Download LEARNING OBJECTIVE 5: Explain how an injured nerve fiber may

CHAPTER 10
NERVOUS SYSTEM I: BASIC STRUCTURE AND FUNCTION
LEARNING OBJECTIVE 1: Explain the general functions of the nervous system.
Lecture Suggestions and Guidelines
1. Introduce three general functions of the nervous system: a) sensory; b) integrative; and c) motor.
2. Discuss the concept that the nervous system can detect changes in the body, make decisions based on
information received and stimulate muscles or glands to respond.
3. Describe the nervous system s role in maintaining homeostasis.
Application Question(s)
1. Ask students to develop an organizational flow chart which illustrates the relationships among the central
nervous system, peripheral nervous system, sensory division, motor division, autonomic nervous system,
somatic nervous system, sympathetic division and parasympathetic division. Briefly describe the function of
each.
Answer: Flow charts will vary.
Critical Thinking Issue(s)
1. Divide the class into small groups and ask each group to define brain death. Consider the legal, moral, ethical
and medical implications as the groups prepare their viewpoints. Discuss the groups findings.
Answer: Viewpoints will vary but may include criteria such as inability to respond to stimuli, cessation of
respiration, absence of reflexes, non-responsive EEG, etc.
LEARNING OBJECTIVE 2: Describe the general structure of a neuron.
Lecture Suggestions and Guidelines
1. Illustrate the structure of a typical motor neuron. Label the major structures such as dendrites, myelin sheath,
cell body, neurilemma, Schwann cell, Nodes of Ranvier, axon, and synapse.
2. Describe the structures of a neuron cell body, including the cytoplasm, mitochondria, lysosomes, Golgi
apparatus, microtubules, neurofibrils, and Nissl bodies.
3. Discuss different types of neurons based on structural differences, including bipolar neurons, unipolar neurons,
and multipolar neurons.
4. Discuss different types of neurons based on functional differences, including sensory neurons, interneurons, and
motor neurons.
Application Question(s)
1. Neuron processes that generally carry impulses away from the nerve cell body are axons and neuron processes
that generally carry impulses toward the nerve cell body are dendrites. What would one call the portion of the
neuron process which connects the dendrites to the axon?
Answer: In unipolar sensory neurons, the portion of the neuron process which connects dendrites to axon
conveys properties of both. Therefore, that portion from dendrites to cell body, is sometimes referred to as the
peripheral process, whereas the second portion, from cell body to the CNS, is referred to as the central process.
Critical Thinking Issue(s)
1. A 35 year old female patient experiences occasional tingling sensations in the extremities, numbness in the
facial area, muscular weakness, loss of balance and bladder dysfunction. The signs and symptoms are
characterized by periods of remission and exacerbation. What might be a probable diagnosis?
Answer: A chronic, progressive disease of unknown origin which affects the central nervous system by the
degeneration of the protective myelin sheath called Multiple Sclerosis would be a possible diagnosis which
should be confirmed via MRI and other clinical testing.
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LEARNING OBJECTIVE 3: Explain how neurons are classified.
Lecture Suggestions and Guidelines
1. Discuss the concept that neurons are classified according to structure and/or function. Sensory neurons are
regarded as afferent neurons, motor neurons are considered to be efferent neurons. Association neurons, or
interneurons, connect sensory and motor neurons in neural pathways.
2. Introduce the terms cutaneous sense organs and proprioceptors.
3. Discuss the structural characteristics and location of bipolar neurons, unipolar neurons, and multipolar neurons.
Application Question(s)
1. How might you stimulate the following types of sensory receptors: a) Meissner s corpuscle b) Ruffini s
corpuscle c) Pacinian corpuscle d) Golgi tendon organ e) Krause s end bulb.
Answer: Responses will vary. Students should provide an example of each type of sensory receptor stimulation
and define its primary function, i.e., pain receptor, touch receptor, deep pressure receptor, proprioceptor, etc.
Critical Thinking Issue(s)
1. Based on your knowledge of the integumentary system, sensory receptors, and the immune system, what might
be considered a major threat to a victim of third-degree burns?
Answer: a) After 24 hours, infection becomes a major concern; b) Third-degree burns are generally not
painful, initially, since the nerve endings in the burned area are destroyed; c) Burned respiratory passageways
may result in difficult breathing or suffocation; d) Scar tissue may form; e) Skin grafting may be necessary,
since regeneration is unlikely.
LEARNING OBJECTIVE 4: Name four types of neuroglial cells and describe the functions of each.
Lecture Suggestions and Guidelines
1. Introduce neuroglial cells as accessory cells which fill spaces, support neurons, hold nervous tissue together,
metabolize glucose, regulate potassium ions, produce myelin and phagocytize.
