BSCI440 End of Chapter Questions: 8, 11, 12, 13
In each of the following scenarios, will an action potential be produced? The postsynaptic neuron has a resting membrane potential of -70mV. (a) Fifteen neurons synapse on one postsynaptic neuron. At the trigger zone, 12 of the neurons produce EPSPs of 2 mV each, and the other three produce IPSPs of 3 mV each. The thresh- old for the postsynaptic cell is -50 mV. (b) Fourteen neurons synapse on one postsynaptic neuron. At the trigger zone, 11 of the neurons produce EPSPs of 2 mV each, and the other three produce IPSPs of 3 mV each. The thresh- old for the postsynaptic cell is -60 mV. (c) Fifteen neurons synapse on one postsynaptic neuron. At the trigger zone, 14 of the neurons produce EPSPs of 2 mV each, and the other one produces an IPSP of 9 mV. The threshold for the postsynaptic cell is -50 mV.
(a) (12 * 2mV = 24) + (3 * 93mV = 99) = signalstrength of15mV. Vm = 970 + 15 = 955mV. Threshold is -50 so no action potential. (Vm must be equal to or more positive than threshold.) (b) Net signal = +13 mV. -70 + 13 = -57. Threshold is -60 so action potential will fire. (c) Net signal = +19. -70 + 19 = -51. Threshold is -50 so no action potential.
The GHK equation is sometimes abbreviated to exclude chloride, which plays a minimal role in membrane potential for most cells. In addition, because it is difficult to determine absolute membrane permeability values for Na+ and K+, the equation is revised to use the ratio of the two ion permeabilities, expressed as a = PNa/PK: Thus, if you know the relative membrane permeabilities of the two ions and their intracellular (ICF) and extracellular (ECF) concen- trations, you can predict the membrane potential for a cell. Using a calculator with log function or the free online Nernst/ Goldman equation simulator from the University of Arizona (www .nernstgoldman.physiology.arizona.edu/), do the following calculations. (a) A resting cell has an alpha (a) value of 0.025 and the following ion concentrations: Na+: ICF = 5mM, ECF = 135mM K+: ICF = 150mM, ECF = 4mM What is the cell's membrane potential?
(a) -80 mV
Match the structure to all correct statements about it. a. muscle spindle b. Golgi tendon organ c. joint capsule mechanoreceptor 1. is strictly a sensory receptor 2. has sensory neurons that send information to the CNS 3. is associated with two types of motor neurons 4. conveys information about the relative positioning of bones 5. is innervated by gamma motor neurons 6. modulates activity in alpha motor neurons
(a) 2,3,5,6 (b) 1,2,6 (c) 1,2,4
Use the arm in Figure 12.20c to answer the following questions. (a) How much force would a biceps muscle inserted 4 cm from the fulcrum need to exert to hold the arm stationary at a 90° angle? How does this force compare with the force needed when the insertion point is 5 cm from the fulcrum?
(a) 7.5 kg of force, a 125% increase
One way that scientists study muscles is to put them into a stateof rigor by removing ATP. In this condition, actin and myosin are strongly linked but unable to move. On the basis of what you know about muscle contraction, predict what would happen to these mus- cles in a state of rigor if you (a) added ATP but no free calcium ions; (b) added ATP with a substantial concentration of calcium ions.
(a) Adding ATP allows crossbridges to detach. If insufficient Ca2+ is available, the muscle will relax. (b) With ATP and Ca2+, the muscle will continue in the contraction cycle until it is completely contracted.
At your last physical, your physician checked your patellar tendon reflex by tapping just below your knee while you sat quietly on the edge of the table. (a) What was she checking when she did this test? (b) What would happen if you were worried about falling off the table and were very tense? Where does this additional input to the efferent motor neurons originate? Are these modulatory neu- rons causing EPSPs or IPSPs [p. 297] at the spinal motor neuron? (c) Your physician notices that you are tense and asks you to count backward from 100 by 3's while she repeats the test. Why would carrying out this counting task enhance your reflex?
(a) Assessing the components that regulate limb movement, including quadriceps muscle, the nerves that control it, and the area of the spinal cord where the reflex integrates. (b) The reflex would probably be less apparent. The origin of this inhibition is the primary motor cortex. The inhibitory cells will produce IPSPs in the spinal motor neuron. (c) If the brain is distracted by some other task, the inhibitory signals will presumably stop.
Compare and contrast (a) autonomic ganglia and CNS nuclei (b) the adrenal medulla and the posterior pituitary gland (c) axon terminals and varicosities
(a) Autonomic ganglia—nerve cell bodies of postganglionic autonomic neurons. CNS nuclei—nerve cell bodies in the brain and spinal cord. (b) Both have true endocrine tissue and neuroendocrine tissue. (c) Boutons—ends of axons; varicosities—strung out along the ends of autonomic neurons.
