BIO 109 Chapter 10

How does a nerve impulse elicit a muscle action potential?

A nerve impulse reaches the synaptic end bulb and causes the release of acetylcholine, which diffuses across the synaptic cleft and binds to and activates acetylcholine receptors on the motor end plate. Binding of acetylcholine opens an ion channel in the acetylcholine receptors allowing Na+ to flow into the cell, which generates an action potential in the muscle cell.

What are the three ways that ATP can be produced in muscle fibers?

ATP can be produced from creatine phosphate, by anaerobic cellular respiration, and by aerobic cellular respiration.

List the four steps of the contraction cycle in order of occurrence. What is needed for these steps to continuously repeat?

ATP hydrolysis, attachment of myosin to actin forming crossbridges, the power stroke, then detachment of myosin from actin. The cycle will continue as long as ATP and calcium ions are available.

Describe the factors that lead to muscle fatigue.

Although the precise mechanisms that cause muscle fatigue are still not clear, several factors are thought to contribute. One is inadequate release of calcium ions from the SR, resulting in a decline of Ca2+ concentration in the sarcoplasm. Depletion of creatine phosphate also is associated with fatigue, but surprisingly, the ATP levels in fatigued muscle often are not much lower than those in resting muscle. Other factors that contribute to muscle fatigue include insufficient oxygen, depletion of glycogen and other nutrients, buildup of lactic acid and ADP, and failure of action potentials in the motor neuron to release enough acetylcholine.

Compare and contrast the structural characteristics of the three different types of muscular tissue.

Both cardiac and skeletal muscle tissues are striated and smooth muscle is not, hence its name. Skeletal muscle cells have more than one nucleus, are large and run parallel to each other. Cardiac muscle cells usually have only one, sometimes two, centrally located nuclei and are branched. They also are connected to each other via gap junctions. Smooth muscle cells are small but form thick layers of hollow organs. Like cardiac muscle cells, some smooth muscle cells communicate via gap junctions. Skeletal muscle is voluntarily controlled while both cardiac and smooth muscle tissue are involuntary and autorhythmic.

What is the major difference between the two types of smooth muscle tissue?

In single-unit smooth muscle tissue, action potentials are initiated in response to neurotransmitters, hormones, or an autorhythmic signal. The action potential spreads throughout the tissue by moving through gap junctions that connect all the muscle cells together within the tissue. It is found in the skin and in tubular arrangements that form part of the walls of small arteries and veins and of hollow organs such as the stomach, intestines, uterus, and urinary bladder. In multiunit smooth muscle tissue, muscle cells have few gap junctions with neighboring cells and thus must be excited by their own motor neuron terminal. It is found in the walls of large arteries, in airways to the lungs, in the arrector pili muscles that attach to hair follicles, in the muscles of the iris that adjust pupil diameter, and in the ciliary body that adjusts focus of the lens in the eye.

In embryonic muscle development, what happens to the somites?

Somite cells differentiate into myotome, dermatome, and sclerotome.

Discuss the steps involved in contraction of smooth muscle and explain why smooth muscle has a slower contraction cycle.

Upon neural stimulation of the muscle, Ca2+ stored in the caveolae start to flow into the cell. Calmodulin, the regulatory protein in smooth muscles, will bind with the Ca++ which will activate the enzyme myosin light chain kinase (MLCK). This enzyme will use ATP to add a phosphate to the myosin head so that it can bind to actin so that the contraction can occur. The sliding of the actin and myosin is similar to the skeletal muscle. The slowness of the process is due to slow influx of Ca++ from caveolae into the cells (smooth muscles have a poor SR system, therefore, there is very little intercellular Ca++ storage). Also, the enzyme MLCK works very slowly which in turn causes the muscle to contract slowly.

In skeletal muscles, the combined amounts of creatine phosphate and ATP provide enough energy for the muscle to contract maximally for approximately a) 15 seconds. b) 15 minutes. c) 1.5 minutes. d) 5 seconds. e) one minute.

a) 15 seconds.

