Receptors Receptors are part of the co-ordination system that detect the changes of the environment by means of stimuli. Two types... Interoceptors – receptors detecting internal stimuli, such as hunger, thirst, pain, need to urinate, and blood pressure changes, etc. Exteroceptors – receptors detecting external stimuli, such as light, sound, movement (balance), temperature, pressure, pain, etc.

Sense organs – What to learn: Label diagrams of human eye and ear List functions of parts of eye and ear Using diagrams describe in writing formation of an image, accommodation, binocular vision, pupillary mechanism, balance and hearing Long and short sightedness, astigmatism, cataracts

Internal structure of the eye ciliary body retina choroid yellow spot blind spot sclera vitreous humour lens suspensory ligament iris aqueous humour pupil optic nerve conjunctiva

Function(s) of parts of the eye Sclera: maintains the shape of the eyeball and is the point where the eye muscles attach Cornea front part of the sclera which is transparent to allow light to pass into the eye light refraction occurs here Choroid middle layer contains many blood vessels and brings O 2 & nutrients to the cells of the retina

Function(s) of parts of the eye (cont.) Conjunctiva Thin membrane covers the front of the eye has sensory nerve endings that detect the presence of foreign objects (protect eye) Suspensory ligaments Holds the lens in place Lens responsible for the refraction of light to create a sharp focussed image

Function(s) of parts of the eye (cont.) Retina light-sensitive membrane lines the inside of the eye ball and is made up of photoreceptors Photoreceptors (photo=light+receptors convert stimulus into nerve impulse). Two types.. Rods active in dim light, allow us to see black & white Cones active in bright light, allow us to see colour

Function(s) of parts of the eye (cont.) Yellow spot (fovea) small area on retina which contains only cones the area of sharp vision Blind spot area where the neurons from the photo- receptors leave the eye ball via the optical nerve There are no cones or rods in this area Blood vessels also leaves and enter the eye ball at the blind spot

Accommodation Accommodation is the adjustment of the shape of the lens to see objects clearly whether they are far away or close by. Near vision Far vision Use the two diagrams to memorise the summary of these two processes on the next slide

Summary of eye accommodation Distant vision (objects further than 6 m) Near vision (objects closer than 6 m) Ciliary muscles relaxCiliary muscles contract Suspensory ligaments tighten (become taut) Suspensory ligaments slacken Tension on lens increasesTension on lens decreases Lens is less convex (flatter)Lens becomes more convex (more rounded) Light rays are refracted (bend) less Light rays are refracted (bend) more Light rays are focused onto the retina

Pupillary mechanism Pupillary mechanism is the contraction of the pupil in response to light entering the eye. Bright light Dim light

Summary of pupillary mechanism Bright lightDim light Radial muscles of the iris relax Radial muscles of the iris contracts Circular muscles of the iris contracts Circular muscles of the iris relax Pupils constricts (gets smaller) Pupils widens (gets bigger) Less light enters the eyeMore light enters the eye

Structure of the human ear The human ear consists of the following three parts

Labelled diagram of the ear

Summary of the hearing process