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The Nervous System ReviewAnswer Key
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00Review Questions:
1. What are the 2 main divisions of the nervous system? What do they include2. What are the 3 main parts of all neurons? Distinguish between an axon and a dendrite.3. Distinguish between the 3 types of neurons. What is another name for the sensory and motor neurons?4. What are dendrites and axons of neurons sometimes called? Schwann cells lay down several layers of cellular membrane containing myelin , and are covered by an outermost sheath called the neurilemma , which plays an important role in nerve regeneration in the PNS. 5. What is meant by the resting membrane potential? What is its value? Is it positive or negative?6. Describe the distribution of sodium and potassium ions on either side of the axomembrane. What is this unequal distribution of ions due to? In which direction will the ions be pumped?7. Why are there always more positive ions outside the axomembrane than inside? What accounts for the polarity recorded on the oscilloscope? What contributes toward the negative charge in the axoplasm?8. If an axon is stimulated, the trace that appears on an oscilloscope screen is called the action potential . 9. During the upswing of the action potential, what ion will flow into the axon? What happens to the charge on the inside of the axon? What is this termed?10. What happens when the potassium gates open? What term is used to describe this?11. Why is the sodium-potassium pump important after repolarization has occurred? The time period in which the neuron is unable to conduct a nerve impulse is termed the refractory or recovery period.12. Why is the speed of conduction much faster in myelinated fibers than unmyelinated nerve fibres? What is this type of conduction called?13. What is the difference between the presynaptic membrane, synapse, synaptic cleft, and the postsynaptic membrane?14. What happens when a nerve impulse reaches the axon’s presynaptic membrane? The substances that are released are termed neurotransmitters .15. What happens to the postsynaptic membrane if a neurotransmitter substance is excitatory? If inhibitory?16. List 2 excitatory neurotransmitters and the enzymes that break them down.17. What will determine whether a neuron will fire? This is called threshold 18. Name the part of our body that integrated the information it receives from all over our body in order to make decisions.19. What is the peripheral nervous system made up of? Where are the cell bodies found within the PNS?20. Define the all-or-none law. Why doesn’t a nerve obey this law?21. Distinguish between the 3 types of nerves.22. 23. What type of nerves are found in the dorsal and ventral roots? What does the somatic nervous system do?24. What is a reflex? List the path in a simple reflex arc.25. What is the function of the autonomic nervous system?26. Where does the sympathetic nervous system arise? What neurotransmitter is associated with this system?
The Nervous System ReviewAnswer Key
227. What are the 2 parts of the CNS? What is the function of the meninges and the cerebrospinal fluid?28. What are the 2 main functions of the spinal cord? 29. Which part of the unconscious brain lies closest to the spinal cord and contains centers for the heartbeat, respiration, vasoconstriction, and various reflex centers?30. Which part of the brain functions to:
a. maintain homeostasis and control the pituitary gland?b. regulate breathing rate along with the medulla?c. act as a central relay station for incoming sensory impulses traveling to the
cerebrum?d. act as a gatekeeper to the cerebrum? Name the specific part that achieves
this function.e. coordinate muscle activity, muscle tone, and maintain power?
31. Name the largest part of the human brain that is responsible for consciousness. List the lobes of the brain. 32. What is the role of association areas? What is the function of the corpus callosum?33. Describe what takes place during epilepsy.34. What is the relationship between learning and the number of synapses?
Completion and Short Answer Questions:
1. The peripheral nervous system may be divided into the somatic and
autonomic divisions.
2. A motor neuron has a long (long/short) axon and
short (long/short) dendrites.
3. During depolarization of the nerve impulse, the sodium ion moves to the inside of the neuron.
4. The junction between one neuron and another is called a synapse .
5. Reflexes are automatic, involuntary responses to changes inside or outside the body.
6. Each division of the autonomic nervous system controls the same organs, but they
generally have opposite effects. I.e. Sympathetic Vs parasympathetic
7. The largest portion of the human brain is the cerebrum (cerebral cortex) .
8. The parasympathetic nervous system causes the heartbeat to decrease (increase/decrease)
The Nervous System ReviewAnswer Key
39. The meninges are protective membranes covering the central nervous system.
10. The limbic system lies just below the cortex of the cerebrum that when stimulated will cause the individual to experience rage, pain, pleasure or sorrow.
