The Sensory System Different Senses Touch Sight Hearing Sense Organs Smell Taste A stimulus is something that causes us to take an action What are receptors? • Receptor cells are usually a neuron ending. • Receptors are specialised to respond to stimuli such as heat, light, pressure and chemicals. Sense Organs Sense Sense Organ Hearing Ears Sight Eyes Smell Nose Touch Skin Taste Tongue Structure of the Skin Touch • There are few touch receptors in the skin at the heel of the foot. • There are a lot of temperature receptors at the elbow. The tongue and taste Taste • Four taste receptors: 1) Sour 2) Sweet 3) Salt 4) Bitter NOTE: a suggested fifth taste called umami which can be found in chinese cooking. Smell • 20 million neurons used to detect smell. • 10,000 different smells The Eye • • • • • • • • • • • Iris Lens Pupil Cornea Ciliary muscle Optic nerve Retina Conjunctiva Sclera Choroid Fovea Functions of parts of eye Iris: Controls the amount of light entering the eye. Contains melanin which controls what colour your eyes are. Pupil: Allows light to enter the eye. In bright light, pupil is small In dark room, pupil is large WHY? Pupil Parts of the eye: Aqueous humour: A salt solution which holds the front of the eye in shape. Vitreous humour: Supports the eye by exerting outward pressure on the eyeball. Blind Spot: There are no rods or cones found in the blind spot and is not sensitive to light. The Blind Spot Testing The Blind Spot Parts of the eye: Lens: Focus light onto the retina (lens can change shape) Fovea: The area of eye that only has cones. Region of sharp vision (yellow spot) Optic nerve: carries messages from the eye to the brain. Cornea: allow light to pass into the eye and bends it to retina Ciliary muscle: muscles contract or relax to cause the lens to change shape. This is a reflex action (accommodation) Parts of the eye: Retina: Contains the light receptors (rods and cones). Rods Cones 120 million per eye 6 million per eye Detect black and white Work in dim light Found all over retina Detect colours Work in bright light Found at the fovea Rods and Cones Rods and Cones Parts of the eye Choroid: Contains blood vessels to nourish the eye. Has black pigment to absorb light in the eye. Sclera: Is the white of the eye. It is opaque (no light is let through). Holds the eye in shape. Conjunctiva: Thin membrane protecting the sclera. Inflammation causes conjunctivitis. Conjunctivitis When the lens doesn’t work properly • If the lens doesn’t take the correct shape, our sight will appear blurred. • Glasses or contact lens are used to correct our sight. Wearing glasses to correct our sight Short Sight Eye Dissection • Cow's Eye Dissection | Exploratorium Hearing Function of ear: 1) Hearing 2) Balance Ear divided into three sections: Inner ear, middle ear and outer ear Structure of the Ear Structure of the Ear How do we hear? • Sound is caused by vibrations • Vibrations are collected by the outer ear • Vibrations pass through middle ear where vibrations are increased and passed onto the lymph fluid in the cochlea (inner ear) How do we hear? • The receptors create electrical impulses from the pressure waves in the lymph which are sent to the brain. Pinna: Parts of the ear made of cartilage collects vibrations into auditory canal Auditory canal: carries vibrations to the eardrum wax is excreted here to trap dust Eardrum: separates the outer ear from the middle ear Vibrations cause the eardrum to vibrate Parts of the ear Ossicles: Consist of three bones in the middle ear (hammer, anvil and stirrup) NOTE: Stirrup is smallest bone in the body. These bones transmit vibrations from outer ear to inner ear and increase the vibrations The Ossicles The Ossicles Parts of the ear Eustachian tube: equalises pressure on either side of eardrum prevents damage to the eardrum NOTE: usually closed but opens with a pop when we swallow or yawn. When we climb a mountain, the outside pressure falls which might force the eardrum outwards. The Eustachian tube opens and air moves out of middle The Eustachian tube Google Image Result for http://web2.stmaryssenh.schools.nsw.edu.au/site/rick/Biology%2520web%2520site/HSC_9_5%25 20communications/Eustachian%2520tube/eustachian_files/airtube.gif Cochlea • Spiral tube (3.5 cm long) • Converts pressure waves caused by vibrations into electrical impulses that travel to the brain. How does the cochlea work? • Vibrations arrive at the cochlea from the stirrup through the oval window. • Vibrations form pressure waves in the lymph in the cochlea. • Pressure waves stimulate the receptors in the cochlea which cause electrical impulses to be sent to the brain. NOTE: these receptors are hairs that form the organ of corti. How does the cochlea work? • These electrical impulses travel along the auditory nerve. • The round window allows the pressure waves to escape out of the cochlea into the ear of the middle ear. How we hear? The Ear and balance Balance is detected by the vestibular apparatus in the inner ear. Damage to the vestibular apparatus causes loss of balance. Vestibular apparatus is filled with liquid. Receptors in the vestibular apparatus detect if the head is vertical or not. Structure of the vestibular apparatus Vestibular apparatus consists of three semi circular canals Hearing disorder Glue ear is common in children. Caused by sticky fluid collecting in the middle ear Prevents the free movement of the ear drum Correction of hearing disorder • Nose drops to unblock eustachian tube • In severe cases, grommets are inserted into the eardrum • Grommets allow air into middle ear which forces fluid down the eustachian tube. Grommets
