Sensory receptors
ƒ Are dendrites specialized to detect certain types of stimuli
ƒ Exteroceptors: detect stimuli from outside the body
ƒ (e.g. taste, hearing, vision)
ƒ Interoceptors: receive stimuli from inside the body
ƒ (e.g. change in blood pressure)
Types of sensory receptors
ƒ Chemoreceptors: respond to nearby chemicals (molecules)
ƒ Pain receptors – Chemoreceptors that respond to chemicals released by damaged
tissue
ƒ Taste, Smell: Cells in the mouth with specific binding sites for particular molecules
ƒ Photoreceptors – respond to light energy
ƒ Vision: Changes in the flow of light energy
ƒ Mechanoreceptors – respond to mechanical forces such as pressure
ƒ Pressure, Position, Balance , Hearing
ƒThermoreceptors – stimulated by temperature changes
How does sensation occur?
1) Sensory receptors
respond to
environmental stimuli
2) Nerve impulses travel
to the cerebral cortex
3) Sensation (conscious
perception) of stimuli
occurs
4) Sensory adaptation,
decrease in stimulus
response, can occur
with repetitive stimuli
(i.e. odor)
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Mechanoreceptors 1: Proprioceptors
ƒ Mechanoreceptors involved in reflex actions that maintain muscle tone
ƒ is the continuous and passive partial contraction of the muscles. It helps
maintain posture
Axon terminal
Muscle fiber
Mechanoreceptors 2:
Cutaneous receptors
ƒ Receptors in the
dermis (skin) that make
the skin sensitive to
touch, pressure, pain
and temperature
Pain, temperature
touch
touch
pressure
touch
pressure
touch
Chemoreceptors 1: Taste
ƒ Cells in the mouth with specific binding sites for particular molecules
ƒ Sensitive to sweet, sour, salty and bitter tastes in food
ƒ~ 3,000 taste buds
Sensory nerve fiber
mostly on the tongue
Taste cell
Chemoreceptors 2: Smell
ƒ Depends on 10-20 million
olfactory cells (modified
neurons) in the roof of the
nasal cavity
ƒ 80-90% of what we perceive
as taste is actually due to the
sense of smell
Sensory nerve fiber
Olfactory (smell) cell
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Mechanoreceptors 3: Hearing
Outer ear: functions
in hearing; filled
with air
Middle ear:
functions in
hearing; filled
with air
Inner ear: functions in hearing
and balance; filled with fluid
Cochlea: Converts vibrations
into nerve impulses
ƒ Contains the organ of Corti
(spiral organ)
ƒ Sense organ containing
hairs for hearing
ƒ Nerve impulses are sent to
Cochlear the cochlear nerve and then
to the brain
nerve
Auditory
canal: directs
sound waves
to the
tympanic
membrane
Ossicles: (malleus, incus, stapes): 3 small bones
that amplify sound waves
Timpanic membrane: vibrates to carry the wave to the bones
Mechanoreceptors 4: Balance
ƒ The Semicircular canals detect angular movement (rotational equilibrium)
ƒ Depends on hair cells at the base of each semicircular canal (ampulla)
Semicircular canals: rotational (balance) equilibrium
ƒ Semicircular canals are arranged in such a way that
each provides a different dimension of space
ƒ Hair cells with cilia embedded in
a gelatinous material (cupula)
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Mechanoreceptors 5: Position
ƒ Detects movement of the head in the vertical and horizontal planes (gravitational
equilibrium)
ƒ Depends on hair cells in the utricle and saccule
Vestibule: gravitational
(position) equilibrium
Vestibular
nerve Æ to
the brain
Utricle
Saccule
ƒ Two membranous sacs located at the base
of the semicircular canals
ƒ Utricle is sensitive to horizontal
(back-forth)
ƒ Both have hair cells with cilia
embedded in a gelatinous material
ƒ That has otholits, calcium
carbonate granules resting on it
ƒ Saccule is sensitive to vertical
(up-down)
Photoreceptors: Vision
ƒ 2 compartments:
ƒ Anterior chamber:
ƒ Changes in the flow of light energy
(A) between the cornea
and lens filled with a
clear fluid called
aqueous humor
ƒ Made of 2 compartments
ƒ Made of 3 layers
1-Sclera: outer layer,
mostly white and
fibrous except the
cornea
ƒ Posterior chamber:
(P) most of the eye,
behind the lens contains
a gelatinous material
called vitreous humor
(P)
(A)
Anterior
light
Posterior
3-Retina: inner layer
containing photoreceptors
2- Choroid: middle
layer, darkly, pigmented
vascular layer
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Sclera: the white of the eye that
maintains eye shape
3 layers of
the eyes
Cornea Transparent, important in
refracting light
Pupil A hole that allows light into
fovea
centralis
the eyeball
Choroid – Absorbs light rays that
are not absorbed by the retina
lens: Refract and focus light rays
Iris: regulates the size of the pupil
(and the amount of light that
enters the eye)
Ciliary body Contains a muscle that
retina
controls the shape of the lens
The retina in the eyes has two types of receptors.
ƒ Rods are responsible for black and white vision.
ƒ Cones are more sensitive to particular wavelengths of light: color vision
ƒ The fovea centralis is an area densely packed with cones where images are focused
The Retina:
ƒ Where light is actually sensed and the image is formed
ƒ Sensory receptors
Choroid
from the retina form
the optic nerve that
takes impulses to the
brain
Retina: Rod and cone
cells layer
ƒ Rods are sensitive to
light: black and white vision
optic nerve
ƒ Important for peripheral
and night vision
ƒVitamin A is important
for proper functioning
ƒ Cones are located mostly
to optic nerve
ƒ The blind spot is where the optic nerve
attaches: no vision is possible because there are
not photoreceptors there
in the fovea centralis
LIGHT
ƒ Allow us to detect fine
detail and color
ƒ3 different kinds of
cones containing red,
green and blue pigments
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Abnormalities of the eye
• Color blindness – genetic disease most common in males in which
they usually cannot see red or green
• Cataracts – lens of the eye is cloudy
• Glaucoma – fluid pressure builds
up in the eye
• Astigmatism – condition in which
the cornea or lens is uneven leading to a fuzzy image
• Nearsightedness – eyeball is too long making it hard to see far
away objects
• Farsightedness – eyeball is too short making it hard to see
near objects
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