Compare and contrast: fast-twitch oxidative-glycolytic, fast-twitch glycolytic, and slow-twitch muscle fibers
(a) Fast-twitch oxidative-glycolytic—smaller, some myoglobin, use both oxidative and glycolytic metabolism, more fatigue-resistant. Fast- twitch glycolytic fibers—largest, rely primarily on anaerobic glycolysis, least fatigue-resistant. Slow-twitch—develop tension more slowly, maintain tension longer, the most fatigue-resistant, depend primarily on oxidative phosphorylation, more mitochondria, greater vascularity, large amounts of myoglobin, smallest in diameter.
It's Halloween, and you are walking through the scariest haunted house around. As you turn a corner and enter the dungeon, a skeleton reaches out and grabs your arm. You let out a scream. Your heart rate quickens, and you feel the hairs on your arm stand on end. (a) What has just happened to you? (b) Where in the brain is fear processed? What are the functions of this part of the brain? Which branch (somatic or autonomic) of the motor output does it control? What are the target organs forthis response? (c) How is it possible for your hair to stand on end when hair is made of proteins that do not contract? [Hint: See p. 122.] Given that the autonomic nervous system is mediating this reflex response, which type of tissue do you expect to find attached to hair follicles?
(a) Fright activates the sympathetic nervous system fight-or-flight response. (b) Limbic system processes fear. Other functions include regulating drives such as sex, rage, aggression, and hunger, and reflexes including urination, defecation, and blushing. Limbic system influences autonomic motor output. Heart, blood vessels, respiratory muscles, smooth muscle, and glands are some of the target organs involved. (c) Smooth muscles attach to the base of each hair and pull them upright. [See Focus on: The Skin, p. 122.]
Choose from the following ions to fill in the blanks correctly: Na+, K+, Ca2+, Cl- (a) The resting cell membrane is more permeable to _____ than to _____. Although _____ contribute little to the resting membrane potential, they play a key role in generating electrical signals in excitable tissues. (b) The concentration of _____ is 12 times greater outside the cell than inside. (c) The concentration of _____ is 30 times greater inside the cell than outside. (d) An action potential occurs when _____ enter the cell. (e) The resting membrane potential is due to the high _____ permeability of the cell.
(a) K+, Na+, Na+ (b) Na+ (c) K+ (d) Na+ (e) K+
Compare and contrast: a) neuroeffector junctions and neuromuscular junctions b) alpha, beta, muscarinic, and nicotinic receptors. Describe where each is found and the ligands that bind to them.
(a) Neuroeffector junction—distal ends of autonomic axons, anywhere there is a varicosity. Neuromuscular junction—axon terminals of the somatic motor neuron. (b) Alpha and beta adrenergic; nicotinic and muscarinic cholinergic. Nicotinic—on skeletal muscle and postgangli- onic autonomic neurons. Adrenergic and muscarinic receptors—autonomic targets.
There are several theories about how presynaptic inhibition works at the cellular level. Use what you have learned about membrane potentials and synaptic transmission to explain how each of the fol- lowing mechanisms would result in presynaptic inhibition: (a) Voltage-gated Ca2+ channels in axon terminal are inhibited. (b) Cl- channels in axon terminal open. (c) K+ channels in axon terminal open.
(a) Prevents Ca2+ activated transmitter release. (b) Cell hyperpolarizes and voltage-gated Ca2+ channels in terminal will not open. (c) Same as (b).
