phys ch 12

12. List the events in that occur at the neuromuscular junction in chronological order beginning with ACh binding to receptors on the motor end plate. 1.End-plate potentials trigger action potentials. 2.Transverse tubules convey potentials into the interior of the cell. 3.Acetylcholine binds to receptors on the motor end plate. 4.Ca2+ is released from the sarcoplasmic reticulum.

3,1,2,4

Which of the following statements is NOT correct regarding the motor units and their activation? ANSWER: -The metabolic capacity of muscle fibers within a motor unit can be altered. -All muscle fibers in a single motor unit are of the same fiber type. -A weak contractile stimulus activates fast-twitch motor units. -At its peak intensity, a contractile stimulus will activate muscle fibers that are easily fatigued. -A motor unit in muscles of gross movement can have thousands of muscle cells.

A weak contractile stimulus activates fast-twitch motor units.

The calcium release channel in the smooth muscle sarcoplasmic reticulum that is opened by increases in phospholipase C activity is the A) inositol trisphosphate (IP3) receptor channel. B) ryanodine receptor. C) dihydropyridine (DHP) receptor. D) voltage-gated Ca2+ channel. E) Ca2+-ATPase.

A) inositol trisphosphate (IP3) receptor channel.

When comparing complete tetanus with unfused (incomplete) tetanus, which is true? ANSWER: -Complete tetanus would occur when there is more time between twitch contractions. -Complete tetanus involves development of maximum tension. -Complete tetanus involves some relaxation between twitches. -Complete tetanus occurs at a lower frequency of stimulation than unfused tetanus.

Complete tetanus involves development of maximum tension.

Which of the following is NOT a property of single-unit smooth muscles? ANSWER: -Only a proportion of the smooth muscle cells receive autonomic nervous input. -Their contraction occurs in a coordinated manner. -Electrical responses travel directly between cells. -All smooth muscle cells are connected by gap junctions. -Each cell functions independent of its neighbor.

Each cell functions independent of its neighbor.

________ is the backup energy molecule that can be rapidly converted to ATP in active skeletal muscle. ANSWER: Phosphocreatine Fatty acid Glucose Protein

Phosphocreatine

Compared to skeletal muscle, contraction of smooth muscle cells is ANSWER: -a slower response to a stimulus, sustained without fatigue, and controlled by the somatic nervous system. -a slower response to a stimulus and sustained without fatigue. -only a slower response to a stimulus. -only controlled by the somatic nervous system. -only sustained without fatigue.

a slower response to a stimulus and sustained without fatigue.

In order for high force crossbridges to form in contracting skeletal muscle, calcium must ANSWER: -phosphorylate the troponin to move the tropomyosin. -bind to troponin which moves the tropomyosin. -phosphorylate the tropomyosin which moves it. -bind to calmodulin to phosphorylate the myosin. -bind to tropomyosin which moves the troponin.

bind to troponin which moves the tropomyosin.

The binding of acetylcholine to its receptor at the neuromuscular junction causes the opening of a ANSWER: channel for both Na+ and K+. ryanodine receptor. Na+ channel. calcium channel.

channel for both Na+ and K+.

The action potential traveling along the t-tubule is detected by the ANSWER: -dihydropyridine (DHP) receptor (L-type calcium channel). -Ca2+ ATPase. -ryanodine receptor. -acetylcholine receptor.

dihydropyridine (DHP) receptor (L-type calcium channel).

Muscle fatigue arises primarily from failure in ANSWER: initiation of contraction by the motor cortex. signal relay from brain to spinal cord. neuromuscular transmission. calcium pumps in the skeletal muscles. excitation-contraction coupling.

excitation-contraction coupling.

Motor units that control skeletal muscles involved with fine motor movements (eye muscles or the hands) have ________ muscle fibers than motor units that control more gross movements (gastrocnemius muscle of the lower leg). ANSWER: more fewer the same number of

fewer

The tension generated in a skeletal muscle fiber is directly proportional to the number of ANSWER: low energy crossbridges formed. thick and thin filaments present. active sarcomeres. nebulin and titin molecules present. high energy crossbridges formed.

high energy crossbridges formed.

The force generated by a single muscle fiber can only be increased by increasing the frequency of A) increasing frequency of action potentials only. B) increasing muscle length beyond optimal only. C) increasing the asynchrony of recruitment only. D) increasing frequency of action potentials and increasing muscle length beyond optimal only.

increasing frequency of action potentials only.

The calcium release channel in the smooth muscle sarcoplasmic reticulum that is opened by increases in phospholipase C activity is the ANSWER: voltage-gated Ca2+ channel. dihydropyridine (DHP) receptor. inositol trisphosphate (IP3) receptor channel. ryanodine receptor. Ca2+-ATPase.

inositol trisphosphate (IP3) receptor channel.

Which of the following is a characteristic of slow-twitch oxidative skeletal muscle fibers? ANSWER: -long contraction duration, few mitochondria, and high capillary density -few mitochondria only -long contraction duration only -high capillary density only -long contraction duration and high capillary density

long contraction duration and high capillary density

This protein is activated by the Ca2+-calmodulin complex to phosphorylate the myosin light chain protein. ANSWER: myosin light chain kinase myosin light chain phosphatase tropomyosin myosin heavy chain

myosin light chain kinase

A motor unit consists of ANSWER: -one axon terminal branch and the myofibrils it controls. -one neuron and all the skeletal muscle fibers it controls. -one skeletal muscle fiber and the neuron that controls that fiber. -one skeletal muscle fiber and all the neurons that control that fiber.

one neuron and all the skeletal muscle fibers it controls.

The function of transverse tubules is to ANSWER: -rapidly conduct action potentials to the interior of the muscle fiber. -conduct ATP molecules out of the mitochondria throughout the sarcoplasm. -ensure a supply of glycogen throughout the muscle sarcoplasm. -store Ca2+ ions inside the muscle fiber.

rapidly conduct action potentials to the interior of the muscle fiber.