Sense Organs: Eyes & Ears Section 9.5 & 9.6

The Human Eye - Vision

3 layers Outside layer = Sclera Middle layer = Choroid Inside layer = Retina

Sclera Thick, white external layer that gives the eye its shape Protective Helps to absorb some of the light that hits the surface of the eye

Cornea Transparent part of the sclera that covers the area where the light enters Space behind the cornea is filled with a liquid called the aqueous humour which supplies it with nutrients

Choroid Middle layer of the eye Coloured membrane that absorbs the light which is not absorbed by the sclera

Iris Part of the choroid that opens and closes to change the size of the pupil Coloured due to melanin pigments (blue eyes have less pigment)

Pupil Hole in the iris through which light passes to enter the eye

Lens Clear, flexible structure behind the iris Allows the eye to focus on objects & changes its shape depending on whether the object is near or far

Accomodation Close objects: ciliary muscles contract, lens becomes thicker Far objects: ciliary muscles relax, lens becomes thinner

Retina Internal layer Composed of photoreceptors Also contains blood vessels that supply oxygen and nutrients to the eye The empty space in the eye is filled with a liquid called the vitreous humour

Photoreceptors Fovea Centralis Concectrated region of cones Require light to be stimulated Identify colours Rods Sensitive to light Cannot distinguish colours Fovea Centralis Concectrated region of cones Found directly behind the center of the lens

Blind Spot The optic nerve, located at the back of the eye is a gap in the retina No rods or cones at this spot Therefore, no image can be formed with the light that hits this spot

Find your blind spot!

Pathway of nerve impulse Stimulus (light) Photoreceptors Bipolar cells (in the retina) Optic Nerve CNS (Occipital Lobe) Pathway of nerve impulse

The Human Ear – Hearing & Equilibrium

3 sections Outer ear: Pinna & auditory canal Middle ear: Eardrum  Oval window Inner ear: Vestibule, semicircular canals & cochlea

Pinna External structure of the ear “funnel” that collects sound

Auditory Canal Channel that connects the external environment to the interior of the ear Ends at the eardrum Sweat glands produce earwax – traps foreign particles

Tympanic Membrane AKA: eardrum Thin layer of tissue, separates outer ear from middle ear Sound waves cause it to vibrate

Ossicles 3 small bones Malleus (hammer) Incus (anvil) Stapes (stirrup) Amplify sound when they vibrate Sound is passed from eardrum through ossicles to oval window (covered with a thin membrane – leads to inner ear)

Eustachian Tube Channel that leads from the middle ear to the mouth & nose Swallowing, chewing, yawning allow air to be released & pressure on either sides of the eardrum to be equalized

Vestibule Chamber in the inner ear Involved in balance (static equilibrium) Allows you to determine the position of your head

Semicircular Canals Channels filled with fluid Involved in balance (dynamic equilibrium) Allows you to identify body movement

Cochlea Shaped like a snail shell Converts sound waves into nerve impulses

Organ of Corti Sound receptor located in the cochlea Auditory nerves relay impulses from the cochlea to the temporal lobe