Arrange the following terms to describe the sequence of events after a neurotransmitter binds to a receptor on a postsynaptic neu- ron. Terms may be used more than once or not at all. (a) action potential fires at axon hillock (b) trigger zone reaches threshold (c) cell depolarizes (d) exocytosis (e) graded potential occurs (f) ligand-gated ion channel opens (g) local current flow occurs (h) saltatory conduction occurs (i) voltage-gated Ca2+ channels open (j) voltage-gated K+ channels open (k) voltage-gated Na+ channels open
(f)-(c)-(g)-(e)-(b)-(k)-(c)-(a)-(h)-(j)-(i)-(d)
Define, compare, and contrast the following concepts: (a) threshold, subthreshold, suprathreshold, all-or-none, overshoot, undershoot (b) graded potential, EPSP, IPSP (c) absolute refractory period, relative refractory period (d) afferent neuron, efferent neuron, interneuron (e) sensory neuron, somatic motor neuron, sympathetic neuron, autonomic neuron, parasympathetic neuron (f) fast synaptic potential, slow synaptic potential (g) temporal summation, spatial summation (h) convergence, divergence
(a) Threshold signals trigger action potentials. Suprathreshold also trigger action potentials, but subthreshold do not unless summed. Action potentials are all-or-none events. Overshoot—portion of the action potential above 0 mV. Undershoot—after-hyperpolarization portion of the action potential. (b) Graded potentials may be depolar- izing or hyperpolarizing. Graded potential in a postsynaptic cell is an EPSP if depolarizing and an IPSP if hyperpolarizing. (c) No stimulus can trigger another action potential during the absolute refractory period, but a suprathreshold stimulus can trigger an action potential during the relative refractory period. (d) See answer to question 1. (e) Sensory are afferents; all others are efferents. (f) Fast synaptic poten- tials result from neurotransmitters altering ion channel gating, occur rapidly, and are short-lived. Slow synaptic potentials are mediated through second messengers, may involve protein modification, and last longer. (g) Temporal summation—multiple stimuli arrive at the trigger zone close together in time. Spatial summation—multiple stimuli from different locations arrive simultaneously at the trigger zone. (h) Divergence—a single neuron branches and its collaterals synapse on multiple targets. Convergence—multiple presynaptic neu- rons provide input to a smaller number of postsynaptic neurons.
A neuron has a resting membrane potential of -70 mV. Will the neuron hyperpolarize or depolarize when each of the following events occurs? (More than one answer may apply; list all those that are correct.) (a) Na+ enters the cell (b) K+ leaves the cell (c) Cl- enters the cell (d) Ca2+ enters the cell
(a) depolarize (b) hyperpolarize (c) hyperpolarize (d) depolarize
You have discovered a neuron that innervates an endocrine cell in the intestine. To learn more about this neuron, you place a marker substance at the endocrine cell synapse. The marker is taken into the neuron and transported in a vesicle by retrograde axonal trans- port to the nerve cell body. (a) By what process is the marker probably taken into the axon terminal? (b) The nerve cell body is found in a ganglion very close to the endocrine cell. To which branch of the peripheral nervous system does the neuron probably belong? (Be as specific as you can.) (c) Which neurotransmitter do you predict will be secreted by the neuron onto the endocrine cell?
(a) endocytosis (b) parasympathetic autonomic (c) acetylcholine
Somatic motor pathways (a) are excitatory or inhibitory? (b) are composed of a single neuron or a preganglionic and a post-ganglionic neuron? (c) synapse with glands or with smooth, cardiac, or skeletal muscle?
(a) excitatory (b) single neuron (c) synapse with skeletal muscle
Which of the following statement(s) is (are) true about cardiac muscle? (a) Cardiac muscle fibers are longer than skeletal muscle fibres. (b) Cardiac muscles fibers are multinucleated. (c) Cardiac muscle fibers contain intercalated discs. (d) Cardiac muscle is under the control of the autonomic nervous system.
(a) false (b) false (c) true (d) true
Describe the event (muscle contraction/relaxation) that would occur in the following situations: (a) the treatment of nicotinic acetylcholine receptors with nicotine (b) the treatment of nicotinic acetylcholine receptors with curare (c) the treatment of nicotinic acetylcholine receptors with α-bungarotoxin (d) the treatment of muscarinic acetylcholine receptors with atropine
(a) skeletal muscle contraction (b) skeletal muscle relaxation (c) skeletal muscle relaxation (d) smooth muscle relaxation
Characterize each of the following stimuli as being mechanical, chemical, or thermal: (a) bath water at 106 °F (b) acetylcholine (c) a hint of perfume (d) epinephrine (e) lemon juice (f) a punch on the arm
(a) thermal (b) chemical (c) chemical (d) chemical (e) chemical (f) mechanical
Which of the following statements is true regarding demyelinating diseases? (Choose all correct answers): (a) Demyelinating diseases are characterized by muscle weakness. (b) Multiple sclerosis is the most common demyelinating disease. (c) A loss of myelin occurs in demyelinating diseases. (d) The conduction of action potentials is increased in demyelinating diseases.
