Why is it necessary to have an action potential (electrical signal) in the muscle for contraction? a. Actin and myosin must be electrically charged to create a cross-bridge. b. The SR will only release Ca2+ if it has been electrically stimulated. c. Sarcomeres require a negative electrical charge to start sliding. d. ATP cannot be split into ADP and Pi without an action potential.

Which statement CORRECTLY describes a motor unit? O a. A single muscle fibre plus all the motor neurons that innervate it. O b. All the motor neurons supplying a single muscle O c. A pair of antagonistic muscles O d. A single motor neuron plus all the muscle fibres it innervates

In what type of muscle would the structure illustrated in the image at right be found? A. The flight muscle of a bumblebee B. The longitudinal muscles underlying the cuticle in C. elegans C. The longitudinal muscles of the vertebrate intestine D. The cardiac muscle of mammals E. None of the above actin filament Dense body Relaxed myosin filament Contracted

Which of the following statements about skeletal muscle is CORRECT? Select one: a. An increase in Na+ concentration in the cytosol starts muscle filament sliding. b. The muscle is non-striated and involuntary. c. The muscle is involved in shivering thermogenesis. d. The muscle contracts in response to parasympathetic stimulation. e. The muscle contracts in response to hormones.

Which statement about striated skeletal muscle is true?   A. The tension generated by a muscle is invariable.   B. Mechanical summation of twitches in a muscle fiber leads to a graded increase in the tension that is above that generated by a single twitch.   C. A single action potential arriving at the neuromuscular junction is not sufficient to cause a muscle fiber to twitch.   D. Muscle twitches are able to mechanically sum when Ca2+ is quickly and completely removed from the sarcoplasm between action potentials.   E. An action potential in the muscle cell activates contraction by releasing Na+ into the sarcoplasm.

You know from experience that skeletal muscle tires quite quickly, especially if there is not enough oxygen. Interestingly, shellfish such as clams can maintain a month-long contraction in the muscle that keeps the shell closed. No oxygen gets in this situation. These muscles have a different version of myosin called paramyosin. Knowing what you know about the cellular mechanism of muscle contraction, propose a hypothesis to explain how paramyosin might work.

Which of the following statements is true of the chameleon tongue but not of the human tongue? A. It is a muscular hydrostat. B. Force generation reflects the binding of myosin crossbridges to actin thin filaments. C. The organization of the actin and myosin filaments produces a regular pattern of bands, or striations. D. Gaps or holes in the Z-discs allow supercontraction (shortening beyond the normal limit). E. All of the above statements are true of both the chameleon tongue and the human tongue.

Which protein is not part of the thin filament in a muscle fiber?   A. Actin B. Myosin  C. Tropomyosin D. Troponin

On the molecular level, why does lifting weights consume energy? A. To contract a muscle, acetylcholine binds and pulls calcium ions. ATP binding and hydrolysis are required in the cycle of acetylcholine and calcium-binding and unbinding. B. To contract a muscle, myosin and actin filaments shorten, requiring ATP binding and hydrolysis. O C. To contract a muscle, myosin binds and pulls actin, ATP binding and hydrolysis are required in the cycle of myosin and actin-binding and unbinding. D. To contract a muscle, acetylcholine and calcium filaments shorten, requiring ATP binding and hydrolysis.

What is the physiological mechanism that produces a quick and efficient skeletal muscle response to an external stimulus?   A. voluntary motor commands from the brain   B. temporal and spatial summation   C. sensory nerve input to the brain   D. spinal reflex arc   E. endocrine secretory response