BI SC 004
Human Body:
Form and Function
STUDY GUIDE:
The General & Special Senses
Dr. Martha Aynardi
aynardi@psu.edu
Table of Contents

The Nervous System: Section Learning Objectives
◦ The General Senses
◦ Olfaction
◦ Gustation
◦ Vision
◦ Hearing & Equilibrium
◦ Static vs. Dynamic Equilibrium
◦ Additional Terms

Activities
◦ Chapter Review Questions

Learning Resources
◦ Chapter key terms
The General Senses
Section Learning Objectives

Upon completion of this section, you should
be able to:
◦ Distinguish between the general and special
senses.
◦ Identify the receptors for the general senses
and describe how they function.
◦ Define what a receptive field is.
◦ Describe sensory adaptation and its function.
The General Senses:

Distinguish between the general and special
senses (pg. 294).
 General
senses – include temperature, pain,
touch, pressure, vibration, and proprioception
(body position). The receptors for the general
senses are scattered throughout the body.
 Special
senses – include smell (olfaction), taste
(gustation), vision, balance (equilibrium), and
hearing. The receptors for the special senses
are concentrated within specific structures – the
sense organs.

Identify the receptors for the general senses
and describe how they function (pg. 294 –
298).
1. Nociceptors (pain) – free nerve endings. When
pain receptors in a region are stimulated, 2
types of axons carry the painful sensations:
A.
Myelinated fibers carry very localized sensations
of fast pain (prickling pain), such as that caused
by an injection or a deep cut. These sensations
reach the CNS quickly, where they often trigger
somatic reflexes, and are relayed to the primary
sensory cortex so they receive conscious
attention.
B.
Unmyelinated fibers carry sensations of slow
pain (burning or aching pain). Unlike fast pain
sensations, slow pain sensations enable you to
identify only the general area involved.
2. Thermoreceptors (temperature receptors) – free
nerve endings located in the dermis, in skeletal
muscles, in the liver and in the hypothalamus.

These receptors are relayed along the same
pathways that carry pain receptors. They are very
active when the temperature is changing, but
quickly adapt to a stable temperature.

For example, when you enter an air conditioned
room on a hot summer day, the temperature seems
extreme at first, but you quickly become
comfortable as adaptation occurs.
3. Mechanoreceptors – sensitive to stimuli such as
stretching, compression, or twisting (pg. 295).

3 classes of mechanoreceptors:
A.
Tactile receptors (touch) – provide sensations of
touch, pressure, and vibration (pg. 296).
B.
Baroreceptors (pressure) – provide information
essential to the regulation of autonomic activities
by monitoring changes in pressure (pg. 297).
C.
Proprioceptors (position) – monitor the position
of joints, the tension in tendons and ligaments,
and the state of muscular contraction (pg. 297).
4. Chemoreceptors generally respond only to
water-soluble and lipid-soluble substances that
are dissolved in the surrounding fluid (pg. 298).
5. Photoreceptors are the rods and cones of the
retina – they detect photons, basic units of
visible light

Define what a receptive field is (pg. 294).
 The
area monitored by a single receptor cell is
its receptive field. When a strong stimulus
arrives in the receptive field, the CNS receives
the information “stimulus arriving at receptor
X”.

Describe sensory adaptation and its function
(pg. 294).
 Adaptation
is a reduction in sensitivity in the
presence of a constant stimulus.

Adaptation reduces the amount of information
arriving at the cerebral cortex.

For example, stepping into a hot bath or jumping
into a cold lake; within moments neither
temperature
seems as extreme as it did initially.
Olfaction
Section Learning Objectives
Upon completion of this section, you should
be able to:
 Describe
the receptors and processes involved in
the sense of smell.
 Define
role.
olfactory receptor cells and describe their
Olfaction:

Describe the receptors and processes
involved in the sense of smell (pg. 299-300).
 Olfactory
receptor cells are highly modified
sensory neurons.
 Olfactory
reception occurs as dissolved
chemicals (odorants) interact with receptors
(odorant binding proteins) located on the
surfaces of the receptor cell cilia (olfactory
hairs).
 Odorants
are chemicals that stimulate olfactory
receptors. The binding of an odorant changes
the permeability of the receptor membrane,
producing action potentials. This information is
relayed to the CNS, which interprets the smell
on the basis of the particular pattern of
receptor activity.
Gustation
Section Learning Objectives
 Describe
the receptors and processes involved in
the sense of taste.
 Differentiate
between a taste bud and a
gustatory cell.
 Recall
the 6 taste sensations.
 Describe
the key structural difference between
gustatory and olfactory receptors.
Gustation:

