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Senses: Classification Sensory Process1. Sensation refers to the activation of sensory receptors & generation/transmission of an AP by those sensory receptors to the brain2. Perception refers to Classification1. General Senses senses wide spread throughout the body & are simple senses a. ex: sense of touch &/or pain2. Special Senses utilized senses that are localized in a particular region of the bodya. ex: smell &/or taste there are 5 special senses:1. Olfactory sense smell, nasal utilizes the olfactory receptors localized in the nose2. Gustatory sense taste, mouth utilizes the gustatory receptors localized within the taste buds of the tongue3. Visual sense sight, eyes utilizes photoreceptors localized within the eyeball4. Auditory sense hearing, ear utilizes hair cells localized within the inner ear5. Vestibular sense balance & equilibrium, ear utilizes hair cells localized within the inner ear

Sensory Receptors: Classification According to their structure, sensory receptors can be classified as:1. Simple composed of unipolar, sensory neurons** refers to both simple & complex receptors the unipolar, sensory neurons have a simple process that splits into 2 branches close to the cell body of the neurona. 1 of the branches is the receptor of the neuronb. the other/outer branch synapses with the secondary sensory neuron Structure:a. generally lack myelin sheaths, unmyelinatedb. have free nerve endings dendrites are free ex: nociceptors (pain receptors; sensation of pain) & thermoreceptors (allows to perceive various temperatures) that are in the skin. utilized by general senses2. Complex composed of unipolar, sensory neurons Structure:a. axons are myelinated causing transmission of AP to be fasterb. nerve endings are closed dendrites are enclosed within several layers of CT forming a capsule ex: tactile receptors (allows to perceive sensation of touch) in the skin utilized by general senses3. Special composed of non neuronal cells highly complex & highly modified epithelial cells utilized by all special senses except for the olfactory sensea. Olfactory sense utilizes a bipolar neuron

According to where the stimulus originates, sensory receptors can be classified as:1. Exteroceptors located in the periphery of the body, superficially (exterior of the body) best suited for detecting external stimuli examples include:a. tactile receptorsb. nociceptorsc. thermoreceptors *all those receptors are located towards the surface of the body (in the skin) & therefore is activated by external stimuli such as mechanical energy, touch, heat, etc.

2. Interoceptors located deep within the body; typically within visceral organs best suited for detecting internal stimuli (stimuli that arises from the body) examples include:a. central thermoreceptors in the hypothalamus that monitor temperature b. baroreceptors in the aorta that monitor BP3. Proprioceptors located within the skeletal muscle tissue & joint cavity communicates with the cerebellum the location of the limbs (arms & legs) relative to the trunk of the body to maintain balance

According to type of stimuli to which they respond, sensory receptors can be classified as:1. Mechanoreceptors activated by mechanical energy (via the physical deformation of the cell membrane) examples include: a. osmoreceptors - within hypothalamus & regulates the blood osmolarity of the body by shrinking/expanding depending on concentrationb. tactile receptors in the skin; when you touch something, it will deform the cell membrane of the receptor, activating the tactile receptor = resulting in the perception of touch2. Chemoreceptors activated by various chemicals/ligands that bind to the receptors located within the cell membranes of the cells examples include:a. olfactory cells that processes smell binding of chemicals of various odors simulates the olfactory cells resulting in perception of various smells/odorsb. gustatory cells that processes taste binding of various chemicals of food, drinks, etc simulate the gustatory cells resulting various perceptions of taste sweet, sour, salty, etc.i. ex: enzymes such as amylase in the saliva, break down carbohydrates in food to maltose, glucose, etc & it is those broken down compounds the maltose & glucose, etc that will then simulate the gustatory cell)3. Thermoreceptors activated by various degrees of heat a. heat refers to types of kinetic energy (movement of molecules) allows to determine when an object is hot or cold to touch4. Electromagnetoreceptors activated by various forms of electromagnetic energy examples include:a. photoreceptors activated by photons of visible light rods & conesb. some receptors not found in humans: infrareceptors activated by infrared energy of the light/electromagnetic spectrum i. found in some snakes (ex: rattlesnake) infrareceptors in the tip of the snakes head detects infrared energy emitted by another animal, in which the animal will appear glowy to the snake, enabling them to detect & attack their prey in complete darkness electroreceptors activated by electrical fieldsi. all living things have an electrical field due to the generation of AP, nerve impulses = electricityii. found in sharks electroreceptors within their head enables sharks to detect their prey that is hidden, buried in the sand, &/or camouflaged magnetoreceptors activated by magnetic fieldsi. found in some migratory birds magnetoreceptors in the outstretch of the neck allow birds to correlate their magnetory paths with the magnetic field of the earth (north pole/south pole)

