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