Option E2
Perception
of Stimuli
Assessment Statements
E.2.1 Outline the diversity of stimuli that can be
detected by human sensory receptors.
E.2.2 Label a diagram of the structure of the human
eye.
E.2.3 Annotate a diagram of the retina to show the cell
types and the direction in which light moves.
E.2.4 Compare rod and cone cells.
E.2.5 Explain the processing of visual stimuli,
including edge enhancement and contralateral
processing.
E.2.6 Label a diagram of the ear.
E.2.7 Explain how sound is perceived by the ear
E.2.1 Outline the diversity of stimuli that can
be detected by human sensory receptors.
Mechanoreceptors
What do each
of these
receptors
respond to?
Chemoreceptors
Thermoreceptors
Photoreceptors
Mechanoreceptors
Provide information to the CNS on:
touch
pressure
vibration
stretch
Chemoreceptor
Provides information on:
Molecules
Solutes
e.g. blood pH/CO2 levels
Thermoreceptor
Feeds back information on:
Temperature
Hot/Cold
skin
rods and cones
Photoreceptors
Provides information on:
Light
Visible wavelength
400-700 nm
retina
r
E.2.2 Label a diagram of the structure of the
human eye.
E.2.3 Annotate a diagram of the retina
Rods
Cones
Horizontal Cells
Bipolar Cells
Amacrine neuron
Ganglion
Optic nerve
Convergence
● 3 rods are connected to 1 bipolar cell and 1
ganglion cell.
● When interpreted in the brain it is not
possible to tell which of the receptors was
activated.
● This reduces the detail in this region of the
field of vision.
● This is typical of the arrangement of rods
and other neurons in areas outside of the
fovea.
● 1 cone synapses with 1 bipolar and 1 ganglion.
● The impulse traveling along the axon of the
ganglion neuron can be mapped to a precise
region of the retina and therefore the field of
vision.
● This provides detailed visual information
(resolution).
● This arrangement is typical of the fovea where
there are 1.6 X105 mm-2 cone cells.
● Other species, particularly birds that have far
greater densities of photoreceptors and indeed
more than one fovea.
Distribution of rods and cones
E.2.4 Compare rod and cone cells
Similarities
Both cells are photoreceptors
Both are found in the retina
Differences
E.2.5 Explain the processing of visual stimuli
Photoreceptors (rod and cone
cells) in the retina convert light
into nerve impulses
The impulses pass to bipolar cells,
which relay the signal to the optic
nerve (via ganglion cells)
Edge enhancement is a ‘pre-central nervous
system’ processing of information on the
retina itself. This processing is not carried out
by part of the brain but by the organisation of
the retinal cells.
Contralateral processing is the way in which
the brain collects and integrates information
from the eyes to create the perception of
seeing.
Edge Enhancement
● The edges of the square
appear to glow brightly
● This is edge enhancement
- a result of retinal processing
● Provides greater contrast at
the edges of objects
● Gives greater detail of the visual
environment
Edge Enhancement
Signals from rods and
cones follow both vertical
and lateral pathways
Photoreceptors stimulate
opposing bipolar cells
but inhibit adjacent
bipolar cells (lateral
inhibition)
This makes light spots
lighter and dark spots
darker, with the contrast
greatest at the edges
(edge enhancement)
Visual Processing
Contralateral Processing
When stimuli is processed on the opposite side of
where it was detected
Information
from the left
half of the
visual field is
detected by
the right half
of the retina in
both eyes and
is processed
by the right
hemisphere
Information
from the right
half of the
visual field is
detected by
the left half of
the retina in
both eyes and
is processed
by the left
hemisphere
•
•
•
At the optic chiasma, information from both
eyes may swap so that the left or right visual
field is processed together
The optic nerves that swap sides are
transmitting signals contralaterally, while
the optic nerves that do not swap are
transmitting signals ipsilaterally (same side)
Impulses continue to the thalamus where
the optical information is processed before
an image forms in the visual cortex
E.2.6 Label a diagram of the ear
Pinna
Oval and round
Auditory nerve
windows
Semicircular
Ear drum
canals
Cochlea
Ossicles
Auditory canal
Eustachian tube
E.2.7 Explain how sound is perceived
Sound travels as pressure waves in the air which push the
membrane of the eardrum, causing it to vibrate
The degree of vibration will vary according to the frequency
and amplitude of the sound waves
The ear drum pushes on the bones of the middle ear
(ossicles) which magnify the vibrations up to 20 times
The ossicles push against the oval window, displacing fluid
within the cochlea
Movement of the cochlear fluid affects the position of cilia on
sensory hair cells
Cilia on hair cells vary in length and each resonates to a
different frequency of sound
Activation of the hair cells generates nerve impulses which
are transmitted via the auditory nerve to the brain
The kinetic motion of the cochlear fluid is dissipated by the
movement of the round window
1. List two groups of sensory receptors,
giving the stimulus each perceives (2)
Mechanoreceptors — pressure;
Chemoreceptors — chemical substances/pH;
Thermoreceptors — temperature;
Photoreceptors — light;
Mechanoreceptors/proprioceptors —
stretching/pressure;
Hydroreceptors — humidity;
2. Explain the role of receptors, sensory
neurons and motor neurons in the response
of animals to stimuli (3)
receptors detect stimuli;
transmit information regarding stimuli to the CNS;
via sensory neurons;
central nervous system sends impulse to effector;
via motor neuron;
3. Identify structures I to IV (2)
I.
cornea;
II.
lens;
III. vitreous humour;
IV. choroid;
Two correct for [1]
and four correct for [2].
4. Outline contralateral processing of visual
stimuli (3)
both retinas receive information/stimuli from left and right
fields of vision;
left and right optic nerves cross in optic chiasma;
neurons from both eyes carrying impulses from left field of
view go to right
hemisphere / vice versa / right field of vision is processed in
left side of brain / vice versa;
neurones from the optic nerve synapse (in the lateral
geniculate nucleus) with neurones to the (primary) visual
cortex;
allowing brain to have perception of depth, distances and
sizes;
Accept any of these points made on an annotated diagram.
5. Compare rods and cones (3)
6. Identify structures A to D (4)
A: pinna;
B: eardrum;
C: stapes / bones of the middle ear;
D: semicircular canals;
Award [2] for 4 correct answers, [1] for three
correct answers, [0] for two or one correct
answer(s)
7.Explain how sound is perceived by the ear (6)
eardrum moved by sound waves;
eardrum/tympanic membrane causes movement of the
malleus/bones of the middle ear/ossicles;
bones of the middle ear/malleus, incus and stapes/hammer,
anvil and stirrup amplify/magnify movement;
bones of the middle ear/stapes push on the oval window;
causing movement of fluid/vibration within the cochlea/inner
ear;
hair cells are mechanoreceptors;
which release a chemical neurotransmitter when stimulated;
sounds/vibrations are transformed into nerve impulses/action
potentials;
carried by auditory nerve to brain;