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Human Physiology An Integrated Approach 5th Edition Silverthorn Test Bank

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Human Physiology An Integrated Approach 5th Edition Silverthorn Test Bank

ISBN-13: 978-0321559807

ISBN-10: 0321559800

 

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Human Physiology An Integrated Approach 5th Edition Silverthorn Test Bank

ISBN-13: 978-0321559807

ISBN-10: 0321559800

 

 

 

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Human Physiology, 5e (Silverthorn)

Chapter 11   Efferent Division: Autonomic and Somatic Motor Control

 

1) Nicotine is thought to cause approximately __________ deaths per year, worldwide.

  1. A) 500
  2. B) 5000
  3. C) 50,000
  4. D) 500,000
  5. E) 5,000,000

Answer:  E

Skill:  Level I: Reviewing Facts and Terms

 

2) The two divisions of the efferent side of the peripheral nervous system are

  1. A) somatic motor neurons and voluntary neurons.
  2. B) somatic motor neurons and autonomic neurons.
  3. C) the sympathetic and parasympathetic divisions.
  4. D) voluntary nervous system and somatic motor neurons.

Answer:  B

Skill:  Level I: Reviewing Facts and Terms

 

3) The division of the autonomic nervous system that prepares the body for intense levels of activity and stress is the

  1. A) sympathetic division.
  2. B) parasympathetic division.
  3. C) craniosacral division.
  4. D) intramural division.
  5. E) somatomotor division.

Answer:  A

Skill:  Level I: Reviewing Facts and Terms

 

4) Which statements apply to the parasympathetic division of the nervous system?

  1. A) It is dominant during “resting and digesting.”
  2. B) Its ganglia are nearby, on or within their target organs.
  3. C) Epinephrine is the primary neurotransmitter of the parasympathetic division.
  4. D) A and B
  5. E) A, B, and C

Answer:  D

Skill:  Level I: Reviewing Facts and Terms

 

5) Nicotine enhances the release of __________ in the brain.

  1. A) serotonin
  2. B) dopamine
  3. C) acetylcholine
  4. D) epinephrine
  5. E) glutamate

Answer:  B

Skill:  Level I: Reviewing Facts and Terms

6) Which area is NOT normally considered to be an autonomic control center?

  1. A) pons
  2. B) medulla
  3. C) amygdala
  4. D) hypothalamus

Answer:  C

Skill:  Level I: Reviewing Facts and Terms

 

7) Antagonistic control of efferent output is typical of the __________ division.

  1. A) somatic
  2. B) sensory
  3. C) autonomic
  4. D) A and B
  5. E) A and C

Answer:  C

Skill:  Level I: Reviewing Facts and Terms

 

8) The presence of two peripheral efferent neurons in a pathway is typical of the __________ division.

  1. A) somatic
  2. B) sensory
  3. C) autonomic
  4. D) A and B
  5. E) A and C

Answer:  C

Skill:  Level I: Reviewing Facts and Terms

 

9) The adrenal medulla is important to the sympathetic branch of the autonomic nervous system because

  1. A) it is a source of catecholamines.
  2. B) it is considered a modified sympathetic ganglion.
  3. C) it releases epinephrine and norepinephrine directly into the blood.
  4. D) A and B
  5. E) A, B, and C

Answer:  E

Skill:  Level I: Reviewing Facts and Terms

 

10) Each of these statements is true except one. Identify the exception.

  1. A) Monoamine oxidase is the main enzyme responsible for the degradation of catecholamines.
  2. B) β1receptors respond equally well to both epinephrine and norepinephrine.
  3. C) β2receptors are not innervated by sympathetic neuronsRemember, are more sensitive to epinephrine, delivered via the blood.
  4. D) Activation of α receptors opens Na+channels in the membrane.

Answer:  D

Skill:  Level I: Reviewing Facts and Terms

 

11) Which of the following has its cell body in the ganglion?

  1. A) preganglionic neuron
  2. B) postganglionic neuron
  3. C) somatic motor neuron
  4. D) A and B
  5. E) all of the above

Answer:  B

Skill:  Level I: Reviewing Facts and Terms

 

12) Which area(s) of the brain exert(s) control over the autonomic nervous system?