According to the level of adaptation (refers to a process by which the sensory receptors adapts to a certain stimulus & shuts off, ceasing to generate an AP towards the brain), sensory receptors can be classified as:1. Tonic receptors slow adapting receptors that continue to generate an AP as long as the stimulus is present (does not shut down) ex: pain receptors2. Phasic receptors fast adapting receptors that generate an AP once stimulus is applied, then adapts to the stimulus, & shuts down, ceasing to generate an AP ex: tactile receptors, or olfactory sense (odors/smell that you are initially aware of & get used to as time progresses where you do not notice it anymore)

Sensory Process consists of 5 related processes:1. Sensory Reception refers to the detection of the environmental energy/stimulus by sensory receptors & activate different receptors examples:a. sensory receptors in the eyeball detect photons (stimulus) in visible light & be activatedb. hair cells in the inner ear detect sound waves & be activated2. Sensory Transduction a complex process by which sensory receptors convert the energy of an environmental stimulus into chemical energy (changing the membrane potential of the receptor cell depolarization & hyperpolarization) leading to the activation of the sensory receptor & generation of APs toward the brain3. Sensory Amplification occurs when an environmental stimulus is too weak to activate a sensory receptor, & the energy of the environmental stimulus is therefore, amplified, before it can activate a sensory receptor example:a. sound waves do not possess sufficient energy by themselves to activate the hair cells of the inner ear so the energy of the sound waves must be amplifiedb. the auditory ossicles (malleus, incus & stapes) of the middle ear amplifies the energy of sound waves up to 25x, making it sufficient enough to activate the hair cells of the inner ear4. Sensory Transmission refers to the propagation of AP/nerve impulses from some sensory receptor towards the brain via the ascending pathway of the spinal cord

5. Sensory Integration all APs generated by a stimulus are put together/integrated, giving rise to conscious perception of the stimulus by the brain example:a. visual information projects into the thalamus & ultimately ends at the primary visual cortex of the occipital lobe, allowing us to seeb. auditory sensory information projects to the thalamus & then the primary auditory cortex of the temporal lobec. olfactory information from the nasal cavity projects into the primary olfactory cortex of the temporal lobed. gustatory information from the gustatory cells of the taste buds, project to the primary gustatory cortex of the insular lobeCh. 15 Sensory System Senses (Classification & Processes)2/4/15 6:06 PMe. information relating to touch, projects to the primary somatosensory cortex of the parietal lobe (post central gyrus)

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Sense of Touch Sense of touch utilizes the tactile receptors in the skin, there are 2 varieties of tactile receptors:1. Simple Structure:a. lack myelin sheaths, unmyelinatedb. free nerve endings: project deep into the epidermis of the skin come in 2 varieties:i. nociceptors record the sensation of painii. thermoreceptors activated by various degrees of heatc. root hair plexus: located around the root of the hair follicle responsible for detecting the movement of haird. tactile discs: represent flattened parts of dendrites which synapses with a specialized tactile cell located within the basal layer of the epidermis responsible for detecting light or fine touch2. Complex Structure:a. contain myelin sheaths, myelinated axonsb. dendritic ends enveloped within the several layers of CT capsule*from deep to superficial*c. lamellated corpuscles: located deep within the dermis responsible for detecting deep pressure & high frequency vibrationsi. activated by deep tissue massages (pressure) & electric toothbrush (high frequency vibrations)d. bulbous corpuscles: activated by the distortion of the skin (stretching of the skin; ex: pulling on the skin to stretch it)e. end bulbs: located in the midsection of the dermis (more superficial relative to lamellated corpuscles) responsible for detecting light pressure & low frequency vibrationsf. tactile corpuscles: located on the border of the dermis & epidermis responsible for the sensation of discriminative touchi. allows to identify an object by its texture & shape

Referred Pain Referred pain is a phenomenon by which the brain interprets a sensation, not coming from the visceral organ itself, but from the skin overlaying that visceral organ it involves 2 neurons:1. somatic sensory neuron: carries somatosensory (touch) info towards the brain2. visceral sensory neuron: carries the sensory info from the internal organs towards the brainthe 2 neurons enter the posterior form where their 2 pathways merge together, which then confuses the brain of the true origin of the stimulusreferred pain is typically present in patients experiencing a heart attack, & report a shooting pain down their left arm (usual symptom of a heart attack)during a heart attack, the cardiac muscle tissue is being deprived of oxygen & the tissue starts to dieas the tissue starts to die off, it releases chemicals that activate nociceptors the nociceptors then activate the visceral sensory neuron, leading toward the brainduring the heart attack, the patient will feel a shooting pain down their left arm, where nociceptors in that arm are then activatedthe nociceptors in the left arm activate the somatic sensory neuron, leading toward the brain, to report the pain from the skin associated with the left armas both visceral sensory & somatic sensory neurons travel towards the brain, they merge in which they share a common pathway to the primary somatosensory cortexCh. 15 Sensory System Touch 2/4/15 6:06 PMwhen both neurons reach the primary somatosensory cortex, the brain mistakenly interprets the sensation of pain coming from the skin of the left arm rather than from the internal organ

