MCQ ON MUSCLE

Action potential:

• a- is a graded potential.

• b- is produced by sub threshold stimulus.

• c- starts with repolarization caused by outward movement of Cl- .

• d- is conducted slower in thin nerve fibers.

The energy of muscle contraction is derived from the following except:

• a- ATP.

• b- muscle glycogen.

• c- lactic acid

• d- Creatine phosphate.

Depolarization:

• a- is associated with increase in membrane permeability to Na+ .

• b- is terminated with closure of voltage activated K + channels.

• c- is followed by muscle relaxation.

• d- is caused by K+ efflux.

- As regard conduction of action potential in a nerve:

• a- in thick myelinated nerve fibers can reach up to 120 meter / second.

• b- can be increased by increase calcium.

• c- can be increased by cooling.

• d- is conducted with decrement.

Myelin sheath:

• a- Present in the myelinated and unmyelinated nerve fibers.

• b- Formed of lipoprotein complex and acts as electric insulator.

• c- It is formed of successive wrappings of the membrane of Schwann cells.

• d- It is the cause of decreased conduction of nerve impulse.

The resting membrane potential is caused by:

• a- Diffusion of K+ ions outside the nerve fibers.

• b- Diffusion of Na+ ions inside the nerve fibers.

• c- Opening of the chemically activated ion channels.

• d- Opening of the voltage activated ion channels.

- Muscle fatigue is due to:

• a- Inability of the action potential to spread over the muscle.

• b- Failure of transmission in the motor nerve.

• c- Failure of neuro-muscular transmission.

• d- Depletion of energy stores.

The function of tropomyosin in skeletal muscle include:

• a- binding to myosin during contraction

• b- acting as a relaxing protein at rest by covering the binding sites on actin.

• c- sliding on actin to produce shortening.

• d- releasing Ca++ after propagation of action potential.

Contraction of skeletal muscles:

• a- produces more work when the muscle contracts isometrically than when the muscle contracts isotonically.

• b- depends on external Ca++ .

• c- decrease in magnitude with rapid repeated stimulation.

• d- does not depend on action potential.

Neuromuscular transmission is blocked by:

• a- prostigmine . .

• b- increase Ca++ ions

• c- acetylcholine

• d- succinylcholine.