  1. cerebrum
  2. cerebellum
  3. hypothalamus
  4. pons
  5. medulla
  6. thalamus
  7. A) 1, 2, 3, 4, 5, 6
  8. B) 1, 3, 5
  9. C) 1, 3, 4, 5
  10. D) 1, 2, 3, 5
  11. E) 2, 3, 4, 5

Answer:  C

Skill:  Level I: Reviewing Facts and Terms

 

13) Which functions are controlled through the autonomic nervous system?

  1. blood pressure
  2. heart rate
  3. water balance
  4. temperature regulation
  5. A) 1 and 2
  6. B) 1 and 3
  7. C) 1, 2, 3
  8. D) 2, 3, 4
  9. E) 1, 2, 3, 4

Answer:  E

Skill:  Level I: Reviewing Facts and Terms

 

14) Sweat glands contain

  1. A) cholinergic receptors.
  2. B) alpha receptors.
  3. C) beta receptors.
  4. D) all of the above
  5. E) none of the above

Answer:  A

Skill:  Level I: Reviewing Facts and Terms

 

15) Increased parasympathetic stimulation

  1. A) increases heart rate.
  2. B) increases gastric motility.
  3. C) causes sweat glands to release sweat.
  4. D) causes blood vessels in the skin to dilate.
  5. E) causes the pupils to dilate.

Answer:  B

Skill:  Level I: Reviewing Facts and Terms

 

16) “Dual innervation” refers to an organ receiving

  1. A) two nerves from the spinal cord.
  2. B) both autonomic and somatomotor nerves.
  3. C) both sympathetic and parasympathetic nerves.
  4. D) nerves from both the brain and the spinal cord.
  5. E) none of the above

Answer:  C

Skill:  Level I: Reviewing Facts and Terms

 

17) The motor end plate is

  1. A) a folded area of muscle cell membrane with ACh receptors clustered at the top of each fold.
  2. B) the same as the neuromuscular junction.
  3. C) the same as the synaptic cleft.
  4. D) formed by the membrane of enlarged axon terminals, or boutons, that lie on the surface of skeletal muscle cells.
  5. E) a special fibrous matrix whose collagen fibers hold the axon terminal in proper position.

Answer:  A

Skill:  Level I: Reviewing Facts and Terms

 

Match the following with its description.

 

  1. acetylcholine
  2. norepinephrine
  3. cholinergic nicotinic receptor
  4. adrenergic receptor
  5. cholinergic muscarinic receptor

 

18) parasympathetic tissue receptor

Answer:  E

Skill:  Level I: Reviewing Facts and Terms

 

19) target receptor for preganglionic neurons

Answer:  C

Skill:  Level I: Reviewing Facts and Terms

 

20) released by all autonomic preganglionic neurons

Answer:  A

Skill:  Level I: Reviewing Facts and Terms

21) primary sympathetic neurotransmitter

Answer:  B

Skill:  Level I: Reviewing Facts and Terms

 

22) sympathetic tissue receptor

Answer:  D

Skill:  Level I: Reviewing Facts and Terms

 

Match the answers to the questions.

 

  1. true only for the sympathetic division
  2. true only for the parasympathetic division
  3. true for both divisions

 

23) The neural pathway from the spinal cord to the target tissue has two neurons, the preganglionic neuron and the postganglionic neuron.

Answer:  C

Skill:  Level I: Reviewing Facts and Terms

 

24) Most preganglionic neurons originate in the thoracic and lumbar regions of the spinal cord.

Answer:  A

Skill:  Level I: Reviewing Facts and Terms

 

25) The cell bodies of preganglionic neurons are found either in the brain stem or in the sacral region of the spinal cord.

Answer:  B

Skill:  Level I: Reviewing Facts and Terms

 

26) Inside the ganglia are interneurons, which modulate messages.

Answer:  C

Skill:  Level I: Reviewing Facts and Terms

 

27) The neurotransmitter acetylcholine is released by neurons at the neuroeffector synapse.

Answer:  B

Skill:  Level I: Reviewing Facts and Terms

 

28) The ganglia are found in a chain that runs close to the spinal cord or along the descending aorta.

