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Sensory
Reception
SENSORY RECEPTORS
• The senses are the human brain’s connection to the outside
world.
SENSORY RECEPTION AND PERCEPTION
• Sensation is initiated in the senses through sensory reception,
but sensation and perception take place in the brain.
• Everyone’s perception of the world is unique.
• Sensory receptors convert different forms of energy into
electrochemical energy, which the nervous system interprets.
DIAGRAM OF THE EYE
Label the diagram of the eye
• http://www.sumanasinc.com/webcontent/too
lsamples/sampledd.html
Parts of the Eye
Structure
Function
Sclera
Supports and protects delicate photocells
Cornea
Refracts light toward the pupil
Aqueous humour
Supplies cornea with nutrients and refracts light
Choroid layer
Contains blood vessels that nourish the retina
Iris
Regulates the amount of light entering the eye
Vitreous humour
Maintains the shape of the eyeball and permits light
transmission to the retina
Lens
Focuses the image on the retina
Pupil
The opening in the iris that allows light into the eye
Retina
Contains rods used for viewing in dim light and cones used for
identifying colour
Fovea centralis
Most light-sensitive area of the retina –contains only cones
Blind spot
Where the optic nerve attaches to the retina
PHOTORECEPTION
• The cornea, lens, and humours (aqueous – in front and
vitreous – in behind the lens) focus light on the retina.
The pathway of light: light enters the eye through the
pupil, and is gathered on the pigmented epithelium of
the retina. Photoreceptors on the retina are stimulated
by the light and relay the message via the bipolar cells
and the ganglion cells to the optic nerve which then
relays the message to the CNS.
Optic nerve
Thalamus
Primary visual cortex
Visual association cortex
ACCOMODATION
• The lens is flexible.
Its ability to
change shape in
order to focus on
near or far objects
is called
accommodation.
• The ability to focus is impaired if the cornea is uneven
(causes astigmatism), or if the eyeball is too long (myopia) or
too short (hyperopia).
---nearsightedness
– a concave lens is
used to correct vision
--farsightedness – a
convex lens is used to
correct vision
Astigmatism unevenly ground
glasses or contacts
can be used to
correct vision
Corrective procedures for eye problems:
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BLIND SPOT
• Each eye has a blind spot, where the optic nerve connects to
the eyeball, but each eye compensates for what the other
cannot see. Binocular vision (both eyes pointing the same
way) also allows us to see in three dimensions.
RODS AND CONES
• The retina contains
the photoreceptor
cells. The rods
function in dim
light and produce
black and white
images. The cones
function in bright
light and produce
colour images.
The Chemistry of Vision:
An estimated 160 million rods surround the
colour-sensitive cones in the centre of the
retina.
The rods contain a light-sensitive pigment called
rhodopsin.
Rhodopsin is composed of a form of vitamin A
and a large protein molecule called opsin.
When a single photon strikes a rhodopsin
molecule, it divides into two components:
retinene, the pigment portion, and opsin, the
protein protion.
• This division alters the cell membrane of th
rods and produces an action potential.
• For the rods to continue to work, rhodopsin
levels must be maintained.
• A long term vitamin deficiency can
permanently damage the rods.
• Extreme sensitivity of rhodopsin to light can
cause rhodopsin to break down faster than it
can be restored.
• The opsins used for colour vision are much less
sensitive to light and, therefore, operate best
with greater light intensity.
Colour Perception:
• The cones are responsible for colour vision
• Each cone is sensitive to one of the three
primary colours of source light: red, blue and
green.
• When combinations of cones are stimulated,
the brain perceives different colours.
• The three types of cones firing in different
combinations allow humans to see millions of
different shades of colour.
• Colour blindness occurs when one or more
types of cones are defective.
Afterimages:
• Positive afterimages occur after you look into
a bright light and then close our eyes.
• Negative afterimages occur when the eye is
exposed to bright light for an extended
period of time.
VISUAL PROCESSING
• Once stimulated, the
rods and cones send
a neural message to
the occipital lobe of
the brain, which
processes and
integrates the
information, and
then perceives it as
an image.
MECHANORECEPTORS - HEARING
• The mechanoreceptors for hearing and balance are located
in the inner ear.
Hair cells on the basilar membrane synapse with dendrites of the
auditory nerve which transmit an electrochemical impulse to the
temporal lobe of the brain.
• The cochlea, semicircular canals, utricle, and saccule all
contain hair cells that react to movement.
rotational
equilibrium
head position
and balance
HEARING AND PROPRIOCEPTION
• The hair cells synapse with nerve fibres, which
transmit the sensory information to the nerves.
The nerves then send an impulse to the brain.
• Proprioceptors in the muscles, joints, and
tendons also inform the brain about the position
of body parts.
• http://calgary.ctv.ca/servlet/an/local/CTVNew
s/20110518/CGY_neto_jose_110518/2011051
8?hub=CalgaryHome
• Calgarian Jose Neto “sees” with his tongue!
• Sensory receptors in the tongue (taste buds), nose (olfactory
cells), and skin (temperature, pressure, and pain receptors)
provide additional information to the brain.
OLFACTORY (SMELL) RECEPTORS
TASTE RECEPTORS
Chapter 12 Concept Organizer
Chapter 12 Summary
• Sensory reception occurs at the senses. Sensation and
perception occur in the brain. Photoreceptors detect light.
Chemoreceptors detect tastes, odours, and internal conditions,
such as blood pH and volume. Thermoreceptors detect
temperature. Mechanoreceptors function in hearing, balance,
and coordination.
• The cornea, lens, and humours of the eye direct light on the
photoreceptor cells in the retina. Rods function in dim light and
produce black and white images. Cones function in bright light
and produce colour images. The optic nerve transmits signals
from the rods and cones to the occipital lobe of the brain,
where images are perceived.
Chapter 12 Summary
• The outer ear transmits sound waves to the middle ear,
which makes the tympanum and, in turn, the bones of the
middle ear vibrate. These bones amplify and transmit the
vibrations to the oval window in the inner ear. The
vibrations in the oval window produce pressure waves in
the fluid of the cochlea in the inner ear. The pressure
waves are detected by hair cells, which relay
electrochemical messages to the brain via the auditory
nerve.
• Hearing aids that amplify sound can sometimes be used to
treat conduction deafness caused by damage to the outer
or middle ear. Noise-induced hearing loss, caused by
destruction of the hair cells, is more difficult to treat. It
results in a loss of ability to hear sounds of specific
frequencies.
Chapter 12 Summary
• Hair cells in the semicircular canals of the inner ear allow for
rotational equilibrium (balance). Hair cells in the utricle and
saccule of the inner ear allow for gravitational equilibrium
(balance). Proprioceptors are another type of
mechanoreceptor involved in coordination.
• Tastes are detected by chemoreceptors in the taste buds of
the tongue. Smells are detected by chemoreceptors in the
nose.
• The skin contains receptors for light touch, pressure, pain,
heat, and cold. Sensors in the nose, tongue, and skin all help
the nervous system maintain homeostasis.