C35: Senses Mr. E Murphy

Objectives Touch Taste Smell Sight Hearing

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

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

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

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

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

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

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

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 http://mathsci.werribeesc.vic.edu.au/science7/multimedia/How%20the%20ear%20works.swf#

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)

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

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

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

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

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

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

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

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 http://www.bbc.com/news/health-13358608

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)

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

Exam Questions 2011 Q15a 2009 Q15b 2007 Q15c

Solutions 2011 Q 15a

Solutions 2009 Q 15b

Solutions 2007 Q 15c