Answer:  A

Skill:  Level I: Reviewing Facts and Terms

 

29) Releases norepinephrine at the neuroeffector synapse.

Answer:  A

Skill:  Level I: Reviewing Facts and Terms

 

 

30) Contains cholinergic neurons.

Answer:  C

Skill:  Level I: Reviewing Facts and Terms

 

31) The adrenal medulla is closely allied with this system.

Answer:  A

Skill:  Level I: Reviewing Facts and Terms

32) On average, one preganglionic neuron synapses with eight or nine postganglionic neurons, each innervating a different target.

Answer:  C

Skill:  Level I: Reviewing Facts and Terms

 

33) Important during stress or emergencies (fight-or-flight).

Answer:  A

Skill:  Level I: Reviewing Facts and Terms

 

34) Dominates during resting-and-digesting activities.

Answer:  B

Skill:  Level I: Reviewing Facts and Terms

 

35) The two types of cholinergic receptors are __________ and __________.

Answer:  nicotinic, muscarinic

Skill:  Level I: Reviewing Facts and Terms

 

36) Cholinergic receptors respond to the neurotransmitter __________.

Answer:  acetylcholine

Skill:  Level I: Reviewing Facts and Terms

 

37) Cholinergic nicotinic receptors are found in the __________ of the ANS.

Answer:  autonomic gangliz

Skill:  Level I: Reviewing Facts and Terms

 

38) Cholinergic muscarinic receptors are found at the __________ in the ANS.

Answer:  parasympathetic neuroeffector junctions

Skill:  Level I: Reviewing Facts and Terms

 

39) The __________ is the major source of parasympathetic output.

Answer:  vagus nerve

Skill:  Level I: Reviewing Facts and Terms

 

40) __________ are swellings that contain vesicles filled with neurotransmitter.

Answer:  varicosities

Skill:  Level I: Reviewing Facts and Terms

 

41) Autonomic neurotransmitters are synthesized in the __________.

Answer:  axon

Skill:  Level I: Reviewing Facts and Terms

 

42) The two varieties of adrenergic receptors are __________ and __________.

Answer:  alpha, beta

Skill:  Level I: Reviewing Facts and Terms

 

43) The signal molecule __________ elicits the stronger response from alpha receptors.

Answer:  norepinephrine

Skill:  Level I: Reviewing Facts and Terms

44) The signal molecule __________ elicits the stronger response from beta2 receptors.

Answer:  epinephrine

Skill:  Level I: Reviewing Facts and Terms

 

45) __________ postganglionic sympathetic neurons secrete __________ onto their target cells.

  1. A) All, norepinephrine
  2. B) Most, norepinephrine
  3. C) All, acetylcholine
  4. D) Most, acetylcholine

Answer:  B

Skill:  Level II: Reviewing Concepts

 

46) Epinephrine and norepinephrine that are released from the adrenal glands affect target tissue for a longer period of time than the same substances released from neurons at their peripheral receptors. Why?

  1. A) The adrenal gland releases larger amounts of the neurotransmitters than the neurons.
  2. B) The hormones released from the adrenal glands bind to different receptors than those released from neurons.
  3. C) There are no enzymes to break down epinephrine and norepinephrine in the blood and very little in peripheral tissues.
  4. D) The effectors are less sensitive to epinephrine and norepinephrine released by the adrenal glands.
  5. E) The epinephrine and norepinephrine from the adrenal glands are released by sympathetic neurons, whereas parasympathetic neurons release these substances at the effector organs.

Answer:  C

Skill:  Level II: Reviewing Concepts

 

 

An alien retrieved alive from a crashed UFO has had a thorough medical examination. A hormone with a distinct but similar structure to epinephrine has been isolated, and named

ufo-epi.

 

47) If humans administered a physiological dose of ufo-epi responded to the chemical, which of the following would indicate ufo-epi is an epinephrine agonist?

  1. A) constriction of respiratory tubes
  2. B) hyperglycemia (high blood glucose)
  3. C) increase in fatty acids in the blood
  4. D) localized sweating
  5. E) decreased heart rate

Answer:  C

Skill:  Level II: Reviewing Concepts

 

48) If the results of ufo-epi treatment of humans included pupil dilation, localized sweating, high blood pressure, and high blood glucose, which conclusion would be indicated?

