1. A.3 Perception of Stimuli

2. Understandings
Receptors detect changes in the environment
Rods and cones are photoreceptors located in the retina
Rods and cones differ in their sensitivities to light intensities and wavelengths
Bipolar cells send the impulses from the rods and cones to the ganglion cells
Ganglion cells send messages to the brain via the optic nerve
The information form the right field of vision from both eyes is sent to the left part of the visual cortex and vice versa
Structures in the middle ear transmit and amplify sound
Sensory hairs of the cochlea detect sounds of specific wavelengths
Impulses caused by sound perception are transmitted to the brain via the auditory nerve
Hairs in the semicircular canals detect movement of the head
Application
Red-green color blindness as a variant of normal trichromatic vision
Detection of chemicals in the air by the many different olfactory receptors
use of cochlear implants by deaf patients
Skill
Labelling a diagram of the structure of the human eye
Annotation of a diagram of the retina to show the cell types and the direction in which light moves
Labelling a diagram of the structure of the human ear

3. Mechanoreceptors
Stimulation: mechanical force (pressure)
Sense of touch  pressure sensors on skin
Arteries  pressure receptors detect change in blood pressure
Lungs  stretch receptors respond to lung inflation
Position of legs/arms  proprioceptors (muscle fiber, tendons, joints, ligaments)
Help maintain posture and balance
Ear: pressure receptors – information about equilibrium

4. Response to chemical substances
Chemoreceptors
Response to chemical substances
Provide information about internal body environment
Taste and Smell
Blood vessels  monitor pH changes  which adjusts breathing rates
Pain receptors  respond to chemicals released by damaged tissue
DNA codes for each receptor for each smell,

5. Thermoreceptors
Respond to change in temperature

6. Ciliary body
Posterior humuor
Optic nerve: transmit impulses to the brain
Suspensory pigment
Iris: regulates the size of the pupil
Anterior humuor: transmit light rays, supports eyeball
Fovea: densely packed cone cells, most acute vision
Lens: focuses light rays
Sclera: protects, supports eyeball
Cornea: focusing begins here
Choroid: absorbs stray light
Conjunctiva: covers sclera/cornea, keeps eye moist
Retina: contains photorecepotrs

8. More sensitive to light (function well in dim light)
Rods and Cones
Rods
Cones
More sensitive to light (function well in dim light)
Less sensitive to light (function well in bright light)
Only 1 type found in retina: it can absorb all wavelengths of visible light
3 types found in retina: 1 – sensitive to red light, 1 – to blue, 1 – green
Impulses from group of rod cells pass to single nerve fiber
Impulse from single cone cell passes to single nerve fiber
Dichromatic
Red blindness – presence of blue/green cones
Green blindness – presence of red/green cones
Variations lead to range of color-blindness
Trichromatic

10. Stapes (stirrup)
Incus (anvil)
Malleus (hammer)
Semicircular canal
Pinna
Tympanic membrane
cochlea
Cochlea nerve
Oval window
Round window
Auditory canal
Auditory tube

11. Bones (malleus, incus, stapes) receive vibrations from tympanic membrane, multiply 20x
Travel down auditory canal, causing ear drum (tympanic membrane) to move back and forth
Stapes strikes oval window, causing vibration
Vibration passed to fluid in cochlea
Outer ear = catches sounds waves
Fluid causes special cells (hair cells) to vibrate
Hair cells (receptors) release chemical message across synapse to sensory neuron of auditory nerve, moves to brain
Wave in fluid dissipates as it reaches round window

12. High/loud frequency too often kills hair cells  do not grow back
Detect sounds of specific wavelength
Bend back and forth  internal change  electrical impulse carried by auditory nerve
Short, high frequency waves = high pitch sounds
Long, low-frequency waves = low pitch sounds
Cerebral cortex

13. Semicircular canals
Control our equilibrium
Contain fluid and hair cells
Detects rotational movement of head
Send message via vestibular nerve

14. External processor digitizes sound – transfers electrical signal to implant – surgically placed in cochlear
Implant deciphers digitized sound and transfers into electric signal
Auditory nerve sends electric signal to brain
External processor behind the ear
Microphone picks up sound signal
Brain interprets sound