) In the diagram, where is the axon terminal? a) A b) B c) C d) D e) E

a) A

In the diagram, which structure(s) moves towards the center of the sarcomere (closer together) when the fiber contracts? a) A b) D c) J d) Both A and D. e) None of these are correct.

a) A

Which figure exhibits concentric contraction of the biceps brachii muscle? a) A b) B c) C d) none of these choices

a) A

Which portion of this myogram shows a single twitch of the muscle? a) A b) B c) C d) D e) none of these choices

a) A

In the diagram, the neurotransmitter, acetylcholine, is released from this area. a) B b) C c) D d) G e) H

a) B

In the diagram, which labeled structure contains motor proteins that convert the energy in ATP into mechanical movements? a) C b) A c) E d) D e) None of these are correct.

a) C

In the diagram, a tendon is formed by the merging of the following structures a) C, D, and H b) D and E c) H and C d) C and D e) All of these choices are correct.

a) C, D, and H

In the diagram, where is the I band? a) G b) H c) I d) J e) D

a) G

Calcium ions are released from the sarcoplasmic reticulum into the cytosol a) at the beginning of a contraction. b) in response to acetylcholine binding to Ca2+ release channels. c) by active transport using Ca2+ pumps in the SR membrane. d) after the contraction ends. e) All of these answers are correct.

a) at the beginning of a contraction.

Which of the following types of muscle tissue contract when excited by their own autorhythmic muscle fibers? a) cardiac muscle b) slow twitch oxidative skeletal muscle c) multi-unit smooth muscle d) fast twitch glycolytic skeletal muscle e) All of these choices are correct.

a) cardiac muscle

During which period of a twitch contraction does the muscle action potential move along the sarcolemma of the muscle cell and trigger calcium release into the sarcoplasm? a) latent period b) contraction period c) relaxation period d) absolute refractory period e) relative refractory period

a) latent period

In an isometric contraction the muscle develops tension but does not a) lengthen. b) widen. c) does not expend energy. d) conduct electrical current. e) exhibit elasticity.

a) lengthen.

The contractile organelles of a skeletal muscle fiber are thread-like structures called a) myofibrils. b) myoglobin. c) mitochondria. d) Z discs. e) M lines.

a) myofibrils.

Which of the following is referred to as the period of lost excitability in skeletal muscle fibers? a) refractory period b) contraction period c) latent period d) relaxation period e) wave summation

a) refractory period

This is the least powerful type of skeletal muscle fiber. a) slow oxidative fiber b) fast oxidative fiber c) fast glycolytic fiber d) slow glycolytic fiber e) None of these choices.

a) slow oxidative fiber

Which of the following structures are made of dense regular connective tissue? a) F b) A c) I d) Both F and I e) All of these choices.

b) A

) On the diagram, where is the outer most layer of connective tissue encircling the entire muscle a) A b) B c) C d) D e) E

b) B

Which figure exhibits a contraction of the biceps brachii muscle in which its length increases? a) A b) B c) C d) none of these choices

b) B

Which of the labeled structures on the diagram holds muscles with similar functions together, allows free movement of muscles, carries nerves, blood vessels and lymphatic vessels, and fills spaces between muscles? a) A b) B c) E d) G e) H

b) B

In the diagram, where are thick filaments found? a) C b) E c) A d) B e) All of these choices

b) E

Smooth muscle tone is maintained by the prolonged presence of _____ in the muscle cell's cytosol? a) ATP b) calcium ions c) phosphate ions d) myoglobin e) None of these choices.

b) calcium ions

Skeletal muscle contraction will continue to occur as long as the following chemicals are available in the cytosol of the muscle fiber. a) ATP and acetylcholine (ACh) b) calcium ions and ATP c) ACh and potassium ions d) sodium ions and ATP e) calcium and ACh

b) calcium ions and ATP

Which of the following describe the regeneration capacity of cardiac muscle cells? a) limited, via satellite cells b) limited, under certain conditions c) considerable (compared with other muscle cells, but limited compared with epithelium), via pericytes d) all of these are correct e) none of these are correct

b) limited, under certain conditions

Which of the following consists of a somatic motor neuron and all the skeletal muscle fibers it stimulates? a) sarcomere b) motor unit c) neuromuscular junction d) muscle unit e) multi-unit smooth muscle

b) motor unit

Which of the following disorders is characterized by the wasting away of muscles due to the progressive loss of myofibrils? a) muscular hypertrophy b) muscular atrophy c) fibromyalgia d) myasthenia gravis e) tremors

b) muscular atrophy

Which of the following functions as a motor protein in all three types of muscle tissue? a) actin b) myosin c) troponin d) titin e) tropomyosin