Describe the receptors and processes
involved in the sense of taste (pg. 300-301).
 Gustatory
receptors (taste receptors) are
distributed over the surface of the tongue and
adjacent portions of the pharynx and larynx.
The most important taste receptors are on the
tongue.
A
conscious perception of taste is produced as
the information received from the taste buds is
correlated with other sensory data.
 Information
about the texture of food, along
with taste-related sensations (like “peppery” or
“spicy”) is provided by sensory afferents in the
trigeminal nerve (V).
 Information
from olfactory receptors plays an
overwhelming role in taste perception. You
are several thousand times more sensitive to
tastes when your olfactory organs are fully
functional.
 In
contrast, when you have a cold and your nose
is stuffed up, airborne molecules can’t reach
your olfactory receptors, so meals taste dull
and unappealing – even though your taste buds
are responding normally.

Differentiate between a taste bud and a
gustatory cell (pg. 300).
 Taste
buds – sensory structures formed from
taste receptors and specialized epithelial cells.
 Gustatory
cells – are slender sensory receptors
contained within the taste buds, along with
supporting cells.

Recall the 6 taste sensations (pg. 300-301).
 Primary
taste sensations:
1. Sweet
2. Salty
3. Sour
4. Bitter
 Additional
tastes:
5. Umami – a pleasant taste that is characteristic of
beef broth, chicken broth, and Parmesan cheese
6. Water – most say water has no flavor, yet water
receptors are present. Their sensory output is
processed in the hypothalamus and affects
several systems involved in water balance and
regulation of blood volume.

Describe the key structural difference
between gustatory (taste) and olfactory
(smell) receptor (from lecture).
 Which
one is a sensory neuron (modified)?
 Which
one is an epithelial cell?
Vision
Section Learning Objectives

Upon completion of this section, you should
be able to:
 Identify
the parts of the eye encountered by
photons of light traveling to the retina and
describe their functions.
 Differentiate
 Discuss
between the rods and the cones.
the layers of the eyeball and describe
their roles.
 Describe
the roles visual pigments and
rhodopsin play in the process of vision.
 Describe
how night blindness, vitamin A, and
retinal are related.
 Define
blind spot.
 Describe
the process of vision (photoreception),
and explain how we are able to see objects and
distinguish color.
 Differentiate
between the following terms:
cataracts, hyperopia, myopia, presbyopia,
astigmatism, night blindness, color blindness,
glaucoma, and eye strain.
Vision:

Identify the parts of the eye encountered by
photons of light traveling to the retina and
describe their functions.
 Incoming
light interacts with visual pigment (i.e.,
rhodopsin) of the photoreceptor.
Refer to Figure 9-10a

Differentiate between the rods and the cones
(pg. 306 & 312).
 Rods
do not discriminate among colors of light.
These light-sensitive receptors enable us to see
in dimly lit rooms, at twilight, or in pale
moonlight.
Refer to Figure 9-19
Vision
Differentiate between the rods and the cones

(pg. 306 & 312).


Cones provide us with color vision.
There are 3 types of cones present: blue, green
& red cones.
Their stimulation in various combinations
provides the perception of different colors.
Cones give us sharper, clearer images, but
require bright light than rods.

Discuss the layers of the eyeball and
describe their roles (pg. 305-306).
 The
wall of the eye contains 3 layers (tunics):
Fibrous tunic (outermost layer), vascular tunic,
and neural tunic (innermost layer).
 Fibrous
tunic, the outermost layer of the eye.
Consists of the sclera and the cornea.
7. Provides mechanical support & some degree of
physical protection
8. Serves as an attachment site for the extrinsic eye
muscles
9. Assists in the focusing process
Refer to Figure 9-10c

Discuss the layers of the eyeball and
describe their roles (pg. 305-306), cont.
 The
vascular tunic, consists of the iris, the ciliary
body and the choroid. It contains numerous
blood vessels, lymphatic vessels, and the
intrinsic eye muscles.
10. Provides a route for blood vessels and lymphatic
vessels that supply tissues of the eye
11. Regulates the amount of light entering the eye
12. Secretes and reabsorbs the aqueous humor that
circulates within the eye
13. Controls the shape of the lens

Discuss the layers of the eyeball and
describe their roles (pg. 305-306), cont.
 Neural
tunic (retina), the innermost layer of the
eye. Consists of a thin outer pigment layer
(pigmented part), and a thick inner layer (neural
part).
 The
neural part contains:
14. The photoreceptors that respond to light
15. Supporting cells and neurons that perform
preliminary processing and integration of visual
information
16. Blood vessels supplying tissues that line the
posterior cavity

Describe the roles visual pigments and
rhodopsin play in the process of vision (pg.
312).
 Visual
pigments are special organic compounds
contained in the discs of the outer segment in
both rods & cones. The absorption of photons
by visual pigments is the first key step to
detecting light (photoreception).
 Rhodopsin
is the visual pigment of the rods. It
consists of a protein (opsin) bound to the
pigment (retinal). Retinal is identical in both
rods & cones, but a different form of opsin is
found in the rods and in each of the 3 types of
cones (red, blue & green).