2. Describe four major types of neuroglial cells, including characteristics and functions of each. Discussion should
include astrocytes, oligodendrocytes, microglia, and ependymal cells.
Application Question(s)
1. Ask students to develop a table which summarizes four major types of neuroglial cells, including name,
characteristics, and functions. Sketch and label each type.
Answer: The table should include astrocytes, oligodendrocytes, microglia, and ependymal cells.
Critical Thinking Issue(s)
1. In what ways might implanted neuroglia (provided perhaps from fetal tissue), help victims suffering from
Alzheimer s disease or AIDS?
Answer: By replacing needed neurotransmitters, repairing damaged spinal cords, or alleviating harmful side
effects of chemotherapy.
LEARNING OBJECTIVE 5: Explain how an injured nerve fiber may regenerate.
Lecture Suggestions and Guidelines
1. Lecture should include a discussion of the concept that the proximal portion of a peripheral nerve fiber may
regenerate if severed.
2. Discuss regeneration of axons within the central nervous system.
Application Question(s)
1. Are neurons likely to be a site for tumorigenesis in adults?
Answer: Supporting cells, such as neuroglia and Schwann cells, all of which are mitotically active, are more
likely sites for the development of a tumor. Fully mature neurons, as well as some precursor cells, are not
capable of mitosis.
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Critical Thinking Issue(s)
1. Discuss redundancy of the brain following a CVA. What actually happens in the brain? Does redundancy occur
in all patients following a CVA?
Answer: Redundancy occurs in the brain by establishing new pathways, i.e., utilizing previously little used
neurons to carry impulses. Recovery from a CVA is dependent upon the site and extent of damage. However,
for many patients, timely rehabilitation and phenomenon such as redundancy greatly increase the chances for
effective recovery.
LEARNING OBJECTIVE 6: Explain how a membrane becomes polarized.
Lecture Suggestions and Guidelines
1. Introduce two major functional properties of neurons: a) irritability; and b) conductivity.
2. Briefly describe polarization during the resting potential. Discussion should include a description of the major
extracellular and intracellular ions.
3. Describe the exodus of positive ions leaving the cell to create a positive charge on the outside of the cell
membrane with respect to the inside.
Application Question(s)
1. Explain what happens when your arm falls asleep after awkwardly lying on it for an extended period of time.
Answer: The pressure exerted on your arm by your body weight has caused a decrease in supply of oxygen and
nutrients to the neurons. When the pressure is alleviated, you feel a tingling in your arm due to the return of
nerve impulse transmission.
Critical Thinking Issue(s)
1. Compare the events leading to the generation of a nerve impulse to the events leading to an impulse within
muscle tissue.
Answer: The events are very similar in terms of polarization, depolarization and repolarization. Ask students to
review information from Chapter 9-Muscular System, as necessary.
LEARNING OBJECTIVE 7: Describe the events that lead to the conduction of a nerve impulse.
Lecture Suggestions and Guidelines
1. Discussion should include a description of local potential changes, action potentials, the refractory period, the
all-or-none response, and impulse conduction.
2. Summarize the events of the generation of a nerve impulse in terms of polarization, depolarization,
development of an action potential, and repolarization.
3. Introduce the concept that nerve impulse transmission is both electrical and chemical in nature.
Application Question(s)
1. What factors can affect nerve impulse conduction?
Answer: The textbook mentions calcium deficiency, increases and decreases in extracellular potassium, and
anesthetics. Ask students to make a list of other factors which may effect conduction such as alcohol, sedatives,
cold , and pressure, and give a brief explanation of how conduction is impaired, e.g., decreased membrane
permeability to sodium ions, decreased circulation, etc.
Critical Thinking Issue(s)
1. Ask students to write a brief report on the dangers associated with cocaine use and the mechanism by which it
produces its effect.
Answer: Points of interest will vary from student to student, but each report should contain a statement
regarding cocaine s ability to block the reabsorption of the neurotransmitters dopamine and norepinephrine.
LEARNING OBJECTIVE 8: Explain how a nerve impulse is transmitted from one neuron to another.
Lecture Suggestions and Guidelines
1. Lecture should include a discussion of synaptic transmission, neurotransmitters, and neuropeptides.
2. Discuss factors which may affect impulse conduction.
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3. Introduce the terms presynaptic neuron and postsynaptic neuron.
4. Discuss the release of neurotransmitters by exocytosis as a result of increased calcium concentration inside the
cell.