11. In the diagram below, label a, b, and c as either the motor neuron, interneuron, or sensory neuron.
1. All the parts labeled #1 in the diagram below are called dendrites
Their function is to conduct nerve impulses to cell bodies
2. All the parts labeled #2 in the diagram below are called cell bodies
Their function is to take the sum of all impulses collected by dendrites, restores nerve
impulse if required
3. All the parts labeled #3 in the diagram below are called axons
Their function is to conduct nerve impulses away form the cell bodies
4. All the parts labeled #4 in the diagram below are called axon bulbs-terminals)
Their function is to conduct nerve impulses across the synapses to the next neuron
The Nervous System ReviewAnswer Key
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12. Dendrites and axons of neurons are sometimes called fibers or processes .
Schwann cells have a supportive, nutritive and communicative function for
neurons. Schwann cells are found in the PNS and encircle a fiber,
leaving gaps called Nodes of Ranvier . Myelin a lipid
substance that is an excellent insulator, gives nerve fibers a white, glistening
appearance.
13. The nerve cell of the nervous system is called the neuron , of
which there are three types, sensory (afferent) , motor (efferent)
and interneurons (association neurons) . Nerves are composed of a number of
neurons . Cell bodies are found in the central system and in
ganglia of the peripheral system.
14. The voltage is a measure of the electrical potential difference
between two points, and the instrument that shows the change in voltage with time is
called an oscilloscope . When the nerve impulse jumps
from node of Ranvier to node of Ranvier, it is called saltatory (jumping)
conduction.
15. The resting membrane potential, when an axon is not conducting an impulse, is
about -65mV which indicates that the inside of the neuron is negatively charged
compared to the outside. The concentration of sodium ions is
The Nervous System ReviewAnswer Key
5greater outside the axon, and the concentration of K+ is greater inside the
axon. This unequal distribution of ions is due to the action of the sodium/potassium
pump in which Na+ are pumped out and K+ into the axon. Polarity of the axon is
due to
potassium ions being more permeable than Na+ and the presence of large,
negatively charged organic molecules in the axoplasm.
16. An action potential , which is the nerve impulse, occurs when a
threshold is reached. Upon stimulation, the sodium gates open, Na+ flows into
the axon, and the action potential swings up from -65mV to +40 mV. During
depolarization the inside of the fiber becomes positive as Na+ enters. During re-
polarization, K+ move to the outside, and the action potential swings down to -65mV. In
the refractory period, the fiber is unable to conduct an impulse.
17. The site where an axon meets a dendrite (or cell body) is called a synapse
The membrane of the first neuron is called the presynaptic membrane,
and the membrane of the next neuron is called the postsynaptic membrane. The gap
between the two is called the cleft . When a nerve impulse
reaches a synaptic ending, the membrane becomes permeable to calcium ions
which interact with actin causing microfilaments to pull the synaptic vesicles
to the presynaptic membrane. When the neurotransmitter is discharged, it
diffuses across the cleft to a receptor on the postsynaptic membrane. If excitation
occurs,
sodium channels open and a nerve impulse may form.
The Nervous System ReviewAnswer Key
618. Acetylcholine and norepinephine can be excitatory or inhibitory according to
the type of receptor. The enzyme acetylcholinesterase breaks down
acetylcholine, and in other synapses, the neurotransmitter is rapidly reabsorbed so as to
prevent continuous stimulation of postsynaptic membranes.
19. What are the two main divisions of the nervous system? central
peripheral . The peripheral nervous system (PNS) contains cranial nerves
and spinal nerves. In the PNS., the somatic system controls the
skeletal muscles, and the autonomic system controls the smooth
muscles, cardiac muscles, and glands.
20. Nerves are bundles of fibers which are processes of
neurons . Collections of cell bodies found within the PNS are called
ganglia . Humans have 12 pairs of cranial nerves and 31 pairs
of spinal nerves, which are all classified as mixed nerves. An individual nerve fiber, but
not a nerve, obeys an all-or-nothing law. (fires maximally or not at all)
21. What does the somatic nervous system serve? Musculoskeletal system
exterior sense organs . Receptors receive
environmental stimuli and initiate nerve impulses. Effectors bring about a
reaction to the stimulus.
22. Reflexes are automatic, involuntary responses to changes occurring inside
or outside the body. In the spinal reflex, (reflex arc), a receptor in the skin generates a
The Nervous System ReviewAnswer Key
7nerve impulse that moves along a sensory neuron that passes to many
interneurons in the spinal cord. The interneurons send impulses to a motor
neuron whose axon causes the muscle fibers (an effector) to contract.