Describe how night blindness, vitamin A,
and retinal are related (pg. 312-313).

The visual pigments (retinal) of the photoreceptors
are synthesized from vitamin A. The body stores
enough vitamin A (a significant amount is stored in
the cells of the pigmented part of the retina)
sufficient for several months.

When this reserve of vitamin A is gradually exhausted
(as a result of inadequate dietary sources), the
amount of visual pigment in the photoreceptors
begins to drop.

As a result, vision is affected. Daytime light is
usually sufficient enough to stimulate any remaining
visual pigments, but dim or low light is insufficient to
activate the rods. This condition is known as night
blindness.

Define blind spot (pg. 307-308).

Because the optic disc has no photoreceptors or other
retinal structures, light striking this area goes
unnoticed. This area is commonly known as the
blind spot.

What is the optic disc?

You do not notice a blind spot in your visual field
because involuntary eye movements keep the visual
image moving and allow your brain to fill in the
missing information.

Define blind spot (pg. 307-308), cont.
 Try
this demonstration of the presence of a blind
spot:
Refer to Figure 9-13

Describe the process of vision
(photoreception), and explain how we are
able to see objects and distinguish color
(pg.312).

Differentiate between the following terms:
cataracts, hyperopia, myopia, presbyopia,
astigmatism, night blindness, color
blindness, glaucoma, and eye strain (pg.
311, 313 & 325).
 Cataracts
– opacity (loss of transparency) of the
lens.
 Hyperopia
(farsightedness) – a condition in which
nearby objects are blurry but distant objects
are clear.
 Myopia
(nearsightedness) – a condition in which
vision at close range is normal, but distant
objects appear blurry.

Differentiate between the following terms:
cataracts, hyperopia, myopia, presbyopia,
astigmatism, night blindness, color
blindness, and eye strain (pg. 311, 313 &
325).
 Presbyopia
– a type of hyperopia that develops
with age as the lens becomes less elastic.
 Astigmatism
– visual disturbance due to an
irregularity in the shape of the cornea.
 Night
blindness – a condition where insufficient
amounts of vitamin A result in the inability to
activate the rods sufficiently to see in dim lit
environments.

Differentiate between the following terms:
cataracts, hyperopia, myopia, presbyopia,
astigmatism, night blindness, color
blindness, and eye strain (pg. 311, 313 &
325).
 Color
blindness – a condition in which a persona
is unable to distinguish certain colors.
 Glaucoma
– a condition characterized by
increased fluid pressure within the eye due to
the impaired reabsorption of aqueous humor.
 Eye
strain – a condition which occurs when your
eye gets tired from intense use.

Equilibrium and Hearing
Section Learning Objectives
Upon completion of this section, you should
be able to:

Identify the type of receptor cell common to our
senses of hearing and equilibrium.

Identify the 3 ossicles of the middle ear.

Describe how sound is transmitted to the inner
ear.

Define the Organ of Corti.

Describe the roles the following structures play in
the process of hearing:

the tectorial membrane

the basilar membrane

the vestibulocochlear nerve

Identify the parts of the ear and describe the
processes involved in the sense of hearing.

Differentiate between pitch and intensity.

Differentiate between conductive and nerve
(sensori-neural) deafness.
Equilibrium and Hearing:

Identify the type of receptor cell common to
our senses of hearing and equilibrium (pg.
315).
 The
receptor for both equilibrium and hearing
are hair cells, simple mechanoreceptors.

Identify the parts of the ear (pg. 315).
Refer to Figure 9-22

Identify the 3 ossicles of the middle ear (pg.
316).
 (1)
Malleus (hammer) – attaches at 3 points to
the interior surface of the tympanum.
 (2)
Incus (anvil) – attaches
the malleus to the inner
bone, the (3) stapes (stirrup).

Describe how sound is transmitted to the
inner ear (pg. 316, 320-323).

Define the Organ of Corti.
 Located
in the middle ear, the Organ of Corti
provides the sensation of hearing.