(a), (b) and (c) are true. (d) is false
If a target cell's receptor is _________ (use items in left column), the neuron(s) releasing neurotransmitter onto the receptor must be ___________ (use all appropriate items from the right column). (a) nicotinic cholinergic (b) adrenergic alpha (c) muscarinic cholinergic (d) adrenergic beta 1. somatic motor neuron 2. autonomic preganglionic neuron 3. sympathetic postganglionic neuron 4. parasympathetic postganglionic neuron
(a)1,2 (b)3 (c)4 (d)3
Match the numbers of the appropriate characteristics with the two types of potentials. Characteristics may apply to one or both types. (a) action potential (b) graded potential 1. all-or-none 2. can be summed 3. amplitude decreases with distance 4. exhibits a refractory period 5. amplitude depends on strength of stimulus 6. has no threshold
(a)1,4 (b)2,3,5,6
Match (a) axon (b) dendrite (c) afferent (d) efferent (e) trigger zone 1. process of a neuron that receives incoming signals 2. sensory neuron, transmits information to CNS 3. long process that transmits signals to the target cell 4. region of neuron where action potential begins 5. neuron that transmits information from CNS to the rest of the body
(a)3 (b)1 (c)2 (d)5 (e)4
Match the glial cell(s) on the right to the functions on the left. There may be more than one correct answer for each function. (a) modified immune cells (b) help form the blood-brain barrier (c) form myelin (d) separate CNS fluid compartments (e) found in peripheral nervous system (f) found in ganglia 1. astrocytes 2. ependymal cells 3. microglia 4. oligodendrocytes 5. satellite cells 6. Schwann cells
(a)3 (b)1 (c)4,6 (d)2 (e)5,6 (f)5
The GHK equation is sometimes abbreviated to exclude chloride, which plays a minimal role in membrane potential for most cells. In addition, because it is difficult to determine absolute membrane permeability values for Na+ and K+, the equation is revised to use the ratio of the two ion permeabilities, expressed as a = PNa/PK: Thus, if you know the relative membrane permeabilities of the two ions and their intracellular (ICF) and extracellular (ECF) concen- trations, you can predict the membrane potential for a cell. Using a calculator with log function or the free online Nernst/ Goldman equation simulator from the University of Arizona (www .nernstgoldman.physiology.arizona.edu/), do the following calculations. (b) The Na+ permeability of the cell in (a) suddenly increases so that a = 20. Now what is the cell's membrane potential?
(b) +63 mV
Compare and contrast: a twitch and tetanus
(b) Twitch—a single contraction-relaxation cycle. Tetanus—contraction with little to no relaxation.
Use the arm in Figure 12.20c to answer the following questions. Suppose a 7-kg weight band is placed around the wrist 20 cm from the fulcrum. How much force does the biceps inserted5 cm from the fulcrum need to exert to hold the arm station- ary at a 90° angle? How does this force compare with the force needed to keep the arm horizontal in the situation shown in Figure 12.20c, with the same weight in the hand (25 cm from the fulcrum)?
(b) an additional 28 kg of force. This is less than if the weight is placed in the hand.
The motor end plate (choose all that apply) (a) is a modification of the preganglionic neuron (b) is a modification of the muscle membrane (c) contains clusters of nicotinic ACh receptors (d) contains voltage-gated Ca2+ channels
(b) is a modification of the muscle membrane (c) contains clusters of nicotinic ACh receptors
A subthreshold graded potential would result in (a) an action potential. (b) no action potential. (c) a subthreshold action potential (d) a reversal in the direction of propagation of the action potential.
(b) no action potential.
One of the pills that Ji takes for high blood pressure caused his blood K+ level to decrease from 4.5 mM to 2.5 mM. What happens to the resting membrane potential of his liver cells? (Circle all that are correct.) (a) decreases (b) increases (c) does not change (d) becomes more negative (e) becomes less negative (f) fires an action potential (g) depolarizes (h) hyperpolarizes (i) repolarizes
(b), (d), and (h)
The GHK equation is sometimes abbreviated to exclude chloride, which plays a minimal role in membrane potential for most cells. In addition, because it is difficult to determine absolute membrane permeability values for Na+ and K+, the equation is revised to use the ratio of the two ion permeabilities, expressed as a = PNa/PK: Thus, if you know the relative membrane permeabilities of the two ions and their intracellular (ICF) and extracellular (ECF) concen- trations, you can predict the membrane potential for a cell. Using a calculator with log function or the free online Nernst/ Goldman equation simulator from the University of Arizona (www .nernstgoldman.physiology.arizona.edu/), do the following calculations (c) Mrs. Nguyen has high blood pressure, and her physician puts her on a drug whose side effect decreases her plasma (ECF) K+ from 4 mM to 2.5 mM. Using the other values in (a), calculate the membrane potential with decreased plasma K+.
(c) -86 mV
Compare and contrast: action potentials in motor neurons and action potentials in skeletal muscles
(c) Both result from inward Na+ current and outward K+ current through voltage-gated channels. Motor neuron action potential triggers ACh release. Muscle action potential triggers Ca2+ release from the sarcoplasmic reticulum.
