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BIOB32H3 Lecture Notes - Ear Canal, Scarpa'S Ganglion, Depth Perception

Biological Sciences
Course Code
Kenneth Welch

of 5
The Special Senses
Olfactory organs
Contain olfactory epithelium with olfactory receptors, supporting cells, basal cells
Olfactory receptors are modified neurons
Surfaces are coated with secretions from olfactory glands
Olfactory reception involved detecting dissolved chemicals as they interact with
odorant binding proteins
Olfactory pathways
No synapse in the thalamus for arriving information
Olfactory discrimination
Can distinguish thousands of chemical stimuli
CNS interprets smells by pattern of receptor activity
Olfactory receptor population shows considerable turnover
Number of receptors declines with age
Taste receptors
Clustered in taste buds
Associated with lingual papillae
Taste buds
Contain basal cells which appear to be stem cells
Gustatory cells extend taste hairs through a narrow taste pore
Gustatory pathways
Taste buds are monitored by cranial nerves
Synapse within the solitary nucleus of the medulla oblongata
Then on to the thalamus and the primary sensory cortex
Gustatory discrimination
Primary taste sensations
Sweet, sour, salty, bitter
Receptors also exist for umami and water
Taste sensitivity shows significant individual differences, some of which are
The number of taste buds declines with age
Accessory structures of the eye
Eyelids (palpebrae) separated by the palpebral fissue
Tarsal glands
Lacrimal apparatus
external structures of the eye
Conjunctiva covers most of eye
Cornea is transparent anterior portion
Lacrimal apparatus
Secretions from the lacrimal gland contain lysozyme
Tears form in the lacrimal glands, wash across the eye and collect in the lacrimal
Pass through the lacrimal punctae, lacrimal canaliculi, lacrimal sac and
nasolacrimal duct
The eye
Three layers
Outer fibrous tunic
Sclera, cornea, limbus
Middle vascular tunic
Iris, ciliary body, choroid
Inner nervous tunic
internal structures of the eye
Ciliary body
Ciliary muscles and ciliary processes, which attach to suspensory ligaments of
Outer pigmented portion
Inner neural part
Rods and cones
The Special Senses
Retina contains rods and cones
Cones densely packed at fovea (center of the macula lutea)
Retinal pathway
Photoreceptors to bipolar cells to ganglion cells, to the brain via the optic nerve
Axons of ganglion cells converge at blind spot (optic disc)
Horizontal cells and amacrine cells modify the signal passed along the retinal
Eye anatomy
Ciliary body and lens divide the anterior cavity of the eye into posterior (vitreous)
cavity and anterior cavity
Anterior cavity further divided
anterior chamber in front of eye
posterior chamber between the iris and the lens
Fluids in the eye
Aqueous humor circulates within the eye
diffuses through the walls of anterior chamber
passes through canal of Schlemm
re-enters circulation
Vitreous humor fills the posterior cavity.
Not recycled permanent fluid
Posterior to the cornea and forms anterior boundary of posterior cavity
Posterior cavity contains vitreous humor
Lens helps focus
Light is refracted as it passes through lens
Accommodation is the process by which the lens adjusts to focus images
Normal visual acuity is 20/20
Visual physiology
Rods respond to almost any photon
Cones specific ranges of specificity
Photoreceptor structure
Outer segment with membranous discs
Narrow stalk connecting outer segment to inner segment
Light absorption occurs in the visual pigments
Derivatives of rhodopsin
Color sensitivity
Integration of information from red, blue and green cones
Colorblindness is the inability to detect certain colors
retinal adaptation
Dark adapted most visual pigments are fully receptive to stimulation
Light adapted pupil constricts and pigments bleached.
the visual pathway
Large M-cells monitor rods
Smaller more numerous P cells monitor cones
Seeing in stereo
Vision from the field of view transfers from one side to the other while in transit
Depth perception is obtained by comparing relative positions of objects from the
two eyes