Human eye

Light sensitive cells respond to the light resulting in action potentials being sent along the optic nerves to the visual cortex at the back of the cerebrum.

Key terms:

Conjuctiva- protective, thin layer of epithelial cells
Cornea- curved front of the eye, transparent and helps converge light rays
sclera: fibrous, outer protective structure.
choroid: supplies nutrients to all cells and removes waste, pigmented to prevent internal reflection. it has a network of blood cells.
Iris: muscular structure with an inner ring of circular muscle and an outer layer of radial muscle. it controls the amount of light entering the eye.
Pupil: hole in the middle of the iris where light continues into the eye
Vitreous humour: jelly like mass located behind the lens, it suspends the lensso it is not damaged.
Lens: transparent, flexible, curved structure. focus's incoming light onto the retina as it is refractive.
Retina: layer of sensory neurones, photoreceptors which respond to light. the rods and cones
Blind spot: this is where the bundle of sensory fibers form the optic nerve.
Uses of ATP: resynthesis of rhodopsin / sodium pump

A receptor is a cell or group of cells that detect a specific stimulus.

Rod cells:sensitive to light intensity. not sensitive to colour. they can respond to very dim light.
rhodopsin ---light---> opsin + retinal

Rhodopsin is stored in flattened membranous vesicles
low visual acuity in dim light.
opsin opens ions channels for the generation of action potentials.

Rod cells are absent in the fovea
The inner segments have lots of mitochondria which provide atop for the resynthesis of rhodopsin.
Rhodopsin is regenerated when there is no light. These are used at Night

a generator potential is produced which causes nerve impulses to be transmitted along a sensory neurone. Hyperpolarisation then depolarisation.
you have many 3/4 rods to one bipolar and ganglion cell.

around 120 million per retina

light hitting the pigment causes it to split.opsin iniates reaction ledin to the surafe becoming negative. Hyperpolarisation. When this reaches past a threshold, an action potential is stimulated in the sensory neruone. and this passes to the brain. this is to the visual cortex

Cone cells: require high light intensity to be stimulated. High visual acuity.
iodpsin----> photopsin + retinal
3 different types:
red-stimulated by red light
green- '' green light
blue- '' blue light
there are less cones than rods, and they are more focussed around and at the fovea.
Trichromatic theory states, colour vision is perceived according to the degree of stimulation of each type of cone.
1 cone cell is connected to 1 bipolar and ganglion cell.
6-7 million per retina.
Ganglion cell: transmitts action potential along neruones.
Bipolar cell:form an intermeidiate which connect photosensitive cells to ganglion cells.

Iris/pupil reflex:
the amount of light coming into the eye is detected by recpetors in the retina. reflex pathways lead to the circular and radial muscles of the iris contracting or relaxing.
High intensity light, leads to constricted pupils (small) circular muscle contract and radial relax.
low intensity light, leads to a dilated pupil (large) circular muscles relax and radial contract.