How the eye works

Accommodation The lens will change shape according to distance of object Distant object: lens stretches, becomes flat Close-up object: lens shortens, becomes spherical Brain superimposes image from each eye to estimate distance & object contours

Pathway of Light 1. Light from object 2. Passes through cornea, through pupil 3. Lens focusses image on retina 4. Retina transforms light into nerve impulse 5. nerve impulse passes along the optic nerve to brain 6. Nerve impulse travels to region of brain that controls vision 7. Info. Processed and analyzed by brain and we see!

The Ear

Sound Waves Variations in air pressure cause the sound wave to move through the air (medium) Ex. Loudspeakers, musical instruments, thunder

Amplitude Intensity of Sound depends on: The Amplitude (loudness of the sound) Measured in: decibels (dB) Sound tones: frequency in Hertz (Hz)

Decibel Scale Scale is a relative scale that represents the perception of the intensity of sound by the human ear. Measured: by a factor of 10 Each increase of 10, sound is 10 times louder Ex. Human breathing 10dB Soft music 50 dB 50-10= 40 So, 10 x 10 x 10 x 10 = 10 000 times louder!

Pathway of Sound 1. Vibrations create sounds waves (changes in air pressure) 2. Sound waves channelled into ear by pinna 3. Sound passes through auditory channel, vibrates the tympanic membrane 4. Vibrations passed along by Hammer, Anvil, and Stirrup 5. Sound waves stimulate nerve cells in liquid of Cochlea 6. Nerve cells of cochlea transform vibrations into nerve impulses 7. Nerve impulses travel along auditory nerve to the hearing centre of the cerebrum. 8. We hear!

Balance Vestibule: specialized cells monitor position of head (stationary) Semi-circular canals: maintain balance when in motion (direction, speed) Ex. Walking, dancing etc.

The Skin Sensory organ of touch 3 layers: epidermis, dermis, hypodermis

Epidermis Dead layer: outer skin, cells burst & die (atmospheric pressure) Living layer: constantly dividing, new cell push old to surface, healing

Dermis Sensory receptors: pick-up stimuli Blood vessels: nourish skin Sebaceous glands: secrete sebum(oily), lubricates skin Sweat glands: produce sweat, through pores to skin surface Hair: dermis to epidermis, goose bumps (muscle contracts, makes hair stand on end)

Hypodermis Fat cells: energy reserve, thermal insulator

Nose Nose: - nerve cells in upper wall of nasal cavity (olfactory epithelium) - Olfactory bulb contains 15 million - Olfactory nerve transmits impulses to cerebrum

Tongue Muscle scattered with sensory receptors(taste) Taste buds are sensory receptors 3 cranial nerves carry taste nerve impulses to cerebrum 5 tastes(sweet, sour, salty, bitter, umami) Smell & taste interrelated(smell 90%, 10 % taste) Other receptors-cold/hot, texture, discomfort