Repeated neuron stimulation over a short period may strengthen certain synapses. This process is called (a) denaturation (b) long term memory (c) long term potentiation (d) long term deviation
(c) long term potentiation
Axonal transport refers to the (a) release of neurotransmitters into the synaptic cleft. (b) use of microtubules to send secretions from the cell body to the axon terminal. (c) movement of organelles and cytoplasm up and down the axon. (d) movement of the axon terminal to synapse with a new postsyn- aptic cell. (e) none of these.
(c). Answer (b) is only partly correct because not all axonal transport uses microtubules and not all substances moved will be secreted.
The GHK equation is sometimes abbreviated to exclude chloride, which plays a minimal role in membrane potential for most cells. In addition, because it is difficult to determine absolute membrane permeability values for Na+ and K+, the equation is revised to use the ratio of the two ion permeabilities, expressed as a = PNa/PK: Thus, if you know the relative membrane permeabilities of the two ions and their intracellular (ICF) and extracellular (ECF) concen- trations, you can predict the membrane potential for a cell. Using a calculator with log function or the free online Nernst/ Goldman equation simulator from the University of Arizona (www .nernstgoldman.physiology.arizona.edu/), do the following calculations (d) The physician prescribes a potassium supplement for Mrs. Nguyen, who decides that if two pills are good, four must be better. Her plasma (ECF) K+ now goes to 6 mM. What happens to her membrane potential?
(d) -73 mV
Compare and contrast: temporal summation in motor neurons and summation in skeletal muscles
(d) Motor neuron temporal summation determines whether or not the neuron fires an action potential. Muscle cell summation increases force of contraction.
Compare and contrast: isotonic contraction and isometric contraction
(e) Isotonic contraction moves a load. Isometric contraction creates tension without moving a load.
Arrange the following events in the proper sequence: (a) Efferent neuron reaches threshold and fires an action potential. (b) Afferent neuron reaches threshold and fires an action potential. (c) Effector organ responds by performing output. (d) Integrating center reaches decision about response. (e) Sensory organ detects change in the environment.
(e)-(b)-(d)-(a)-(c)
Compare and contrast: slow-wave and pacemaker potentials
(f) Slow-wave potentials—cycles of depolarization and repolarization in smooth muscle cells. Pacemaker potentials—repetitive depolarizations to threshold in some smooth muscle and cardiac muscle.
List four things that can happen to autonomic neurotransmitters after they are released into a synapse.
1. Diffuse away from the synapse 2. Broken down by enzymes in the syn- apse 3. Taken back into the presynaptic neuron 4. Bind to a membrane receptor.
Name any four neurotransmitters, their receptor(s), and tell whether the receptor is an ion channel or a GPCR.
1. Dopamine - Dopamine - GPCR 2. Glycine - Glycine - ICR (Cl-) 3. Adenosine - Purine - GPCR
Match the following characteristics with the appropriate type(s) of muscle. a. has the largest diameter b. uses anaerobic metabolism, thus fatigues quickly c. has the most blood vessels d. has some myoglobin e. is used for quick, fine movements f. is also called red muscle g. uses a combination of oxida- tive and glycolytic metabolism h. has the most mitochondria 1. fast-twitch glycolytic fibers 2. fast-twitch oxidative- glycolytic fibers 3. slow-twitch oxidative fibers
1. a,b,e 2. d,f,g 3. c,d,f,h
What is the optimum resting length of a sarcomere? Explain how resting fiber length affects muscle tension.
2.0 - 2.3 μm. The tension developed by a muscle fiber is proportional to the number of crossbridges. If the sarcomere is long, there will be little overlap between the thick and thin filament and fewer cross- bridges will be formed. If too short, the thin filaments overlap with each other, preventing crossbridge formation.
During contraction, the __________ band remains a constant length. This band is composed primarily of __________ mol- ecules. Which components of the sarcomere approach each other during contraction?
A band; myosin. Z disks approach each other.
List the steps of skeletal muscle contraction that require ATP.
ATP binding—myosin dissociates from actin. ATP hydrolysis—myo- sin head swings and binds to a new actin. Release of Pi initiates the power stroke.
Which neurotransmitter is released by somatic motor neurons?
Acetylcholine
Which neurotransmitter does a cholinergic neuron secrete? Name the two subtypes of cholinergic receptors.
Acetylcholine (Ach). Cholinergic and muscarinic.
What is the purpose of alpha-gamma coactivation? Explain how it occurs.
Alpha-gamma coactivation allows muscle spindles to continue func- tioning when the muscle contracts. When the muscle contracts, the ends of the spindles also contract to maintain stretch on the central portion of the spindle.
