It talks about all senses such as touch, smell, taste, see, etc

1. THE
SENSES
Biology 14

2. Sensory Reception
 Sensory receptors
- specialized neurons or other cells that are
tuned to the conditions of the external world or
internal organs. - It sweeps its wide head
back and forth, like a
beachcomber scanning
the shore with a metal
detector.
- Electroreception, the
ability to sense electric
field.
Hammerhead
shark
(Sphyrna
mokarran)

3. Sensory receptors convert stimulus energy
to action potentials
 In stimulus detection, the receptor cell
converts one type of signal (the stimulus)
to another type, an electrical signal.
 This conversion, called sensory
transduction, produces a change in the
cell’s membrane potential (the potential
energy stored by the plasma membrane
of the receptor cell.

4. • Changes in the flow of
ions create a graded
change in membrane
potential called a
receptor potential.

5. Sensory adaptation, the
tendency of some
sensory receptors to
become less sensitive
when they are stimulated
repeatedly.

6. Five Categories of Stimuli
1. Pain Receptors
respond to excess
heat or pressure or to
chemicals released
from damaged or
inflamed tissues.
2. Thermoreceptors
detect either heat
or cold.

7. 3. Mechanoreceptors
are stimulated by
various forms of
mechanical energy, such
as touch and pressure,
stretching, motion, and
sound.
Five Categories of Stimuli
• light touch- transduce
very slight inputs of
mechanical energy
into action potentials.
• pressure sensor-
lying deeper in the
skin, is stimulated by
strong pressure.
• touch receptor
around the base of
the hair, detects hair
TYPES
Another type of mechanoreceptor
(not shown) is found in our skeletal
muscles. Sensitive to changes in
muscle length, stretch receptors
monitor the position of
body parts.

8. 4. Chemoreceptors
include the sensory
receptors in our nose and
taste buds, which are attuned
to chemicals in the external
environment, as well as some
receptors that detect
chemicals in the body’s
internal environment.
 Internal chemoreceptors
include sensors in some of
our arteries that can detect
Five Categories of Stimuli

9. 5. Electromagnetic
Receptors
detected as Energy
occurring as electricity,
magnetism, or various
wavelengths of light.
 Photoreceptors, including
eyes, are probably the most
common type of
electromagnetic receptor.
Photoreceptors detect the
electromagnetic energy of light,
Five Categories of Stimuli

10. For each of the following
senses in humans, identify
the type of receptor: seeing,
tasting, hearing, smelling.
 Photoreceptors
 Chemoreceptors
 Mechanoreceptors
 Chemoreceptors

11. Hearing and Balance
Basic principle: the stimulation of long
projections on hair cells (mechanoreceptors) in
fluid-filled canals.
Three regions:
1. Outer ear
2. Middle ear
3. Inner ear

12. 1. outer ear consists of
the flap-like pinna— the
fleshy structure we
commonly refer to as
our “ear”—and the
auditory canal.
2. The pinna and the
auditory canal collect
sound waves and
channel them to the
eardrum, a sheet of
tissue that separates the
outer ear from the middle
ear.

13. When sound pressure waves strike the eardrum,
the eardrum vibrates and passes the vibrations to
three small bones:
 the hammer (more formally, the malleus), anvil
(incus), stirrup (stapes)
The middle ear
also opens into a
passage called the
Eustachian tube,
which connects
with the pharynx
(back of the throat),
allowing air
pressure to stay
equal on either

14.  The inner ear consists of fluid-filled channels in
the bones of the skull. Sound vibrations or
movements of the head set the fluid in motion.
One of the channels, the cochlea (Latin for
“snail”), is a long, coiled tube.• Our actual hearing
organ, the organ of
Corti, is located within
the middle canal.
• The organ of Corti
consists of an array
of hair cells
embedded in a
basilar membrane,
the floor of the middle

15. Hearing
Sound waves, which move as pressure
waves in the air, are collected by the pinna
and auditory canal of the outer ear.

