Ch 10 Somatic and Special Senses powerpoint 2006

Anatomy and Physiology : Anatomy and Physiology Somatic and Special Senses


Sensory Receptors : Sensory Receptors Detect environmental changes and trigger nerve impulses that travel on sensory pathways into the CNS for processing and interpretation.


Two Categories of Receptors : Two Categories of Receptors Somatic Senses: touch, pressure, temperature, and pain. Distributed throughout skin and deeper tissues. Special senses: smell, taste, hearing, equilibrium, vision. (more complex)


Selective Response : Selective Response Each type of receptor is particularly sensitive to a distinct type of environmental change and less sensitive to other forms of stimulation


Five Types of Sensory Receptors : Five Types of Sensory Receptors Chemoreceptors: stimulated by changes in the chemical concentration of substances. Pain receptors: stimulated by tissue damage Thermoreceptors: changes in temp. Mechanoreceptors: changes in pressure or movement Photoreceptors: by light energy


Sensations : Sensations A feeling that occurs when the brain interprets sensory impulses All the nerve impulses that travel away from sensory receptors into the CNS are alike. The resulting sensation depends on which region of the brain receives the impulse.


Slide7 : Projection: the cerebral cortex causes the feeling to seem to come from the stimulated receptors. Sensory Adaptation: when sensory receptors are continually stimulated, receptors adapt and impulses leave them at decreasing rates, until signals are terminated.


Somatic Senses : Somatic Senses Senses associated with receptors in the skin, muscles, joints, and viscera


Touch and Pressure Senses : Touch and Pressure Senses Derived from 3 kinds of receptors that sense mechanical forces that deform or displace tissues Sensory Nerve Fibers: sense touch and pressure and are located in epithelial tissue


Slide10 : Touch and pressure receptors include A.) free ends of sensory nerve fibers, B.) Meissner’s corpuscles and C.) Pacinian corpuscles.


Slide11 : Meissner’s Corpuscles: respond to very light touch and are located in connective tissues of hairless portions of the skin Pacinian corpuscles: respond to heavy pressure and are located in deeper subcutaneous tissues, muscle tendons, joint ligaments.


Temperature Senses : Temperature Senses Two types of nerve endings stimulate pain receptors. Both adapt rapidly (fade within 1 minute of continuous stimulation) Warm receptors: 25˚ - 45˚C – burning sensation Cold receptors: 10˚ - 20˚C -- freezing sensation


Sense of Pain : Sense of Pain Widely distributed throughout the skin and internal tissues (except nervous tissue of brain) Protects the body. Tissue damage stimulates pain which is perceived as unpleasant and signals person to take action to remove stimulation. Adapts poorly if at all. Pain persists. The way in which tissue damage stimulates pain receptors is poorly understood. Injuries promote the release of certain chemicals that build up and stimulate pain receptors. Ischemia in a tissue or stimulation of certain mechanoreceptors also trigger pain sensations


Visceral Pain : Visceral Pain Localized damage may not elicit pain but wide-spread stimulation may produce strong pain sensation Mechanoreceptor stimulation and ischemia both produce visceral pain.


Slide15 : Referred Pain: visceral pain may feel as if it is coming from some part of the body other than the part being stimulated. May arise from common nerve pathways. Example: Pain originating in the heart may be referred to the left shoulder and left upper limb.


Slide16 : Pain originating in the heart may feel as if it is coming from the skin because sensory impulses from those two regions follow common nerve pathways to the brain.


Slide17 : Surface regions to which visceral pain may be referred


Pain Nerve Fibers : Pain Nerve Fibers Acute Pain Fibers: conduct impulses rapidly. Sharp pain. Restricted area of skin. Seldom continues after stimulation stops. Chronic Pain Fibers: slower, dull, aching pain. Diffuse and difficult to pinpoint. May continue after stimulus ceases. May be felt in deeper tissues. An event usually triggers both acute and chronic pain fibers (dual sensation)


Regulation of Pain Impulses : Regulation of Pain Impulses Awareness of pain results when impulse reaches the thalamus. Cerebral cortex determines pain intensity, locates pain source and mediates emotional and motor responses to the pain. Impulses descending from the brain stimulate neurons to release pain-relieving neuropeptides such as enkephalins, serotonin, and endorphins.


