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PHY 503: EXAM 2 PRACTICE TEST QUESTIONS WITH
ACCURATE SOLUTIONS
- The fibers of the corticospinal tract pass through which structure? A) medial lemniscus B) medullary pyramid C) posterior funiculus D) medial longitudinal fasciculus E) anterior roots -- Correct Answer ✔✔ B) medullary pyramid
- Which term applies to the combination of a motor neuron and all the skeletal muscle fibers contacted by that motor neuron? A) Golgi tendon organ B) motor unit C) propriospinal neurons D) skeletal muscle fibers -- Correct Answer ✔✔ B) motor unit
- Cells of the adrenal medulla receive synaptic input from which type of neuron? A) preganglionic sympathetic B) postganglionic sympathetic C) preganglionic parasympathetic D) postsynaptic parasympathetic E) presynaptic parasympathetic -- Correct Answer ✔✔ A) preganglionic sympathetic Preganglionic sympathetic axons synapse on cells in the adrenal medulla that function as postganglionic sympathetic neurons.
- In a muscle spindle receptor, which type of muscle fiber is responsible for the dynamic response? A) extrafusal muscle fiber
B) static nuclear bag fiber C) nuclear chain fiber D) dynamic nuclear bag fiber E) smooth muscle fiber -- Correct Answer ✔✔ D) dynamic nuclear bag fiber The dynamic nuclear bag fiber responds to the rate of change of length of the muscle spindle receptor. This fiber is responsible for the dynamic response of the muscle spindle.
- The sweat glands and piloerector muscles of hairy skin are innervated by which type of fibers? A) cholinergic postganglionic parasympathetic B) cholinergic postganglionic sympathetic C) adrenergic preganglionic parasympathetic D) adrenergic postganglionic sympathetic E) adrenergic preganglionic sympathetic -- Correct Answer ✔✔ B) cholinergic postganglionic sympathetic
- Which cells receive direct synaptic input from Golgi tendon organs? A) type Ia inhibitory interneurons B) dynamic gamma motor neurons C) alpha motor neurons D) type Ib inhibitory interneurons E) type II excitatory interneurons -- Correct Answer ✔✔ D) type Ib inhibitory interneurons GTOs provide direct synaptic input to type Ib inhibitory interneurons. Type Ia interneurons and alpha motor neurons receive input from muscle spindle afferents, while dynamic gamma motor neurons and excitatory interneurons receive their input from supraspinal systems.
- The excitatory or inhibitory effect of a postganglionic sympathetic fiber is determined by which feature or structure? A) function of the postsynaptic receptor to which it binds B) specific organ innervated C) ganglion where the postganglionic fiber originates
Lesions to the PMC and surrounding motor cortical areas lead to spastic paralysis in affected muscles.
- Which substance activates adrenergic alpha and beta receptors equally well? A) ACh B) norepinephrine C) epinephrine D) serotonin E) dopamine -- Correct Answer ✔✔ C) epinephrine Epinephrine activates alpha and beta-adrenergic receptors equally well. Norepinephrine activates both, but has a markedly greater effect on alpha receptors.
- In the patellar tendon reflex, which of the following items will synapse directly on alpha motor neurons that innervate the muscle being stretched? A) Ia sensory fiber B) Ib sensory fiber C) excitatory interneurons D) gamma motor neurons E) inhibitory interneurons -- Correct Answer ✔✔ A) Ia sensory fiber Type Ia sensory fibers synapse directly with alpha motor neurons, whereas Ib sensory fibers synapse with inhibitory interneurons. Excitatory interneurons play an important role in the withdrawal reflex. Gamma motor neurons receive input primarily from supraspinal systems.
- The withdrawal reflex is initiated by stimulation delivered to which receptor? A) muscle spindle B) joint capsule receptor C) cutaneous free nerve ending D) Golgi tendon organ E) Pacinian corpuscle -- Correct Answer ✔✔ C) cutaneous free nerve ending
Withdrawal reflex is activated by stimuli from free nerve endings. Muscle spindles provide the afferent signals for the stretch reflex, and Golgi tendon organs are the source of stimuli for the inverse myotatic reflex.
- Nasal, lacrimal, salivary, and GI glands are stimulated by which substance? A) ACh B) norepinephrine C) epinephrine D) serotonin E) dopamine -- Correct Answer ✔✔ A) ACh All of these glands are simulated by cholinergic postganglionic parasympathetic neurons.