  1. A) It acts on AMPA receptors.
  2. B) It acts at the neuromuscular junction.
  3. C) It acts on muscarinic receptors.
  4. D) It acts on alpha adrenergic receptors.
  5. E) It acts on beta adrenergic receptors.

Answer:  D

Skill:  Level II: Reviewing Concepts

49) The drug Chantix, which treats nicotine addiction, is an __________ for the nicotine receptor.

  1. A) agonist
  2. B) antagonist

Answer:  A

Skill:  Level II: Reviewing Concepts

 

Match the response with the type of chemical.

 

  1. sympathetic agonist
  2. parasympathetic agonist

 

50) pupil dilation

Answer:  A

Skill:  Level II: Reviewing Concepts

 

51) salivation

Answer:  B

Skill:  Level II: Reviewing Concepts

 

52) decreased activity in digestive tract

Answer:  A

Skill:  Level II: Reviewing Concepts

 

53) fat breakdown

Answer:  A

Skill:  Level II: Reviewing Concepts

 

Match the response with the type of chemical.

 

  1. sympathetic antagonist
  2. parasympathetic antagonist

 

54) blocks secretion of pancreatic enzymes

Answer:  B

Skill:  Level II: Reviewing Concepts

 

55) blocks secretion of adrenal catecholamines

Answer:  A

Skill:  Level II: Reviewing Concepts

 

56) blocks urination

Answer:  B

Skill:  Level II: Reviewing Concepts

 

57) blocks sweating

Answer:  A

Skill:  Level II: Reviewing Concepts

58) Explain what is meant by antagonistic control.

Answer:  For fine-tuned control over the body’s internal state, one autonomic branch may have an excitatory effect on a particular organ while the other branch is inhibitory.

Skill:  Level II: Reviewing Concepts

 

59) Map the divisions of the autonomic nervous system down to their receptors.

Answer:  See Fig. 11-11 in the chapter.

Skill:  Level II: Reviewing Concepts

 

60) Describe the different types of adrenergic receptors in the autonomic nervous system. Which neurotransmitter binds to each type? For those that bind more than one neurotransmitter, how does the response to the neurotransmitters compare?

Answer:  Alpha 1, alpha 2, beta 1, beta 2, and beta 3 receptors are described in Table 11-2. Most of these receptors are more sensitive to norepinephrine than to epinephrine, but they will all respond to either neurotransmitter. These neurotransmitters are nearly identical structurally, and the response of the target tissue to the binding of either is the same.

Skill:  Level II: Reviewing Concepts

 

 

61) Describe the different types of cholinergic receptors in the nervous system. Which neurotransmitter binds to each type?

Answer:  Cholinergic receptors are either nicotinic or muscarinic; they are distinguishable by the binding of either nicotine or muscarine to the same receptors. Both receptors bind to acetylcholine.

Skill:  Level II: Reviewing Concepts

 

62) Which tissues contain both cholinergic and adrenergic receptors, and how does this relate to their autonomic control?

Answer:  A list is provided in Fig. 11-5 in the chapter. For most target organs listed, acetylcholine and (nor)epinephrine have opposite effects on the target organ.

Skill:  Level II: Reviewing Concepts

 

63) Describe the major anatomical differences between the sympathetic and parasympathetic branches.

Answer:  Sympathetic pathways exit the spinal cord in the thoracic and lumbar regions whereas parasympathetic pathways exit through the cranial and sacral regions. Also, sympathetic ganglia are located near the spinal cord; and therefore, sympathetic pathways typically have short preganglionic fibers and long postganglionic fibers. In contrast, parasympathetic ganglia are located on or near their target tissue; and therefore, parasympathetic pathways have long preganglionic fibers and short postganglionic fibers.

Skill:  Level II: Reviewing Concepts

64) Describe the general rules for the identity of neurotransmitters secreted by pre- and postganglionic neurons in the autonomic division. Be sure to specify the types of receptors, where relevant, and describe the exceptions.