Headaches : Headaches Nervous tissue of the brain lacks pain receptors but nearly all other tissues of the head including meninges and blood vessels are richly innervated Many headaches are associated with stressful life situations that cause fatigue, emotional tension, anxiety, or frustration


Tension Headache : Tension Headache Triggered by various physiological changes such as prolonged contraction of skeletal muscles in forehead, sides of head, back of neck. Contractions stimulate pain receptors


Vascular Headache : Vascular Headache Accompanies constriction or dilation of cranial blood vessels. Ex. Throbbing headache of “hang-over” from drinking too much alcohol may be due to blood pulsating through dilated cranial vessels


Migraine : Migraine Form of vascular headache Certain cranial vessels constrict producing a localized cerebral blood deficiency Variety of symptoms: seeing patterns of bright light that obstruct vision, numbness in limbs or face Vasoconstriction subsequently leads to vasodilation of affected vessels causing severe headache usually on one side of the head. Can last several hours or more Drug treatments are available


Other Causes of Headaches : Other Causes of Headaches Sensitivity to food additives High blood pressure Increased intracranial pressure due to tumor or hematoma Decreased cerebrospinal fluid pressure following lumbar puncture Sensitivity to or withdrawal from certain drugs


Special Senses : Special Senses Those whose sensory receptors are within large, complex, sensory organs in the head. Smell: olfactory organs Taste: taste buds Hearing, equilibrium: ears Sight: eyes


Sense of Smell : Sense of Smell


Sense of Smell : Sense of Smell Associated with complex sensory structures in the upper region of the nasal cavity Olfactory Receptors and taste receptors are chemoreceptors Chemicals dissolved in liquids stimulate them Smell and taste function closely together and aid in food selection


Olfactory Organs : Olfactory Organs Contain olfactory receptors. Yellowish-brown masses that cover the upper parts of the nasal cavity, superior nasal conchae and a portion of the nasal septum Olfactory receptor cells are bipolar neurons surrounded by columnal epithelial cells


Slide29 : Olfactory receptors. A.) Columnar epithelial cells support olfactory receptor cells, which have cilia at their distal ends. B.) The olfactory area is associated with the superior nasal concha.


Slide30 : Hair-like cilia cover tiny knobs at the distal ends of these neuron’s dendrites Cilia project into the nasal cavity and harbor 500 types of olfactory receptor proteins Oderant molecules Enter the nasal cavity as gases but must dissolve partially in watery fluids before receptors can detect them Bind to the receptors in different patterns and stimulate the receptors.


Olfactory Nerve Pathways : Olfactory Nerve Pathways Stimulated olfactory receptor cells send nerve impulses along their axons which form the first cranial nerves and synapse with neurons located in enlargements called olfactory bulbs. Impulses are analyzed in the olfactory bulbs and travel along olfactory tracts to the limbic system Major interpreting areas (olfactory cortex) for these impulses are located within the temporal lobes and at the bases of the frontal lobes


Slide33 : Humans smell using 12 million olfactory receptor cells Bloodhounds have 4 billion olfactory receptor cells Much better sense of smell. Specially trained for search and rescue – find victims of World Trade Center collapse in 2001


Olfactory Stimulation : Olfactory Stimulation One hypothesis suggests that the shapes of gaseous molecules fit complementary shapes of membrane receptor sites. Binding to a receptor triggers a nerve impulse. Each odor stimulates a distinct set of receptor subtypes. The brain interprets different combinations as an olfactory code. Ex. Parsley stimulates receptors 3, 4, 8 Chocolate stimulates receptors 1, 5, 10


Slide35 : Olfactory organs are located high in the nasal cavity above the usual pathway of inhaled air. May have to sniff and force air up to the receptor areas to smell a faint odor Olfactory receptors undergo sensory adaptation rapidly If receptors are adapted to one scent, sensitivity to other odors persists


