nervous system review answer key

The Nervous System ReviewAnswer Key

1

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?


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)


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


4

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


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.


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


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


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


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.


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


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!)


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


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.


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)


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


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:


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


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

nervous system review answer key

Documents