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Transcript
SPECIAL SENSES Making Sense of The World Sensation • relationship between physical energies in the environment & psychological experience of those energies • to perceive & detect physical energies & encode them into neural signals Basic Senses • • • • • • • • • • • • Sight Hearing Touch Smell Taste also Pain Pressure Temperature Joint position Muscle sense Movement SENSES • systems that translate outside information into activity in nervous system • gather information by detecting energies • environment contains many different forms of energies Receptors • detect only the energies have receptor for • restricted awareness • receptor cells transduce or change physical energy into a signal brain can understand Transduction • conversion of physical energies into language of brain • receptor cells convert physical energies into neural impulses which travel to cerebral cortex to be decoded • all sense signals except smell go to relay station-thalamus • from there to primary sensory areas in cerebrum-different for each sense • here they are modified and sent on to higher regions of brain Olfaction • sense of smell • • • • • • chemical sense air borne chemicals detected oldest sense all organisms have some type of chemical sense major senses in most animals help locate food, recognize trails & territories identify kin & find receptive mates • social insects send & receive intricate chemical signals which tell them where to go and how to behave • social behavior of most animals is controlled by chemical signals • olfactory receptor area in German Shepherd-72X bigger than in humans Olfactory System • humans are able to distinguish 10,000 smells • detected in paired olfactory organs in nasal cavity by specialized receptor cells found in olfactory epithelium-olfactory receptor neurons • • • • Olfactory System olfactory organs posses 2 layers olfactory epithelium lamina propria olfactory epithelium covers inferior cribifrom plate, superior perpendicular plate & superior nasal conchae of ethmoid bone • covered by mucus which contains olfactory receptors • lamina propria-comprised of areolar tissue, blood vessels, nerves & olfactory or Bowman’s glands – produce secretions that bathe surface of olfactory receptors Olfactory System • 10 – 100 million olfactory receptors • modified bipolar neurons • have terminal enlargements or knobs which project above epithelial surface • from each 8-20 olfactory cilia extend into mucus • contain smell receptors • cilia project from knob & lie parallel to epithelia surface • exposes considerable surface area to dissolved compounds • at other end of receptor cell, axons project to olfactory bulb • 10-100 axons form into bundles, penetrate cribriform plate terminate in olfactory bulb • stem cells allow neurons to regenerate Olfaction • refers to breathing in chemicals • Inhaletake in chemicals or odorants – chemicals that stimulate olfactory receptors • must be small enough to be volatile to vaporize, reach the nose & dissolve in mucus to stimulate olfactory receptors • at olfactory organswater & lipid soluble materials diffuse into mucus OLFACTION • dissolved chemicals interact with receptorsodorant binding proteins • 4 odorant molecules will activate an olfactory receptoractivates adenylate cyclaseconverts ATPcAMPopens Na channels in membrane local depolarizationdepolarization large enough action potential in axon conveyed to CNS • • • • • • Olfactory Pathways axons of receptors extend through olfactory foramina in cribiform plate to form right & left olfactory nerves terminate in brain in the olfactory bulbsaxons of bulbs extend posteriorlyform olfactory tract projects to primary olfactory cortex located at inferior & medial surface of the temporal lobe projects to hypothalamus & amygdala parts of limbic system amygdale associate experiences with smellsproducing emotion projections are sent to thalamus and to frontal cortex-recognition Olfactory Discrimination • can recognize 2000-4000 chemical stimuli • several primary smells for which thousands of receptors are needed • 1) ethereal 2) camphoraceous 3) musky 4) floral 5) minty 6) pungent 7) putrid • 1% of genes are needed to make receptor proteins to recognize smells • no distinct receptor for each detectable odor Gustation • chemical sense • chemicals are taken into the body & dissolved in oral cavity • drives appetite • protects from poisons – bitter & sour tastes produce aversive, avoidance reactions – most poisons are bitter – off food goes sour or has an acidic taste • • • • • • Taste Discrimination 5 primary sensations Sweet Salty Sour Bitter Umami – MSG – taste of beef, chicken broth & parmesan cheese • taste combined with smell gives flavor – when nose is blocked foods seem bland or tasteless Anatomy of Gustation • receptor-taste bud • 10,000 • tongue, soft palate, pharynx & epiglottis • survives about 10 days • Consists of: • taste receptors or gustatory cells • basal or stem cells • supporting cells Anatomy of Gustation • Supporting cells • surrounds about 50 gustatory receptors cells