Anosmia : Anosmia Partial or complete loss of smell May result from a variety of factors including inflammation of the nasal cavity lining due to respiratory infection, tobacco smoke, or using certain drugs such as cocaine


Sense of Taste : Sense of Taste


Taste Buds : Taste Buds Special organs of taste Located primarily on the surface of the tongue and are scattered on the roof of the mouth and walls of throat. (1000/10,000 taste buds are not on tongue) Associated with tiny elevations called papillae and epithelial supporting cells


Slide39 : Taste receptors. A.) Taste buds on the surface of the tongue are associated with nipple-like elevations called papillae. B.) A taste bud contains taste cells and has an opening, the taste pore, at its free surface.


Taste cells / Gustatory Cells : Taste cells / Gustatory Cells A group of modified epithelial cells on a taste bud that function as receptors 50-150 receptor cells per taste bud; replaced every 3 days


Slide41 : Taste Pore: opening at the free surface Taste hair: tiny projections that protrude from outer ends of taste cells and extend from taste pore Believed to be the sensitive parts of the receptor cells A network of nerve fibers is interwoven among the taste cells. Stimulation of receptor cells triggers an impulse


Slide42 : Before a particular chemical can be tasted it must dissolve in the watery fluid (provided by the salivary gland) surrounding taste buds Similar hypothesis as smell – food molecules combine with specific receptor sites on taste hair surfaces stimulating sense of taste. Combinations generate sensory impulses on nerve fibers.


Slide43 : Taste cells appear alike microscopically but are of at least 4 types. Each type is most sensitive to a particular kind of chemical stimulus. 4 Primary Taste (gustatory) Sensations Sweet: sugar Sour: lemon Salty: table salt Bitter: caffiene, quinine Other Taste Sensations Alkaline Metallic Umami: detects MSG (monosodium glutamate) a flavor enhancer


Slide44 : A flavor results from one or a combination of primary sensations Experiencing flavors involves taste as well as odor, texture (touch), and temperature. Also stimulation of pain receptors (burning from chili peppers or ginger)


Slide45 : All taste cells are responsive to at least 2 taste sensations although one may predominate. Distribution of Taste Cells: Sweet: greatest at tip of tongue Sour: greatest at margins of tongue (sides) Bitter: back of tongue Salty: widely distributed


Slide46 : Locations of the four primary taste sensations.


Slide47 : Due to the fact that all receptors are sensitive to all stimuli to some degree – a wide range of individual variations in responses The pattern of responses from differentially sensitive receptor cells provides the brain with information necessary to create what we call taste.


Slide49 : Taste receptors (like olfactory receptors) undergo sensory adaptation rapidly. Moving bits of food over the surface of the tongue stimulates different receptors at different moments avoiding loss of taste from sensory adaptation.


Taste Nerve Pathway : Taste Nerve Pathway Sensory impulses from taste receptors in the tongue Fibers of the facial, glossopharyngeal, and vagus nerves Medulla oblongata Impulses ascend to the thalamus Then are directed to the gustatory cortex in the parietal lobe of the cerebrum


Sense of Hearing : Sense of Hearing


Ear : Ear Organ for hearing Also functions in sense of equilibrium 3 sections: external, middle, inner


Slide53 : Major parts of the ear


External Ear : External Ear Auricle (pinna): Outer funnel-like structure Collects sound waves traveling through air and directs them into the external auditory meatus External Auditory Meatus Also called External Auditory Canal S-shaped tube that leads inward through the temporal bone for 2.5 cm


Middle Ear : Middle Ear Tympanic Cavity: air-filled space in the temporal bone Tympanic Membrane (eardrum) Semitransparent membrane covered by a thin layer of skin on the outer surface and by mucous membrane on the inside Oval margin, cone-shaped with apex directed inward toward the malleus The eardrum moves back and forth in response to sound waves entering the external auditory meatus reproducing the vibrations of the sound wave source.


Slide56 : Major parts of the ear.


