Option E2 Perception of Stimuli
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Transcript of Option E2 Perception of Stimuli
Option E2 Perception of Stimuli
Assessment StatementsE.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
Chemoreceptors
Thermoreceptors
Photoreceptors
What do each of these receptors respond to?
MechanoreceptorsProvide information to the CNS on:touchpressurevibrationstretch
ChemoreceptorProvides information on:MoleculesSolutese.g. blood pH/CO2 levels
Thermoreceptor
Feeds back information on:TemperatureHot/Cold
skin
Photoreceptors
Provides information on:LightVisible wavelength400-700 nm
rods and cones
retinar
E.2.2 Label a diagram of the structure of the human eye.
E.2.3 Annotate a diagram of the retina
Ganglion
Amacrine neuronBipolar Cells
Rods
Cones
Horizontal Cells
Optic nerve
● 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.
Convergence
● 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 cellsSimilaritiesBoth cells are photoreceptorsBoth are found in the retina
Differences
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)
E.2.5 Explain the processing of visual stimuli
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 squareappear 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 EnhancementSignals 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)
Contralateral ProcessingWhen 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
Auditory canal
Ear drum
Ossicles
Semicircular canals
Auditory nerve
Cochlea
Eustachian tube
Oval and round windows
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 wavesThe ear drum pushes on the bones of the middle ear
(ossicles) which magnify the vibrations up to 20 timesThe ossicles push against the oval window, displacing fluid
within the cochleaMovement of the cochlear fluid affects the position of cilia on
sensory hair cellsCilia on hair cells vary in length and each resonates to a different frequency of soundActivation 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 righthemisphere / 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;round window releases pressure so fluid in cochlea can vibrate;