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Instructor’s Guide
The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
Introduction
This program is part of the nine-part series The Human Body: How It Works. The series uses physiologic animations and illustrations, microscopic imaging, expert commentary, and footage of the body
in motion to provide a thorough overview of the amazing human machine. The series includes:
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Cells, Tissues, and Skin
The Immune System
Human Development and the Reproductive System
The Respiratory System
The Circulatory System
The Skeletal and Muscular Systems
Digestion and Nutrition
The Endocrine System
The Nervous System and the Senses
Topics
Chapter 1: Introduction to the Nervous System
The program begins with a description of neurons, detailing their function and how they differ from
other cells. Animations clarify what happens when receptors in a neuron’s dendrite are activated,
and an electrical impulse travels to the end of an axon, where neurotransmitters carry it across the
synapse. Also covered: Pre- and postsynaptic neurons.
Chapter 2: Organization of the Nervous System
The two parts of the nervous system — central, and peripheral — are outlined in this section, along
with the regions of the brain and their main functions. Also covered: The reticular formation; fiber tracts.
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
Chapter 3: Sensory Receptors and Sensation
This section defines “sensation,” and the process of transduction that causes it. Viewers learn that
though all nerve impulses are identical in nature, the brain distinguishes different sensations by the
type of nerve fibers an impulse travels on. Also covered: Perception.
Chapter 4: Vision
Our dominant sense — vision — is discussed in this section. Animations help viewers understand
the process of “seeing,” starting with light entering the eye, activating the cones and rods, and firing
action potentials before eventually being relayed to the rest of the brain.
Chapter 5: Hearing
This section relates how sound is produced, and what happens after sound waves reach the ears.
It explains the functioning of the inner, middle, and outer ears by describing the journey of vibration
from pinna to tympanic membrane, ossicles, oval window, cochlea, and organ of Corti, all the way
to the auditory cortex.
Chapter 6: Taste and Smell
The “chemical senses” — gustation and olfaction — are the focus of this section. Viewers learn how
taste buds are actually involved in tasting; and the how’s and why’s of the complex sense of smell,
as a scent travels up the nose, across the cilia, to the olfactory bulbs and glomeruli, before being sent
to another part of the brain. Also covered: Umami; why odors can be such powerful emotional triggers.
Chapter 7: Other Senses
This section introduces the idea that the perceptions of temperature, pressure, equilibrium, and pain
are also “senses,” involving mechanoreceptors, chemoreceptors, thermoreceptors, and nociceptors.
Viewers also learn how motor neurons control the muscles. Also covered: Cranial nerve motor nuclei.
Chapter 8: Sleep and Wakefulness
The final section presents an overview of how the ARAS operates, and why sleep is important.
Learning Objectives
Students will learn…
• The structure of a neuron, how neurons differ from other cells, and how neurons transmit electrical
impulses
• The parts and functioning of the central and peripheral nervous systems
• The parts of the brain, and the main role of each part
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
• The meaning of transduction, and how the brain perceives different sensations
• How the senses of vision, hearing, taste, and smell work
• How mechanoreceptors, chemoreceptors, thermoreceptors, and nociceptors are responsible
for the senses of temperature, pressure, equilibrium, and pain
• How motor neurons work
• How the ARAS operates, and why sleep is important
Vocabulary
ARAS: Ascending Reticular Activating System, a fiber system located in the brainstem that causes
activation of the cerebral cortex, and which is involved in sleep and wakefulness.
action potential: An electrical impulse that carries the neural message down the axon.
autonomic nervous system: The part of the peripheral nervous system that regulates involuntary
actions, made up of the nerves that serve the internal organs and glands.
axon: An extension of a neuron that carries messages away from the cell.
axon hillock: The area where an axon connects with a neuron, and where electrical impulses
combine to generate an action potential.
axon terminals: The branches at the end of an axon.
brainstem: The part of the brain located at the base of the brain and made up of the medulla
oblongata, pons, and midbrain. The brainstem controls and regulates vital body functions, including
respiration, heart rate, and blood pressure.
central nervous system: The part of the nervous system made up of the brain and spinal cord.
cerebellum: Located behind the brainstem, it performs critical functions including coordination
of movement, maintenance of posture, and the learning of motor skills.
cerebral cortex: Also called “gray matter,” it is a layer of neurons about three millimeters thick
that covers the cerebrum. The cerebral cortex is largely responsible for higher brain functions such
as sensation, voluntary muscle movement, thought, reasoning, and memory.
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
cerebrum: The largest part of the brain, consisting of two halves called the cerebral hemispheres.
