Download Preception of stimuli - IB

PERCEPTION OF STIMULI
Sensory Receptors & diversity of
Stimuli
• Sensory receptors for pleasure
• Sensory receptors elicit emotion
• Sensory receptors elicit memory
We see, smell, taste & feel with…
E.2.1 Outline the diversity of
stimuli that can be detected by
human sensory receptors,
including mechanoreceptors,
chemoreceptors, thermoreceptors
and photoreceptors.
Mechanoreceptors
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Mechanical force or pressure
• Skin
• Arteries
• Lung inflation
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Proprioceptors
• Maintain posture and position
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Pressure receptors
• sensitive to waves of fluid = equilibrium
Chemoreceptors
• Respond to chemical substances
• External
• Taste and smell
• Internal
• pH – adjust breathing rate
• Pain receptors
• Respond to chemicals released by damaged tissue
Thermoreceptors
• Change in temperature
Photoreceptors
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Respond to light energy
Found in the eyes
Rod cells respond to dim light = black & white vision
Cone cells respond to bright light = colour vision
E.2.2 Label a diagram of the structure
of
the human eye
Ciliary muscle
Anterior chamber
with aqueous
humour
Posterior chamber filled
with vitreous humour
Part
Function
Iris
Regulates the size of the pupil
Pupil
Admits light
Retina
Contains receptors for vision
Aqueous humour
Transmits light rays and supports the eyeball
Vitreous humour
Transmits light rays and supports the eyeball
Rods
Allow black and white vision in dim lighjt
Cones
Allow colour vision in bright light
Fovea
An area of densely packed cone cells where
vision is most acute
Lens
Focuses the light rays
Sclera
Protects and supports the eyeball
Cornea
Focusing begins here
Choroid
Absorbs stray light
Conjunctiva
Covers the sclera & cornea & keeps eye moist
Optic nerve
Transmits impulses to the brain
Eye lid
Protects the eye
EYE Lecture
E.2.3 Annotate a diagram of the
retina to show the cell types
and the direction in which the
light moves
The Retina – photoreceptor cells
The Retina
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The retina is the only part of the CNS which is directly observable
Light is coming through the eye from the right
There are 3 layers of neurons shown, photoreceptors, bipolar & ganglion cells
(reflect the order of activity)
The ganglion cells and bipolar cells are transparent & don’t significantly reduce
the intensity of light passing to the photoreceptor
video
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The photoreceptor absorbs the light which changes the rate of
neurotransmitter produces at the first synapse (S1)
The head of the photoreceptor cell contains the light sensitive pigments
The Bipolar cell (named after its 2 processes at either side of the cell
body) responds by changing rate of neurotransmitter released to the
Ganglion cell
The ganglion cell generates the impulse which will travel along the axon
of the ganglion to the brain. Notice that these axons are grouped
together to form the optic nerve. Also, note that the cell body of the
ganglion is in the retina.
(a) Bipolar cell forming synapses with
more than one photoreceptor.
(b) Bipolar cells connecting together
rods and cones
(c) Ganglion cell collecting input from
a group of photoreceptors (receptive
field)
(d) Axon of the ganglion cell forming
the optic nerve at (i)
(e) Summation of rod photoreceptors
gives low visual acuity (resolution)
Non-fovea arrangement
(f) Another form of summation
(g) The arrangement of cones in the
fovea provides a high level of visual
acuity (resolution).
E.2.4. Compare rod and cone cells
Rods
Cones
These cells are more
sensitive to light and
function well in dim light.
These cells are less
sensitive to light and
function well in bright light
Only one type of rod is
found in the retina. It can
absorb all wavelengths of
visible light.
Three types of cone are
found in the retina. One
type is sensitive to red light,
one type to blue light and
one type to green light.
The impulses from a group
of rod cells pass to a single
nerve fibre in the optic
nerve.
The impulse from a single
cone cell passes to a single
nerve fibre in the optic
nerve.
E.2.5 Explain the processing of
visual stimuli, including edge
enhancement and contralateral
processing
Processing of Visual Stimuli
Watch 5:35 –
8:20
 Light passes through the pupil
 Light is focused by the cornea, lens & the
humours
 Image on retina is upside down and reversed
 Photoreceptors stimulated
 Optic nerve carries message to cerebral cortex
of the brain
 Brain corrects the position of the image (right
side up & not reversed)
 Coordinates images coming from left & right
Edge Enhancement
 Optical illusions – Hermann grid
Watch 1st 1:25 minutes
Edge Enhancement
 Why did you see the grey blobs?
 Theory
 Areas where you see grey are in your
peripheral vision
 Fewer light-sensitive cells than in the
center of your retina (fovea)
 Some cells present may even be turned
off
 This sends message of grey instead of
white
Edge Enhancement
 Now look at the “grey” area
Edge Enhancement
 Eye is fooled because of extreme contrast
between black & white
 Special mechanism for seeing edges
 “light-sensitive receptors switch off their
neighbouring receptors”
 Makes edges look more distinct
Contralateral processing
 Due to the optic chiasma
Contralateral processing
 Nerve fibres bringing information from the
right half of each visual field converge at the
optic chiasma & pass to the left side of the
brain
 Nerve fibres bringing information from the
left half of each visual field converge at the
optic chiasma & pass to the right side of the
brain
 Information ends up in the visual cortex of
the brain
 Must share information to make a complete
image
Contralateral processing
 The cerebral cortex rebuilds all the parts
into a visual image
 This process can be illustrated by looking
at patients with brain lesions (injuries)
 We look at a
and
we see a
Video 
 Lesion to right side of brain do not
recognize this. They will DENY it is a
bucket
 Lesion to left side of brain can tell you
the function but cannot name “bucket”
E.2.6 Label a diagram of the ear
The ear
E.2.7 Explain how sound is
perceived by the ear, including
the roles of the eardrum, bones
of the middle ear, oval and
round windows and the hair
cells of the cochlea
How sound is perceived
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Outer ear catches sound waves
Vibrates air
Down the auditory canal
Tympanic membrane (eardrum) vibrates
Bones of ear receive vibrations & multiply
them 20 times
Stapes strikes the oval window – vibrates
Vibrations pass to fluid in cochlea
Hair cells vibrate
Release a chemical message to sensory
neuron
To auditory nerve  brain
Sounds
 Loud noises = high degree of vibration
 Hair cells bend greatly
 High volume
 Pitch = function of sound wave frequency
 Short, high-frequency = high pitch
 Long, low-frequency = low pitch
The Bozeman
Start at 8:22