The Senses

The Senses

• There are five senses; smell, sight, touch, taste and hearing.

• Balance is now thought of as a sense.• Touch detects pressure, pain and hot and cold

substances.• Our senses are based on receptor cells and nerve

endings, which combine to form the sense organ.• Receptors respond to heat, light, pressure and

chemicals. They are forms of energy, which are converted to electrical impulses and produce a message, which is sent along the neurons.

Sense Organs StimulusTouch Skin Touch

&temperature

Taste Tongue & lining of throat

Dissolved chemicals

Smell Nose Chemicals in gas state

Sight Eyes Light

Hearing Ears Sound

Taste

Taste

• Receptors for taste are located in the buds.• They are found on the top and sides of the

tongue and in the lining of the throat. • There are four taste receptors; sweet, sour,

bitter and salt.• Tastes dissolve and lodge in the grooves of the

taste buds where the flavour of the food is a combination of taste, smell, texture and temperature

Structure of the Eye

Functions of the parts of the eye.

• Sclera: tough white outer coat that holds the eye in shape.

• Choroids: dark brown layer, which contains blood vessels that nourish the eye and absorbs any light that passes through the retina thus preventing the reflection of light within the eye.

Functions of the parts of the eye.

• Retina: light sensitive layer that contains rod and cone receptors.

• Fovea: located at the centre of the retina, cones are found here and images are formed when we look at an object.

Functions of the parts of the eye.

• Optic Nerve: carries impulses from the eye to the brain.

• Blind Spot: there are no rods or cones here. We cannot see any images formed here.

• Cornea: transparent section of the eye that allows light in.

Functions of the parts of the eye.

• Lens: changes shape to focus light on the retina.

• Ciliary Muscle: changes the shape of the lens.

• Iris: coloured part of the eye, which controls the amount of light entering the eye.

The Pupil

The Pupil

• The pupil is the black circle in the centre of the eye, which allows light into the eye.

• In dim light, the size of the pupil enlarges or dilates to allow more light to enter the eye.

Aqueous and vitreous humours

• The aqueous and vitreous humours are liquids that support the eye while the external muscles allow movement.

Rods and Cones

Rods Cones

Shape Rod shaped Cone shaped

Detect Black & white light Colours

Active in Dim light Bright light

Location All over the retina At the fovea

No. per eye 120 million 6 million

Rods and Cones

• The pigment in the rods is called rhodopsin, which is formed from vitamin A.

• The cones have three pigments, red, green and blue light.

The Ear

Functions of the parts of the ears.

• The functions of the ear are hearing and balance.

• The ear is composed of three sections, the outer, middle and inner ear.

• The outer and middle ear is filled with air and the inner ear is filled with fluid called lymph

Functions of the parts of the ears.

• Sound is caused by vibrations in the air, which are collected by the outer ear, passed through the middle ear where they are amplified and transferred to fluid lymph in the cochlea of the inner ear.

• The cochlea is stimulated by pressure waves in the lymph, which sends electrical impulses to the brain, which in turn interprets them.

The Outer Ear (Air).

• The pinna is made of cartilage, which collects vibrations in the air and channels them into the ear.

• The auditory canal carries vibrations to the eardrum.

• The eardrum is a tightly stretched membrane that vibrated when stimulated by vibrations in the auditory canal.

The Middle Ear (Air)

The Middle Ear (Air)

• The ossicles are three bones, the hammer, anvil and stirrup.(The stirrup is the smallest bone in the body, which increases the vibrations and pass them on to the oval window).

• The Eustachian tube connects the middle ear to the throat. (It equalises pressure on either side of the eardrum).

The Inner Ear(Diagram not on course)

The Inner Ear (Lymph Fluid).

• The cochlea is a spiral tube, which allows hearing. Vibrations hit the lymph in the cochlea through the oval window. As the vibrations pass through the window they stimulate the pressure receptors in the cochlea. Impulses are sent along the receptors to the cerebrum along the auditory canal.

The Semi-Circular Canals

The Semi-Circular Canals

• The three semi circular canals are at right angles to each other and form part of the vestibular apparatus.

• The function of the semi circular canals is balance. Receptors in the canals detect when our head is moving or rotating. The receptors send impulses to the cerebrum of the brain through the vestibular nerve.

Glue Ear - A hearing disorder.

Cause• Glue ear is caused by too much fluid

collecting in the middle of the ear in young children.

• The build up of fluid is often the result of a viral infection

Glue Ear - A hearing disorder.

Syptoms• Can cause loss of hearing as it prevents

the three bones in the middle ear from moving properly.

Glue Ear - A hearing disorder.

Corrective measures• Decongestant drugs are taken which

break up the fluid and allow drainage of the fluid through the Eustachian tubes.

• In severe cases grommets are placed in the eardrums, which allow air to enter the middle ear and force the fluid down through the Eustachian tubes.