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Chapter 15
Our SensesVisionSmellTasteHearingBalanceTouch*
Anatomy of an EyeballAccessory structures3 tunics (layers)
Fibrous (blue)Vascular (yellow)Sensory (red)
Segments Anterior divided into
chambersPosterior Filled with humors (fluid)
Lens
Eye muscles Rectus as named; obliques lateral and opposite Diplipia: muscle weakness/alcohol Strabismus: eyes not aligned
EyebrowsEyelids
Blink to spread secretions Eyelashes trigger blinking
Conjunctiva Mucus prevents drying out Conjunctivitis
Lacrimal apparatus Tears clean, protect, and moisten Excess secretions
Emotional tears unique to humans Stuffy/runny nose when cry Watery eyes with cold
Accessory Eye Structures
Fibrous TunicAvascular CTSclera (white of the eye)
Protects and shapesMuscle attachmentContinuous with dura mater
Cornea (transparent)Outer stratified squamous, why?Inner simple squamous maintain clarity InnervatedTransplants not rejected between people
Vascular TunicChoroid
Vascularized to supply nutrientsMelanocytes to absorb light
Ciliary bodySmooth muscle ring ciliary muscles control lens
shapeCiliary processes secrete aqueous humorSuspensory ligaments hold lens in place
IrisColored portion of ciliary body
Brown pigment only (varies) Less scatters light = blues/greens/grays (babys)
Encircles the pupil (2 smooth muscle layers)
Sensory TunicPigmented layer (outer)
Prevents light scatteringPhagocytize damaged photoreceptors
Neural layer (inner)Photoreceptors, bipolar cells, ganglion cells
Rods and cones Blind spot (optic disc) filled Macula lutea and fovea centralis
Rapid eye movement for rapid scene changesVascular supply from choroid and central vein/artery
Opthalmologist examinesRetinal detachment when layers separate
Vitreous humor seeps in Photoreceptors lose nutrients = blindness
HumorsAnterior segment with aqueous
humorSimilar to bloodContinual developmentNutrients & O2 to lens, cornea, &
retinaBlocked drainage = up pressure =
glaucomaPosterior segment with vitreous
humorTransmits light, support lens, &
intraocular pressureEmbryonic development
The Functioning EyeLight enters the pupil, regulated by the irisPasses through a convex lens
AvascularLens fibers added through life
Cataracts = clouding of lens due to loss of nutrients
Lens is shaped by the ciliary body to focus light on the retina (accommodation)Refraction of light converges to a focal pointReal image forms upside down and reversed
Visual PathwaysVisual field
Overlap to provide depth perception = 3D vision
Ganglion cells Optic nerveOptic chiasm
Nasal and temporal visual field
Optic tractThalamus
LGNPrimary visual cortex
Conscious perception of images
Olfactory ReceptorsCiliated bipolar cells
Located in olfactory epithelium (psuedostratified )
Mucus captures and dissolves odorantsPass through cribriform platesSynapse in olfactory bulbsOdorant detection
Humans can distinguish 10,000 odorsSome is pain (ammonia, chili, methanolCombinations of different
odorant/receptor binding
Olfactory Neural PathwayOlfactory receptors
synapse with mitral cellsContained in glomeruliReceptor type specificRefines smell
Mitral cells signal via olfactory tracts
2 pathwaysOlfactory cortexHypothalmus, limbic
system = emotional connection
TasteTaste buds detect molecules in solution
About 10,000Four familiar and 1 other found in papillae
Sweet: organic substances Alcohol, sugar, amino acids
Sour : acids, H+ in solutionSalty: inorganic saltsBitter: alkaloids
Aspirin, nicotine, caffeineUmami: glutamate & aspartate
meats, cheeses, and protein-rich foods (MSG)Each receptor responsive to a particular type of
substanceOften mixesMany ‘tastes’ (80%) are really smell (head colds)
PapillaeFungiform
Mushroom shapedTops of, all over tongue
FoliateFold is side walls
CircumvallateLargets, fewest, back of tongue
FiliformHair like projections all over
tongueDo not have taste buds
Gustatory Neural PathwayCranial nerves carry
sensations to medulla
Relay through the thalamus into primary gustatory cortex
Pathway initiates digestive process too
Regions of the EarOuter ear
Pinna, external auditory canal, and tympanic membrane (separates)
Middle earPharyngotympanic tube
equalizes pressure b/w middle ear and atmosphere (‘pop’)
Function of tympanic membraneOssicles (malleus, incus, & stapes)
amplify signalInner ear
Bony and membranous labyrinthsSemicircular canals for rotation
of headVestibule report on changes of
head position Saccule and utricle with equilibrium
sensors called maculaeCochlea houses the hearing organ
The CochleaScala vestibuli
Perilymph: like CSFOval window
Scala TympaniPerilymph Round window
Scala media (Cochlear duct)Endolymph: K+ rich intercellular fluidOrgan of Corti
Contains hair cells embedded in a basilar membrane Vestibular membrane Tectorial membrane bends cells as basilar
membrane moves Signal to auditory nerve
Frequency and AmplitudePitch depends on frequency
High pitch = higher frequency
Basilar membrane responsive to certain frequencies
Sounds detected as increase in AP’s by the brainGreater volume = higher
amp of generated waveVigorous vibrations in
cochlea = more bending = more AP’s
Hair cells easily damaged due to prolonged exposure to certain frequencies
Physiology of HearingPinna collects sound waves
Travel down auditory canal to tympanic membrane Moves ossicles as it vibrates
Stapes pushes on oval window, in and outCreates fluid pressure waves in scala vestibuli
perilymphPressure waves deform scala tympani to push
round window in and outPressure changes move endolymph
Pressure changes in endolymph, from perilymph changes, moves the basilar membrane
Hair cells on Organ of Corti bend as they move against the tectorial membraneGenerates nerve impulses that leave via the cochlear
nerve
AP signals from cochlea to medullaCochlear nuclei
Some fibers cross, all ascend, from olives into MGN in the thalamusPass through inferior
colliculi (reflex area) Interactions with superior
colliculi to turn toward soundSynapse in primary
auditory cortexLocalization utilizes
relative intensity and timing
http://openlearn.open.ac.uk/file.php/3373/SD329_1_027i.jpg
Auditory Pathway
EquilibriumStatic
Respond to changes only, keeps head still and balanced
Maculae embedded in otolithic membranes in saccule/utricle
Dynamic Maintenance of body position
after sudden movement Crista in ampullae of
semicircular canalsBoth operate by bending hair
cells Head movements cause fluid
movement (slower) Changes action potentials Sudden stop, but fluid still
moving = dizzy Brain interprets and
commands skeletal muscles
Motion SicknessResults from conflict between eyes and
equilibrium sensors in the inner earFeeling motion, but not seeing it (inside car)One system is hallucinating, implying toxins in
system = vomitingDramamine inhibits input from equilibrium
sensorsAstronauts learn to control