The Senses Reception of stimuli

2 Contents The Senses & Organs Classification of the senses Interoceptors Exteroceptors How they work Taste and Smell – smell Taste and Smell - taste Touch Ear Hearing Hearing defects Balance Vision Eye – Parts & function Eye defects Visual disorders

3 The Senses & Organs SenseOrgan Taste Smell Touch Hearing Sight Balance Pressure

4 Classification of the senses Classified according to type of stimulus to which they respond. Two groups – Interoceptors and Exteroceptors

5 Interoceptors interoceptors: sensory receptors that respond to changes in the internal environment, e.g. stretch receptors in the muscles.

6 Exteroceptors exteroceptors: sensory receptors that respond to external changes in the environment, e.g. taste receptors.

7 Further division of receptors Type of ReceptorResponds to … ChemoreceptorChemicals e.g. taste PhotoreceptorsLight e.g. rods & cones Mechanoreceptors Physical change e.g. pressure ThermoreceptorsTemperature change Proprioreceptors Movement of the body & position

8 How they work The sense organs contain receptors which receive the stimuli and send messages to the brain along sensory neurons. The brain acts as the interpreting centre for received information. All nervous messages are the same. How they are interpreted by the various parts of the brain is different.

9 Taste and Smell - smell Closely related senses – chemoreceptors. Chemicals enter the nose and stimulate the olfactory membranes in the back of the nose. Different chemicals stimulate different receptors resulting in different “ smells ”.

10 The human smell receptors What happens to your sense of smell when you have a cold? Why?

11 Taste and Smell - taste Taste buds in the tongue are similar. They respond to chemicals dissolved in the mouth. Sweet, sour bitter and salt – four basic tastes on different parts of the tongue.

12 The human taste receptors

13 Tongue, rabbit, showing taste buds

14 Touch Found in the skin. Involves the ability to sense a number of stimuli e.g. Touch receptors – gentle force on hairless skin – palm of hand Pressure receptors – greater force – found all over the body Pain receptors – found over the whole skin.

15 Various sense receptors in the skin

16 Skin of the scalp

17 Skin, hair follicle, sebaceous gland

18 Skin, sweat glands

19 Ear Divided into three sections: - Outer- Air filled- up to eardrum Middle- Air filled- to oval window Inner- Fluid filled- cochlea

20 Hearing (1/3) hearing: perception by the brain of the action of sound on the eardrum. Sound picked up by pinna Funnelled into ear canal Strikes off eardrum (tympanum) Eardrum vibrates Pressure on both sides of the eardrum is kept the same by the Eustachian tube This connects the middle ear to the throat.

21 The human ear

22 Hearing (2/3) This is why your ears ‘ pop ’ with sudden pressure changes e.g. airplane take off. Vibration of eardrum passed on to the ear ossicles and amplified twentyfold by them (hammer, anvil, stirrup). Stirrup connected to oval window which leads into the cochlea – a coiled fluid filled tube.

23 The human ear

24 Hearing (3/3) In the cochlea the vibrations are converted into nerve impulses and transmitted along the auditory nerve to the brain where they are interpreted as sound. The vibrations pass along the cochlea and are lost back to the middle ear at the round window.

25 Hearing defects (1/2) Usually caused by damage to the receptors in the cochlea. Continuous loud noise – pneumatic drills, rock concerts, listening to loud musin on earphones. Sudden very loud noise (gunshot) Some loss of receptors occurs with age

26 Hearing defects (2/2) Problems with outer or middle ear e.g. glue ear in young children (usually of smokers) – sticky fluid in middle ear – inserting drainage tubes into ear usually cures this.

27 Balance A function of the inner ear – the semi- circular canals. Fluid filled structures that detect movement and position of the head. They are used to keep you balanced.

28 Vision vision: the sensation resulting from the stimulation of the light receptors in the eye that allows the shape and colour of an object to be perceived – the sense of seeing, sight. The eye contains photoreceptors.

29 A section through the eye

30 Whole eye, mammalian

31 Parts and function (1/6) Eyebrow – directs sweat away from eye. Eyelid – blink - keep eye clear and moist. Eyelashes – trap dust and dirt. Conjunctiva – transparent membrane covering front of eye.

32 Parts and function (2/6) Lacrimal glands – produce tears - wash away dust and bacteria. Sclerotic coat (sclera) – maintains eyeball shape, strong, opaque and provides muscle attachment. Cornea – transparent part of sclera - allows light to enter eye.

33 Parts and function (3/6) Choroid – dark in colour - prevents light reflection in the eye - contains blood vessels. Retina – light sensitive layer, contains Rods (dim light) and Cones (colour vision). Ciliary body – contains muscles, which alter the shape of the lens.

34 Parts and function (4/6) Lens – transparent - biconvex - focus light on retina. Suspensory ligament Attaches ciliary body to lens - helps control / adjust shape of lens Iris – coloured part of eye - controls the amount of light entering the eye.

35 Parts and function (5/6) Pupil – hole in centre of Iris through which light enters eye. Aqueous humour – clear liquid found between lens and cornea - maintains eyeball shape. Vitreous humour – jelly like substance found between lens and retina - maintains eyeball shape.

36 Parts and function (6/6) Optic nerve – transmits messages from eye to brain. Blind spot – where optic nerve leaves eye - no rods or cones on retina => no vision at this spot. Fovea – area of most acute vision on retina - directly behind centre of lens.

37 Eye defects COMMON NAME MEDICAL TERM DIAGNOSISDEFECT SOLVE BY WEARING LONG SIGHT Hyperm- etropia Cannot see near objects Eyeball too short Convex lenses SHORT SIGHT Myopia Cannot see distant objects Eyeball too long Concave lenses

38 Long-sightedness and its correction

39 Short-sightedness and its correction

Visual disorders Not examinable for information only

41 Visual problems

42 Glaucoma

43 END