in each taste bud • one single long micovillus (gustatory hair) projects from each gustatory receptor cell to surface through taste pore • Basal cells – stem cells – found in periphery of taste buds Anatomy of Gustation • gustatory receptors – embedded in specializations of surrounding epithelium called papillae • three types contain taste buds • vallate • fungiform papillae • folliate PapillaeTypes • Vallate or circumvallate papillae – have 100 taste buds – back of tongue • Fungiform papillae – possess 5 taste buds – over entire tongue • Folliate – lateral margins – taste buds degenerate in early childhoog • Filiform papillae – no taste buds – Tactile receptors – provide friction sensations Gustatory Transduction • dissolved chemicals contact taste hairs • bind to receptor proteins on gustatory cell • causes series of chemical reactions producingaction potential Gustatory Transduction • different tastes involve different receptor mechanisms • salt receptorsdepolarize after Na channels open • sweet receptors depolarize after K channels open Gustatory Transduction Gustatory Pathways • Taste is monitored by cranial nerves VII-facial – picks up sensation from anterior 2/3rds of tongue • IX-glossopharyngeal – covers posterior 1/3rd of tongue • X-vagus – receives information from epiglottis • axons from these nerves synapse on nucleus solitarius in medulla oblongata • axons of postsynaptic neurons enter medial lemniscus & synapse in thalamus • then project to gustatory cortex conscious perception • here information is correlated with other sensory data such as texture, peppery, hot Vision • primary sense in humans • sensory organs-eyes Accessory Eye Structures • Eyelids or palpebrae – continuations of skin – blink continually to keep surfaces lubricated & things out of eyes • Palpebral fissure – gap separating free margins of upper & lower eyelids • Medial & Lateral canthus – where eyelids are connected • Eyelashes – keep foreign materials out Lateral Canthus Medial Canthus Accessory Eye Structures • Tarsal glands – sebaceous glands associated with eyelashes at inner margin – secrete lipids to keep eyelids from sticking together • Lacrimal Caruncle – medial canthus – makes a thick, gritty secretion often found in eyes after sleeping ACCESSORY STRUCTURES • Palpebral conjunctiva – epithelium covers inner surface of eye • Ocular conjunctiva – covers anterior surface –extends to edges of cornea • transparent part of outer fibrous layer ACCESSORY STRUCTURES-Lacrimal Apparatus • • • • • produces, distributes & removes tears – tears reduce friction, remove debris, prevent bacterial infections & provide nutrients and O2 to eye consists of – lacrimal gland – lacrimal canaliculi – lacrimal sac – nasolacrimal duct lacrimal gland produces key ingredients and most of volume tears accumulate at medial canthus or lacrimal lake lacrimal puncta drains lakeempties into lacrimal caniliculilacrimal sacnasolacrimal duct nasolacrimal canalnasal cavity • • • • • • • THE EYE irregular spheroid three layers or tunics outer fibrous tunic intermediate vascular tunic inner neural tunic two hollow cavities posterior, vitreous chamber – contains gelatinous vitreous body – helps stabilize shape of eye • anterior chamber – filled with aqueous humor – functions to retain shape of eyeball Fibrous Tunic • • • • • • • • • • • • • sclera & cornea Functions: mechanical support physical protection attachment site-extrinsic eye muscles housing of focusing structures Sclera white of eye site for insertion of 6 extrinsic eye muscles contains blood vessels & nerves Cornea-continuous with sclera cornea & lens comprise-refractive system focuses light on retina – where photosensitive pigments are found Vascular Tunic-Uvea • site of attachment for • intrinsic eye muscles provides route for blood & lymph regulates amount of light entering eye secretes & reabsorbs aqueous humor controls shape of lens • • • • Parts: iris cilliary body choroid • • • • • • • • THE IRIS consists of pigment cells & 2 layers of smooth muscle contraction of muscle produces change in diameter of pupil – central opening in iris controlled by ANS bright light causes constriction via consensual light reflex – parasympathic pathway dim light causes dilatation via pupillary reflex – sympathetic pathway Cilliary Body • thicken area at periphery of eye • iris is attached to it • composed of cilliary muscles CHOROID • separates fibrous & neural tunics Neural Tunic-Retina • light sensitive • thin, pigmented outer layer • sheet of melanin containing cells • thick, inner layercontains light receptors • begins visual pathway • consists of three layers Retina Layers • Photoreceptor layer • Bipolar cell layer • Ganglion cell layer • • • The Retina Third layer – light energy converted into neural activity • contains specialized photoreceptor cells-rods & cone • transduce light wavelengths into information the brain understands Second layer – bipolar cells – magnifies image First layer – ganglion cells – further adjust image – axons form optic nerve Retina • if eyes simply transferred stimuli from retina to brainimages would