b) myosin

To stimulate skeletal muscle contraction, acetylcholine must cross the _____ of the neuromuscular junction and bind to receptors on the motor endplate. a) node of Ranvier b) synaptic cleft c) sarcolemma d) synaptic end bulb e) transverse tubule

b) synaptic cleft

What regulatory proteins can be found in the thin filaments of skeletal muscle fibers? a) troponin and titin b) tropomyosin and troponin c) myosin and titin d) titin and tropomyosin e) tropomyosin and myosin

b) tropomyosin and troponin

Which area of the myogram shows sustained contraction with partial relaxation? a) A b) B c) C d) D e) none of these choices

c) C

Which figure exhibits isometric contraction of the biceps brachii muscle? a) A b) B c) C d) none of these choices

c) C

In the diagram, which structure helps return a stretched sarcomere to its resting length? a) B b) C c) E d) Both B and C e) All of these choices are correct.

c) E

) In the diagram, what is the basic functional unit of a myofibril? a) B b) C c) F d) Both B and C e) All of these choices are correct.

c) F

In the diagram, individual muscle fibers are covered by this layer. a) K b) I c) L d) M e) A

c) L

During muscle contraction by the sliding filament mechanism, thin filaments are pulled towards the a) Z disc. b) H zone. c) M line. d) A band. e) I band.

c) M line.

Which property of muscle gives it the ability to stretch without damage? a) electrical excitability b) contractility c) extensibility d) elasticity e) thermogenesis

c) extensibility

Leg muscles are predominantly composed of which type of muscle fiber? a) slow oxidative b) fast glycolytic c) fast oxidative-glycolytic d) slow glycolytic e) fast oxidative

c) fast oxidative-glycolytic

What is being shown by the axis labeled E? a) time b) tetanus c) force of contraction d) twitch factor e) wave summation

c) force of contraction

Increasing the number of active motor units within a skeletal muscle is called a) wave summation. b) fused tetanus. c) motor unit recruitment. d) muscle tone. e) flaccidity.

c) motor unit recruitment.

Cross bridges are formed during muscle contraction when _____ on the thick filaments binds to _____ on the thin filaments. a) myosin; troponin b) myosin; troponin c) myosin; actin d) actin; myosin e) actin; tropomyosin

c) myosin; actin

Myasthenia Gravis is an autoimmune disorder that targets the ACh receptors at the NMJ and ultimately reduces the number of available receptors. Predict what happens if you treat the patient with a drug that inhibits the activity of acetylcholinesterase? a) prevent contraction b) weak contraction c) normal contraction d) cause spasm e) none of these choices

c) normal contraction

In a neuromuscular junction, the effect of acetylcholine (ACh) binding to receptors on the motor end plate lasts only briefly due to a) rapid uptake of the ACh into the myofiber. b) endocytosis of the ACh receptor into the myofiber. c) rapid destruction of ACh in the synaptic cleft by acetylcholinesterase. d) rapid destruction of ACh in the synaptic cleft by monoamine oxidase. e) diffusion of the ACh out of the synaptic cleft.

c) rapid destruction of ACh in the synaptic cleft by acetylcholinesterase.

Release of calcium from these structures triggers skeletal muscle contraction. a) myofibrils b) mitochondria c) terminal cisterns of sarcoplasmic reticulum d) T-tubules e) none of the answer choices

c) terminal cisterns of sarcoplasmic reticulum

What energizes the myosin head? a) the actin filaments b) calcium ions c) potassium ions d) ATP hydrolysis reaction e) ADP synthesis

d) ATP hydrolysis reaction

After prolonged strenuous exercise has stopped, heavy breathing will often continue for several minutes in order to provide the oxygen needed to a) convert the lactic acid produced during exercise back into glycogen. b) resynthesize creatine phosphate. c) replace oxygen displaced from muscle myoglobin. d) All of these choices e) None of these choices

d) All of these choices

Which of the following are commonly used to produce ATP during skeletal muscle contraction? a) creatine phosphate b) anaerobic cellular respiration c) aerobic cellular respiration d) All of these choices are correct. e) None of these choices are correct.

d) All of these choices are correct.

Which of the following regions of a sarcomere contain thin filaments? a) I band b) A band c) H zone d) Both I band and A band. e) All of these answer choices are correct.

d) Both I band and A band.