Internal organs receive innervation from both parasympathetic and sympathetic neurons of the autonomic nervous system, which exert _____ control over the target.
Antagonistic
Botulinum toxin causes flaccid paralysis of skeletal muscles by interfering with neurotransmitter action. Knowing that somatic motor neurons are solely excitatory, describe how the toxin may exert such an effect.
Botulinum toxin is likely to prevent the release of the neurotransmitter ACh. This may prevent muscle contraction and cause flaccid paralysis.
Explain the roles of troponin, tropomyosin, and Ca2+ in skeletal muscle contraction.
Ca2+ binds to troponin, which repositions tropomyosin, uncovering actin's myosin-binding sites.
Explain the different factors that influence Ca2+ entry and release in smooth muscle fibers
Ca2+ release from smooth muscle SR uses RyR and IP3-activated channels. Influx from ECF uses mechanically, chemically, or voltage- gated channels.
Neurons that secrete acetylcholine are described as __________ neurons, whereas those that secrete norepinephrine are called either __________ or __________ neurons.
Cholinergic—acetylcholine, adrenergic or noradrenergic—norepinephrine.
To prepare for examinations, students are encouraged to revise by reading their study notes many times. How does rereading notes help remember them?
Each time we revise, the neural pathway is activated which strengthens the synapses along the network. This is known as long-term potentiation.
In reaction to a stimulus, the CNS initiates action potentials in __________ neurons to produce a response in a target tissue.
Efferent
What is acetylcholinesterase? Describe its action.
Enzyme that breaks down ACh
Muscle fibers depend on a continuous supply of ATP. How do the fibers in the different types of muscle generate ATP?
Generate ATP by energy transfer from phosphocreatine. Oxidative fibers use oxygen to make ATP from glucose and fatty acids; glycolytic fibers get ATP primarily from anaerobic glycolysis.
List the three types of sensory receptors that convey information for muscle reflexes.
Golgi tendon organ, the muscle spindle, and joint capsule mechanoreceptors
Where in the brain are the three main autonomic control centers located? What functions do each of these regions regulate?
Hypothalamus—controls temperature, water balance, and eating behavior. Pons—controls urinary bladder, respiration, and blood pressure. Medulla—controls blood pressure and respiration.
Fast synaptic action potentials are always associated with the opening of ion channels. How can the opening of ion channels in fast synaptic potentials lead to both inhibitory and excitatory postsynaptic potentials?
If more Na+ enters, the synaptic potential will be depolarizing which will result in an excitatory postsynaptic potential. If more K+ leaves, or more Cl- enters, the synaptic potential will be hyperpolarizing, resulting in an inhibitory post-synaptic potential.
A reflex that you are born with is known as a(n) __________ reflex.
Innate
Why is the adrenal medulla, which releases hormone epinephrine, not considered to be a true endocrine gland?
It is composed of modified postganglionic neurons.
What would be the consequence of treating skeletal muscle cells with an intracellular calcium chelator such as BAPTA-2AM?
It would lead to a loss in muscle contraction.
Which part of the brain transforms emotions into somatic sensation and visceral function? List three autonomic reflexes that are linked to emotions.
Limbic system. Emotional reflexes: blushing, heart rate, gastrointestinal function
Monoamine oxidase, which can degrade catecholamines, is located in the __________.
Mitochondria
On the basis of what you have learned about muscle fiber types and metabolism, predict what variations in structure you would find among these athletes: (a) a 7-foot, 2-inch-tall, 325-pound basketball player (b) a 5-foot, 10-inch-tall, 180-pound steer wrestler (c) a 5-foot, 7-inch-tall, 130-pound female figure skater (d) a 4-foot, 11-inch-tall, 89-pound female gymnast
Muscle length is related to bone length. Assuming these athletes are lean, differences in weight are correlated with muscle strength, so heavier athletes should have stronger muscles. More important factors are the relative endurance and strength required for a given sport. Any given muscle will have a combination of three fiber types, with the exact ratios depending upon genetics and specific type of athletic training. (a) Basketball: endurance and strength. Leg muscles—fast- twitch glycolytic fibers, to generate strength, and fast-twitch oxida- tive, for endurance. The arm and shoulder muscles—fast-twitch glycolytic, because shooting requires fast and precise contraction. (b) Steer wrestler: great strength but less endurance. Fast-twitch glycolytic fibers. (c) Figure skaters: strength and endurance. Trunk muscles— slow-twitch oxidative fibers for endurance. Leg muscles—fast-twitch oxidative, for moving across the ice, and fast-twitch glycolytic, for powering jumps. (d) Gymnastics—great strength in arms and legs, and great endurance in trunk and limb muscles. Arm and leg muscles— fast-twitch glycolytic fibers. Limb and trunk muscles—slow-twitch oxidative fibers.