- Which of the following reflexes best describes incoming pain signals that elicit movements performed by antagonistic muscle groups on either side of the body? A) crossed extensor reflex B) withdrawal reflex C) reciprocal inhibition D) autogenic inhibition -- Correct Answer ✔✔ A) crossed extensor reflex The crossed extensor reflex depends on incoming pain signals distributed to both sides of the spinal cord via excitatory interneurons.
- Which reflex is correctly paired with the sensory structure that mediates the reflex? A) autogenic inhibition --> muscle spindle B) reciprocal inhibition --> Golgi tendon organ C) reciprocal inhibition --> Pacinian corpuscle D) stretch reflex --> muscle spindle E) Golgi tendon reflex --> Meissner corpuscle -- Correct Answer ✔✔ D) stretch reflex --> muscle spindle Autogenic inhibition involves GTOs. Reciprocal inhibition is also related to muscle spindles.
- The function of which organ or system is dominated by the SNS?
A) macula of the utricle B) macula of the saccule C) crista ampullaris of the anterior semicircular duct D) crista ampullaris of the horizontal semicircular duct -- Correct Answer ✔✔ B) macula of the saccule
- Drugs that stimulate specific adrenergic receptors are called sympathomimetic drugs. Which drug is a sympathomimetic? A) reserpine B) phentolamine C) propranolol D) L-dopa E) phenylephrine -- Correct Answer ✔✔ E) phenylephrine All others are sympathetic antagonists.
- Which of the following best describes an attribute of visceral smooth muscle not shared by skeletal muscle? A) contraction is ATP-dependent B) contracts in response to stretch C) does not contain actin filaments D) high rate of cross-bridge cycling E) low maximal force of contraction -- Correct Answer ✔✔ B) contracts in response to stretch Stretch results in depolarization and potentially generation of APs. These APs coupled with normal slow-wave potentials stimulate rhythmical contractions. Like skeletal muscle, smooth muscle contraction depends on actin and ATP, however the cross-bridge cycle is slower in smooth muscle, allowing for higher maximal force of contraction.
- A single contraction of skeletal muscle is most likely to be terminated by which of the following actions? A) closure of the postsynaptic nicotinic ACh receptor B) removal of ACh from the NMJ C) removal of Ca2+ from the terminal of the motor neuron D) removal of sarcoplasmic Ca2+
E) return of the dihydropyridine receptor to its resting conformation -- Correct Answer ✔✔ D) removal of sarcoplasmic Ca2+ Skeletal muscle contraction is tightly regulated by the concentration of Ca2+ in the sarcoplasm. As long as it is sufficiently high, none of the remaining events (removal of ACh from NMJ, removal of Ca2+ from presynaptic terminal, closure of AChR channel, and return of DHPR to resting conformation) would have any effect on the contractile state of the muscle.
- Calmodulin is most closely related, both structurally and functionally, to which of the following proteins? A) G-actin B) myosin light chain C) tropomyosin D) troponin C -- Correct Answer ✔✔ D) troponin C In smooth muscle, binding of four Ca2+ ions to calmodulin permits interaction of Ca2+-calmodulin complex with MLCK. This activates MLCK and results in phosphorylation of myosin light chains, and ultimately muscle contraction. In skeletal muscle, the activating Ca2+ signal is received by troponin C.
- During a demonstration for medical students, a neurologist uses magnetic cortical stimulation to trigger firing of the ulnar nerve in a volunteer. At relatively low- amplitude stimulation, APs are recorded only from muscle fibers in the index finger. As the amplitude of the stimulation is increased, APs are recorded from muscle fibers in both the index finger and the biceps muscle. What is the fundamental principle underlying this amplitude-dependent response? A) large motor neurons that innervate large motor units require a larger depolarizing stimulus B) recruitment of multiple motor units requires a larger depolarizing stimulus C) the biceps muscle is innervated by more motor neurons D) the motor units in the biceps are smaller than those in the muscles of the fingers E) the muscles in the fingers are innervated only by the ulnar nerve -- Correct Answer ✔✔ A) large motor neurons that innervate large motor units require a larger depolarizing stimulus
- Weight-lifting can result in a dramatic increase in skeletal muscle mass. This increase in muscle mass is primarily attributable to which of the following? A) fusion of sarcomeres between adjacent myofibrils B) hypertrophy of individual muscle fibers C) increase in skeletal muscle blood supply D) increase in the number of motor neurons E) increase in the number of NMJs -- Correct Answer ✔✔ B) hypertrophy of individual muscle fibers Prolonged or repeated maximal contraction results in a concomitant increase in the synthesis of contractile proteins and an increase in muscle mass, or hypertrophy, is observed at the level of individual fibers.
