Transcript E.2 Perception of Stimuli

E.2 Perception of Stimuli
Types of Sensory Receptors
• Mechanoreceptors respond to mechanical
energy in the form of movement, sound,
pressure or gravity
EX. Hair cells in inner ear move due to
sound waves and conduct impulse to
brain.
• Chemoreceptors response to chemical
substance
EX. Nerve cells in tongue send impulses to
brain when specific chemicals bind to
receptor cells
Types of Sensory Receptors cont.
• Thermoreceptors response to temperature
EX. Warm and cold nerve endings in the
skin conduct message to brain or spinal
cord at a
• Photoreceptors respond to
electromagnetic radiation usually in the
form of light
• EX. Rods and cones in the eye send
messages to the brain, when they absorb
light
Structure of the Human Eye
• Sclera- tough, white layer of
connective tissue that protects
the eye
• Cornea- where sclera
becomes transparent at the
front of the eye to let light in
• Choroid- thin pigmented layer
under sclera that provides
nourishment to retina
• Iris- the black screen that
regulates the size of the pupil.
• Conjuctiva – very thin
membrane that covers
the sclera and keeps it
moist
• Pupil – opening in the
middle of iris that allows
light to pass through
• Lens – transparent
protein disk that focuses
light onto the retina
• Retina – photosensitive
layer of the eyeball.
Contains the
photoreceptor cells
• Fovea – center of
visual field. On
retina at back of eye
• Optic nerve – nerve
that transmits
messages from retina
to brain
• Blind spot – place
where optic nerve
attaches to retina.
Does not contain
photoreceptors
• Lens divides the eye
into two cavities
• Aqueous humour –
watery liquid between
the lens and cornea
(blockage in this
causes glaucoma
which can lead to
retina damage)
• Vitreous humour – jelly
like fluid that transmits
light from lens to optic
nerve. Acts as a liquid
support.
Diagram of Retina
– Rods and cones
synapse with bipolar
neurons
– Bipolar neurons
synapse with a
ganglion cell
– Axons of the
ganglion cells make
up the optic nerve
Transfer of stimulus at Retina
• Light must pass through
cornea, lens and the
humours before it reaches
the retina
• Light then strikes the
photoreceptors (rods and
cones)
• Rods and cones then
transmit the information to
bipolar neurons that
combine the information
• The bipolar cells transmit
information to ganglion cells
that feed into the optic
nerve
RETINA
• The more
photoreceptors that
feed a ganglion cell, the
blurred the image
because the optic nerve
can’t perceive ______
where the stimulus is
coming from
• Thus rod information is
________ and cone
info. is ___________
Rods cells vs. Cone cells
• Rods
• Cones
– A group of rods send
impulses along a
single neuron
– Work well in dim light
– Each has an individual
neuron
– Black and white vision
– Three types(named by
colour that they
absorb)
– Does not work well in
dim light
• Red
• Green
• Blue
Rods and Cones
• Both are
photoreceptor cells
found on the retina of
the eye
• Both pass their
information to the
optic nerve
• Account for ______ of
all sensory receptors
in the human body
Rods
• ~125 million rod cells/retina
• Absorb all visible
wavelengths of light which
results in dim light vision
(black and white)
• More numerous than cones
• Function better in dim light
• In greatest density in the
peripheral retina
• _many cells transmit
information to one neuron
of optic nerve
Cones
• ~6 million per retina
• 3 types, each absorbs
different wavelength of
light (blue, green, red)
gives color vision
• Function better in bright
light
• Have better visual
perception
• One cone cell transmits
to one neuron of optic
nerve
• Very dense at fovea
Perception of visual stimuli
The Hermann grid
Edge Enhancement
• Part of retina where image is projected is called
receptive field
• If different parts of an image fall onto different
receptive fields in the retina, stimulation is reduced
• This will lead to _________ when trying to focus on
one diagram
• To compensate, stimulation of some receptors may
actually ________ neighboring ones so that you
can get ____________
Contra-lateral processing
• Some impulses from
_________ actually
travel to __________
(and vice versa)
• Exchange occurs in
________________
• Right side _________
images from left eye,
and vice versa
Processing of Visual Stimuli
• Right optic nerve
carries information from
the right eye :left optic
nerve from left eye
• At a place in the brain
called the optic
chiasmata impulses
from both eyes cross
over
• ½ of the right optic
nerve fibers cross over
to left side of brain, and
vice versa
• For this reason each
side of the brain
receives input from the
__________________
• Optic nerves feed into
the
where they are
processed
• It is finally carried to
visual cortex in the
_____________ of the
brain where the image
is finally formed
• Discovered by
___________ patients
with brain lesions
Ear
Detection of sound
•
•
•
•
Sound waves collected by pinna
Passed into ear canal
Cause reverberations of ear drum
_Ear ossicles (bones of middle ear) vibrate
against each other due to movement of eardrum
• Final ossicle (Stapes) moves against oval
window of cochlea causing movement of fluid
inside
• Round window provides ________________ of
fluid in cochlea
In the inner ear
• Fluid moves across hair cells in Cochlea
• These hairs cells release chemical
messages to the _______________ that
relay messages to brain
• Hair movement then analyzed and
interpreted into a sound by analyzing the
___________ of the sound (pitch) and the
____________ of hair movement (volume)