1. C35: Senses
Mr. E Murphy

3. Objectives
Touch
Taste
Smell
Sight
Hearing

4. Introduction Balance may be a sixth sense
Senses are based on receptor cells forming a sense organ
Specialised to respond to various stimuli e.g. heat, light etc.
Receptors absorb these forms of energy and convert into electrical impulses that travel along neurons

5. Touch Receptors found at different concentrations around the body
Many in the elbow, few in the heel

6. Taste Receptors for taste are in taste buds
Located on the top and side of the tongue, also parts of the lining of the throat
Sweet, sour, bitter and salt
Taste may stay longer if it dissolves into the grooves of the taste buds
Flavour is a combination of taste, smell, texture and temperature

7. Smell
Root of nasal cavity has about 20 million neurons to detect smell (olfactory neurons)
Respond to about 50 different gaseous chemicals making up 10,000 smells
Extremely sensitive, adjust quickly to smells
Within a second of detecting a new smell, 50 % of the sensation will disappear

8. Sight Conjunctiva: Thin membrane protecting the sclera
Sclera: White of the eye. Tough and opaque. Does not allow light in.

9. Cornea: Transparent part of the sclera
Cornea: Transparent part of the sclera. Allows light into the eye and bends it towards the retina
Choroid: Black pigment (melanin) to absorb light in the eye
Retina: Light receptors (rods and cones) are located
Fovea: Area of retina only contains cones. Sharpest vision

10. Blind spot
Optic nerve: Carry impulses to the brain
Lens: Elastic transparent structure. Changes shape to focus light on the retina
Ciliary muscle: Surrounds the lens and causes the shape of lens to change
Iris: Controls amount of light entering the eye (eye colour)
Pupil: Opening in the iris
Aqueous and vitreous humour
External muscle

11. Hearing Hearing and balance Outer, middle and inner ear
Functions of hearing
Hearing and balance
Outer, middle and inner ear
Outer and middle ear filled with air
Inner ear filled with fluid (lymph)
Structure of the ear

12. The ear and hearing Vibrations in the air (or water etc.)
What causes sound?
Vibrations
Vibrations in the air (or water etc.)
Vibrations collected at the outer ear, passed through the middle ear (amplifications)
Transferred to the fluid in the inner ear
Cochlea has receptors which are stimulated by pressure waves in lymph
Electrical impulse travels to the brain (creates sound)

13. Parts of the ear
Pinna: made of cartilage. Helps collect and channel vibrations into the ear canal
Auditory (ear) canal: Tube carries vibrations to the eardrums. Wax traps dust (protection)
Eardrum (tympanic membrane): Small, tightly stretched membrane separates the outer ear from the middle ear
- Vibrates due to air vibrations

14. Parts of the ear Ossicles: 3 tiny bones in the middle ear
Stirrup is the smallest bone in the body
These 3 bones transmit vibrations from the outer to the inner ear and amplify (increase) the vibrations
Hammer, anvil and stirrup

15. Parts of the ear Eustachian tube: Not really part of the ear
Runs from the middle ear to the pharynx (throat)
Equalises pressure on either side of the ear drum
Prevents damage to the eardrum caused by the difference in pressure

16. Parts of the ear Yawn or swallow
Why would the eustachian tube open?
Yawn or swallow
Up a mountain: external air pressure increases
Underwater: Air moves into middle ear to equalise the increased pressure from the water
Common for infections to travel between the throat and middle ear

17. Parts of the ear Spiral tube, 3.5 cm long (snail’s shell) Cochlea
Converts pressure waves from sound vibrations into electrical impulses which travel to the brain

18. Parts of the ear How the cochlea works:
Vibrations arrive at the cochlea from the stirrup, which is attached to the oval window
Vibrations pass through the oval window and form pressure waves in the lymph
Pressure waves stimulate receptors (hairs) in the cochlea (The organ of corti)
Receptors cause electrical impulses to travel to the brain (auditory or cochlear nerve)
Round window allows the pressure waves to exit

19. The ear and balance
Vestibular apparatus in the inner ear detects balance
Made up of 3 semi-circular canals
Balance also maintained due to vision, receptors in muscles, ligaments and tendons and pressure receptors in the soles of feet
If the vestibular apparatus is damaged, balance can be lost
Vestibular apparatus

20. Parts of the ear Its filled with lymph
What the vestibular apparatus does?
Vestibular apparatus
Its filled with lymph
Receptors detect whether the head is vertical or not
Other receptors can detect movement of the head
All these receptors send impulses to the cerebellum through the vestibular nerve

21. Hearing Defects Glue ear Common in children
Surplus sticky fluid in the middle ear
Prevents free movement of the eardrum and the small bones
Results in some deafness
Correction
Nose drops
Grommets (small tubes allowing air into the middle ear)

22. Summary
The 5 senses
Structure of the eye + roles of the different parts
Structure of the ear + roles of the different parts
6 revision classes before test

23. Exam Questions
2011 Q15a
2009 Q15b
2007 Q15c

24. Solutions
2011 Q 15a

25. Solutions
2009 Q 15b

26. Solutions
2007 Q 15c