1. E2 – Perception of stimuli
Human eye
Human ear

2. Human sensory receptors
receptors detects the changes in both internal and external environment
they transform the stimuli energy into a nerve impulse that can be sent to the central nervous system (CNS) which in turn coordinates an appropriate response.
receptors are located in the sense organs such as the eye, ear, skin, tongue etc.

3. Human sensory receptors & stimuli that can detect
Type of receptor
Stimulus detected
Example of receptors
mechanoreceptors
pressure, sound
hair cells in the ear
chemoreceptors
chemical substances
taste buds on the tongue & olfactory cells along the nose
thermoreceptors
temperature
nerve endings in the skin & hypothalamus of the brain
photoreceptors
light
rods and cone in the retinas of the eye
hydroreceptors
humidity ?
nocireceptors
pain
sensory nerve ending in the skin

4. Human eye
Eye lashes
Sclera
Pupil
Iris
Eye lid

5. Label the diagram of the human eye below
sclera
pupil
choroids
retina
ciliary body / muscles
iris
lens
cornea
fovea
blind spot
optic nerve

7. Structure
Function(s)
Sclera
tough outer layer of the eye which overs and protect eyeball.
Choroid
prevents internal reflection of light and nourish retina.
Retina
contains rods and cones which convert light into nerve impulses.
Ciliary Body
a ring of muscle controlling the shape and curvature of the lens.
Iris
controls the pupil size thus controls entry of light.
Pupil
a hole in the iris that lets light into the back of the eye.
Lens
accommodation & focusing of light onto the retina.
Cornea
bends incoming light focusing it on the retina.
Fovea
a tiny area of densely packed cones for detailed and coloured vision.
exit point of the optic nerve cutting through the retina so no rods or cones
Blind Spot
Optic Nerve
carries the impulses from the rods and cones to the visual center of the brain.

9. Annotate the diagram of the retina below
Axon of the ganglion cell
direction of light movement
Ganglion cell
Bipolar cell
Synapse
Rod
Cone
Pigment
Sclera

10. Compare rod and cone cells
Rod Cells
Cone Cells
rod cells more effective in low light intensity
cone cells more effective in high light intensity
rod cells detect a broad range of colours (wavelength)
cone cells are sensitive to a specific colours (wavelength)
groups of rod cells pass impulses to a single nerve fibre
a single cone cell passes impulses to a single nerve fibre
rod cells more sensitive to movement
cone cells give higher visual acuity (sharpness )
rod cells respond more slowly to light
cone cells respond more rapidly to light
rod cells spread through retina
cone cells concentrated in centre of retina (at fovea )
rod cells contains one type of pigment (rhodopsin)
cone cells contains three types of pigment (iodopsin)
rod and cone cells are both are photosensitive

11. Compare rod and cone cells
Rod Cells
rod cells more effective in low light intensity
rod cells detect a broad range of colours (wavelength)
groups of rod cells pass impulses to a single nerve fibre
rod cells more sensitive to movement
rod cells respond more slowly to light
rod cells spread through retina
rod cells contains one type of pigment (rhodopsin)
cone cells more effective in high light intensity
cone cells are sensitive to a specific colours (wavelength)
a single cone cell passes impulses to a single nerve fibre
cone cells give higher visual acuity (sharpness )
cone cells respond more rapidly to light
cone cells concentrated in centre of retina (at fovea )
cone cells contains three types of pigment (iodopsin)
rod and cone cells are both are photosensitive

12. Contralateral processing of visual stimuli
rod & cone cells in the retina convert light into nerve impulses
impulses pass to bipolar cells
bipolar cells pass impulses to sensory neurons of the optic nerve
at the optic chiasma, impulses cross over to the opposite optic nerve
impulses continue to the thalamus where optical information is processed
images form in the visual cortex of the brain

13. Edge enhancement
edge enhancement is a ‘pre- central nervous system ‘processing of information on the retina
it enhances contrast at the edges (boundaries of different objects) and provides more detail to the visual system of the environment
in certain regions of the retina, single ganglion cell receives information form a number of rods and cones, such a region is called receptive field
the fewer the rods and cones that supply a single ganglion the smaller the receptive field & the higher visual acuity i.e. the detailed information one sees

14. Label the diagram of the ear below
Middle ear bones
Semi circular canals
Oval Window
Auditory Nerve
Round window
Cochlea
Eustachian tube
Eardrum
Auditory canal
Pinna

17. How sound is perceived by the ear
sound waves reaching eardrum cause it to vibrate
vibrations are passed to bones of middle ear which amplify them
the bones pushes the oval window which cause a pressure wave in the fluid-filled cochlea
As the oval window moves in, the round window moves out, this allows the fluid in the cochlea to move freely backward & forward
the vibrations caused by fluid movement pushes the membrane on which the hair cells (mechanoreceptors) sits, triggering nerve impulses in the auditory nerves
the nerve impulse is carried to the auditory cortex in brain through auditory nerve for interpretation