The cerebrum controls voluntary movements and coordinates mental functioning (such as thoughts,
emotions, and memories).
chemoreceptors: Receptors that respond to chemicals in solution, including taste and smell receptors,
and receptors that sense changes in the concentration of dissolved substances in the blood.
cochlea: The fluid-filled spiral chamber in the inner ear containing nerve receptors essential for hearing.
cones: Photoreceptive cells in the retina of the eye that are responsible for daylight and color
vision. There are three types of cones, each of which is sensitive to either red, blue, or green.
dendrites: Extensions of a neuron that conduct impulses from other neural cells inward toward
the cell body.
dendritic spines: Short, knobby projections on a dendrite that increase the dendrite’s surface area
and thus the amount of room it has for receiving signals from other neurons.
diencephalon: The back part of the forebrain, it connects the midbrain with the cerebral hemispheres, and contains the thalamus and hypothalamus.
equilibrium: Balance.
fiber tracts: Pathways within which axons from neurons in the brain travel down the spinal cord
and out to their targets through the peripheral nerves.
frontal lobe: A part of the cerebral cortex that controls thinking, speech, emotion, and the
planning and production of movements.
glomerulus (plural is glomeruli): A structure formed by the connection of olfactory nerves with
mitral cells. Each glomerulus receives one type of odor signal and then sends it on to another region
of the brain (e.g., cerebral cortex, limbic system, etc.).
gustation: The sense of taste.
hypothalamus: A region of the brain that functions as the main control center for the autonomic
nervous system. The hypothalamus helps regulate sleep cycles, body temperature, appetite, and many
metabolic processes, and also controls some of our hormones. The posterior hypothalamus is involved
with wakefulness, while the anterior hypothalamus promotes sleep.
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
lingual papillae: Projections on the surface of the tongue, some of which contain taste buds.
mechanoreceptors: Receptors that are stimulated by touch, pressure, stretch, tension, or vibration
(such as hearing receptors), and located in the skin, internal organs, joints, and muscles.
medulla: Also known as the medulla oblongata, it is the lowest part of the brainstem, and connects
with the spinal cord. It controls functions such as respiration, swallowing, and circulation.
middle ear: A small, air-filled portion of the skull between the eardrum and the inner ear that
contains the ossicles.
mitral cells: Neurons located in the brain that are associated with the sense of smell.
motor neurons: Neurons in the spinal cord that control (either directly or indirectly) muscle movements.
neuron: The basic signaling unit of the nervous system, it is an irregularly shaped cell that has a
number of extensions (usually, one axon and from one to twenty dendrites), and that can conduct
electrochemical signals. Neurons carry messages to muscle fibers, blood vessels, glands, and other
organs.
neurotransmitters: Chemicals that transmit nerve impulses across synapses between neurons,
traveling from the presynaptic neuron to receptors on the postsynaptic neuron.
nociceptors: Receptors that perceive pain.
occipital lobe: A part of the cerebral cortex that receives and interprets input from the eyes.
olfaction: The sense of smell. Olfactory receptors are located in two small areas within the nasal
cavity; each area contains about five million olfactory neurons.
olfactory bulb: Enlarged portion of the olfactory lobe (at the base of the brain) from which
olfactory nerves originate.
organ of Corti: Located in the center of the cochlea, it is the receptor organ for the sense of
hearing. The organ of Corti contains cilia, the movement of which fires action potentials that send
nerve impulses through the auditory nerve to the brain.
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
ossicles: The three bones in the middle ear that transmit sound vibrations through the oval window
to the cochlea.
oval window: The opening into the inner ear.
parietal lobe: A part of the cerebral cortex that receives sensory messages from the skin, joints,
and muscles, and that interprets them as pain, touch, and the position of our arms and legs in space.
perception: The process in which the cerebral cortex combines, organizes, and interprets sensations.
peripheral nervous system: The part of the nervous system made up of the nerves outside
the central system. The peripheral nervous system is divided into the somatic nervous system, and
the autonomic nervous system.
pinna: The outer ear, responsible for conducting air vibrations to the tympanic membrane.
postsynaptic neuron: The neuron receiving a message.
presynaptic neuron: The neuron sending the message; it releases neurotransmitters across
the synapse, to bind to receptors on the postsynaptic neuron.
reticular formation: A web-like network of neurons throughout the length of the brainstem
that relates to cardiovascular and respiratory control, sleep, consciousness, and alertness.
rods: Rod-shaped cells in the retina that respond to dim light. Rods cannot distinguish color.
sensation: The process of receiving information through the sense organs.
sensory receptor: An organ having nerve endings (such as in the eye or ear) that respond
to stimulation.
somatic nervous system: The part of the peripheral nervous system made up of the motor nerves
that activate skeletal muscles.
synapse: A gap of about ten to twenty nanometers between the tip of an axon terminal and
the dendrites of the target neuron, across which neurotransmitters carry messages.
taste buds: The receptor organs for gustation. Each taste bud is actually a cluster of about 100
taste-receptor cells.