23. List three characteristics of both the sympathetic and parasympathetic autonomic
system.
a. function automatically and subconsciously
b. service all internal organs
c. use 2 neurons and 1 ganglion per impulse
Where is the cell body of the first and second neuron found? 1 st - in CNS and a
“preganglionic fiber 2 nd - cell body in the ganglion and a postganglionic fiber.
24. Most preganglionic fibers of the sympathetic system arise from the middle
portion of the spinal cord. The preganglionic fiber is short , but
the postganglionic fiber is long. This system is important during emergency
situations and is associated with “fight or flight” . The parasympathetic system is
referred to as the craniosacral (don’t need to know!) portion of the autonomic
system, and the preganglionic fiber is long compared to a short
postganglionic fiber. The parasympathetic system promotes responses associated with a
relaxed state while releasing acetylcholine .
25. The central nervous system consists of the brain and spinal cord which
are wrapped in three protective membranes known as meninges .
cerebrospinal fluid is found between the meninges, within the ventricles
of the brain, and in the central canal of the spinal cord. Neuroglial cells
The Nervous System ReviewAnswer Key
8outnumber neurons nine to one, and they take up more than ½ the volume Neuroglial
cells absorb the neurotransmitter glutamate and lie between neurons and the capillary.
Microglial cells are phagocytes that clean up debris, whereas oligo-
denrocytes form myelin sheaths in the CNS.
26. What are the two main function of the spinal cord? Center for reflex actions
2. Communication between brain and spinal nerves (rest of bodies
nerves)
The gray matter has unmyelinated cell bodies, looks like a butterfly, and
contains short interneurons that connect sensory and motor neurons. White
matter has myelinated interneurons that run together in bundles called tracts.
Dorsal
ascending tracts take information to the brain.
27. The medulla-oblongata contains vital and non-vital reflex centers for head
movements. The mid-brain acts as a relay station between the
cerebrum and spinal cord or cerebellum.
Transmission across a synapse: Label the numbered parts in the diagram.
1. synapse 8. Presynaptic membrane
2. vesicles 9. Postsynaptic membrane (with receptors)
3. axon (the end) 10. Cell body
4. postsynaptic dendrite 11. dendrites
5. postsynaptic membrane 12. vesicles
The Nervous System ReviewAnswer Key
96. synaptic cleft
7. neurotransmitters
28. The hypothalamus maintains homeostasis by containing
centers for hunger, thirst, body temperature, and water balance and serves as a link
between the nervous and endocrine systems. The thalamus serves as a central
relay station for sensory impulses traveling to the cerebrum (except for smell). The
cerebellum functions in muscle coordination, muscle tone, and
posture.
29. The cerebrum , the largest part of the brain, is responsible for
consciousness. The outer layer, called the cerebral cortex is gray in
colour and unmyelinated. The right and left cerebral hemispheres are connected by the
corpus callosum , and the cerebrum has 4 lobes.
The Nervous System ReviewAnswer Key
10 association areas integrate information into higher, complex levels of
consciousness. The basal nuclei constitute the central gray matter of
the cerebrum and control some voluntary muscle, but precise functions are not known.
The limbic system, when stimulated, causes the subject to experience pain,
pleasure, etc., as well as learning and memory.
DRUG ABUSE - good background knowledge!
30. Stimulants can either enhance the action of an excitatory
neurotransmitter or block the action of an inhibitory neurotransmitter.
Depressants can either enhance the action of an inhibitory neurotransmitter or
block the action of an excitatory neurotransmitter. Drug abusers are apt to display either
a psychological and/or physical dependence on the drug. With
physical dependence the person is tolerant to the drug - he or she must
increase the amount of the drug to get the same effect and has withdrawal symptoms
when he or she stops taking the drug.
31. Alcohol disrupts the normal workings of glycolysis and the Kreb’s cycle
by using up the supply of NAD in liver cells. Lactic acid builds up, pH of the
blood decreases, and excess active acetate cannot be broken down. As
a result, the liver turns fatty , the first stage in liver deterioration. In the
second stage, fibrous scar tissue appears. Finally, cirrhosis
of the liver occurs. Alcohol crosses the placenta freely and causes
fetal alcohol syndrome , characterized by mental retardation. The calories
produced from alcohol breakdown are empty because they do not supply
amino acids, vitamins, and minerals.