What is the power stroke in muscle contraction?
Myosin heads swivel towards the M-line, simultaneously sliding the actin filaments along with them.
Modulatory neuron M synapses on the axon terminal of neuronP, just before P synapses with the effector organ. If M is an inhibitory neuron, what happens to neurotransmitter release by P? What effect does M's neurotransmitter have on the postsynaptic membrane potential of P? (Hint: Draw this pathway.)
Neurotransmitter release will decrease when M's neurotransmitter hyperpolarizes P.
Patients with Parkinson's disease show a range of symptoms including loss of memory and difficultly moving. Use what you have learnt in this chapter to explain these symptoms.
Parkinson's disease is caused by a loss of dopaminergic neurons in the basal ganglia. Basal ganglia neurons are involved in controlling cognitive function and the coordination of movement. Therefore, loss of neurons in this region will reduce dopamine output, leading to a range of symp- toms, including uncoordinated movement and memory loss.
Andy is working on improving his golf swing. He must watchthe ball, swing the club back and then forward, twist his hips, straighten his left arm, then complete the follow-through, where the club arcs in front of him. Which parts of the brain are involved in adjusting how hard he hits the ball, keeping all his body parts moving correctly, watching the ball, and then repeating these actions once he has verified that this swing is successful?
Parts of the brain include the brain stem, cerebellum, basal ganglia, thalamus, cerebral cortex (visual cortex, association areas, motor cortex).
List the four structural categories of neurons. Which of these usually have the most axons?
Pseudounipolar; biopolar; anaxonic; multipolar. Multipolar neurons have the most axons.
What are Purkinje cells?
Purkinje cells are CNS neurons which are highly branched so they can receive information from many neurons.
List and differentiate the three categories of movement. Give an example of each.
Reflex movements, such as the knee jerk, can be integrated in the spinal cord. Voluntary movements, such as playing the piano, and rhythmic movements, such as walking, must involve the brain. Reflex movements are involuntary; the initiation, modulation, and termina- tion of rhythmic movements are voluntary.
List the three functional classes of neurons, and explain how they differ structurally and functionally.
Sensory afferents carry messages from sensory receptors to CNS. Their cell bodies are located close to the CNS. Interneurons are com- pletely contained within the CNS and are often extensively branched. Efferents carry signals from the CNS to effectors. They have short, branched dendrites and long axons.
The Huaorani Indians of South America use blowguns to shoot darts poisoned with curare at monkeys. Curare is a plant toxin that binds to and inactivates nicotinic ACh receptors. What happens to a monkey struck by one of these darts?
Skeletal muscles would become paralyzed. Monkey could not flee.
Compare and contrast: the source and role of Ca2+ in skeletal and smooth muscle contraction
Skeletal muscle—sarcoplasmic reticu- lum. Smooth muscle—ECF and sarcoplasmic reticulum.
Some autonomic reflexes are spinal reflexes; others are integrated in the brain. List some examples of each.
Spinal reflexes: urination and defecation. Cranial reflexes: control of heart rate, blood pressure, and body temperature.
If all action potentials within a given neuron are identical, how does the neuron transmit information about the strength and dura- tion of the stimulus?
Strength is coded by the frequency of action potentials; duration is coded by the duration of a train of repeated action potentials.
Increasing the stimulation rate of a muscle fiber results in progres- sively more forceful muscle contractions known as __________. In a sustained muscle contraction, the nervous system avoids fatigue by __________.
Summation; asynchronous recruitment
What are the two branches of the autonomic nervous system? How are these branches distinguished from each other anatomically and physiologically?
Sympathetic and parasympathetic divisions. Sympathetic neurons exit the spinal cord in the thoracic and lumbar regions; ganglia are close to the spinal cord. Parasympathetic exit from the brain stem or sacral region; ganglia on or close to their targets. Sympathetic—fight-or- flight; parasympathetic—rest-and-digest.
Explain how the autonomic nervous system uses antagonism to regu- late heart rate. Which tissues are not regulated by antagonistic control?
Sympathetic neurons increase heart rate, whereas parasympathetic neurons decrease heart rate. Sweat glands and the smooth muscles in blood vessels are not regulated by antagonistic control.
T-tubules form a triad with two flanking units of which structure of the sarcoplasmic reticulum?
Terminal cisternae
Explain the difference between incomplete and complete tetanus.