- The delayed onset and prolonged duration of smooth muscle contraction, as well as the greater force generated by smooth muscle compared with skeletal muscle, are all consequences of which of the following? A) greater amount of myosin filaments present in smooth muscle B) higher energy requirement of smooth muscle C) physical arrangement of actin and myosin filaments D) slower cycling rate of the smooth muscle myosin cross-bridges E) slower uptake of Ca2+ ions after contraction -- Correct Answer ✔✔ D) slower cycling rate of the smooth muscle myosin cross-bridges Slower cycling rate of cross-bridges means that a higher percentage of possible cross-bridges is active at any point in time. The more active cross-bridges there are, the greater the force that is generated. Although the relatively slow cycling rate means that it takes longer for the myosin head to attach to the actin filament, it also means that the myosin head remains attached longer, prolonging the contraction. Because of the slow cross-bridge cycling rate, smooth muscle actually requires less energy to maintain a contraction compared with skeletal muscle.
- An experimental drug is being tested as a potential therapeutic treatment for asthma. Preclinical studies have shown that this drug induces the relaxation of cultured porcine tracheal smooth muscle cells pre-contracted with ACh. Which of the following mechanisms of action is most likely to induce this effect? A) decreased affinity of troponin C for Ca2+
B) decreased plasma membrane K+ permeability C) increased plasma membrane Na+ permeability D) inhibition of the SR Ca2+ ATPase E) stimulation of adenylate cyclase -- Correct Answer ✔✔ E) stimulation of adenylate cyclase The stimulation of adenylate or guanylate cyclase induces smooth muscle relaxation. The cyclic nucleotides produced by these enzymes stimulate cAMP and cGMP-dependent kinases, which phosphorylate enzymes that remove Ca2+ from the cytosol. In doing so, they inhibit contraction. In contrast, either a decrease in K+ or an increase in Na+ permeability results in membrane depolarization and contraction. Likewise, inhibition of SERCA would also favor muscle contraction. Smooth muscle does not express troponin.
- A 55 y/o female visits her physician because of double vision, eyelid droop, difficulty chewing and swallowing, and general weakness in her limbs. All these symptoms worsen with exercise and occur more frequently late in the day. The physician suspects myasthenia gravis and orders a Tensilon test. The test is positive. The increased muscle strength observed during the Tensilon test is due to an increase in which of the following? A) amount of ACh released from the motor nerves B) levels of ACh at the muscle end plates C) number of ACh receptors on the muscle end plates D) synthesis of norepinephrine -- Correct Answer ✔✔ B) levels of ACh at the muscle end plates MG is an autoimmune disease in which antibodies damage postsynaptic nicotinic AChRs. This damage prevents the firing of an AP in the postsynaptic membrane. Tensilon is a readily reversible AChE inhibitor that increases ACh levels in the NMJ, thereby increasing the strength of muscle contraction.
- A 55 y/o female visits her physician because of double vision, eyelid droop, difficulty chewing and swallowing, and general weakness in her limbs. All these symptoms worsen with exercise and occur more frequently late in the day. The physician suspects myasthenia gravis and orders a Tensilon test. The test is positive. What is the most likely basis for the symptoms described in this patient? A) autoimmune response
E) uptake of Ca2+ ions into the SR -- Correct Answer ✔✔ B) dephosphorylation of myosin light chain Smooth muscle contraction is regulated by both Ca2+ and myosin light chain phosphorylation. When the cytosolic Ca2+ concentration decreases after the initiation of contraction, MLCK becomes inactivated. However, cross-bridge formation continues, even in the absence of Ca2+, until the myosin light chains are dephosphorylated through the action of MLCP.
- A 56 y/o male sees a neurologist because of weakness in his legs that improves over the course of the day or with exercise. Extracellular electrical recordings from a single skeletal muscle fiber reveal normal miniature end plate potentials. Low- frequency electrical stimulation of the motor neuron, however, elicits an abnormally small depolarization of the muscle fibers. The amplitude of the depolarization is increased after exercise. Based on these findings, which of the following is the most likely cause of the patient's leg weakness? A) AChE deficiency B) blockade of postsynaptic ACh receptors C) impaired presynaptic voltage-sensitive Ca2+ influx D) inhibition of Ca2+ reuptake into the SR E) reduced ACh synthesis -- Correct Answer ✔✔ C) impaired presynaptic voltage-sensitive Ca2+ influx The normal miniature end-plate potentials indicate sufficient synthesis and packaging of ACh and the presence and normal function of ACh receptor channels. The most likely explanation is a presynaptic deficiency, in this case, an impairment of voltage-dependent Ca2+ channels responsible for the increase in cytosolic Ca2+ that triggers release of ACh into the synapse. The increase in postsynatpic depolarization observed after exercise is indicative of an accumulation of Ca2+ in the presynaptic terminal after multiple APs have reached the nerve terminal.