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
temporal lobe: A part of the cerebral cortex that interprets “sound” from primary auditory input.
The temporal lobe also plays a role in emotion, understanding speech, perceiving form and color, and
in the sense of smell.
thalamus: The middle part of the diencephalon through which sensory impulses pass to reach the
cerebral cortex.
thermoreceptors: Receptors that are sensitive to temperature changes, used by the body to regulate
both its surface and core temperatures.
transduction: The process by which physical or chemical stimuli are translated into neural signals
by the sensory receptors. The signals are then conducted by nerve cells to the central nervous system.
tympanic membrane: Eardrum.
umami: A taste that is brought out by amino acids like monosodium glutamate, often described as
“meaty” or “savory.”
Student Projects
• Create a map of the brain, labeling its various lobes and regions and noting what each part is
responsible for. Then, do some additional research on the brain. Are there differences between the
male and female brain? Between the brains of teens and adults? Creative thinkers and “linear”
thinkers? How about between the brains of religious and non-religious people? Use Web sites such
as www.PhysOrg.com and www.sciam.com (Scientific American) to research your answers. If you
find differences, mark them on your map of the brain.
• Choose a process such as the action of neurons and neurotransmitters, transduction, or the
mechanics of sight, hearing, smell, or taste and explain it in detail to your classmates. Use visual
aids (posters, PowerPoint, animations, etc.) to help make the information clear.
• Fact or fiction? Using the library and Internet, find the answers to one or more of the following
questions about the nervous system and senses. Write a brief report (citing your sources), then quiz
the rest of the class.
— Does we really only use 10% of our brain?
— Can use of cell phones cause brain cancer?
— Does drinking alcohol kill brain cells?
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
— Do women feel cold more often than men do?
— Will reading in dim light damage your eyes?
— Can using earbuds cause hearing loss later in life?
• What’s going on in the nervous system when we feel pain? How do painkillers work? Write a brief
paper outlining the physiological basis for the following pain management techniques: pharmacological medications; exercise; application of heat or cold; biofeedback and cognitive therapy.
• Compare the human being’s senses with those of other creatures. Make a chart, poster, or other
visual representation showing which animals have the best eyesight, hearing, sense of smell, etc.,
and where humans fit in. For instance, a catfish has roughly 100,000 taste buds (humans have only
about 10,000); snakes can detect the presence of prey by picking up on its body heat; birds can
see colors that humans can’t, and in fact it has been theorized that they follow migration routes
by seeing magnetic lines as streaks of color (called “magnetoception”). Using your chart as a
basis, discuss as a class these differences in sensory receptors — and what it would be like to
experience life with the heightened senses of other creatures.
• Explore the nervous system and senses further by writing a brief paper on the neurological basis
of one of the following subjects ... or any other condition, disease, or disorder of this physiological
system that interests you.
— Synesthesia (the ability to see sound as color, etc.)
— What happens when we fall asleep, wake up, and the stages in between
— Hallucinations (visual, auditory, olfactory, etc.)
— Alzheimer’s Disease, stroke, Parkinson’s Disease, or Multiple Sclerosis
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
Quiz
1. Neurons differ from other cells in the following ways: _____.
a) they are regular in shape
b) they can conduct electrochemical signals, using axons and dendrites
c) they contain both a presynaptic and postsynaptic terminal
d) (all of the above)
2. (Circle the correct word.) Axons carry messages [away from / into] the cell, and dendrites carry
messages [away from / into] the cell.
3. Neurotransmitters _____.
a) create action potentials that are carried across synaptic gaps
b) are specialized cells that travel between the cerebrum and the cerebellum
c) are the electrical impulses that relay messages to the rest of the body
d) are the chemicals that carry messages from one neuron to another
4. A nerve impulse can travel _____ in one second.
a) 20 nanometers
b) more than the length of a football field
c) the distance to the moon and back
d) up to 5 feet
5. A synapse is _____.
a) the gap between the axon terminal and the dendrites of the target neuron, across which
neurotransmitters carry messages
b) the gap between dendritic spines across which neurotransmitters carry messages
c) an electrochemical message conveyed from one neuron to the next
d) the neuronal chemical responsible for cognition
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
6. Match the lobe of the brain with its main function(s). (Choose all that apply.)
a) frontal lobe
b) occipital lobe
c) temporal lobe
d) parietal lobe
1) involved with the sense of smell
2) receives and interprets input from the ears
3) thinking, speech, emotion, and the planning and production of movements
4) receives and interprets input from the eyes
5) receives sensory message from the body and interprets them as pain or touch
6) plays a role in perceiving form and color
7. Match the part of the nervous system with the correct phrase below. (Choose all that apply.)
a) central nervous system
b) peripheral nervous system
c) somatic nervous system
d) autonomic nervous system
1) includes the nerves that exit the spinal cord
2) made up of the nerves that regulate the internal organs and glands (unconscious body
functions)
3) is divided into the somatic and the autonomic nervous systems
4) made up of the motor nerves that activate the skeletal muscles
5) consists of the brain and spinal cord
8. _____ is the process by which physical or chemical stimuli are translated into neural signals by
the sensory receptors. The signals are then conducted by nerve cells to the central nervous system.