16. Volume and Pitch
 The brain senses a sound as an increase in the
frequency of action potentials from the auditory
nerve.
How is the quality of the sound
determined?
“The higher the volume (loudness) of sound, the
higher the amplitude (height) of the pressure wave
it generates.”
 The pitch of a sound depends on the frequency
of the sound waves.

17. Deafness
 Deafness can be caused by the inability of the
ear to conduct sounds, resulting from middle-ear
infections, a ruptured eardrum, or stiffening of
the middle-ear bones (a common age-related
problem).
 Can also result from damage to sensory
receptors or neurons.
 In recent years, however, many deaf people
have received cochlear implants, electronic
devices that convert sounds to electrical
impulses that stimulate the auditory nerve

18.  These fluid-filled
structures lie next to the
cochlea (Figure 29.5)
and include three
semicircular canals and
two chambers, the
utricle and the saccule.
 The ear contains three
semicircular canals
that detect changes in
the head’s rate of
The inner ear houses our organs of balanc

19.  What causes motion sickness?
Motion sickness is believed to be
caused when the brain receives
signals from equilibrium receptors in
the inner ear that conflict with visual
signals from the eyes.
Symptoms maybe relieved by
closing the eyes, limiting head
movements, or focusing on a stable
horizon.

20. Vision
2 types of image-forming
eyes:
1. compound eye consists
of up to several
thousand light- etectors
called ommatidia.
2. Single-lens eye
evolved independently in
vertebrates.

21.  The human eye has a
small opening at the
center of the eye, the
pupil, through which
light enters.
 An adjustable
doughnut shaped iris
changes the diameter
of the pupil to let in
more or less light.
 After going through
the pupil, light passes
through a single
disklike lens.
 The lens focuses
light onto the retina,
which consists of
many photoreceptor
cells.
Photoreceptor cells are highly concentrated at
the retina’s center of focus, called the fovea.

22.  The outer surface
of the human
eyeball is a tough,
whitish layer of
connective tissue
called the sclera.
 At the front of the
eye, the sclera
becomes the
transparent
cornea, which lets
light into the eye
and also helps
focus light.
The sclera surrounds a
pigmented layer called the
choroid. The anterior choroid
forms the iris, which gives the
eye its color.

23.  The lens and ciliary
body divide the eye
into two fluid-filled
chambers.
 The large chamber
behind the lens is
filled with jellylike
vitreous humor.
 The much smaller
chamber in front of
the lens contains the
thinner aqueous
humor.
• A thin mucous
membrane helps keep
the outside of the eye
moist. This membrane,
called the conjunctiva

25. Arrange the following eye parts into
the correct sequence encountered
by photons of light traveling into
the eye: pupil, retina, cornea, lens,
vitreous humor, aqueous humor.
Cornea aqueous humor pupil
vitreous humor lens

26. Artificial lenses or surgery can
correct focusing problems
 Reading from an eye chart measures your visual
acuity, the ability of your eyes to distinguish fine
detail.
 People with nearsightedness cannot focus well
on distant objects, although they can see well at
short distances (the condition is named for the
type of vision that is unimpaired).

27.  Farsightedness (also known as hyperopia) is
the opposite of nearsightedness. It occurs when
the eyeball is shorter than normal, causing the
lens to focus images behind the retina.

28. 2 types of photoreceptors:
1. Cones- are stimulated by bright light and can
distinguish color, but they contribute little to
night vision.
• Cones contain visual pigments called
photopsins, which absorb bright, colored

29. 2. Rods are extremely sensitive to light and
enable us to see in dim light, though only in
shades of gray.
 Rods contain a visual pigment called
rhodopsin, which can absorb dim light.

30. Taste and Smell
Taste and odor receptors detect chemicals present
in solution or air
 Olfactory (smell) receptors are sensory neurons
that line the upper portion of the nasal cavity
and send impulses along their axons directly to
the olfactory bulb of the brain

31.  Many animals rely heavily on their sense of
smell for survival. Most other mammals have a
much more discriminating sense of smell than
humans.
 Odors often provide more information than
visual images about food, the presence of
mates, or danger.four familiar taste perceptions:
sweet, sour, salty, and bitter and
fifth,
UMAMI (Japanese for “delicious”)