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Vision: Accessory StructuresOrbit:structure that supports & protects the eyeballs within the bony depressions in the skull formed by the fusion of 7 facial bonesEyebrows: consists of short & thick hairprotects the eyes by:providing shade against direct sunlightpreventing sweat (on the forehead) from entering the eyesEyelids (including eyelashes):protects the eyes in various ways:Reflexive blinking (occurs every 7-8 seconds) provides protection by:moving the lacrimal fluid (tears) across the anterior surface of the eyeballs, preventing the eyes from drying out & therefore, keeping the eyes moistpreventing foreign objects/debris (ex: dust) from entering the eye & landing on the anterior surface limiting the amount of light that can enter the eyeballSkeletal muscles associated with the eyelids:*both skeletal muscles contract to open/close the eyes)Orbicularis oculi closes the eyelids Levator palpebrae superioris opening the eyelids Glands associated with the eyelids:Ciliary glands sebaceous glands located at the base of the eyelashes that produce oily secretions to lubricate the eyelashes, preventing it from drying out & being prone to breakageTarsal glands set of ciliary glands (sebaceous glands) located at the base of each eyelid (superior & interior) that produce oily secretions to prevent the eyelid from sticking to one another as we blinkConjuctiva:thin, transparent, mucous membrane made up of stratified squamous epithelium (multiple layers of flat cells)conjuctiva divides into 2:ocular conjuctiva covers the anterior surface of the eyepalpebral conjuctiva covers the inner surface of each eyelid & continues with the ocular conjuctiva it is a very vascular tissue; it contains a large supply of blood vesselsallows it to heal rapidly if damagedit is instrumental in protecting the lower layers of the eye, mainly the sclerasclera is avascular lacks blood supplyit heals slowly if damagedConjuctivitis (pink eye): inflammation of the conjuctivacaused by a bacterial infection highly contagioustreated by antibiotics Lacrimal Apparatus:Lacrimal glands:located laterally & superiorly to each eyeproduces lacrimal fluid (tears) which are composed of:water prevents desiccation (drying) of the eye & keeps the eyes clean by washing out any foreign objects/debris (dust) as it flows across the anterior surface of the eyelysozyme an antimicrobial agent that destroys the cell wall of bacteria, allowing it to swell up with water & cause it to lyse openexcess lacrimal fluid (tears) drains via the lacrimal canaliculithe lacrimal canaliculi are little channels that go into the nasolacrimal ductthe excess lacrimal fluid then goes into the nasal cavitylacrimal fluid keeps the nasal cavity moistimportant in air conditioning in which the lacrimal fluid adds moisture to the incoming airExtrinsic Ocular Muscles:these skeletal muscles attach to the eyes & contract to move the eyes6 muscles associated with each eye are divided into 2 groups:Rectus:Superior: moves the eyes upInferior: moves the eyes downLateral: moves the eyes away from the midline of the bodyMedial: moves the eyes towards the midline of the body

Oblique: divided into 2 oblique muscles:Superior obliqueInferior obliqueboth oblique muscles are responsible for rotating the eyes lightly on its axisnormally the actions/movements of the eyes are coordinated, so that the eyes move in parallel a process known as conjugated case

