physically blocks the myosin binding sites on each molecule of actin whilst a muscle fibre is at rest is called which of the following?

a) myosin

b) trypsin

c) troponin complex

d) toponin

e) tropomyosin

Answer 13

e)

Question 14

The motor-end plate is the name given to which pf the following?

a) The cover that seals the drive shaft on a Holden Commodore.

b) The part of the neuromuscular junction that is closest to the motoneurone soma.

c) The region where the motoneurone axon terminal and the sarcolemma are in close apposition.

d) The region where the motoneurone axon terminal loses its’ myelin sheath.

e) The group of myofibrils immediately below the neuromuscular junction.

Answer 14

c)

Question 15

Which of the following statements about the sliding filament mechanism of muscle contraction is FALSE?

a) The cross-bridge cycle is repeated many times following just a single action potential.

b) One cross bridge cycle only decreases the sarcomere length by approximately 20 nm.

c) Shortening of the myofibril is active.

d) Lengthening of the myofibril is passive.

e) A single action potential causes a shortening of around 1 % of the length of the sarcomere.

Answer 15

e)

Question 16

Which of the following is the CORRECT sequence of events according to the sliding-filament mechanism?

1. Energy released from the breakdown of the ATP is used to return the cross bridge to its “primed” position.
2. Binding of the cross bridges to the thin filaments triggers the cross bridges to flick.
3. Ca2+ binds to the calcium binding sites on the troponin complex.
4. Movement of the tropomyosin filament exposes the myosin binding sites on the actin molecules.
5. Cross-bridges detach from the thin filaments.

a) 4, 3, 2, 5, 1

b) 3, 4, 2, 5, 1

c) 3, 2, 4, 5, 1

d) 3, 5, 2, 4, 1

e) 3, 4, 2, 1, 5

Answer 16

b)

Question 17

Put the following stages of neuromuscular transmission into the correct temporal sequence.

1. Acetylcholine diffuses across the cleft.
2. Voltage-gated Ca2+ channels in the axon terminal open.
3. Generation of the end-plate potential.
4. Reabsorption of choline by the axon terminal
5. Binding of acetylcholine to receptors on the sarcolemma.

a) 1, 5, 4, 3, 2

b) 5, 4, 2, 1, 3

c) 2, 1, 5, 3, 4

d) 2, 1, 3, 4, 5

e) 1, 5, 3, 4, 2

Answer 17

c)

Question 18

An end-plate potential is the direct consequence of which of the following?

a) The flow of Na+ out of the cell and K+ into the cell along their respective concentration gradients.

b) The opening of ligand-gated Ca2+ channels in the motoneurone axon terminal.

c) Some mystical force which bridges the gap between the motoneurone and the muscle fibre.

d) The binding of acetylcholine to muscarinic acetylcholine receptors.

e) The flow of Na+ into the cell and K+ out of the cell along their respective concentration gradients.

Answer 18

e)

Question 19

Which of the following structures are typically 1-2 microns thick?

a) muscle fibres

b) thin myofilaments

c) sarcolemma

d) transverse tubules

e) myofibrils

Answer 19

e)

Question 20

A number of muscle fibres collected together by a connective tissue sheath are known as which of the following?

a) tendon

b) motor unit

c) fibula

d) sarcolemma

e) fascicle

Answer 20

e)

Question 21

Which of the following statements about muscle is/are TRUE?

1. Cardiac and smooth muscle collectively constitute about 40% of total body weight.
2. One of the functions of muscle is the maintenance of body temperature through heat production.
3. Smooth muscle is found primarily lining the walls of hollow structures.

a) Only 2 & 3

b) Only 2

c) 1, 2 & 3

d) Only 1

e) Only 1 & 2

Answer 21

a)

Question 22

Which of the following structures contains a fluid which is most like extracellular fluid?

a) motoneurones

b) transverse (T-) tubules

c) sarcoplasm

d) myofibrils

e) mitochondria

Answer 22

b)

Question 23

Which of the following statements concerning muscle contraction is FALSE?

1. If a second action potential arrives in a muscle fibre before the tension generated by the first action potential has declined, then the two will summate to produce a larger twitch.
2. A Titanic contraction is where increasing the action potential frequency even more produces no further increase in the tension produced.
3. The maximal force which can be generated is usually is around the normal resting length of the muscle.

a) Only 2 & 3

b) Only 2

c) 1, 2 & 3

d) Only 1

e) Only 3

Answer 23

b)

Question 24

Which of the following statements about skeletal muscle contraction is/are FALSE?

1. The force generated during a muscle contraction is independent of the number of motor units recruited.
2. During an isometric contraction the muscle produces tension but the length of the muscle does not change.
3. During an isotonic contraction the length of the muscle decreases but he tension remains the same.

a) Only 1 & 2

b) Only 1

c) Only 3

d) 1, 2 & 3

e) Only 2

Answer 24

b)

Question 25

Which of the following statements about motoneurones is/are TRUE?

1. they have their cell bodies in the posterior horns of the spinal cord.
2. they have myelinated axons.
3. they have axons which do not branch.
4. they usually form a contact with one muscle fibre.

a) 1 & 2 only

b) 1, 2 & 3 only

c) 2 only

d) 1 only

e) 1, 2 & 4 only

Answer 25

c)

Question 26

Which of the following ARE features of skeletal muscle fibres?

1. A plasma membrane known as the sarcoplasm.
2. Multiple nuclei.
3. High cytoplasmic concentrations of a polymer of glucose.
4. Low cytoplasmic concentrations of myoglobin.
5. Specialised endoplasmic reticulum.

a) 3 & 4 only

b) 1, 2, 3 & 5 only

c) 3, 4 & 5 only

d) 2, 3 & 5 only

e) 1, 2, 3, 4 & 5

Answer 26

d)