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The Senses

The brain interprets sensory messages form different sense receptors.

Sense	Organ	Type of Stimulus
Heat Touch Pressure Pain	Skin	Object touching hot and cold temp. Object or force pushing or pressing
Taste	Taste buds in tongue	Chemicals in food
Smell	Nose	Odour Chemicals
Sight	Eye	Light
Hearing	Ear- Cochlea	Sound waves/vibrations.

SIMPLE MAP OF THE TONGUE:

Taste receptors are concentrated in small organs in taste buds.
Chemicals in food are detected by the taste receptors
A message is sent to the part of the brain concerned with taste.

LOCATION OF RECEPTORS FOR SMELL IN THE NOSE:

Mucous traps and dissolves odour chemicals
Receptor cells are stimulatrd and a message is sent to the area of the brain concerned with smell.
Note that our sense stop responding to an unchanging stimulus and we become tolerant, e.g. noise,pain.

THE EYE

EXTERNAL EYE STRUCTURE:

INTERNAL EYE STRUCTURE:

Part	Function
Sclera (scleratic coat)	Protection Provides attachment for muscles to move eyeball
Choroid Layer	Has blood vessels to supply food and oxygen Has pigments to absorb light rays and prevent internal reflection of light
Retina	Contains the receptor cells -Rods for Black/White vision (dark/night) –Cones for colour vision (in light) The receptor cells convert light to an electrical impulse(nerve)
Cornea	Allows light into the eye Bends light rays
Iris	Has muscles to control amount of light entering the eye
Pupil	Allows light entering the eye (appears black as no light rays are reflected back)
Ciliary Muscles and Suspensory Ligaments	Alter the curvature of the lens to enable focusing on near and distant objects.
Aqueous and Vitreous Humour	Exert an outward pressure to give shape to the eyeball
Fovea(yellow spot)	Has a high concentration of ‘cones’. When light rays focus here the object is seen most cleary. (Area of most accurate vision)

EYE DEFECTS:

LONG- SIGHTEDNESS:

SHORTSIGHTEDNESS:

THE EAR

Part	Function
Pinna	It picks up sound waves and funnels them into the external auditory canal
Exteral Auditory Canal	It has hairs and cells to secrete a wax to trap dirt, dust and bacteria It allows soundwaves to travel to the ear drum
Ear Drum	It vibrates due to sound/pressure waves and passes the vibrations into the middle ear
Ear Ossicles(Hammer,Anvil,Stirrup)	They all vibrate and magnify the intensity of the vibrations 20 fold times greater Passes vibrations into the fluid in the middle ear.
Eustachian Tube	Opens during swallowing to equalise the pressure at either side of the eardrum(and during yawning)
Oval Window	It passes vibrations into the cochlea (by causing agitated movement of the perilymph and endolymph)
Cochlea	Cochlea contains sensory cells with hairs (sensory receptors) which are stimulated b the moving fluid and they send a message to the brain via the auditory nerve.
Semi-Circular canals	BALANCE: They provide information about movement of the head in any plane.
Utricle and Saccule	BALANCE: They provide infomation about the position of the head
Auditory Nerve	It passes messages to the hearing area of the brain.