Vision: the Eyethe eye is a hollow sphere, where the wall of this hollow sphere is made up of 3 layers:Fibrous coat/tunic outer layer made up of 2 (avascular) structures:Sclera thin, firm, opaque & white part of the eyecovered & protected by the ocular conjuctivamade up of dense, irregular CTcontains tough collagen & elastic fibers that give shape to the eye & protects its innermost structure mainly the lens & photoreceptors in the back of the retinagives points of attachment for the extrinsic ocular musclescontains sensory receptors for painit transitions interiorly, giving rise to the dome shaped corneaCornea transparent portion of the eyeconvex cornea is responsible for the refraction/reflection (bending of the light rays) as part of the focusing system of the eyeit is covered & protected by the corneal epithelium which is continuous with the ocular conjuctivacells of the corneal epithelium contain nuclear ferritinnuclear ferritin protects the cells DNA from UV light exposureUV light is a carcinogen, a cancer causing agentwithout nuclear ferritin, UV light can mutate the DNA, causing it to transform & become cancerthe corneas transparent structure allows light to enter the eye through the pupil corneal transparency is attributed to 3 things:smaller collagen & elastic fibers (& more proteoglycans)cells & fibers are arranged in a regular pattern which allows for light rays to pass in between themlow water content prevents the scattering of the light raysthe avascularity of the cornea allows for few complications with corneal transplantsthe cornea does not have a direct blood supplyso White Blood Cells do not have access to the newly transplanted corneawithout access, WBCs cannot recognize the new cornea as foreign & therefore, cannot initiate a new response to destroy the tissue Vascular coat/tunic middle layercontains a large amount of blood vesselscomposed of the Choroid:contains pigment producing melanocytesmelanocytes produce melanin (brown black pigment)melanin absorbs refracted & reflected light to minimize the glare within the eyethe choroid gives rise to 2 structures:Ciliary bodyconsists of the ciliary process that produces the aqueous humor the aqueous humor is the fluid that fills the anterior cavitythe anterior cavity is the space that extends from the lens to the corneathe ciliary process & associated ciliary muscle (both make up the ciliary body) are attached to the chrystalline lens via fibers/strings called suspensory ligamentsit is responsible for regulating the shape of the lens through the contraction of the smooth muscle, a process known as Lens Accommodation the lens system is involved on focusing the image on the back of the retinaDistant Vision when a person looks at an object at some distance from them:ciliary muscles automatically relaxsuspensory ligaments become tautthis then causes the chrystalline lens to assume a flattened shapethis then allows for the object at some distance to be precisely focused on the back of the retinaNear Vision when a person switches their gaze to a nearby object:the ciliary muscles automatically contractsuspensory ligaments relaxcausing the chrystalline lens to assume a spherical shape allowing the light rays to be precisely focused on the back of the retina resulting in a clear imageIris (the colored part of the eye)the color of the iris is determined genetically eye color is a complex trait determined by several genes (hereditary) & is modulated by environmentvarious amounts of melanin give the iris a different color:a great amount of melanin = brown black irisan intermediate amount of melanin = yellow green irislittle amount of melanin = results in a blue irisit is responsible for controlling the diameter of the pupil & regulating the amount of light that enters the eye, a process known as Pupil Accommodationit is made up of 2 sets of smooth muscles:Radial group: the dilator pupillaein low light, the dilator pupillae contracts increasing the diameter of the pupilCircular group: the sphincter pupillae in bright light, the sphincter pupillae contracts decreasing the diameter of the pupilthis prevents excess light from damaging the sensitive photoreceptors in the back of the eyeRetinal coat/tunic inner layersubdivides into 2 layers:pigmented layerlies next to the middle layer (vascular coat/choroid) of the eye made up of simple, cuboidal epithelial a single layer of melanocytesthe melanin produced, absorbs any light rays that escapes the photoreceptors to prevent the destruction of light rays from reflecting inside the eye, distorting the visual image neural layerconsists of several types of cells:photoreceptors:consists of rods & cones (the functional unit of site)conducting neurons:consists of:bipolar cells synapses with photoreceptors at 1 end & synapses with the ganglion cells on the other endganglion cells its axons form a collection which leads the eye to form the optic nerve leading to the brain responsible for transmitting APs from photoreceptors towards the brain (primary visual cortex of the occipital lobe)association neurons:includes:Horizontal cells synapses with photoreceptors & the amacrine cellsAmacrine cells synapses with horizontal cells & ganglion cellsmini processors involved in the modification of signals generated by photoreceptors; clean up the visual image before sending it to the brain neurogliaprovides physical & metabolic support to photoreceptors ex: Mullers cellslarge cells that transverse the entire neuronal layerform a blood retinal layer which prevents various toxic chemicals from the blood from penetrating & contacting the photoreceptors photoreceptors need to be protected since they are non dividing cells, so once they are gone - theyre gone foreveras the light rays enter the eye, the light rays have to penetrate through both the ganglion & bipolar cells before making contact with photoreceptors to stimulate themthe APs generated by bipolar cells travel in the opposite direction from the bipolar cells to the ganglion cells to the axons which form the optic nerve to the primary visual cortex of the occipital lobe of the brain

Cavities of the EyeAnterior cavityextends from the lens to the corneafilled with aqueous humor (produced by the ciliary process of the ciliary body)the aqueous humor continuously formed & as it travels, it exits the posterior chamber through the pupil, enters the anterior chamber & drains from the anterior cavity into the scleral venous sinuses that is filled with blood (similar to dural venous sinuses which drain blood away from the brain)as it forms with the blood, it carries various nutrients (amino acids, glucose, oxygen etc) to supply it to avascular tissues the sclera & corneasubdivides into 2 chambers:anterior chamber space between the iris & cornea posterior chamber space between the lens & iris Posterior cavityextends from the lens to the back of the eye (the inner, retinal coat)filled with vitreous humorjelly like substanceprovides for pressure, which along with the sclera, maintains the spherical shape of the eyeimportant for focusing the light rays to the back of the retina to form crystal clear imagespressure created keeps the retinal coat attached to the eye puncture wounds to the eye can cause the vitreous & aqueous humor to leak out of the eye in which the pressure becomes lost, causing the retinal coat to detach from the back of the eye, potentially severing the optic nerve, resulting in permanent blindnessCh. 15 Sensory System Vision & Eye2/4/15 6:06 PM