Slide57 : Auditory Ossicles Malleus, Incus, Stapes Tiny ligaments attach these bones to the wall of the tympanic cavity Covered by mucous membrane Bridge the eardrum and inner ear, transmitting vibrations between these parts Ligaments hold the stapes to an opening in the wall of the tympanic cavity, called the oval window, that leads to the inner ear Amplify (increase force of) vibrations as they pass from eardrum to oval window. Vibrations are concentrated as the move from a relatively larger surface area to a smaller area


Slide58 : Auditory Ossicles bridge the tympanic membrane and the inner ear.


Auditory Tube : Auditory Tube Also called eustachian tube Connects middle ear to throat Conducts air between the tympanic cavity and the outside of the body by way of the throat (nasopharynx) and mouth


Slide60 : Helps maintain equal air pressure on both sides of the eardrum, which is necessary for normal hearing (this function is noticeable when you hear a popping sound during rapid changes in altitude) Mucous membrane infections of the throat may spread through these tubes and cause middle ear infection


Inner Ear : Inner Ear Labyrinth Complex system of communicating chambers and tubes 2 in each ear Osseous Labyrinth: bony canal in the temporal bone Membranous Labyrinth: tube that lies within the osseous labyrinth


Slide62 : Perilymph: fluid between osseous and membranous labyrinths Endolymph: fluid within membranous labyrinths


Slide63 : Perilymph separates the osseous labyrinth of the inner ear from the membranous labyrinth, which contains endolymph.


Parts of the Labyrinths : Parts of the Labyrinths 3 semicircular canals provide sense of equilibrium Cochlea: Functions in hearing Contains a bony core and a thin bony shelf that winds around the core like threads of a screw


Slide65 : 2 compartments Upper scala vestibuli leads from oval window to apex of the spiral Lower scala tympani extends from apex of cochlea to membrane-covered opening in the wall of the inner ear, called the round window Cochlear duct Portion of the membranous labyrinth within the cochlea. Contains endolymph Lies between the 2 bony compartments and ends as a closed sac at the apex of the cochlea Separated from the scala vestibuli by a vestibular membrane (Reissner’s membrane) Separated from scala tympani by a basilar membrane


Slide66 : Cochlea. A.) Cross section of the cochlea. B.) Organ of Corti and the tectorial membrane.


Slide67 : Basilar membrane Contains many thousands of stiff, elastic fibers Sound vibrations entering the perilymph at the oval window travel along the scala vestibuli, pass through the vestibular membrane into the endolymph of the cochlear duct where they move the basilar membrane Then vibrations enter the perilymph of the scala tympani to the round window and dissipate into the tympanic cavity


Slide68 : Organ of Corti Contains the hearing receptors Located on the upper surface of the basilar membrane and stretches from the apex to base of the cochlea Receptor cells (hair cells) are organized in rows and have many hairlike processes that project into the cochlear duct


Slide69 : Cochlea. A.) Cross section of the cochlea. B.) Organ of Corti and the tectorial membrane.


Slide70 : SEM of hair cells on the organ of Corti


Slide71 : Tectorial membrane Attached to the bony shelf of the cochlea, passing over the receptor cells and contacting the tips of their hairs As sound vibrations move back and forth against the tectorial membrane causing mechanical deformation and stimulating the receptor cells Various receptor cells have slightly different sensitivities to deformation. A particular sound frequency may excite certain receptor cells and another frequency excites a different set of hair cell


Slide72 : Hearing receptor cells are epithelial but function somewhat like neurons Membrane is polarized when at rest and depolarized when stimulated and more permeable to Ca+ ions Has no axons or dendrites but has neurotransmitter-containing vesicles near its base As Ca+ ions diffuse into the cell, some fuse with cell membrane and release neurotransmitter which stimulates the ends of nearby sensory nerve fibers Impulses are transmitted along the cochlear branch of the vestibulocochlear nerve to the auditory cortex of the temporal lobe of the brain


Auditory Nerve Pathway : Auditory Nerve Pathway Nerve fibers associated with hearing Pass into the auditory cortices of the temporal lobe of the cerebrum where they are interpreted on both sides of the brain Some fibers cross over so that impulses from each ear are interpreted on both sides of the brain Damage to the temporal lobe on one side does not necessarily cause complete hearing loss on that side


Decibels (dB) : Decibels (dB) Measure of sound intensity Scale begins at 0dB = intensity of sound least perceptible by a normal human ear Scale is logarithmic: 10dB is 10x as intense as 0dB, 20dB is 100x more intense, 30dB is 1000x more intense


Slide76 : Whisper = 40dB Normal Conversation = 60-70dB Heavy traffic = 80dB Rock Concert = 120dB, causes discomfort Jet plane take off = 140dB, pain Frequent or prolonged exposure to sounds with intensities above 90dB can damage hearing receptors and cause permanent hearing loss.


