The Muscular System

Which of these is true of skeletal muscle?

• spindle-shaped cells

• under involuntary control

• many peripherally located nuclei per muscle fiber

• forms the walls of hollow internal organs

Which of these is not a major property of muscle?

• contractility

• elasticity

• excitability

• extensibility

• secretability

Given these structures:

(1) whole muscle

(2) muscle fiber (cell)

(3) myofilament

(4) myofibril

(5) muscle fasciculus

Choose the arrangement that lists the structures in the correct order from largest to smallest.

• 1,2,5,3,4

• 1,2,5,4,3

• 1,5,2,3,4

• 1,5,2,4,3

Each myofibril

• is made up of many muscle fibers

• contains sarcoplasmic reticulum

• is made up of many sarcomeres

• contains T tubules.

• is the same thing as a muscle fiber.

Myosin myofilaments are

• attached to the Z disk.

• found primarily in the I band.

• thinner than actin myofilaments.

• absent from the H zone.

• attached to filaments that form the M line.

Which of these statements about the molecular structure of myofilaments is true?

• Tropomyosin has a binding site for Ca2+.

• The head of the myosin molecule binds to an active site on G actin.

• ATPase is found on troponin.

• Troponin binds to the rodlike portion of myosin.

• Actin molecules have a hingelike portion, which bends and straightens during contraction.

The part of the sarcolemma that invaginates into the interior of skeletal muscle fibers is the

• T tubule system

• sarcoplasmic reticulum

• myofibrils

• mitochondria

During the depolarization phase of an action potential, the permeability of the plasma membrane to

• Ca2+ increases

• Na+ increases

• K+ increases

• Ca2+ decreases

• Na+ decreases.

During repolarization of the plasma membrane,

• Na+ move to the inside of the cell.

• Na+ move to the outside of the cell.

• K+ move to the inside of the cell.

• K+ move to the outside of the cell.

Given these events:

(1) Acetylcholine is broken down into acetic acid and choline.

(2) Acetylcholine diffuses across the synaptic cleft.

(3) An action potential reaches the terminal branch of the motor neuron.

(4) Acetylcholine combines with a ligand-gated ion channel. (5) An action potential is produced on the muscle fiber’s plasma membrane.

Choose the arrangement that lists the events in the order they occur at a neuromuscular junction.

• 2,3,4,1,5

• 3,2,4,5,1

• 3,4,2,1,5

• 3,4,2,1,5

• 5,1,2,4,3