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Refraction of Lightrefers to the process of bending the light rays every time light passes through the medium of an optical density (ex: air) into another optical density (ex: water), the light rays are bent ex: spoon placed in water appears bent (optical illusion)4 eye structures responsible for the refraction of light:Cornea its convex, dome shape allows for it to perform the largest degree of refraction Aqueous humor contributes to the refraction of lightLens only structure that can change shape via lens accommodation to precisely focus the light rays on the back of the retina to produce a clear imageloss of its ability to change shape or loss in the shape of the eye would cause the light rays to be focused either in front or back of the retina resulting in blurred visionVitreous humor contribute to the refraction of light

Photoreceptorsact as tranducers 2 types include:Rods involved with monochromatic (black/white) visionactivated by low intensity lightallow us to see in darkness (night vision)Conesactivated by high intensity lightinvolved with visual acuitythe ability to see objects in fine detailex: reading a book rich in fovea centralis & macula lutea (surrounds the fovea centralis)as you move away to the periphery of the retina, the rods become more exclusiveboth rods & cones contain lectin membranes known as discs discs are made up of a phospholipid bilayer photopigments are embedded in the membranePhotopigmentmade up of 2 proteins:opsinretinal (derived from vitamin A)when light hits the photopigments in the rods/cones, it bleaches the opsin & retinal separate the separation causes the photoreceptors to become hyperpolarized hyperpolarization removes the inhibition on bipolar cells to allow them to generate APs that are propogated via ganglions & optic nerve towards the brain Optic disk blind spotcontains no photoreceptorsno image can be formed in this areaarea where axons of the ganglion cells leave the eye to form the optic nerve which carries the AP from the photoreceptors to the thalamus & then to the primary visual cortex of the occipital lobe where all the APs are integrated to from an image Macular degeneration loss of photoreceptors in the fovea centralis & macula lutea results in central blindness where individual cannot see or perceive an image in the central area of the retinaperipheral vision remains in tact

Cones & Colorelectromagnetic spectrum consists of waves of different wavelengths & frequenciesUV light wavelengths 700nmunable to activate photoreceptors as they lack infrared receptorsunable to perceive UV light

Dark & Light AdaptationDark adaptationoccurs when you enter into a dimly lit room at 1st, you see blackness & after a minute, you are able to see objects in the room the cones cease to function as they are only activated by bright lightrods are activated by low light & slowly take over the photopigments become bleached & takes time for retinol to recombine with opsin to make the rods functional, allowing us to see during low lightLight adaptationoccurs when you enter from a dark room into a light roomat 1st, you see a white glaremass activation of cones & rods occur, generating APsall the APs & the brain result in the white glareCh. 15 Sensory System Eye & Light2/4/15 6:06 PMafter a minute or 2, photopigments within rods that have been bleached will make the rods non-functional, which decreases the number of APs reaching the brain = restoring vision

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Disorders of the Eye *most common eye conditions are myopia & hyperopia*Myopia: near sightednessresults from the change of shape of the eyeeye assumes an elongated shape where light rays are focused in front of the retina rather than on top of the retinacauses the the blurriness of the visual imagecharacterized by the inability to see objects far away & can only see objects near the eyetreatment includes convex corrective lens & lasik eye surgery

Hyperopia: far sightednessresults from the change of shape in the eyeeyeball assumes a compressed shape where light rays are focused behind the retina rather than on top of the retina results in the blurriness of the visual imagecharacterized by the inability to see nearby objects, can only see objects far from the eyetreatment includes concave corrective lens & lasik eye surgery

Presperopiaoccurs with aging where the lens loses its elasticityloss of elasticity makes it more difficult for the lens to change shaperesults in the blurriness of the visual image

Astigmatismresults from the irregular curvature of the cornea certain light rays are focused in front of the retina & some behind the retina resulting in irregular spots of blurriness across the visual field treatment includes corrective lens

Glaucomaresult of the increase of intraocular pressure within the eyeaqueous humor flows to the posterior chamber, through the pupil, into the anterior chamber & drains away into the blood via scleral venous sinuseswhen scleral venous sinuses are clogged & the aqueous humor is not being drained, it results in a build up of the fluid aqueous humor built up pushes on the lens, causing the lens to push on the vitreous humor the vitreous humor applies pressure on the photoreceptors in the periphery of the retina, killing themleads to loss of peripheral visionif not treated, photoreceptors in the fovea centralis & macula tulea will also degenerate, resulting in the loss of central vision & complete blindnesssymptom of flashing occurs where build up of aqueous humor activates certain photoreceptors, resulting in the firing of APs = flashing

Cataractsrefers to the clouding of the lens, making the lens a less transparent structureless transparency results in decreasing the ability to transmit light rays back into the posterior cavity primary cause is exposure to UV light/radiation, & over time, changes the chemical structure of the lens, leading to the uniform blurriness across the visual fieldother causes include cigarette smoke (toxins tar, which changes the chemical position of the lens & over time changes transparency)treatment surgically take lens out & replace lensboth tissues are avascular in which they lack a direct blood supplyWBCs cannot make contact with new lens & are unable to recognize it as foreign, so it wont destroy it