Tetanus is a powerful muscle contraction which occurs in response to increased stimulation frequency. In incomplete tetanus, muscle fibers relax between stimulations, whereas in complete tetanus, stimulation is at its maximum and the muscle fiber does not relax in between, and tension remains high.
If nicotinic receptor channels allow both Na+ and K+ to flow through, why does Na+ influx exceed K+ efflux? (Hint: p. 189.)
The electrochemical gradient for Na+ is greater than that for K+
What is the motor end plate, and what kinds of receptors are found there? Explain how neurotransmitter binding to these receptors creates an action potential.
The region of a muscle fiber where the synapse occurs. Contains ACh receptors. Influx of Na+ through ACh receptor-channels depolarizes muscle.
What are the benefits of antagonistic muscle groups?
These muscles exert opposite effects such as flexion and extension at a defined joint, thereby allowing movement.
Briefly explain the functions of titin and nebulin.
They keep actin and myosin in alignment. Titin helps stretched muscles return to resting length.
How many synapses occur in the simplest autonomic reflexes? Where do the synapses occur?
Two neuron-neuron synapses in the spinal cord and the autonomic ganglion, and one neuron-target synapse.
The simplest reflex requires a minimum of how many neurons? How many synapses? Give an example.
Two neurons and one synapse between them (monosynaptic). The knee jerk (patellar tendon) reflex is an example
An unmyelinated axon has a much greater requirement for ATP than a myelinated axon of the same diameter and length. Can you explain why?
Unmyelinated axons have many ion channels, so more ions cross during an action potential and must be returned to their original compartments by the Na+-K+-ATPase, using energy from ATP.
The autonomic nervous system is sometimes called the __________ nervous system. Why is this an appropriate name? List some functions controlled by the autonomic nervous system.
Visceral nervous system because it controls internal organs (viscera) and functions such as heart rate and digestion.
Stretching a skeletal muscle causes sensory neurons to (increase/ decrease) their rate of firing, causing the muscle to contract, thereby relieving the stretch. Why is this a useful reflex?
increase. This reflex prevents damage from overstretching.
List the letters used to label the elements of a sarcomere. Which band has a Z disk in the middle? Which is the darkest band? Why? Which element forms the boundaries of a sarcomere? Name the line that divides the A band in half. What is the function of this line?
Z disk—ends of a sarcomere. I band—Z disk in the middle. A band (thick filaments)—darkest; H zone—lighter region of A band. M line divides A band in half; thick filaments link to each other.
__________ muscles possess the property of contracting spontaneously without signals from the central nervous system.
cardiac
Once rhythmic movements have been activated, spontaneous repetitive activity is maintained by the __________.
central pattern generator (CPG)
In the neural control of movement, the thalamus sends integrative output to the __________.
cerebral cortex
Arrange the following skeletal muscle components in order, from outermost to innermost: sarcolemma, connective tissue sheath, thick and thin filaments, myofibrils.
connective tissue, sarcolemma, myofibrils, thick and thin filaments
The enzyme that transfers a phosphate group from phosphocreatine to ADP is called __________.
creatine kinase
List three ways neurotransmitters are removed from the synapse.
enzymatic degradation, reabsorption, and diffusion
In skeletal muscles, the effector contractile fibers are known as __________ muscle fibers. They are innervated by somatic motor neurons known as _______ motor neurons.
extrafusal muscle fibers; alpha motor neurons
What kind of acetylcholine receptor would you expect drugs like varenicline (used for smoking cessation) to affect?
nicotinic cholinergic receptors
Name the two types of glial cells that can form a myelin sheath.
oligodendrocytes in the CNS and Schwann cells in the PNS
When the axon terminal of a modulatory neuron (cell M) ter- minates close to the axon terminal of a presynaptic cell (cell P) and decreases the amount of neurotransmitter released by cell P, the resulting type of modulation is called __________. [Hint: See p. 297.]
presynaptic inhibition
The lace-like organelle that wraps around each myofibril is called the __________, and it sequesters __________.
sarcoplasmic reticulum, Ca2+ ions
The three types of muscle tissue found in the human body are __________, __________, and __________. Which type is attached to the bones, enabling it to control body movement?
smooth, cardiac, skeletal. Skeletal are attached to bones.
Skeletal muscles are unique in responding solely to __________ neurons.
somatic motor
Skeletal muscles are under the control of _____ neurons, whereas smooth muscles are under the control of _____ neurons.
somatic, autonomic
What is the rigor state?
the tight binding of actin and myosin in the absence of ATP
A single contraction-relaxation cycle in a skeletal muscle fiber is known as a(n) __________.
twitch
Autonomic reflexes are also called __________ reflexes. Why?
visceral reflexes because many of them involve internal organs (the viscera)