An action potential in the motor end plate rapidly spreads to the interior regions of a muscle cell by means of the: A) Z lines. B) sarcoplasmic reticulum. C) H zone. D) transverse tubules. E) pores in the plasma membrane.
What is the function of the transverse tubules in a skeletal-muscle fiber? A) They store the calcium ions that are the main source of activation for the cross-bridge cycle. B) They form the Z lines that mark the end of each sarcomere. C) They allow action potentials to propagate deep into the center of skeletal muscle cells. D) They manufacture and store ATP. E) They run in parallel with the myofibrils, and have abundant Ca2+-ATPase proteins for pumping Ca2+ back into the sarcoplasmic reticulum.
Which of the following statements regarding the motor end plate of a skeletal muscle fiber is TRUE? A) Muscarinic receptors in the end plate are activated by binding to acetylcholine. B) Temporal summation of multiple end plate potentials is required in order to trigger an action potential in the muscle-fiber membrane. C) Acetylcholinesterase in the end plate membrane catalyzes the breakdown of acetylcholine. D) Sympathetic nerve fibers terminate on skeletal muscle fibers at the motor end plate. E) The motor end plate under the axon terminal contains a large number of voltage-gated Na+ channels.
How does the chemical curare affect skeletal muscle function? A) It activates an autoimmune disease that destroys myelin. B) It blocks the action of acetylcholinesterase at the neuromuscular junction. C) It is a muscarinic acetylcholine receptor antagonist that blocks synaptic transmission at the neuromuscular junction. D) It is a nicotinic acetylcholine antagonist that blocks synaptic transmission at the neuromuscular junction. E) It locks ligand-gated channels in the open state, leading to spastic contractions of muscle.