Color Blindness (ex: inability to determine red & green apart)certain cones are not being stimulated & are defective (ex: red & green cones)hereditary, genetic disorderX linked recessive allelepredominantly affects males

Treatment for some eye disorders include:Lasik eye surgery involves the change of shape of the cornea, to modify the focal point of light rays to the back of the retinacorrective lenses - modifies the focal point of the light rays so that it will focus on top of the retina rather than in front/behind it transplants

Ch. 15 Sensory System Eye Disorders2/4/15 6:06 PM

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Ear: Structure of HearingThe ear divides into 3 regions:External Ear (outer region)made up of:Auricle fleshy outer portion with associated holes known as pinnaeresponsible for the localization of sounddamage to the auricle or pinnae results in deafness & difficulty in localizing the origin of the soundex: cauliflower ear often occurs in wrestlingdamage to the auricle causes it to proliferate with respect to the CT, resulting in the difficulty/inability to localize the origin of a soundExternal Acoustic Canaltube that connects the auricle to the tympanic membraneresponsible for conveying sound waves towards the tympanic membranecanal is lined with fine hairs & ceruminous glandsceruminous glands produce cerumen (ear wax)ear wax is composed of various alkaline components giving it a bitter tasteit acts as an insect repellant, keeping insects away from the tympanic membraneTympanic Membrane (ear drum)thin, transparent epitheliumit is highly vascular, therefore, it can heal quickly to restore hearing (heals in about week)rupture in this membrane results in temporary loss of hearing in the affected earcommon in small children who may proliferate the membrane by poking the ear with a small objectthose who are suffering from middle ear infections some children have a tube inserted in the membrane to drain the excess or build-up of fluid within the tympanic cavityseparates the middle ear from the outer ear

Middle Ear (middle region)includes:tympanic cavity (air filled)contains a bony depression that separates the inner ear from the middle earthe bony depression is incomplete, consisting of 2 windows covered by thin membranes:vestibular window oval in shapecochlear window round in shape connected to the nasal cavity via the auditory tube houses auditory ossicles:functions to amplify the energy of sound waves up to 25x due to the difference of surface area between the tympanic membrane & the vestibular (oval) window composed of 3 bones:Malleus articulates on one end of the tympanic membrane & the incus on the other endIncus articulates with the stapesStapes smallest bone in the human body (smaller than a grain of rice)connects to the vestibular (oval) window2 skeletal muscles are found in the tympanic cavity:during loud noise, both skeletal muscles reflexively contract to pull the auditory ossicles apart to decrease the ability of the ossicles in amplifying the energy of the sound wavesthis prevents the sensitive hair cells in the inner ear (responsible for the sense of hearing) from being damaged the 2 skeletal muscles are the:Tensor tympani large muscle that attaches via tendon to the Malleus boneStapedius attaches to the Stapes boneauditory tubeconnects the tympanic cavity to the nasopharynx of the nasal cavityequalizes the pressure within the tympanic cavity & the atmospheric pressure of the outside air ex: flying in an airplanedue to the low atmospheric pressure of the outside air, the auditory tube collapses causing the tympanic cavity to fill up with airthe build-up of air in the tympanic cavity increases the pressurethe pressure then pushes the tympanic membrane out resulting in a decrease of hearingto remedy the pressure, individuals may swallow or yawn which reopens the auditory tube temporarily which allows the pressure to leave the tympanic cavity, therefore decreasing the pressure & restore hearing to normalMiddle ear infectionsinflammation of the tympanic membranemore common in little children the auditory tube is not fully developed, in which it lies horizontally (rather than in a slope in adults), connecting the tympanic cavity directly to the nasopharynxthis allows for mucus from the nasal cavity to enter the tube & accumulate within the middle earex: the common coldthe nasopharynx is affected, where the bacteria can spread from the nasopharynx (via the auditory tube) to the tympanic cavity causing an infection in the middle earduring development, the auditory tube repositions itself more vertically, making it more difficult for the mucus in the nasopharynx to travel to the tympanic cavity, decreasing the likelihood of a middle ear infection

