Physiology Wk 3 Quiz

The protein found in thin filaments

Actin, Troponin, Tropomyosin

Muscle contraction is always the strongest when the muscle is as long as possible. True False

False

The calcium causing smooth muscle contraction usually comes from the extracellular fluid, but the calcium causing skeletal muscle contraction usually comes from the sarcoplasmic reticulum. True False

True

What is the basic mechanism of muscle contraction at the level of myofilaments?

Thick and thin filaments slide past each other, shortening the sarcomere. Multiple sarcomeres generate tension causing muscle contraction.

Myofibril

A bundle of contractile proteins within a muscle cell

Muscle Fiber

A single muscle cell

How does an electrical signal in a neuron create an electrical signal in a muscle fibre?

By stimulating the release of a chemical signal into the neuromuscular junction, which binds a receptor in the sarcolemma and depolarizes the fiber

A somatic motor neuron plus the skeletal muscle fibre it innervates is known as a .....

Motor Unit

A property of all muscle cells is distensibility, which means that the tissue is able to stretch. True False

True

During muscle contraction, sarcomeres and myofibrils shorten, but myofilaments do not change in length. True False

True

In skeletal muscle, contraction strength can be varied by changing the number of contracting muscle fibres. True False

True

Lactic acid is a source of ATP - it can be used by muscle fibres to generate pyruvate, which can be used to generate ATP. True False

True

Skeletal muscle fibres fatigue after repeated contraction. True False

True

What is a neuromuscular junction? a. A chemical synapse between a motor neuron and a muscle fibre. b. An electrical synapse between a motor unit and a muscle. c. Transmission of an electrical impulse to skeletal muscle fibres.

a. A chemical synapse between a motor neuron and a muscle fibre.

The motor end plate is an area of muscle cell membrane with ACh receptors. the same as the neuromuscular junction. the same as the synaptic cleft. formed by the membranes of axon terminals that lie on the surface of skeletal muscle cells.

an area of muscle cell membrane with ACh receptors.

3c. Why does a muscle not constantly shorten and lengthen as crossbridges bind and unbind during a muscle contraction? a. Crossbridges form and break at the same time, but cycling occurs rapidly so the muscle does not have time to relax. b. Crossbridges form independently from one another so that at any one time, there are some crossbridges that are bound and others that are not. c. Dissociation of ADP from myosin causes actin and myosin to remain in an attached and rigid state, until another crossbridge is ready to form.

b. Crossbridges form independently from one another so that at any one time, there are some crossbridges that are bound and others that are not.

Drug X is a nicotinic acetylcholine receptor antagonist. What signs should be expected in an animal who has been given Drug X? a. Normal muscle movement b. Muscle paralysis (lack of muscle activity) c. Muscle spasticity (increased muscle activity)

b. Muscle paralysis (lack of muscle activity)

What is the effect of myelin? a. Chemical receptors are blocked. b. Nerve signals are transmitted more rapidly. c. Sensitivity to chemical receptors is increased. d. Transmission of nerve signals is inhibited.

b. Nerve signals are transmitted more rapidly.

In what order are motor units activated during skeletal muscle contraction? a. Type II (fast-twitch) fibres are recruited first, then type I (slow-twitch) fibres are recruited if more force is needed. b. Type I (slow-twitch) muscle fibres are recruited first, then type II (fast-twitch) are recruited if more force is needed. c. Type I (slow-twitch) and type II (fast-twitch) fibres are recruited together to reach peak muscle force quickly.

b. Type I (slow-twitch) muscle fibres are recruited first, then type II (fast-twitch) are recruited if more force is needed.

Which are characteristics of cardiac muscle? a. long, thin, striated cells b. branched, interconnected, striated cells c. contracts quickly and fatigues easily d. contracts slowly and fatigues easily

b. branched, interconnected, striated cells

If the inside of the cell contains an excess of negative charges, a. the membrane potential will be positive. b. positive ions will be drawn into the cell (if they can cross the membrane). c. negative ions will be drawn into the cell (if they can cross the membrane). d. there is no electrical gradient.

b. positive ions will be drawn into the cell (if they can cross the membrane).

Drug Z blocks the activity of the enzyme acetylcholinesterase in the synaptic cleft. Drug Z is likely to a. have no effect on skeletal muscle contraction. b. prolong skeletal muscle contraction. c. reduce skeletal muscle contraction.

b. prolong skeletal muscle contraction.

