A.3 Perception of Stimuli

Sensory Receptors Type of receptor Stimuli Detected Examples Mechanoreceptor Pressure Gravity Detection of sound waves in the ear Detection of pressure on skin Chemoreceptor Dissolved chemicals Vapor chemicals Detection of chemicals dissolved in taste buds Detection of chemicals in vapor (olfactory or smell) Thermoreceptor Temperature (hot or cold) Detection of warm and cold by the skin Detection of the temperature of blood as it travels through the hypothalamus Photoreceptor Electromagnetic radiation (light) Detection of light (rod cells of the eye) Detection of color (cone cells of the eye)

The Human Eye Detects electromagnetic radiation in light Rods cones

Eye Parts and Functions Sclera: Tough outer layer; protects whites of eyes Cornea: Front of eye, allows light to pass through; clear Conjunctiva: outer lining; provides moisture Eyelid: covers the eye; protection and spreads moisture Choroid: Dark layer; lots of capillaries to nourish retina Aqueous humour: Fluid in the front portion of the eye; provides pressure and contains nutrients Pupil: Opening in the iris; controls amount of light let into the eye Lens: focuses light on the fovea of the retina

Eye Parts Continued Iris: Colored part of the eye; contracts & relaxes to change size of the pupil Vitreous Humour: Thick fluid in the back of the eye Retina: Contains rods & cones (photoreceptors) Fovea: Location of most of the cones; most accurate visual region Optic nerve: Contains all the neurons leaving the retina, and carries visual messages to the brain Blind spot: where the optic nerve leaves the back of the eye

The Retina Contains photoreceptors (rods and cones; more detail on next slides) Absence of, or defect to either red or green cone cells causes red-green color-blindness

Rods Detect black and white Sensitive to all wavelengths of light Groups of rods connect to one neuron (nerve fiber) in the optic nerve (low visual acuity) More numerous (over 100 million) spread out in retina

Cones Detect bright light (color) Sensitive to 3 wavelengths of light; red, blue & green Each cone connects to its own (one) neuron (nerve fiber) in the optic nerve (high visual acuity) Less numerous (less than 10 million) Mostly in fovea

Bipolar Cells Rods and cones synapse with bipolar cells in the retina Send the impulses from rods and cones to the ganglion cells

Ganglion cells Send messages to the brain via the optic nerve

Edge Enhancement & Contralateral Processing Visual processing Main Site of Processing Function Result of Processing Edge Enhancement Retina of the eye Selectively activates only some of the ganglion cells Enhances the sharpness of images (where edges are located) Contralateral Processing Optic chiasma in the brain Sends ganglion cells entering brain close to the nose to the opposite side of the brain Allows the interpretations of distances and sizes of objects

Contralateral processing

Contralateral Processing

The Human Ear Transmit pressure waves into auditory sounds Brain interprets the information from the receptors

Parts & Functions of the Ear Structure Function Pinna Collects sound waves Eardrum (tympanic membrane) Transmits sound waves to the inner ear bones Bones of the middle ear (hammer, anvil, stirrup) Transmit and amplify (by up to 20 times) the sound waves received from the eardrum Also known as the malleus, incus and stapes Oval window Receives pressure from middle ear bones (stirrup) and transmits pressure waves into the middle ear Round window Absorbs pressure waves after they travel through the cochlea, preventing the waves from moving backwards Semicircular canals Help maintain balance by sensing position; hair cells Auditory nerve Made up of neurons that are activated in the cochlea by pressure waves bending hairs in the inner ear; sends messages to brain Cochlea Part of ear that contains hairs that are attached to neurons and activated by pressure waves; transforms the pressure waves into neural impulses

Outer Ear Pinna

Middle Ear Eardrum 3 smallest bones in the body (malleus, Incus and Stapes)

Inner Ear Does both auditory and balance Cochlea and Vestibula or semicircular canals

Transmission of Sound Pinna collects sound waves and passes them to the eardrum The eardrum vibrates Vibration of the eardrum puts pressure on the ear bones Ear bones absorb the vibrations and amplify them Vibrations reach the stirrup and act like a piston to convert it to mechanical energy Mechanical energy is passed on to the cochlea via the oval and round windows As it moves through the cochlea it causes the hair cells to bend

Transmission continued Hair cells are varying heights and are in a jelly-like substance Larger sound waves vibrate more hair cells The more hair cells activated (bent) the louder the sound The more frequent the sound waves the higher the pitch (frequency)