be blurry • images are sharpened by sending information from photoreceptor cells back through first 2 layers of retina • Bipolar cells connect photoreceptors to retinal ganglion cells • axons from ganglion cells form optic nerve Third Layer • light energy is converted into neural activity • contains specialized photoreceptor cells-rods & cones • rods cannot see color – more sensitive than cones – sensitive enough to respond to a single photon of light – basic unit of light • create coarse, gray image • adequate for seeing in poor or dim light • can make out shapes fairly well • colors are completely absent • no color vision in dim light RODS & CONES • • • • 18X more rods than cones approximately 125 million rods 6 million cones arranged to produce best possible combination of night & day vision Cones • color vision • operate in bright light • Three types • Blue • Red • Green • experience of color is due to combination of these three cones Cones • concentrated in macula leutea • center is fovea centralis • site of highest visual acuity or resolution THE LENS • transparent structure located behind pupil in cavity of eyeball • consists of concentric layers of cells, filled with crystallins – transparent proteins responsible for clarity of lens & for focusing Focusing • requires the cornea & lens • light is refracted or bent as it passes from one medium to another with different density • greatest amount of refraction occurs as light passes from air to cornea • more refraction occurs as light passes from aqueous humor to lens • lens provides extra refraction needed to focus light from object to focal point – specific point of interaction in retina • distance between center of lens & focal point is focal length PhotoPathway Horizontal cells extend across outer part of retina at level of synapses between photoreceptor & bipolar cells Amacrine cells found where ganglion cells synapse with bipolar cells Light energy must pass through both ganglion & bipolar cells to get to photoreceptor cells where light energy is converted into neural signals which activates bipolar cells One cone converges on one bipolar cell preserves precise information, provides high acuity and fine detail 1000 or more rods funnel information onto one bipolar cell increases original illumination & activates ganglion cells OPTIC NERVE Axons from 1 X 106 ganglion cells converge on optic disc circular region medial to fovea origin of optic nerve penetrates wall of eye at area known as blind spot no photoreceptors forms optic nerve which partially crosses at optic chiasm continues on to thalamus from there to other areas of cortex all at the same time Refraction • light rays reflected by object enter eye through cornea • light proceeds through pupil – size controlled by iris • behind pupillens focuses light rays into an inverted image onto retina at back of eye Refraction • lens focuses image on photoreceptors by changing shape – accommmoation • shape of lens is determined by tone of ciliary muscles • shape determined by tone of cilliary muscles Accommodation • cilliary muscles relax for far vision – zonular fibers are pulled taut lens is under tension & flat • cilliary muscle contract for near vision – releases zonular fibers from tensionlens assumes a natural, rounder & more refractive state • rounder shape increases refractive power of lens Errors of Refraction • Presbyopia – lens thickensbecomes harder won't accommodate – seen in almost all people over the age of 40 • Myopia-near sightedness – eyeball is too long Errors of Refraction • Hypermetropiafar-sightedness –eyeball is too short • Astigmatism –lens or cornea not smoothly spherical Image Formation • Final stageconstriction of pupil • pupil constricts hole narrows • due to the circular muscles of iris Photoreception • Photoreceptors detect photons of light – basic unit of visible light • light is radiant energy or electromagnetic radiation – comes in waves – referred to by wavelengths • wavelengths eyes detect are found in visible part of spectrum • can detect these because possess receptors excited by wavelengths between 400-700nm LIGHT • 2 physical characteristics of light determine sensory experience of it • Wavelength – distance of one wave peak to next – each wavelength is sensed as a color • Amplitude – indicates amount of energy – determines intensity of light • large amplitude makes for bright color • small amplitude makes dull color Photoreceptors • have outer segment containing discs • shape of outer segment provides name of photoreceptor • Rods – each disc is independent entity – outer segment forms elongate cylinder • Cones – discs are infoldings of cell membrane – outer segment tapers to tip – outer segment is connected to inner by narrow stalk • outer segments of both contain photopigment – absorbs light PHOTOPIGMENTS • one in rods • one in each of 3 cones • derivatives of rhodopsin or visual purple • consists of • protein-opsin-bound to light sensitive chromophoreretinal-made from vitamin A • Retinal-common to all photopigments – attaches to different opsins in cones – opsin determines wavelength