- A 56 y/o male sees a neurologist because of weakness in his legs that improves over the course of the day or with exercise. Extracellular electrical recordings from a single skeletal muscle fiber reveal normal miniature end plate potentials. Low- frequency electrical stimulation of the motor neuron, however, elicits an abnormally small depolarization of the muscle fibers. The amplitude of the
depolarization is increased after exercise. A preliminary diagnosis is confirmed by the presence of which of the following? A) antibodies against the ACh receptor B) antibodies against the voltage-sensitive Ca2+ channel C) mutation in the gene that codes for the ryanodine receptor D) relatively few vesicles in the presynaptic terminal E) residual ACh in the NMJ -- Correct Answer ✔✔ B) antibodies against the voltage-sensitive Ca2+ channel Inhibition of presynaptic voltage-gated Ca2+ channels is most consistent with the presence of Abs against this channel. Abs against the AChR, a mutation in RYR, and residual ACh in the junction are all indicative of postsynaptic defects. Although it is a presynaptic defect, a deficit of ACh vesicles is unlikely given the normal miniature end-plate potentials recorded in the postsynaptic membrane.
- A 56 y/o male sees a neurologist because of weakness in his legs that improves over the course of the day or with exercise. Extracellular electrical recordings from a single skeletal muscle fiber reveal normal miniature end plate potentials. Low- frequency electrical stimulation of the motor neuron, however, elicits an abnormally small depolarization of the muscle fibers. The amplitude of the depolarization is increased after exercise. The molecular mechanism underlying these symptoms is most similar to which of the following? A) ACh B) botulinum toxin C) curare D) neostigmine E) tetrodotoxin -- Correct Answer ✔✔ B) botulinum toxin Botulinum toxin inhibits muscle contraction presynaptically by reducing the amount of ACh released into the NMJ. In contrast, curare acts postsynaptically to block the nAChR and prevent the excitation of muscle cell membranes. Tetrodotoxin blocks voltage-gated Na+ channels, affecting both initiation and propagation of APs in the motor neuron. Both ACh and neostigmine stimulate muscle contraction.
- A physiology experiment is conducted in which a motor neuron that normally innervates a predominantly fast type II muscle is anastomosed to a predominantly
- Smooth muscle that exhibits rhythmical contraction in the absence of external stimuli also necessarily exhibits which of the following? A) "slow" voltage-sensitive Ca2+ channels B) intrinsic pacemaker wave activity C) higher resting cytosolic Ca2+ concentration D) hyperpolarized membrane potential E) action potentials with "plateaus" -- Correct Answer ✔✔ B) intrinsic pacemaker wave activity An intrinsic rhythmical "pacemaker" is required for a muscle to contract spontaneously and rhythmically. Intestinal smooth muscle, for example, exhibits a rhythmical slow-wave potential that transiently depolarizes and repolarizes the muscle membrane. This slow-wave does not stimulate contraction itself, but if the amplitude is sufficient, it can trigger one or more APs that result in Ca2+ influx and contraction. Although they are typical of smooth muscle, neither "slow" voltage-sensitive Ca2+ channels nor APs with "plateaus" play a necessary role in rhythmical contraction. A high resting cytosolic Ca2+ concentration would support sustained contraction, and hyperpolarization would favor relaxation.
- An apparently healthy 15 y/o boy dies during a minor surgical procedure while under general anesthesia. The boy's grandfather also died during a surgical procedure. A clinical assessment team determines that the child had malignant hyperthermia (MH). MH is an inherited disease in which triggering agents, such as certain anesthetics, stimulate calcium release from storage sites in muscle, leading to elevated concentrations of myoplasmic calcium. The MH crisis is most likely to be associated with which of the following? A) decreased anaerobic metabolism B) decreased CO2 production by muscles C) decreased lactic acid production by muscles D) defective calsequestrin E) defective dihydropyridine receptors F) defective ryanodine receptors -- Correct Answer ✔✔ F) defective ryanodine receptors In MH, defective RYRs repsond to certain halogenated anesthetics by opening their associated Ca2+ channels within the muscle fiber and thus causing an
increase in myoplasmic Ca2+. This increase causes continuous contraction of muscles, resulting in increased body temperature, increased anaerobic metabolism, increased CO2 production, and increased lactic acid production. Calsequestrin is a protein molecule that binds Ca2+ within the SR of the muscle fiber, and it is not affected by halogenated anesthetics. DHPRs are activated by skeletal muscle fiber AP, but are not affected by halogenated anesthetics.
