Special Senses

Sensory Receptors Stimuli are forms of energy Sensory receptors convert incoming energy to another form of energy Ex. TASTE receptors convert chemical energy to electrical energy) Have modified ends specific to their function Are grouped within sensory organs Sensory organs enhance and amplify the stimuli to ensure minimum threshold levels are met Types of receptors: photoreceptors, chemoreceptors, mechanoreceptors, thermoreceptors,

Sensory Adaptation Occurs one a sensory receptor becomes “used to” the stimulus The neuron fails to be stimulated even though the minimum threshold has been attained Once the body realizes it is not in danger, and is used to the stimulus, the sense adapts the stimulus and quits responding to it Ex. Perfume “fades” ten minutes after you put it on but when you walk by someone they can smell it

Taste Able to differentiate between edible and non-edible food Taste receptors are found in 4 different locations in the tongue Sweet, Bitter, Salty, Sour Once dissolved, the specific chemical stimulates the receptors on the tongue, and the message is sent to the brain

Smell Olfactory cells are located in the nasal cavity Airborne chemicals combine with these specialized receptor cells to create an action potential May be millions of different receptors specific to certain scents, allowing us to smell a variety of smells ** TASTE AND SMELL WORK TOGETHER** ** Both work by chemical stimulation

Senses Review Student Text, pp. 466-467 http://www.youtube.com/watch?v=FanxCxeaYBE&feature=related Eye Pop http://www.youtube.com/watch?v=HX_5zIXxKEU&NR=1

The Eye http://www.nelson.com/ABbio20-30/teacher/protect/otr/Bio2030OTR/attachments/i_AnimationSimulation/eye_structure_v2.html

How we “see” Rods and cones are the light sensitive cells (humans have many more rods than cones)

The rods contain a light-sensitive pigment called rhodopsin which breaks down in the presence of light to produce the action potential In bright light, rhodopsin breaks down faster than it can be restored. The opsins used for colour vision are much less sensitive to light and, therefore, operate best with greater light intensity Rods work best during low light Cones work best during intense light

Focussing and Image Light strikes the eye and is bent by the cornea toward the pupil Light is bent to a focal point, because the cornea is thicker in the middle than out the outer edges An inverted image is projected on to the retina to stimulate both rods and cones

The shape of the lens is controlled by ciliary muscles When CLOSE objects are viewed, the ciliary muscles CONTRACT, causing the lens to THICKEN, bending the light more When FAR objects are viewed, the ciliary muscles RELAX, causing the lens to THIN, causing the light to bend less THIS IS KNOWN AS ACCOMODATION http://www.nelson.com/ABbio20-30/teacher/protect/otr/Bio2030OTR/attachments/i_AnimationSimulation/accommodation.html

Eye Defects Glaucoma Caused by an increased build up of aqueous humor Blood vessels are blocked, thus cutting off a constant supply of blood, carrying oxygen and other nutrients to the eye

Eye Defects Cataract Caused when the lens of the eye becomes opaque which prevents maximum amount of light from entering the eye Cured by removing the lens and fitting the patient with strong eye glasses, or to replace the lens with a plastic one

Eye Defects Astigmatism The cornea and lens are not symmetrical, which blurs the focal point

Eye Defects Near Sighted (myopia) Eyeball is too long Image is focused before the retina Cannot focus on far objects, only near Far Sighted (hyperopia) Eyeball is too short Image is focused behind the retina Can see far objects, not close

Assignment 2 – Eye and Ear

Friday Write your name on the piece of paper and place in the “YAY ITS FRIDAY” box

The Ear

Ear Functions The ear is associated with TWO functions: Hearing Equilibrium and Balance Sensory cells for both functions are found within the ear Cells respond to mechanical stimuli produced by movement or by sound waves, which create the action potential

http://www. mcgrawhill http://www.mcgrawhill.ca/school/applets/abbio/ch12/soundwaves_effect_of_so.swf Hearing Sound waves push against the tympanic membrane, which transfers sound to the ossicles The bones concentrate and amplify the vibrations, passing sound onto the oval window, pushing it inward The oval window’s force causes the round window to push out This triggers the fluid in the inner ear to move – also causing vibration of the basilar membrane Fluid causes hair cells (stereocilia) in the cochlea, specifically the organ of Corti, to bend, thus stimulating nerve cells Action potential is carried to the brain via the auditory nerve

Stereocilia

Pitch and Loudness Pitch (frequency) Loudness (amplitude) http://www.nelson.com/ABbio20-30/teacher/protect/otr/Bio2030OTR/attachments/i_AnimationSimulation/hearing.html Pitch (frequency) Longer waves move hair structures within the cochlea differently than short waves, thus helping you determine differences in pitch and loudness Close to oval window is high frequency (short waves) Loudness (amplitude) Louder the noise = more pressure fluid puts on hair cells

How can hearing loss occur? How is hearing loss corrected? Two types of hearing loss Conduction deafness (damage to outer or middle ear) Nerve deafness (damage to hair cells – permanent)

Equilibrium and Balance Vestibule (gravitational equilibrium - static) Connects to oval window Contains two small sacs – utricle and saccule Lined with tiny hairs suspended in a jelly like material containing crystals (otoliths – calcium carbonate) When head is in normal position, crystals do not move When head is tilted, gravitational force acts on the crystals, moving the jelly and thus the hairs

Equilibrium and Balance Semicircular Canals (rotational equilibrium – dynamic) 3 canals, arrange at different angles Filled with fluid Movement causes fluid to move, moving the hair within the canal, thus stimulating nerves Brain then interprets movement http://www.nelson.com/ABbio20-30/teacher/protect/otr/Bio2030OTR/attachments/i_AnimationSimulation/dynamic_equilibrium.html

What now?!?! “YAY ITS FRIDAY” Relay Race (choose teams) Choose “mascot” from specimen containers Rules (outside)