32. In the CNS, nicotine causes neurons to release dopamine . In the PNS,
nicotine stimulates the same postsynaptic receptors as acetylcholine , and
The Nervous System ReviewAnswer Key
11leads to increased skeletal muscle activity. What does the affect of marijuana depend
upon? Amount, strength of dose, experience of user, environment of use
Marijuana is classified as a hallucinogen since it may affect
seretonin, and excitatory neurotransmitter. Marijuana use can cause a psycological
dependence and has been called a gateway drug. It may
lead to long-term brain impairment or reproductive dysfunction.
23. Users of cocaine often describe the feeling of euphoria that follows intake of the drug
as a rush . Cocaine prevents the re-uptake of the neurotransmitter
dopamine by the presynaptic membrane. With continued cocaine
use, the body makes less dopamine and the user experiences tolerance, withdrawl
symptoms, and an intense craving for cocaine, indications of addiction.
34. Heroin, derived from morphine, is usually injected and binds to
receptors meant for the endorphins ̧ , neurotransmitters that kill pain and
produce tranquility by preventing the release of substance P in the spinal cord. With
time, the body’s production of endorphins decrease and tolerance and dependence
develops so that the user needs to take more of the drug.
25. A new form of methamphetamine is known as ice and
used as an alternative to cocaine. Designer drugs are analogs , that is,
chemical compounds of controlled substances slightly altered.
Across down
2. cerebellum 1. acetylcholine
4. neuron 3. myelin
6. synapse 5. neuroglia
7. pons 8. ?meninges (not enough spaces!)
The Nervous System ReviewAnswer Key
129. oscilloscope 10. axon
11. brain
12. reflex
13. dendrite
Completion and Short Answer questions:
1. The axon of a neuron conducts nerve impulses away from
the cell body. Neurons that conduct messages from a sense organ to the central
nervous system are called sensory , or afferent neurons. Those
neurons that conduct an impulse from the CNS to a muscle or gland are called
motor , or efferent, neurons. Muscles or glands, in this case, that
respond to a nerve impulse are termed effectors . Neurons
within the CNS that transmit impulses between sensory and motor neurons are called
interneurons .
2. What is a nerve fiber? And axon or a dendrite
The Nervous System ReviewAnswer Key
13Schwann cells in the peripheral nervous system will wrap around an axon and lay down
an insulator called myelin that gives nerve fibers a white, glistening
appearance. Gaps where myelin is not present on the nerve fiber are called
nodes . These gaps allow the speed of nerve impulse
conduction, called saltatory conduction, to be increased.
3. When an axon is not conducting an impulse, the membrane potential is equal to about
-65 mV, with the inside of the neuron being negative compared to the
outside. This polarity is maintained by the sodium/potassium pump
in which sodium ions are pumped outside (inside/outside) the
axon, and potassium ions are pumped into the axon. Another name for
the nerve impulse is the action potential which forms when the axon
is stimulated. When the sodium gates open, Na+ flow into the axon, causing
the action potential to swing up to +40 mV and the membrane to become
depolarized
Now the K+ gates open, K+ flow out (out/into) the axon, and the
oscilloscope records a repolarization .
4. Label the following diagram of the reflex are and spinal cord. a. effector b. sensory neuron c. interneuron d. motor neurone. sensory receptor f. dorsal-root ganglion g. white matter h. gray matteri. ventral horn j. central canal5. In the above diagram of a spinal reflex arc, a stimulus is received by a receptor
such as the skin, which initiates a nerve impulse in the sensory
neuron. This neuron conducts the impulse to the gray matter of the spinal cord.
At this site, a second neuron, called the interneuron , conducts the
impulse to the motor neuron, whose cell body lies in the ventral horn of
the gray matter. This neuron, in turn, innervates an effector ,
usually a muscle or a gland.
The Nervous System ReviewAnswer Key
146. Place each of the following statements in proper sequence by using the numbers 1-9
to describe the transmission of a nerve impulse across a synapse.