Hearing Loss : Hearing Loss Conductive deafness: Interference with transmission of vibrations to the inner ear May be due to plugging of the external auditory meatus or to changes in the eardrum or auditory ossicles Ex. Eardrum may harden as a result of disease and be less responsive to sound waves Ex. Disease or injury may tear or perforate the eardrum


Slide78 : Sensorineural Deafness: Damage to the cochlea, auditory nerve or auditory nerve pathways Can be caused by loud sounds, tumors in the CNS, brain damage as a result of vascular accidents or use of certain drugs


Sense of Equilibrium : Sense of Equilibrium Two senses that come from different sensory organs Static Equilibrium: senses position of the head, maintaining stability and posture when the head and body are still Dynamic Equilibrium: sense sudden movement or rotation of the head and body. Aid in maintaining balance


Static Equilibrium : Static Equilibrium Organs located within the vestibule, a bony chamber between the semicircular canals and the cochlea There are two expanded chambers inside the vestibule – the utricle and the saccule Each chamber has a tiny structure called a macula that contains numerous hair cells which serve as sensory receptors


Slide81 : When the head is upright, the hairs project upward into a mass of gelatinous material containing grains of calcium carbonate (called otoliths) When the head bends forward, backward, or to one side, the hair cells are stimulated as the gelatinous masses of the maculae sag in response to gravity causing the hair to bend Stimulated hair cells signal nerve fibers resulting in impulses traveling to the CNS on the vestibular branch of the vestibulocochlear nerve and informing the brain of the head’s new position Brain responds by sending motor impulses to skeletal muscles to contract/relax to maintain balance


Slide82 : The macula responds to changes in head position. A.) Macula with the head in an upright position. B.) Macula with the head bent forward.


Dynamic Equilibrium : Dynamic Equilibrium Semicircular canals are the organs of dynamic equilibrium and are located in the labyrinth Detect motion of the head and aid in balancing the head and body during sudden movement Semicircular canals lie at right angles to each other and correspond to the different anatomical planes


Slide84 : Ampulla: swelling at the end of a membranous canal that is suspended in the perilymph of the bony portion of each semicircular canal Contains sensory organs called crista ampullaris which are made up of sensory hair cells and supporting cells Hair cells extend upward into a dome-shaped gelatinous mass called the cupula


Slide85 : A crista ampullaris is located within the ampulla of each semicircular canal.


Slide86 : Rapid turns of the head or body stimulate the hair cells of the crista ampullaris (semicircular canals move with the head but the fluid, remains stationary) Hair cells signal associated nerve fibers to send impulses to the brain – cerebellum Analysis of info allows the brain to predict the consequences of the rapid body movements and signal appropriate skeletal muscle to maintain balance


Slide87 : Equilibrium. A.) When the head is stationary, the cupula of the crista ampullaris remains upright. B.) When the head is moving rapidly, C.) the cupula bends opposite the motion of the head, stimulating sensory receptors.


Other Sensory Structures Aid in Maintaining Equilibrium : Other Sensory Structures Aid in Maintaining Equilibrium Mechanoreceptors associated with joints of neck inform the brain about position of body parts Eyes detect changes in posture Visual info is important. Even if organs of equilibrium are damaged, a person may be able to maintain normal balance (eyes open and move slowly)


Motion Sickness : Motion Sickness Boat, airplane, car Caused by abnormal and irregular body motions that disturb the organs of equilibrium Symptoms include nausea, vomiting, dizziness, headache, and prostration (weakness, collapse, exhaustion)


Sense of Sight : Sense of Sight


Sense of Sight : Sense of Sight Eye: organ containing visual receptors Provides vision with assistance of accessory organs Visual accessory organs Eyelids, lacrimal apparatus (protects eye), and a set of extrinsic muscles (move eye)


Orbital Cavity : Orbital Cavity Location of eye and accessory organs Pear-shaped Lined with the periosteum of various bones and contains fat, blood vessels, nerves, and connective tissues.