Inner Earmade up of the labyrinth:membranous labyrinth is enclosed within the bony labyrinthmembranous labyrinth: contains the fluid endolymph bony labyrinth: contains the fluid perilymph divides into 3 regions:Vestibule smallest region responsible for static equilibriumrefers to the ability of the brain to determine the position of the head relative to the trunk of the bodyresponsible for the linear acceleration of the head (both horizontal & vertical planes)2 regions of the head contributing to the acceleration are:Utricleoriented parallel to the base of the skullhorizontal acceleration = riding in the carSaccule oriented perpendicular to the skullvertical acceleration = riding the elevator up/downthe macula is found within the utricle & sacculethe macula consists of hair cells & sustentacular cellsthe stereocilia of hair cells are embedded within the otolithic membranecomposed of a gelatin layerotoliths are little crystals embedded in the gelatin layerresponsible for static equilibrium & linear acceleration (includes the opening of the Na+ channels)ex: tilting head backwards- as you tilt your head backwards, the force of gravity pulls on the otolithic membrane, causing the stereocilia to bend backwards thus activating the hair cells (tonic; consistently generating APs toward the brain) & increases the amount of APsex: tilting head forwardgravity causes the otolithic membrane to slide in the opposite direction, bending the stereocilia forward, activating the hair cells (tonic) but decreases the amount of APs reaching the brain Semicircular canals 3 canals attached to the vestibule responsible for the angular movement composed of ampullae (found at the base)Cristae ampullaris involved in detecting the angular acceleration (rotational movement)Hair cellsStereocilia emedded in the cupulatonically active (continuously generating APs)Sustentacular cellsCupulaExtraocular skeletal muscle movement of the eyescerebellum coordinates with the contraction of the extraocular skeletal muscle to track the visual field during rotational movementpart of the membranous labyrinth (contains perilymph)as you rotate, the endolymph circulates in the direction of the rotation (left/right) within the semicircular canals & the cupula (as well as stereocilia) becomes bent; the cell membrane deforms, activating the hair cells to generate greater frequencies of APs reaching the cerebellum of the brain this allows the brain to determine which way the body is rotatingsuch sensory information & information from propioreceptors are integrated within the cerebellum to maintain the appriopriate muscle tone & to shift the position of the lymphs to shift the weight in order to maintain balance Cochlea attached to the vestibule houses hair cellsinvolved in the sense of hearing sending nerve impulses to the primary auditory cortex of the temporal lobe of the cerebrummade up of 3 chambers Scala vestibuli (upper) part of the bony labyrinth & contains perilymphCochlear duct (middle) separated from the scala vestibuli (via the vestibular membrane) & the scala tympani (via basilar membrane)represents the membranous labyrinth containing endolymphScala tympani (inner) part of the bony labyrinth, containing perilymph includes the spiral organ (organocorti)lies on top of the basilar membraneseparates the cochlear duct from the scala tympaniconsists of 2 types of cells:Hair cells considered the functional units of hearingtectorial membrane (gelatinous cavity) hovers over the hair cellsstereocilia are projections of the hair cells partially embedded within the tectorial membrane hair cells synapses with dendrites of the sensory neurons, where the axons form the cochlear nerve leading to the brainhair cells are mechanoreceptors & transducersSustentacular cells provide physical & metabolic support to the hair cells Ch. 15 Sensory System Ear 2/4/15 6:06 PM

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Sound Transmission through the Earany object that generates vibration is capable of generating sound waves (ex: vocal cords of a person generate vibration that the teeth, tongue, & lips, etc of the oral cavity controls to make a sound) the sound waves propagate through a medium (ex: air, water, etc) to a receiver (ex: human ear or cell phone when recording, etc)

*how sound waves travel in the ear when a person is talking to you*the auricle & pinnae of the external ear localizes the sound waves generated by a person talking to them (voice)it then directs the sound waves through the external acoustic meatus/canal toward the tympanic membranethe sound waves cause the tympanic membrane to oscillate (vibrate up & down)the vibrations are then transferred to the auditory ossicles (malleus, incus & stapes) to amplify the energy of the sound waves enough to stimulate the hair cellsamplification occurs due to the differential surface area between the tympanic membrane & the vestibular oval window concentrates the sound waves from a larger surface area (tympanic membrane) to a smaller surface area (oval window)stimulation of the hair cells by the sound waves results in the perception of hearing the sound waves in the stapes cause it to beat on the oval window, creating a pressure, generating a fluid wave within the scala vestibuli chamber the fluid wave disturbs the basilar membrane, causing the membrane to oscillateas the basilar membrane oscillates, the stereocilia embedded in the tectorial membrane (tectorial membrane stays stationary) becomes bent as the stereocilia bends, it activates the hair cells in which it depolarizes & releases neurotransmitters onto the dendrites (of the primary sensory neurons) to initiate an AP towards the brain the hair cells are mechanoreceptors the sound waves that cause the stereocilia to bend, deforms the cell membrane through the process opening mechanically-gated Na+ channels the hair cells are also transducers it transforms the energy of the sound waves into chemical energyas stereocilia bends & the cell membrane deforms, it results in the depolarization (interior of hair cell becomes more negative)Any extraneous sound energy dissipates across the cochlear duct & into the scala tympani, eventually exits the labyrinth through the round window dissipates into the tympanic cavity of the middle ear

Sound Waves: CharacteristicsAmplituderefers to the height of the crest of the wave the higher the crest, the higher the amplitude of the wavethe higher the amplitude, the louder the sound is perceived related to the intensity (volume) of the sound wave Wavelengthmeasures the length between one crest & another (distance between crests)related to the frequency of the sound waves higher frequency = shorter wavelengths = perceived as a high pitchlower frequency = longer wavelength = perceived as a low pitch