Answer:  Both sympathetic and parasympathetic neurons secrete acetylcholine onto nicotinic receptors within the autonomic ganglion. Postganglionic sympathetic neurons secrete norepinephrine onto adrenergic receptors. Postganglionic parasympathetic neurons secrete acetylcholine onto muscarinic receptors. Exceptions include sympathetic postganglionic neurons that secrete acetylcholine, and nonadrenergic, noncholinergic neurons that secrete substance PRemember,matostatin, vasoactive intestinal peptide, adenosine, nitric oxide, or ATP.

Skill:  Level II: Reviewing Concepts

 

65) Diagram the events that occur at the neuromuscular junction. Be sure to include the somatic motor neuron, axon terminal, synaptic cleft, synaptic vesicles, motor end plate, and appropriate neurotransmitter(s), ion channel(s), and membrane receptor(s).

Answer:  Variable. See Fig. 11-13 in the chapter.

Skill:  Level II: Reviewing Concepts

 

66) What steps are necessary to terminate neurotransmitter action? What would happen if these steps failed?

Answer:  Neurotransmitter molecules are either enzymatically degraded or are taken back into the presynaptic terminal (reuptake). Calcium ions are removed from the axon terminal. Failure of these steps prolongs the action of the neurotransmitter. Consequences vary according to the identity of the effector organ. In a skeletal muscle, for example, this can lead to spastic paralysis.

Skill:  Level II: Reviewing Concepts

 

67) Explain the use of the terms fight and flight in describing sympathetic motor responses. How does sympathetic activity explain your increased “jumpiness” when you are home alone at night, watching a horror movie on TV?

Answer:  When presented with a real or imaginary threat, the sympathetic motor system produces changes that prepare the body to oppose the threat (“fight”) or run away from the threat (“flight” is the past tense of “flee”). Responses include an increase in heart and respiratory rate, and increased blood flow to cardiac and skeletal muscle. Reading or watching scenes that are threatening to others, even if you could not possibly be at risk, can produce the same sympathetic response in you as if you were actually present in the scene. If the phone rings or there is a knock at the door, you are likely to react to that very quickly, because you are primed for action.

Skill:  Level III: Problem Solving

68) Anne Frank wrote a diary about the years she and a few others spent in hiding from the Nazis during World War II. These people lived in the upstairs rooms of a shop, accessible only by a hidden stairway; Anne called these quarters the Secret Annex. One day Nazis raided the shop below, but were unsuccessful in locating the hideaways or finding proof of their presence during this particular raid. Clearly hearing what was occurring downstairs, Anne and her cohorts cowered in silence, for they feared being transported to “death camps.” Later, Anne wrote that most of the residents of the Secret Annex experienced diarrhea shortly after this close call. Explain this response by their digestive systems.

Answer:  Assuming there is no pathogenic or dietary cause, diarrhea probably resulted from the fight-or-flight response of the sympathetic nervous system. Digestive tract secretion and motility are inhibited during a sympathetic response. When the threat had passed and the sympathetic nervous system released the digestive targets from inhibition, there may have been a rebound effect in which the parasympathetic division overstimulated the motility of the tract. Increased motility with decreased time for reabsorption of water can result in diarrhea. It is also thought that the sympathetic response actually stimulates the lower gastrointestinal tract though it inhibits the upper tract. This could also account for the effects. Students may need to consult other sources to answer this question correctly.

Skill:  Level III: Problem Solving

 

69) Both alpha-bungarotoxin and curare bind to the same neurotransmitter receptor, but only curare binds reversibly. Which receptor is involved? List some locations for this receptor. Would either toxin be appropriate to use as a paralytic during surgery? Explain your answer. Are all such receptors necessarily affected by a given toxin in the same way? Explain the significance of your answer.

Answer:  Both of these toxins bind to the nicotinic acetylcholine receptor. This type of receptor is located on skeletal muscle and in autonomic ganglia. For a paralytic during surgery, curare would be appropriate but bungarotoxin would not, because the irreversibility of bungarotoxin binding results in permanent paralysis of skeletal muscles. Bungarotoxin binds to the receptors in skeletal muscle but not to those in autonomic ganglia, illustrating a structural difference in the receptors in these two sites.

