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 Chemoreceptors Thermoreceptors Photoreceptors What do each of these receptors respond to?

Mechanoreceptors Provide information to the CNS on: touch pressure vibration stretch

Chemoreceptor Provides information on: Molecules Solutes e.g. blood pH/CO 2 levels

Thermoreceptor Feeds back information on: Temperature Hot/Cold skin

Photoreceptors Provides information on: Light Visible wavelength nm rods and cones retina r

E.2.2 Label a diagram of the structure of the human eye.

E.2.3 Annotate a diagram of the retina

Ganglion Amacrine neuron Bipolar 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 cells Similarities Both cells are photoreceptors Both 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 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 I nformation 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 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; round window releases pressure so fluid in cochlea can vibrate;