Eyelid (4 layers) : Eyelid (4 layers) Skin: thinnest skin of body. Covers the lids outer surface. Muscle: Orbicularis oculi: acts as a sphincter and closes lid when it contracts. Levator palpebrae superioris: raises the upper lid Connective tissue Conjunctiva: mucous membrane that lines the inner surfaces of the eyelids and anterior surface of eyeball except for the central portion (cornea).


Slide94 : Sagittal section of the closed eyelids and anterior portion of the eye.


Lacrimal Apparatus : Lacrimal Apparatus Lacrimal Gland: secretes tears continuously. Located in the orbit and series of ducts that carry tears into nasal cavity. Tears exit lacrimal gland through tiny tubules and flow downward and medially across the eye. Superior and inferior canaliculi collects tears  into lacrimal sac located in groove of lacrimal bone  nasolacrimal duct which empties into nasal cavity


Slide96 : Moistens and lubricates surface of the eye and lining of lids Tears contain lysozome – antibacterial agent reducing risk of eye infections. The lacrimal apparatus consists of a tear-secreting gland and a series of ducts.


Extrinsic Muscles : Extrinsic Muscles Arise from bones of the orbit and attach (insert) by broad tendons on the eye’s tough outer surface. 6 extrinsic muscles move the eye in various directions. Eye movements may utilize more than one muscle.


Slide98 : Extrinsic muscles of the right eye (lateral view)


Diplopia : Diplopia Double vision caused by one eye deviating from the line of vision. If condition persists, brain must suppress image from deviated eye


Suppression Amblyopia : Suppression Amblyopia Turning eye becomes blind. Treatment early in life with exercises, eyeglasses and surgery can prevent monocular blindness (one eye)


Structure of the Eye : Structure of the Eye Hollow, spherical structure 2.5cm in diameter 3 layers: fibrous outer tunic, vascular middle tunic, nervous inner tunic Spaces within eye filled with fluids that support its wall and internal parts and help maintain its shape.


Outer Tunic – Fibrous Tunic : Outer Tunic – Fibrous Tunic Cornea Sclera Optic Nerve: in the back of the eye Blood Vessels: pierce sclera


Cornea : Cornea Anterior 6th of outer tunic Bulges forward Transparent window of the eye (contains few cells, no blood vessels, cells and collagenous fibers form unusually regular patterns) Helps focus entering light rays Composed largely of connective tissue with a thin layer of epithelium on its surface. Continuous with the sclera (white portion of the eye)


Slide105 : Transverse section of the right eye (superior view)


Sclera : Sclera White portion of the eye Posterior 5/6th of the outer tunic Opaque due to many large, disorganized collagenous and elastic fibers. Protects the eye and is an attachment for the extrinsic muscles


Most Common Cause of Blindness : Most Common Cause of Blindness Loss of transparency of the cornea Corneal Transplant (penetrating keratoplasty): treat condition by replacing central 2/3 of the defective cornea with similar-sized portion of cornea from a donor eye Corneal tissues lack blood vessels, transplanted tissue usually not rejected Success rate of procedure is very high.


Middle Tunic – Vascular Tunic : Middle Tunic – Vascular Tunic Choroid Coat Ciliary Body Iris


Choroid Coat : Choroid Coat Posterior 5/6th of globe of the eye Loosely joined to the sclera Honeycombed with blood vessels which nourish surrounding tissues Contains many pigment-producing melanocytes which absorbs excess light and helps keep the inside of the eye dark.


Ciliary Body : Ciliary Body Thickest part of the middle tunic Extends forward from the choroid coat and forms an internal ring around the front of the eye. Many radiating folds called ciliary processes Groups of muscle fibers called ciliary muscles. Suspensory ligaments: extend inward from the ciliary processes and hold transparent lens and capsule in position.