Which area of the myogram shows a sustained contraction where individual twitches are indiscernible? a) A b) B c) C d) D e) none of these choices

d) D

In the diagram, where would you find stored Ca2+? a) B b) D c) G d) F e) K

d) F

Which of the following statements does NOT accurately describe aerobic cellular respiration in skeletal muscles? a) Pyruvic acid generated by glycolysis enters the mitochondria. b) O2 is essential. c) CO2 is produced as a waste product. d) Lactic acid is continually produced. e) Can be used to generate ATP from fats, proteins or carbohydrates.

d) Lactic acid is continually produced.

Myofibrils contain a) contractile proteins. b) regulatory proteins. c) structural proteins. d) all of these answers are correct. e) none of these answers are correct.

d) all of these answers are correct.

What type of tendon is formed when the connective tissue elements of a skeletal muscle extend as a broad flat layer? a) perimysium b) deep fascia c) fascicle d) aponeurosis e) endomysium

d) aponeurosis

Which of the following correctly lists the sequence of structures that action potentials must move through to excite skeletal muscle contraction? a) sarcolemma, axon of neuron, T tubules b) T tubules, sarcolemma, myofilament c) muscle fiber, axon of neuron, myofibrils d) axon of neuron, sarcolemma, T tubules e) myofibrils, myofilaments, mitochondria

d) axon of neuron, sarcolemma, T tubules

Which is a NOT a side-effect of anabolic steroid use by male athletes? a) sterility b) baldness c) diminished testosterone secretion d) deepening of the voice e) atrophy of testes

d) deepening of the voice

This is the outermost layer of connective tissue surrounding a skeletal muscle. a) tendon b) ligament c) endomysium d) epimysium e) perimysium

d) epimysium

Which of the regions of a sarcomere contain titin? a) the A band only b) the H zone only c) the zone of overlap only d) from M line to Z disc e) the I band only

d) from M line to Z disc

After the fusion of myoblasts, the muscle fiber loses its ability to do what? a) grow b) lengthen c) contract d) go through cell division. e) all of the answer choices

d) go through cell division.

Which of the following microscopic structures is only found in the cardiac muscle tissue? a) myosin b) tropomyosin c) sarcomeres d) intercalated discs e) striations

d) intercalated discs

Which of the following regions of the sarcomere contain thick filaments? a) zone of overlap b) A band c) H zone d) both A band and H zone e) All of these answer choices are correct.

e) All of these answer choices are correct.

The different types of muscle tissue differ from each other by a) microscopic anatomy. b) location. c) type of Control. d) both microscopic anatomy and location. e) All of these choices are correct.

e) All of these choices are correct.

Which of the following is a common effect of aging on skeletal muscle? a) loss of muscle mass b) decrease in maximal strength c) a slowing of muscle reflexes d) loss of flexibility e) all of these are correct

e) all of these are correct

Which of the following types of abnormal contractions of skeletal muscle may be caused by holding a position for a prolonged period? a) spasm b) fasciculation c) tremor d) fibrillation e) cramp

e) cramp

Which of the following proteins is used to reinforce the sarcolemma and to help transmit the tension generated by the sarcomeres to the tendons? a) troponin b) tropomyosin c) myosin d) actin e) dystrophin

e) dystrophin

Which of following is a common characteristic of fast glycolytic (FG) skeletal muscle fibers? a) large amount of myoglobin. b) many mitochondria. c) low concentration of creatine kinase in the sarcoplasm. d) slow myosin ATPase. e) high amount of glycogen in the sarcoplasm.

e) high amount of glycogen in the sarcoplasm.

Which of the following is NOT a major function of muscle tissue? a) moving blood throughout the body b) generating heat through contractions c) stabilizing the movement of joints d) promoting movement of body structures e) production of vitamins.

e) production of vitamins.

Which of the following types of muscle tissue is capable of undergoing the stress-relaxation response when they are stretched? a) cardiac muscle fibers b) fast glycolytic fibers c) fast oxidative-glycolytic fibers d) slow oxidative fibers e) single-unit smooth muscle fibers

e) single-unit smooth muscle fibers

A brief contraction of all muscle fibers in a motor unit in response to a single action potential moving down the somatic motor neuron is known as a) isometric contraction. b) isotonic contraction. c) tetany. d) refractory period. e) twitch contraction.

e) twitch contraction.