E2.1 Humans can detect taste and smell via chemorecptors in the taste buds of the tongue and the nerve endings in the nose. We have vision because of photoreceptors in the eyes. Touch, pressure, pain, tension and sound all use mechanorectors in the skin and the inner ear.

E.2.4 Rod Cells have equally sized cylindrical disks which hold the photosensitive pigments Rod cells are sensitive to all light wavelengths but do not distinguish color Cone cells have different sized disks and can detect color. Hey are not as sensitive to light as rod cells There are three types of cone cells= RGB

E2.4 Rod cells in groups of 3 send impulses down a fibre of the optic nerve. Thus rods are less good at determining detail Rod impulses can summate at the one bipolar cell they connect to, providing differing strengths of light perceived. Cone cells send impulses down single nerve fibre which connect to the optic nerve. The photosensitive disks have photosensitive membrane proteins (Namely Rhodopsin) that change shape when exposed to a certain light wavelength. When the rhodopsin changes shape, it causes an action potential to travel down the cell.

E2.5 Visual processing occurs in both the brain and the retina. Two types of ganglion cells: on-center and off-center On-center cells are are more stimulated when light falls on the center but become less stimulated when light falls on the edge. Vice-Versa for Off-center cells Both types are more stimulated when light falls on the edge of the cell Cells that are most stimulated emphasize the perceived edge

E2.5 Contralateral processing occurs because of the optic chiasma The optic nerves cross over each other at the optic chiasma: Right goes to left brain and left goes to right brain. The brain interprets the data and can better determine distances and lengths. The visual cortex receives point by point information from the eyes and creates meaningful images in the brain. Sometimes the brain will compare incoming information to memories and further process it.

E2.6

E2.7 Air waves vibrate the eardrum which translates the vibrations to air molecules in the middle ear Bones in the middle ear are vibrated by the eardrum Small muscles around the ossicles (little bones in ear) contract to protect the ear from loud sounds. Ossicles decrease sound wave amplitude but increase the force of the waves

E2.7 The middle ear bones pass the vibrations to the cochlea through the oval window. The cochlea is a spiral shaped, fluid filled tube. The tube has two windows, round and oval. When the oval window vibrates, it moves the incompressible fluid, so the round window compensates Hairs in the cochlear fluid move according to the vibrations in the fluid and create a nerve impulse We can distinguish sounds because the cochlear hairs respond to specific wavelengths of sound The hairs themselves are of varying lengths and gradations. The section of the cochlea with the hairs on it is called the basilar membrane.

Above: the Cochlear Basilar membrane hairs have a size gradient from the base to the apex Right: the mechanism of the cochlear hairs