Slide111 : Lens and ciliary body viewed from behind


Lens : Lens Lies directly behind the iris and pupil Composed of differentiated epithelial cells called lens fibers.


Lens Capsule : Lens Capsule Surrounds the lens Clear, membrane-like structure composed largely of intercellular material Elastic nature keeps it under constant tension. Can assume a globular shape.


Slide114 : Suspensory ligaments attached to margin of capsule and the ciliary muscles. Changing tension changes the shape of the capsule and lens for focusing. Accommodation: the ability of the lens to adjust shape to facilitate focusing. Close objects= lens thickens; distant objects= thinner, less convex


Slide115 : In accommodation, A.) the lens thins as ciliary muscle fibers relax. B.) The lens thickens as ciliary muscle fibers contract.


Cataract : Cataract Common eye disorder in older people Lens or capsule slowly becomes cloudy and opaque. Without treatment it eventually causes blindness Treatment: In past, surgical procedure with 2 week recovery Now, laser treatment on out-patient basis.


Iris : Iris Thin diaphragm composed mostly of connective tissue and smooth muscle fibers The colored portion of the eye Extends forward from the periphery of the ciliary body and lies between the cornea and the lens. Divides the space (anterior cavity) into the anterior chamber (between the cornea and the iris) and posterior chamber (between iris and vitreous body containing the lens)


Aqueous Humor : Aqueous Humor Watery fluid secreted by the epithelium on the inner surface of the ciliary body into posterior chamber.


Pupil : Pupil Circular opening in the center of the iris. Fluid flows through from posterior to anterior chamber. Aqueous humor fills space between cornea and lens. Nourish these parts and aids in maintaining shape of the front of the eye. Leaves anterior chamber through veins and special drainage canal – scleral venous sinus (canal of Schlemm)


Glaucoma : Glaucoma Eye disorder that develops when the rate of aqueous humor formation exceeds the rate of its removal. Fluid accumulates in anterior chamber of the eye, fluid pressure rises and is transmitted to all parts of the eye. Building pressure squeezes shut blood vessels that supply the receptor cells of the retina.


Slide121 : Cells robbed of nutrients and oxygen may die and permanent blindness can result. Early diagnosis allows successful treatment with drugs, laser therapy, or surgery to promote outflow of aqueous humor Early stages typically produce no symptoms. Discovery of the condition by tonometer, an instrument that measures intracellular pressure.


Smooth Muscle Fibers of Iris : Smooth Muscle Fibers of Iris Control size of the pupil through which light passes as it enters the eye. 2 groups Circular set: acts as a sphincter. Contracts smaller, less light enters. Radial set: contracts to increase diameter of pupil allowing more light to enter.


Slide123 : Dim light stimulates the radial muscles of the iris to contract, and the pupil dilates. Bright light stimulates the circular muscles of the iris to contract, and the pupil constricts.


Inner Tunic : Inner Tunic Consist of the retina which contains visual cells (photoreceptors) Nearly transparent sheet of tissue that is continuous with the optic nerve in the back of the eye and extends forward as the inner lining of the eyeball Ends just behind the margin of the ciliary body


Retina : Retina Thin and delicate. Complex structure with a number of distinct layers. Macula lutea: central region. Yellowish spot Fovea centralis: depression in its center. Region that produces sharpest vision.


Slide126 : Optic disc: medial to fovea centralis. Nerve fibers from the retina leave the eye and join the optic nerve. Central artery and vein also pass through optic nerve and vessels are continuous with the capillary networks of the retina and with vessels in the underlying choroid coat. Supply blood to cells of inner tunic Known as the blind spot of the eye. Lacks receptor cells.


Slide127 : The retinal consists of several cell layers.


Slide128 : Note the layers of cells and nerve fibers in this light micrograph of the retina.


Slide129 : Retina. A.) Nerve fibers leave the eye in the area of the optic disc (arrow) to form the optic nerve. B.) Major features of the retina.