Sound: Loudness & PitchLoudness (human ear can detect 20 100 dB)decibels (dB) measures the volume of the sound wavessound < 20 dB = unable to hear some animals can hear less 100 dB = too loud; can destroy stereocilia of hair cells = loss of hearingis a property of the amplitude of a sound wave higher amplitudes = louder soundsgenerate more APsdisturbs basilar membrane to a larger degreecauses extreme bending of stereociliastereocilia releases a larger amount of neurotransmitterslower amplitudes = quieter soundsgenerate less APscauses basilar membrane to move a littlecauses stereocilia to bend to a much smaller degreestereocilia releases a smaller amount of neurotransmitters

Pitch (human ear can detect 200 20,000 Hz)measured in Hz (hertz)frequencies of the sound waves give various pitches of soundhigher frequency = high pitch soundssound waves of higher frequency activates the hair cells of the basal end of the cochlealower frequency = low pitch soundssound waves of lower frequency activates hair cells of the apex of the cochleaCh. 15 Sensory System Sound 2/4/15 6:06 PMis a function of the basilar membrane

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Disorders of the EarDeafness is in 2 forms:Conduction deafnessinvolves the injury to the outer ear or middle earcaused by the infection or rupture of the tympanic membranecan be caused by the bony ossicles in which the bones fuse together (occurs in elderly people)power to amplify sound waves is diminished

Sensorineural deafnessinvolves injury to the inner ear (hair cells)loud noise causes the basilar membrane to oscillate at a larger degree, tearing off the stereocilia of the hair cellshair cells start to die off, resulting in the progressive loss of hearinginvolves direct injury to the primary auditory cortex of the braindue to strokes or tumorsresults in the death of sensory neurons

Ch. 15 Sensory System Ear Disorders2/4/15 6:06 PM

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Smell: Olfactory EpitheliumOlfactory sense depends on the olfactory epitheliumlocated on the roof of the nasal cavity3 types of cells in the olfactory epithelium:Olfactory cells: highly modified bipolar cells1 process extends to the apical surface (presurface), giving rise to non motile cilia known as olfactory hairsolfactory hairs interact with odor molecules from the airother process extends through the foramina of the cribiform plate of the ethmoid bone in the basal surfacesynapses with secondary sensory neurons of the olfactory bulb:- mitral cells- tufted cells

Sustentaculr cells: provides physical & metabolic support to the olfactory cellsBasal cells: stem cell that differentiates, generating new olfactory & sustentacular cells both cells are often replaced by basal cells on an average of 7 daysOlfactory glands: exocrine lands that deliver mucus onto the apical surface of the olfactory epitheliumthe mucus allows for the incoming odor molecules from the air to dissolve within the mucus, enabling them to interact with the olfactory receptors of the olfactory hairs

Smell: Olfactory Bulbolfactory cells each cell responds to 1 specific odor moleculeodor molecules will bind to a specific odorant receptor due to complementary shapesas the odor molecule binds to the cell, it causes the olfactory cell to depolarize, causing it to fire APs towards the olfactory bulbthe olfactory cells synapse with the secondary neuronsCh. 15 Sensory System Smell2/9/15 6:06 PMsecondary neurons release neurotransmitters, exciting the tufted cell which fires another AP towards higher regions of the brain

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Taste: Tongue Papillaesense of taste depends on the tongue papillae; 4 types of tongue papillae include filiform papillae: does not contain taste budsfungiform papillae: spread on the superior surface & has taste budsfoliate papillae: on the sides of the tongue & has taste budscircumvallate papillae: largest; located on the posterior region of the tongue in a V shaped pattern & has taste buds

Taste: Taste Budstaste buds are made up of:gustatory cells on the apical surface, giving rise to non motile cells known as gustatory hairs various tastes binds to the hairs to depolarize the cell resulting in APS towards the brain,on the basal surface, it synapses with primary sensory neurons where the axons project into the relay center of the brain (thalamus) & then synapse with secondary sensory neurons & project into the primary gustatory cortex of the insular lobe sustentacular cells (support cells) give physical & metabolic support to gustatory cellsbasal cells regenerate gustatory & sustenatcular cells every ~7 days.

Taste: Taste Zonessweetelicited by simple sugars (table sugars sucrose)bitteralkaline compounds (poison)souracidic (weak acids, lactic acids; acids = substances that release H ions where H ions depolarize the gustatory cells, resulting in APs towards the brain) saltytable salt (NaCl; when in saliva, it associates into separate ions which depolarize the gustatory cells, resulting in APs towards the brain)umamiglutamate (certain amino acids giving a minty flavor)

flavor combinations of various senses gustatory & olfactory sensetexture of food also adds to the flavorit activates various tactile receptors in the tongue Ch. 15 Sensory System Taste 2/9/15 6:06 PMex: slimy texture initiates a gag reflex

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