Skill:  Level III: Problem Solving

 

 

70) Compare and contrast the voltage-gated sodium and potassium channels introduced in Ch. 8, with the acetylcholine receptor/channel. What may be confusing to the beginning physiology student trying to understand the ion specificity of the acetylcholine receptor? What type of change in the cell is produced by ion movement through each type of channel?

Answer:  The voltage-gated sodium channel opens in response to threshold voltage and allows sodium to enter the cell, thereby depolarizing the membrane potential. The potassium channel is also opened by threshold voltage and allows potassium to exit the cell, repolarizing or hyperpolarizing the membrane potential. The acetylcholine receptor is a neurotransmitter receptor as well as an ion channel. Because the channel is opened by binding of a chemical, it is a chemically gated channel. This channel is permeable to both sodium and potassium; when the channel opensRemember,dium diffuses into the cell and potassium diffuses out. The inward positive charge is sufficient to depolarize the skeletal muscle to threshold. Students are often confused by the fact that more than one type of ion moves through the acetylcholine receptor channel, and that the muscle cell is able to depolarize to threshold despite the exit of potassium.

Skill:  Level III: Problem Solving

71) To perform surgery with a minimum of pain for the patient and hassle for the surgeon, a patient may be administered a general anesthetic to prevent sensation and consciousness, as well as a paralytic to prevent reflexive muscle spasms. From what you have learned of motor control, suggest mechanisms by which a paralytic can prevent muscle contraction. With paralytics, what extra measure must be taken to keep the patient alive? Name such a paralytic agent.

Answer:  From Ch. 9, students should remember that somatic motor control involves the motor areas of the cerebral cortex and the basal nuclei, as well as the cerebellum. A drug that affects activity selectively in those areas could act as a paralytic; however, it is difficult to imagine the nature of the selectivity that would be required, given the use of similar neurotransmitters and receptors throughout the brain. These motor control areas of the brain act upon the spinal motor neurons, which release acetylcholine onto skeletal muscle fibers. These fibers have a type of receptor not found on autonomic targets: the nicotinic acetylcholine receptor. The neuromuscular junction is the single point of control of a skeletal muscle by its motor neuron. A drug that interferes with synaptic transmission at this junction could be a paralytic. Because the respiratory muscles are also controlled by nicotinic neuromuscular junctions, artificial respiration must be provided by the surgical team until the paralytic is cleared from the system. Curare is a drug that works this waycurare binds to the nicotinic ACh receptor, preventing the muscles from being activated by ACh.

Skill:  Level III: Problem Solving

 

72) At the molecular level, what are the effects of nicotine on the nervous system? How are these effects exerted? How are these effects similar to or different from those of curare? How do these effects explain some of the physiological consequences of smoking?

Answer:  Nicotine binds to a type of acetylcholine receptor known as the nicotinic receptor; nicotine does not bind to the other type of acetylcholine receptor, the muscarinic receptor. Like acetylcholine, nicotine activates the receptor and produces a postsynaptic response. Nicotinic receptors are located on skeletal muscles and on the postganglionic neurons of both the sympathetic and parasympathetic nervous divisions. Curare also binds to the nicotinic acetylcholine receptor, but it does not activate the receptor; therefore the effect of curare is paralysis of skeletal muscles. Overall, nicotine is a CNS stimulant, suggesting greater stimulation of the sympathetic division than of the parasympathetic division.

Skill:  Level III: Problem Solving

 

73) In a laboratory experiment, adding curare, which binds to acetylcholine receptors, to the solution around a muscle decreases the size of the end plate potential. Adding prostigmine, an acetylcholinesterase blocker, increases the size of the end plate potential. Explain why.

Answer:  By binding to acetylcholine receptors, curare prevents the binding of acetylcholine. Curare does not open the receptor channels. An end plate potential results from the opening of several ACh receptor channels. Thus, if the receptor is blocked, any end plate potential that is produced would be smaller. Prostigmine blocks the enzyme that stops ACh action by degrading the neurotransmitter. Interfering with this enzyme prolongs the action of ACh, thus more receptor channels open and the end plate potential is larger.