The outer membrane of a muscle cell is called the a. sarcoplasm. b. sarcolemma. c. sarcoplasmic reticulum. d. endosomal membrane.

b. sarcolemma.

Fasicle

bundle of muscle cells

What is the role of tropomyosin in muscle contraction? a. To aid in myosin attaching to the actin filament. b. To release troponin from tropomyosin, allowing myosin to bind to actin. c. To prevent myosin from continuing to slide up the actin filament. d. To release calcium from the sarcoplasmic reticulum.

c. To prevent myosin from continuing to slide up the actin filament.

A sarcomere a. is a neuron and the muscle fibre it innervates. b. runs the entire length of a muscle. c. is joined to adjacent sarcomeres by the Z disc/line. d. is the functional unit of skeletal and smooth muscle.

c. is joined to adjacent sarcomeres by the Z disc/line

What controls crossbridge formation in smooth muscle cells? a. Troponin covering the myosin binding sites of thin filaments b. Troponin regulating the activity of the myosin heads c. Calcium ions covering the myosin binding sites of thin filaments d. Calcium ions regulating activity of the myosin heads

d. Calcium ions regulating activity of the myosin heads

During muscle contraction, a. thick filaments shorten. b. thin filaments shorten. c. both thick and thin filaments shorten. d. neither thick nor thin filaments shorten.

d. neither thick nor thin filaments shorten.

Lipophilic hormones a. usually bind to receptors on the surface of the cell. b. function by way of a second messenger system. c. cannot diffuse through the cell membrane. d. usually bind to receptors inside the cytoplasm or nucleus.

d. usually bind to receptors inside the cytoplasm or nucleus.

Smooth muscle is non-striated. striated.

non-striated.

To generate a stronger contraction in smooth muscle, the force produced by each muscle fibre should be increased. the number of contracting muscle cells should be increased.

the force produced by each muscle fibre should be increased.

A single ATP molecule is generated when creatine is converted into creatine phosphate. True False

False

In the crossbridge cycle, the myosin head detaches from the actin when no additional ATP molecules are available for binding. True False

False

Simple diffusion requires a carrier protein or channel. True False

False

Smooth muscle is voluntary - ie can be contracted and relaxed at will. True False

False

Smooth muscle relaxation begins when membrane transport proteins introduce calcium to the cytoplasm. True False

False

The muscle cell uses up all of its stored ATP before it begins to generate more. True False

False

The amount of tension generated by individual smooth muscle cells varies according to the amount of calcium allowed into the cell from the extracellular fluid, which in turn activates greater or fewer numbers of myosin heads. True False

True

Which of the following correctly identifies muscle components in order from largest to smallest? a. Fascicle, muscle fibre, myofibril b. Muscle fibre, myofibril, fascicle c. Muscle fibre, fascicle, myofibril d. Fascicle, myofibril, muscle fibre

a. Fascicle, muscle fibre, myofibril

The role of calcium in smooth muscle contraction involves a. activating enzymes that activate the myosin heads. b. providing energy for crossbridge cycling. c. revealing myosin binding sites on actin molecules. d. initiating action potentials in the muscle cell.

a. activating enzymes that activate the myosin heads.

Type I (slow-twitch) fibres a. are slow to fatigue. b. contain large stores of glycogen. c. are the strongest type of fibre. d. contain few mitochondria

a. are slow to fatigue

A muscle fibre relaxes when a. the concentration of Ca2+ in the cytosol returns to resting levels. b. the supply of ATP is exhausted. c. acetylcholine is released from the axon terminal and the sarcolemma depolarises. d. Ca2+ floods the cytosol.

a. the concentration of Ca2+ in the cytosol returns to resting levels.

Which way do particles move during active transport? a. From areas of high concentration to areas of low concentration. b. From one area of low concentration to another area of low concentration. c. From one area of high concentration to another area of high concentration. d. From areas of low concentration to areas of high concentration.

d. From areas of low concentration to areas of high concentration.

In skeletal muscle, fresh molecules of ATP are required for a. detaching the myosin heads from the actin. b. maintaining the sodium concentration gradient. c. providing the energy for movement of the myosin heads. d. all of the above.

d. all of the above