- A 24 y/o woman is admitted as an emergency to a hospital after an MVC in which severe lacerations to the left wrist severed a major muscle tendon. The severed ends of the tendon were overlapped by 6 cm to facilitate suturing and reattachment. Which of the following would be expected after 6 weeks compared with the pre-injured muscle? Assume that series growth of sarcomeres cannot be completed in 6 weeks. A) decreased passive tension and decreased maximal active tension B) decreased passive tension and increased maximal active tension C) increased passive tension and increased maximal active tension D) increased passive tension and decreased maximal active tension E) no change in passive tension or maximal active tension -- Correct Answer ✔✔ D) increased passive tension and decreased maximal active tension Stretching the muscle to facilitate reattachment of the tendons leads to an increase in passive tension or preload. This increase in passive tension increases the muscle length beyond its ideal length, which in turn leads to a decrease in the maximal active tension that can be generated by the muscle. The reason maximal active tension decreases is that interdigitation of actin and myosin filaments decreases when the muscle is stretched; the interdigitation of a muscle is normally optimal at its resting length.
- The sensitivity of the smooth muscle contractile apparatus to calcium is known to increase in the steady state under normal conditions. This increase in calcium sensitivity can be attributed to a decrease in the levels of which of the following substances? A) actin B) ATP C) calcium-calmodulin complex D) calmodulin
- Which of the following best describes a physiological difference between the contraction of smooth muscle compared with the contraction of cardiac muscle and skeletal muscle? A) Ca2+ independent B) does not require an action potential C) requires more energy D) shorter in duration -- Correct Answer ✔✔ B) does not require an action potential Smooth muscle can be stimulated to contract without the generation of an AP, whereas both cardiac and skeletal muscle require an AP. Smooth muscle can contract in response to any stimulus that increases the cytosolic Ca2+ concentration, which includes Ca2+ channel openers, subthreshold depolarization, and a variety of tissue factors and circulating hormones that stimulate the release of intracellular Ca2+ stores. Smooth muscle contraction uses less energy and lasts longer compared to skeletal muscle and cardiac muscle contraction. Smooth muscle contraction is heavily Ca2+ dependent.
- A 12 y/o boy presents with a 4-month history of diminished vision and diplopia. He also experiences tiredness towards the end of the day. He has no other symptoms. On exam, the patient has ptosis of the left eye that improves after a period of sleep. Clinical exam is otherwise normal. No evidence of weakness of any other muscles is found. Additional testing indicates the presence of anti-acetylcholine antibodies in the plasma, a normal thyroid function test, and a normal CT scan of the brain and orbit. What is the initial diagnosis? A) astrocytoma B) Graves' disease C) Hashimoto's thyroiditis D) juvenile myasthenia gravis E) multiple sclerosis -- Correct Answer ✔✔ D) juvenile myasthenia gravis Patients with MG often feel well in the morning, but weaker as the day goes on. The major symptom is muscle weakness, which usually causes symptoms of double vision and drooping eyelids. The presence of anti-ACh antibodies in the plasma is specific for MG and rules out the other answer choices.
- A transmitter substance released from a presynaptic neuron activates a 2nd messenger G-protein system in the postsynaptic neuron. Which one of the following postsynaptic responses to the transmitter substance is NOT a possible outcome? A) activation of cAMP B) activation of cGMP C) activation of gene transcription D) closing an ion channel E) opening an ion channel -- Correct Answer ✔✔ D) closing of an ion channel A second messenger system can be activated by a transmitter substance released from an initial neuron by first causing the release of a G protein into the second neuron's cytoplasm. NT activation of G proteins is not known to cause closure of an ion channel. G proteins can activate G-protein-gated ion channels for both Na+ and K+, as well as gene transcription, and cAMP and cGMP. G proteins can also activate intracellular enzymes. E)
- A pool of presynaptic neurons innervate the dendrites of a postsynaptic neuron. Electrical signals are transferred from the dendrites to the soma of the postsynaptic neuron by which process? A) action potential B) active transport C) capacitative discharge D) diffusion E) electrotonic conduction -- Correct Answer ✔✔ E) electrotonic conduction Dendrites have few voltage-gated Na+ channels, which makes it virtually impossible for APs to be initiated here. A neuron can be considered a type of capacitor that discharges during an AP, but this occurs in the axon, not the dendrites. Electrotonic conduction does not occur by diffusion or active transport.
- Which of the following is characteristic of the events occurring at an excitatory synapse? A) there is a massive efflux of Ca2+ from the presynaptic terminal