Skill:  Level III: Problem Solving

74) Phenelzine is a common MAO inhibitor that has been used to treat depression. It is not, however, prescribed as often as other antidepressants due to its effects on the autonomic nervous system. Describe several side effects that may result from taking phenelzine and explain why they might occur.

Answer:  MAO inhibitors prevent the enzymatic breakdown of catecholamines such as norepinephrine. As a result, a higher concentration of norepinephrine remains in the synapse and therefore is able to elicit a longer / stronger response on its target tissues. Consequently, norepinephrine can prolong its activity through sympathetic pathways to increase heart rate and blood pressure, decrease gastric motility causing constipation as well as prevent penile ejaculation leading to sexual dysfunction. This is discussed in “The Autonomic Division” section of the chapter.

Skill:  Level III: Problem Solving

 

75) Though you are an attentive parent, you lost track of your inquisitive toddler for a few minutes, just long enough for him to wander into the garage and open a package of insecticide that you use to control insects in your garden. You have no idea if any of the poison has been ingested, inhaled, or absorbed through his skin. You take the package away from your child and read under the “caution” section that it is an anticholinesterase. Given that this poison was made for insects, not humans, should you be worried? Explain your answer. What would happen to the child if he has indeed been affected? Explain which type of synapses could be affected. Propose an antidote (it’s OK if you don’t remember a specific compound, just describe what type of effect may reverse the effects of the insecticide).

Answer:  Insects have acetycholine receptors that are similar enough to ours so that yes, you should be worried. Anticholinesterases block the degradation of acetylcholine, thereby prolonging its effects in both muscarinic and nicotinic synapses. If the dose is high enough, spastic paralysis could result, in which muscles contract uncontrollably. If this happens with the respiratory muscles, the victim may die of suffocation. Autonomic effects would also be expected, including sweating and nausea. A chemical such as atropine, which blocks muscarinic receptors, will alleviate some of the symptoms. Oximes (not mentioned in text) block nicotinic receptors and can be administered to counteract nicotinic effects of the poison.

Skill:  Level III: Problem Solving

 

You and your fellow deep-sea scientists have discovered a new form of marine invertebrate, and are anxious to determine the similarities and differences to animals already characterized. Chemical analysis reveals the following concentrations of permeable cations:

 

Ion [in] mM [out] mM
Na+ 50 450
K+ 420 20
Mg++ 10 60
Cl- 50 550

 

Nernst equation:  Eion = 61/z × log [ion]out/[ion]in

 

76) Control of the neuromuscular junction in this new invertebrate is found to involve dual innervation, where one motor neuron secretes an excitatory neurotransmitter and another secretes an inhibitory neurotransmitter onto the muscle. How does this compare to the human neuromuscular junction? Propose three different types of inhibitory receptors/channels that would produce inhibition of the invertebrate muscle, specifying ion and direction of ion flow. For each ion, calculate the equilibrium potential. What similarity do you notice in the equilibrium potentials of the ions involved, and how is that significant? How may inhibition be accomplished in human muscle?

Answer:  The human neuromuscular junction is innervated by only an excitatory neuron. The inhibitory motor neuron in the invertebrate may open a channel to potassium, to chloride, or to both, resulting in hyperpolarization as potassium exits and/or chloride enters. EK+ = 61 × log 20/420 = -81 mV. ECl- = -61 × log 550/50 = -64 mV. Both of these equilibrium potentials are negative, indicating that these ions can be useful for inhibition. In humans, inhibition of muscle activity occurs within the CNS, rather than at the muscle.

Skill:  Level IV: Quantitative Problems

 

77) Your studies of the neuromuscular junction reveal that the excitatory neurotransmitter opens a channel permeable to all three cations. Calculate the equilibrium potential for each cation. In which direction will each cation move when the channel is open? Does movement of ions promote muscle depolarization? Explain your answer.

Answer:  ENa+ = 61 × log 450/50 = 58 mV. EK+ = 61 × log 20/420 = -81 mV. EMg++ = 61 × log 60/10 = 47 mV. Sodium and magnesium will enter the cell, potassium will exit. Exit of potassium opposes depolarization, but presumably there will be a net gain in intracellular positive charge sufficient to depolarize the cell.

Skill:  Level IV: Quantitative Problems

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