Describe the roles the following structures
play in the process of hearing (pg. 320,
322-323):

the tectorial membrane - the gelatinous
membrane suspended over the hair cells of
the organ of Corti.

the basilar membrane – the membrane that
supports the organ of Corti and separates
the cochlear duct from the tympanic duct in
the inner ear.

the vestibulocochlear nerve – aka acoustic
nerves. Monitors the sensory receptors of
the inner ear.

Describe the processes involved in the sense
of hearing.

Differentiate between pitch and intensity
(pg. 320).
 Pitch
= frequency
 Intensity

= volume
Differentiate between conductive and nerve
(sensorineural) deafness (pg. 324).
 Conductive
deafness – results from conditions in
the outer or middle ear that block the normal
transfer of vibration from the tympanic
membrane to the oval window.

Example: an external acoustic canal plugged by
accumulated wax or trapped water may cause a
temporary hearing loss.

Differentiate between conductive and nerve
(sensorineural) deafness (pg. 324), cont.
 Nerve
deafness – results from conditions within
the cochlea or somewhere along the auditory
pathway. Vibrations are reaching the oval
window and entering the perilymph, but the
receptor either can’t respond or their response
can’t reach its CNS destination.

Example: very loud (high-intensity) sounds can
produce nerve deafness by breaking stereocilia off
the surfaces of hair cells.
Static vs. Dynamic
Equilibrium
Section Learning Objectives

Describe the receptors and processes
involved in the sense of equilibrium.

Describe the role of the semicircular canals
and the vestibule in maintaining equilibrium.
Static vs. Dynamic
Equilibrium:

Describe the receptors and processes
involved in the sense of equilibrium (pg.
318-320).
 Dynamic
equilibrium – aids us in maintaining our
balance when the head and body are moved
suddenly
 Static
equilibrium – maintains our posture and
stability when the body is motionless.
 All
equilibrium sensations are provided by hair
cells of the vestibular complex.

Describe the role of the vestibular apparatus
(the semicircular canals and the utricle &
saccule) in maintaining equilibrium (pg. 318
& lecture).
 The
semicircular canals, which monitor dynamic
equilibrium, provide information about
rotational movements of the head.
 The
utricle and saccule monitor static
equilibrium and provide information about your
position with respect to gravity (including linear
and vertical acceleration).
Additional Terms to
Know…

Recall the function of the following
structures and where they are located:

Rods

Cones

Schlera

Cornea

Retina

Fovea

Macula
Chapter Review Questions

Can you answer the following questions?
◦ Can you describe the receptors and processes
involved in the sense of smell?
◦ Are you able to distinguish between the general
and special senses?
◦ Can you identify the receptors for the general
senses and describe how they function?
◦ Do you know what a receptive field is?
◦ Can you describe sensory adaptation and its
function?
o
Can you define olfactory receptor cells and describe
their role?
o
Can you recall the receptors and processes involved
in the sense of taste?
o
Can you differentiate between a taste bud and a
gustatory cell?
o
Are you able to recall the 6 taste sensations?
o
Can you describe the key structural difference
between gustatory and olfactory receptor?
o
What parts of the eye are encountered by photons of
light traveling to the retina? Can you describe their
functions?
o
Can you differentiate between the rods and the
cones?
o
Are you able to identify the layers of the eyeball and
describe their roles?
o
Can you describe the roles visual pigments and
rhodopsin play in the process of vision?
o
Can you explain how night blindness, vitamin A, and
retinal are related?
o
What is a blind spot?
o
Can you describe the process of vision
(photoreception), and explain how we are able to see
objects and distinguish color?
o
Are you able to differentiate between the following
terms: cataracts, hyperopia, myopia, presbyopia,
astigmatism, night blindness, color blindness,
glaucoma, and eye strain?
o
What type of receptor cell is common to our senses of
hearing and equilibrium?
o
Can you recall the 3 ossicles of the middle ear?
o
How is sound transmitted to the inner ear?
o
What is the Organ of Corti?
o
Can you describe the roles the following structures
play in the process of hearing?
o
the tectorial membrane
o
the basilar membrane
o
the vestibulocochlear nerve
o
Are you able to identify the parts of the ear and
describe the processes involved in the sense of
hearing?
o
What is the difference between pitch and intensity?
o
What is the difference between conductive and nerve
(sensorineural) deafness?
o
What are the receptors and processes involved in the
sense of static and dynamic equilibrium?
o
Can you describe the role of the semicircular canals
and the utricle and saccule in maintaining
equilibrium?
Questions to consider when
studying for the exam

How does structure relate to function?

Are you able to recognize examples and
apply knowledge?

Do you know the sequential steps of any
mechanisms discussed?