of light that can be absorbed by retinal Photoreception • photon strikes part of rhodopsin molecule • absorbed by visual pigment • retinal has 2 possible configurations • cis & trans forms – normally retinal is in cis form • once light is absorbedcis formtrans formtriggers chain of enzymatic steps Steps in Photoreception • Step 1: Isomerization • Photon of light absorbed • Opsin is activated • cis formtrans form Step 2-Photoreception • Bleaching • trans retinal separates from opsin • Photopigment looks colorless Step 3-Photoreception Regeneration Trans retinal transforms back to the cis form Cis-retinal can bind to opsin Photopigment is functional again Color Deficiency • • • • • • • • • • Humans can discriminate 7X106 colors some have difficulty with color perception color deficient 1 out of 50 individuals gene responsible is sex-linked deficiency seen more in males than in females – 8% of males & 0.05% color deficient usually lacks either red or green opsin have difficulty distinguishing red from green (both appear the same) can’t color blend Vision is said to be di- instead of tri-chromatic Depth Perception • have binocular vision • when looking at an object a representation comes from both retinas • foveas are about 5-7.5 cm apart • visual fields for each eye slightly different • occipital cortex receives both of these images & fuses them into one picture • fusing confers perception of depth • Convergence Visual Processing • axons from all ganglion cellsoptic disc • optic nerves reach diencephalon & incompletely cross over at optic chiasm • From there ½ the fibers lateral geniculate nucleus on same side of brain • ½ the fibers continue to opposite lateral geniculate nucleus • From there image proceeds to occipital cortex via projection fibers • three anatomical areas • External – collects sound waves & directs them toward middle ear • Middle – consists of a chamber in temporal bone • Inner – contains sensory organs for hearing & equilibrium The Ear External Ear • composed of pinna – cartilaginous auricle – surrounds • external auditory canal – channels sound waves through auditory canal to • eardrum or tympanic membrane – thin, semi transparent membrane separates external from middle ear • ceruminous glands • secrete cerumen – waxy substance – needed for protection – helps keep foreign objects out of ear – helps slow infections Middle Ear • filled with air • communicates with nasopharynx through auditory or eustachian tube – equalization of pressures • contains auditory ossicles – 3 tiny bones • malleus • incus • stapes • malleus attaches to tympanic membrane • stapes is bound to oval window – opening in middle ear going to inner ear • incus lies between malleus & stapes • • • • • • • • • • Inner Ear labyrinth contains receptors for hearing & equilibrium Outer bony labyrinth encloses an inner-membranous labyrinth bony labyrinth consists of vestibule, cochlea & semicircular canals filled with perilymph fluid in membranous part is endolymph vestible comprised of membranous sacs: saccule & utricle house receptors for gravity & linear acceleration perception semicircular canals – receptors in canals provide information on head location vestibule + semicircular canals make up vestibular complex Hearing Receptors • receptors for hearing are in cochlea – spiral shaped bony chamber • divided into thee channels • cochlear duct, scala vestibuli & scala tympani • the vestibular membrane separates the cochlear duct from the scala vestibuli • the basilar membrane separates cochlear duct form scala tympani • Resting on basilar membrane is spiral organ or organ or Corti Hearing Receptors • sensory receptors are hair cells – on basilar membrane – 16 X 106 hair cells found in two groups • one-inner group arranged in a row • outer group arranged in three rows • free surface of each hair cell contains 40-80 stereocilia – similar to long microvilli • tectorial membrane covers the hair cells Audition • detection of sound • stimulus is sound waves – from compression & rarefaction of air-or alternating air pressure • distance between pressure peaks is wavelength • frequency determines pitch – measured in terms of cycles or waves per second called hertz-Hz – humans detect sounds in frequency range from 20 to 20,000Hz • • • • longer waves produce lower frequencies & lower pitches shorter wavelengths make higher frequencies & higher pitches amplitude determines loudness greater amplitude louder a sound Sound • measured in decibels • 0 decibels=absolute threshold • 10 decibels indicates 10X increase • normal conversationaround 60 decibels • passing train-about 100 • above 80 damages hair cells • uncomfortable at 120 • painful above 140 Transduction of Sound • when we speak vocal cords vibrate molecules of air movebump into one another producing waves of compressed, expanded air • ears detect these waves & transduce them into nerve impulsesbrain decodes as sound • sound waves enter via external earcontinue on to tympanic membrane • air molecules under pressure cause tympanic membrane to vibrate Transduction of Sound • movement of tympanic membrane