6 Neurotransmitter diffuses across cleft
1 Nerve impulse travels to presynaptic membrane
4 Microfilaments pull synaptic vesicle to presynaptic membrane
3 Ca++ interact with actin filaments
5 Synaptic vesicles fuse with presynaptic membrane
9 Neurotransmitter reabsorbed by presynaptic membrane or inactivated by
enzyme
2 Presynaptic membrane becomes permeable to Ca++
8 Neurotransmitter and receptor initiate excitation or inhibition of postsynaptic
membrane.
7 Neurotransmitter binds to receptor on postsynaptic membrane
7. The peripheral nervous system contains cranial nerves that connect
to the brain and spinal nerves that attach to the spinal cord. The
PNS is subdivided into the somatic system, which serves the
musculoskeletal system and the exterior sense organs, and the autonomic
system, which serves the internal body organs. This last system is divided into
the
sympathetic and parasympathetic systems.
Label the following parts of the human brain.
a. medulla oblongata b. pons c. midbrain
d. brain stem e. cerebrum (cerebral cortex)
The Nervous System ReviewAnswer Key
15f. corpus callosum g. thalamus h. pituitary gland
i. cerebellum j. spinal cord
9. fill in the table below to indicate the functions of the following parts of the brain.
BRAIN PART FUNCTION
CEREBRUM Conscious thought
CEREBELLUM Muscle coordination and balance
THALAMUS Relay station between sensory input and cerebrum
HYPOTHALMUS Junction between nervous/exocrine systems - homeostasis
MIDBRAIN Relay station between spinal cord and cerebrum + reflexes
PONS Bridge between cerebellum and CNS + part of resp. centre
and some reflexes
MEDULLA OBLONGATA Vital centers, reflexes “primitive brain” - SURVIVAL
True/ False: If you believe the statement to be false, rewrite the statement as a true one.
1. Sensory neurons take a message from a sense organ to the CNS and have a short dendrite but a long axon.
Answer: f Restatement: sensory neurons have long dendrites, and
The Nervous System ReviewAnswer Key
16short axons
2. The sodium-potassium pump maintains a high concentration of Na+ inside the membrane and a high K+ concentration outside the membrane.
Answer: f Restatement: sodium outside / potassium inside
3. In the PNS, sensory nerves contain long axons, and motor neurons contain long dendrites.
Answer: f Restatement: opposite!
4. A nerve, when stimulated , will obey the all-or- none law.
Answer: f Restatement : a NEURON wiil - nerves are bundles of neuronsa
and they have an additive effect
5. The corpus callosum is a bridge of nerve fibers that connects the right and left
hemispheres.
Answer: t Restatement :
6. The outer layer of the cerebrum is gray (unmyelinated), whereas the outer layer of the
spinal cord is white.
Answer: t Restatement:
The Nervous System ReviewAnswer Key
17
Matching: Match the following answers to one of the statements below.
a. resting potential d. depolarizationb. sodium-potassium pump e. repolarizationc. action potential f. refractory periode K+ move out of the axon
d Charges inside the axon change to positive
b Active transport system
a,f Axon is not conducting an impulse
f Time when the axon cannot conduct an impulse
c Axon is depolarized, then repolarized
a. central nervous system b. peripheral nervous systemc. somatic nervous system d. autonomic nervous systeme. sympathetic nervous system f. parasympathetic nervous system
c serves the skin and muscles
d serves internal organs
a composed of the brain and spinal cord
e used in “fight of flight”
b composed of cranial and spinal nerves
f used in a relaxed state
a. alcohol b. marijuana c. cocained. heroin e. methamphetamine f. designer drugsf controlled substances that are slightly altered
c an alkaloid that binds to endorphin receptors
a most abused drug in the United States
e called “ice” and effect is similar to cocaine
d causes a rush by affecting dopamine
The Nervous System ReviewAnswer Key
18b “gateway” drug that can cause psychological dependence
a. somatic motor pathwayb. sympathetic autonomic motor pathwayc. parasympathetic autonomic motor pathway
b,c uses two neurons per message
a uses one neuron per message
c uses acetylcholine as neurotransmitter
b uses norepinephrine as neurotransmitter
b,c innervates smooth, cardiac muscle and glands
a innervates skeletal muscles
b,c used in involuntary muscle movement
a used in voluntary muscle movement
c preganglionic motor neuron shorter than postganglionic
b preganglionic motor neuron shorter than postganglionic neuron
b preganglionic nerves arise from thoracic-lumbar region
c preganglionic nerves arise from cranial and sacral region
c called the “housekeeper system”
b used in “fight or flight” activity