Application Question(s)
1. Ask students to devise a set of six index cards, each card describing one major event leading to
neurotransmitter release. Shuffle the index cards and ask students to rearrange them in the correct sequence.
Answer: The major events leading to neurotransmitter release are summarized in Table 10.6.
Critical Thinking Issue(s)
1. Compare the effects of dopamine deficiency to dopamine excess. What pathological conditions and symptoms
are likely?
Answer: Responses should include discussion of diseases such as Parkinson s disease (deficiency), Tardive
dyskinesia (deficiency), and SIDS (excess).
LEARNING OBJECTIVE 9: Distinguish between excitatory and inhibitory postsynaptic potentials.
Lecture Suggestions and Guidelines
1. Introduce the terms EPSP and IPSP.
2. Describe the triggering and inhibition of action potentials. Emphasize that the effects of neurotransmitters may
vary.
3. Discuss the trigger zone, the decision-making part of the neuron, where summation of postsynaptic potentials
takes place.
Application Question(s)
1. What are the major elements involved in a somatic reflex? Have students perform a knee-jerk reflex procedure
on each other and then describe the sensory receptor, the effector organ, the afferent pathway and efferent
pathway.
Answer: The sensory receptors are the Golgi tendon organs in the patellar region, the effector organ is the
quadriceps muscle, the afferent pathway sends a signal from the sensory receptors to the gray matter ventral
horn, and the efferent pathway returns a signal from the gray matter to the effector organ.
Critical Thinking Issue(s)
1. Why does a patient often complain about pain that arises in areas of the body quite removed from the actual
origin?
Answer: This phenomenon is known as referred pain and is the result of specific sites supplied by a single
spinal nerve. These sites are known as dermatomes. Each dermatome produces an action potential that is
always delivered to a precise spinal cord segment. For example, chest pains on the left side as a result of a heart
attack may be explained by pain information being transmitted from the heart to the left side of the spinal cord.
LEARNING OBJECTIVE 10: Explain two ways impulses are processed in neuronal pools.
Lecture Suggestions and Guidelines
1.
2.
3.
4.
Define a neuronal pool as neurons within the central nervous system which are organized into groups.
Discuss facilitation, convergence, and divergence.
Distinguish between divergence and amplification.
Reiterate the concept of efferent vs. afferent pathways
Application Question(s)
1. Apply the students knowledge of this Learning Objective by asking each student to create a flow chart
depicting impulse processing. Begin the flow chart with a box labeled neuronal pools. Be creative and make the
flow chart understandable to a person with limited knowledge of impulse processing. Include any necessary
branches and descriptions but, at a minimum, include boxes labeled facilitation, convergence, divergence, and
amplification.
Answer: Flow charts will vary.
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Critical Thinking Issue(s)
1. Reiterate the students mastery of the concepts of convergence and divergence of nerve impulses by applying
these terms to some other unrelated phenomenon, such as convergence and divergence of vision, convergence
and divergence of two lines, or convergence and divergence of lanes of traffic.
Answer: Basically, convergence is defined as the movement of two objects toward a common point.
Divergence is defined as a separation or movement of objects away from each other.
RELATED DISEASES OF HOMEOSTATIC INSTABILITY
1. Concussion—A transient disorder of the nervous system resulting from a violent blow to the head. Loss of
consciousness is possible. The brain is not actually damaged. Close monitoring of the patient’s condition is
important.
2. Meningitis—An acute inflammation of the first two meninges of the brain and spinal cord (pia mater and
arachnoid mater). Symptoms include high fever, delirium, convulsions, chills, severe headache, stiff neck,
nausea, and vomiting.
3. Encephalitis—An inflammation of the brain and meninges. A viral infection possibly from wild birds and
mosquitoes. It could result in persistent drowsiness, delirium, and possible coma.
SUGGESTIONS FOR ADDITIONAL READING
Barones, Samuel H. February 25, 1994. Thinking about Prozac. Science, vol. 263. The anti-depressant drug Prozac
alters mood by preventing a receptor on a receiving nerve cell from binding the neurotransmitter serotonin.
Kosik, Kenneth S. May 8, 1992. Alzheimer s disease: A cell biological perspective. Science, vol. 256. We are
beginning to understand Alzheimer s disease at the cellular level, with the help of families that inherit it.
Loftus, Elizabeth F. September 1997. Creating False Memories. Scientific American.
Pollen, Daniel A. 1993. Hannah s heirs. New York: Oxford University Press. A fascinating historical discussion of
Alzheimer s disease, first identified in 1844 in a woman named Hannah.
Sapolsky, Robert M., and Dora Y. Ho. June 1997. Gene Therapy for the Nervous System. Scientific American.
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