displaces auditory ossicles • first malleus vibrates • handle of malleus strikes incus causing it to vibrate • vibrating incus moves stapes • vibrates oval window • total force transferred to oval window – because window is much smaller force per unit area increases 15-20X. • vibrations of oval window produce pressure waves that vibrate perilymph in vestibular duct • these waves distort basilar membrane on way to round window of tympanic duct • location of maximum distortion varies with frequency Frequency Coding • basilar membrane is narrow and stiff at window end • wide and flexible at apical end • topographical difference results in different regions vibrating at different frequencies • end near stapes (window end) vibrates at high frequencies • apical end vibrates at low frequencies Transduction of Sound • pressure waves continue into endolymph inside cochlear duct • pressure waves in endolymph cause basilar membrane to vibrate which moves the hair cells of spiral organ against tectorial membrane • leads to bending of stereocillia & generation of nerve impulse Transduction of Sound Auditory Pathways • • • • • • • • • • bending of hair cells opens potassium channels Produces depolarizing potential opens calcium channels causes neurotransmitter vesicles (probably glutamate) release generates nerve impulse impulses pass along axons of forming cochlear branch of vestibulocochlear nerve (VIII) axons synapse with neurons in cochlear nucleus in medulla some axons cross over & ascend in lateral meniscus & terminate in inferior colliculi in midbrain other axons form cochlear nuclei end in superior olivary nucleus in pons • • • • • Localization of Sounds requires binaural fusion brain compares information received from each ear ears are about 6 inches apart makes for intensity differences & time lags to brain very small but allow for stereophonic or 3dimensional hearing • auditory system can detect minute differences • time difference of 0.000027 seconds is all that is needed to be able to identify direction from which 2 sounds are coming • localization is quite accurate unless sound is located directly ahead, behind, overhead or beneath ears-equidistant from both Hair Cells • 16,000 hair cells • extremely vulnerable • overexposure to loud noises, disease, heredity or aging most humans will lose 40% of hearing by age 65 • once destroyed hair cells cannot regenerate Equilibrium • vestibular sense • sensation provided by vestibular complex • Two types • Static • Dynamic Static & Dynamic Equilibrium • Static – maintenance of position of body (mainly head) relative to force of gravity – know where head is when it is tilted • Dynamic – maintenance of body position (mainly head) in response to sudden movements, such as rotational deceleration or acceleration – know where head is if it moves quickly Vestibular Sense Receptors • Vestibular apparatus • Saccule • Utricle • Semicircular ducts Saccule & Utricle • Otolithic organs • walls contain macula • houses receptors for equilibrium • contains two types of cells • 1) hair cells-sensory receptors 2) supporting cells Saccule & Utricle • hair cells of utricle & saccule have 40-80 stereocillia of grduated height & one kinocillium • Longer than longest stereocilia • steorcillia are connected by tip inks • Together sterocilia and kinocillium are-hair bundle Saccule & Utricle • supporting cells secrete a gelatin like glycoprotein layer called otolithic membrane • rests on hair cells • layer of dense calcium carbonate crystals called otoliths extend over surface of otolithic membrane Equilibrium • when head is upright statoconia sit on top of macula – weight presses down • when head is tiltedstatoconia shift to sidedistorting hair cells • sends information to CNS that head is no longer level Semicircular Ducts • contain receptors which respond to rotational head movementsdynamic equilibrium • anterior, posterior & lateral semicircular ducts are continuous with utricle • each semicircular duct has an ampulla-expanded region containing hair cells • hair cells attached to wall of ampulla form crista • each crista consists of hair and supporting cells • covering the cells is a gelatinous structure- cupula Vestibular Sense • when head is rotatedendolymph movespushes cupula distorts processes of receptor • gluid movement in one directionstimulates hair cells • movement in other directioninhibits hair cells Vestibular Sense & Equilibrium • • Hair cells of vestible & semicircular ducts are monitored by sensory neurons-vestibular ganglia Branches form cranial nerve 8vestibulocochlear nerve – innervates vestibular nuclei located between pons & medulla • • • • • nuclei send information to cranial nerves: III, IV, VI and XI-involved with eye, head and neck movements information is then sent down vestibulospinal tracts of spinal cord adjusts peripheral muscle tone & complements reflexive movements of head & neck nuclei also connect with cerebellum to coordinate movement one spins very fast & stops abruptly, liquid cannot return to normalfeel dizzy Neural connections are also made with ANSdigestive system partnausea.