a) Action potential
b) Fiber tracting
c) Transduction
d) Neurotransmitting
9. True or False? Nerve impulses are all identical in nature, but the brain can distinguish between
different sensations because the the nerve impulses arrive via different nerve fibers, which then
stimulate different centers in the brain.
10. The _____ is the actual receptor organ for the sense of hearing.
a) cochlea
b) tympanic membrane
c) auditory nerve
d) organ of Corti
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
11. _____ is our dominant sense. Seventy percent of all sensory receptors are found in the _____,
and almost half of the cerebral cortex is involved in perception of this.
a) Vision; eyes
b) Hearing; eardrum
c) Gustation; taste buds
d) Olfaction; olfactory cells
12. Taste and smell are known as the _____ senses, because their receptors respond to stimuli of
this type rather than physical stimuli.
a) chemical
b) electrical
c) gustatory
d) olfactory
13. Most people can detect between _____ different odors.
a) 200 and 400
b) 500 and 1,000
c) 2,000 and 4,000
d) 5,000 and 10,000
14. Scents can trigger memories and emotions because _____.
a) olfactory signals are sometimes sent to the limbic system, the region of the brain responsible
for memory and emotion
b) olfactory signals are diffused throughout the entire nervous system
c) the fight-or-flight response is very easily activated
d) each glomerulus is responsible for a specific associated memory
15. In addition to “the five senses,” _____ are also classified as senses.
a) temperature, pressure, and pain
b) temperature, pressure, equilibrium, and pain
c) temperature, pressure, and equilibrium
d) “knowing”; and pressure, equilibrium, and pain
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
16. True or False? The number of muscle fibers a particular motor neuron stimulates depends on how
coarse or fine the movements involved are. The branched endings of a motor neuron may activate as many as 1,000 fibers in the muscles of the hip and thigh, while another may stimulate
fewer than ten fibers in the muscles of the finger.
17. Sleep is _____.
a) an active process; research suggests that it is meant to both rest and restore the body
b) an active process; research suggests that it is meant to both rest and restore the brain
c) a reduction of awareness that allows metabolism to temporarily shut down
d) a “resting” phase for both the body and brain
18. The _____ is a fiber system involved with sleep. When we are awake, it helps keep us alert by
allowing the _____ to relay sensory messages to the cerebral cortex; when it is inhibited, transmission of sensory messages is inhibited.
a) ARAS; thalamus
b) peripheral nervous system; chemoreceptors
c) glomeruli; limbic system
d) ARAS; motor neurons
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
Answers to Quiz
1. b) they can conduct electrochemical signals, using axons and dendrites
2. away from; into
3 d) are the chemicals that carry messages from one neuron to another
4. b) more than the length of a football field
5. a) the gap between the axon terminal and the dendrites of the target neuron, across which
neurotransmitters carry messages
6. a 3 (frontal lobe = thinking, speech, emotion, and the planning and production of movements)
b 4 (occipital lobe = receives and interprets input from the eyes)
c 1, 2, 6 (temporal lobe = involved with the sense of smell; receives and interprets input from the
ears; plays a role in perceiving form and color)
d 5 (parietal lobe = receives sensory message from the body and interprets them as pain or touch)
7. a 5 (central nervous system = consists of the brain and spinal cord)
b 1, 3 (peripheral nervous system = includes the nerves that exit the spinal cord; is divided into
the somatic and the autonomic nervous systems)
c 4 (somatic nervous system = is made up of the motor nerves that activate the skeletal muscles)
d 2 (autonomic nervous system = made up of the nerves that regulate the internal organs and
glands [unconscious body functions])
8. c) transduction
9. True
10. d) organ of Corti
11. a) Vision; eyes
12. a) chemical
13. c) 2,000 and 4,000
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The Human Body: How It Works
THE NERVOUS SYSTEM AND THE SENSES
INSTRUCTOR’S GUIDE
14. a) olfactory signals are sometimes sent to the limbic system, the region of the brain responsible
for memory and emotion
15. b) temperature, pressure, equilibrium, and pain
16. True
17. b) an active process; research suggests that it is meant to both rest and restore the brain
18. a) ARAS; thalamus
Please send comments, questions, and suggestions to [email protected]
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