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Sensory Systems
• Sensory system - collection of several cell types that work
together to accomplish a specific receptive process by
transducing various stimuli into nerve impulses.
• Somatic Sensory Systems - pain, touch, stretch, and
temperature receptors and associated neurons
• Special Sensory Systems:
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visual system - photoreceptors
Olfactory - chemoreceptors
Taste – chemoreceptors
auditory - mechanoreceptors
equilibrium sense – mechanoreceptors
Visual System
• Dominant sense in humans
• visual receptors-photoreceptors
• Structure of the eye
¤ External structures
• canthi-medial and lateral corners of the eye
• palpebrae-eyelids
• caruncle-small, fleshy structure in the medial cornercontains sebaceous &sweat glands
white secretion
• tarsal glands-posterior to eyelashes-secrete lubricant;
infection/inflammation
Chalazion
• ciliary glands-modified sweat glands between hair
follicles
infection/inflammation of ciliary or other non-tarsal
glands
sty
Fig
15.1a
Visual System (con’t)
¤ External Structures of the eye (con’t)
• conjunctiva-transparent mucous membrane that lines the eyelid
and whites of the eye
inflammation of the conjunctiva – conjunctivitis
infection of the conjunctiva – pinkeye
• lacramal apparatus-produces protective lacramal fluid
containing mucous, antibodies, lysozymes
tears produced in lacramal gland
lacramal canal
l. sac
nasolacramal duct
nasal cavity
¤ Internal Structures of the eye (eyeball)
• Segments- divided into anterior and posterior segments by lens
posterior segment contains vitreous humor-clear gel
made of collagenous fibers; supports the lens and retina
anterior segment contains aqueous humor-plasma-like fluid that
supplies nutrients and O2 to the lens,cornea and retinal cellscontinually drained and replaced; drainage problem leads to
glaucoma
increased pressure in the eye.
Internal Structures of the Eye-(eyeball) (con’t)
• Wall- comprised of 3 layers (tunics)
« 1) sclera-(fibrous tunic) fibrous outermost layer of the posterior segment of
the eyeball-fuses with the cornea
» cornea-clear collagenous protective layer covering the front of the eye;
covered by epithelial sheets on both sides that allows regeneration
« 2) uvea-middle layer (vascular tunic); contains blood vessels, iris and ciliary
body
» iris-colored part of the eye-made of smooth muscle that acts a as a
diaphragm to open and close pupil (opening for light)
» ciliary body-smooth muscular structure that control lens shape and
secretes aqueous humor
« 3) retina (sensory tunic)- photosensitive layer; comprised of;
» pigmented epithelial layer-absorbs scattered light, stores VitA
» neural layer-contains photoreceptors that mediate phototransduction
and other neurons involved in vision
photoreceptors
bipolar cells
ganglion cells
opticnerve
» optic disc-area where optic nerve exits the eye- “blind spot”
retinal detachment-separation of vascular layer and sensory layer
• Lens-biconvex structure that changes shape to focus light on retina;
made of crystalline proteins; cataract-clouding of the lens
Fig 15.4a
Phototransduction
• Phototransduction-transduction of light into a neural signal
¤ photoreceptors-light-detecting cells (neurons) of the retina that
contain the visual pigments and convert the incoming light into a
neural signal (change in membrane potential)
rod photoreceptors-work in dim light; use rhodopsin;
cone photoreceptors- work in bright light; coneopsin
visual pigments- proteins
containing 11-cis retinal
that absorbs light
¤ visual transduction mechanism:
light
11-cis retinal
*rhodopsin
*G-protein PDE
all trans retinal
cGMP
membrane
cGMP-gated
5’GMP
potential
ion channels close
¤ Visual pathway to the brain:
retina
thalamus (relay)
visual cortex and other areas
Olfactory System
• Odorant molecules detected by chemoreceptor cells called olfactory
receptor cells (neurons)
• olfactory epithelium- located in the upper part of the nasal cavitycontains the olfactory receptor cells
• olfactory cilia- non-motile cilia on the olfactory receptor cells that
contain the receptor surface for odorant molecules
• fiber bundles of olfactory nerves-axons of olfactory receptor cells
that carry neural signal to olfactory bulb (in frontal lobe of brain)
• Physiology/trandsuction of olfaction: Dissolved odorant molecules
bind protein receptors on olfactory cilia
*G-protein
membrane potential
olfactory bulb
thalamus
ion channels
olfactory
cortex
limbic system
Sense of Taste
• Mediated by chemoreceptor cells (gustatory cells-epithelial cells)
located on taste buds; continually regenerated.
• Gustatory hairs (microvilli)- projections of gustatory cells that
contain the protein receptors for taste molecules within their the
gustatory receptor membrane
• sensory nerve fibers-connect with gustatory cells to send neural
signal to the gustatory cortex in the brain
• physiology/transduction of taste- different transduction
mchanisms for different chemical stimuli; some involve a G-protein
mechanism
all involve conversion of a chemical signal
neural (electrical)
signal via ion channels that change the membrane potential of the
gustatory receptor membrane
Auditory System
• Structure of the ear
¤ outer ear- auricles, helix-collect sound waves
external auditory canal
tympanic membrane (ear drum)
¤ middle ear-tympanic cavity ; mucosal-lined; connected to nasopharynx
through the pharyngotympanic (auditory) tube; contains ossicles that transmit
vibrations in tympanic membrane to inner ear.
¤ inner ear- comprised of vestibule, semi-circular canals, cochlea
cochlea-contains organ of corti-receptor organ of hearing that
contains auditory hair cells (mechanoreceptors) that detect
movement; auditory nerve connected to the cochlea
• Mechanism of hearing: “sounds set up vibrations in the air that beat
against the ear drum that pushes a chain of tiny bones that press fluid in
the inner ear against membranes that set up shearing forces that pull on
the hair cells that stimulate nearby neurons that give rise to impulses that
travel to the brain which interprets them, and you hear”
•
Tinnitis-ringing or clicking sound in the ears in the absence of auditory
stimuli caused by inflammation of the middle ear, cochlear nerve
degeneration, side effect of medications
•
Otitis media- middle ear inflammation/infection-can result from sore throat
Fig 15.25a
Semi-circular canals
Cochlea
Equilibrium Sense
• Response to head movements-sense of orientation and balance
• Involves input from inner ear, vision, and stretch receptors
• Vestibular apparatus-semi-circular canals and vestibule contain
equilibrium mechanoreceptors that sense position and acceleration
• Maculae-sensory receptors located in vestibule; contain hair cells
that sense linear acceleration but not rotational motion; when hairs
are bent
membrane potential
vestibular nerve fibers
• Cristae-sensory receptors located in the semi-circular canals that
contain hair cells that respond to angular or rotary movements;
hairs are bent when fluid moves within the semicircular canals
hair cells excited via membrane potential
vestibular apparatus
•
Impulses from the vestibular apparatus are sent via vestibular nerve fibers
to the vestibular complex of the brain stem and the cerebellum. These
centers initiate responses that fix the eyes on objects and activate
muscles to maintain balance
• motion sickness-equilibrium disorder due to vestibular and visual
sensory input mismatch- dramamine, bonine depress vestibular inputs