Posterior Cavity : Posterior Cavity Space bounded by the lens, ciliary body, and retina is the largest compartment of the eye. Filled with transparent, jelly-like fluid called vitreous humor, along with collagenous fibers it comprises the vitreous body. Vitreous body: supports internal parts of the eye and helps maintain its shape.


Floaters : Floaters Specks or clumps of gel or deposits of crystal-like substances that form in the vitreous humor. Cast shadows on the retina. Person sees small, moving specks in the field of vision. Most apparent when looking at a plain background. More numerous as a person ages.


Light Refraction : Light Refraction When a person sees something, the object is giving off light or light waves are reflected from it. Light waves enter the eye and an image of the object is focused on the retina. Refraction: bending of light waves to focus them. Occurs when light waves pass at an oblique angle from a medium of one density into a medium of another density.


Slide133 : A lens with a convex surface causes light waves to converge.


Slide134 : Convex surface causes light waves to refract and converge (cornea, lens, fluids) If eye shape is normal, light waves focus sharply on the retina. Image is upside down and reversed from left to right. Visual cortex interprets the image in its proper position.


Visual Receptors : Visual Receptors Visual receptor cells are modified neurons of two distinct kinds. (rods and cones)


Slide137 : Rods and Cones. A.) A single sensory nerve fiber transmits impulses from several rods to the brain. B. Separate sensory nerve fibers transmit impulses from cones to the brain. C.) Scanning electron micrograph of rods and cones.


Slide138 : Rods and cones are located in a deep portion of the retina, closely associated with the layer of pigmented epithelium. Epithelial pigment absorbs waves not absorbed by receptor cells. Along with pigment of choroid coat, it keeps light from reflecting off surfaces inside the eye.


Slide139 : Projections from receptors are loaded with light-sensitive visual pigments and extend into this pigmented layer. Visual receptors are stimulated only when light reaches them. A light image focused on an area of the retina stimulate some receptors and sends impulses to the brain. This provides only a fragment of info required for the brain to interpret a total scene.


Slide140 : Pigmented epithelium and receptor cells


Visual Pigments : Visual Pigments Both rods and cones contain light-sensitive pigments that decompose when they absorb light energy. Decomposition of the pigments triggers a complex series of reactions that initiate a nerve impulse Pigments are synthesized from vitamin A. Night blindness: poor vision in dim light results from vitamin A deficiency which reduces the supply of retinal (a type of visual pigment) causing low rod sensitivity. Treated with Vitamin A supplements.


Slide142 : Color vision comes from 3 sets of cones containing different light-sensitive pigments Each type of pigment is sensitive to different wavelengths (colors- red, green, blue) of light. The color a person perceives depends on which set of cones or combination of sets the light in a given image stimulates. (all three =white; none=black) Different forms of color blindness result from lack of different types of cone pigments.


Visual Nerve Pathway : Visual Nerve Pathway Axons of retinal neurons leave eyes to form optic nerves. X-shaped optic chiasma. Some fibers cross over Right and left optic tracts A few nerve fibers enter nuclei that function in various visual reflexes The rest enter the thalamus Visual impulses enter nerve pathways called optic radiations which lead to the visual cortex of the occipital lobes.


Slide144 : The visual pathway includes the optic nerve, optic chiasma, optic tract, and optic radiations.


Clinical Terms Related to the Senses : Clinical Terms Related to the Senses


Amblyopia : Amblyopia Dim vision due to a cause other than a refractive disorder or lesion Amblyopia is the medical term for poor development of vision in one eye. The word comes from the Greek. [ambly- (dull) + -opia (vision)] Amblyopia is often referred to as "lazy eye." It affects just two to three percent of the population. Central vision does not develop properly, usually in one eye, which is called amblyopic. The eye is anatomically normal, but visual acuity is reduced even with glasses. Amblyopia develops sometime between birth and 8 or 9 years of age, the critical period of time when the visual system develops and matures. Amblyopia causes more visual loss in the age group under 40 than all the injuries and diseases combined.


Anopia : Anopia Absence of an eye


Audiometry : Audiometry Measurement of auditory acuity for various frequencies of sound waves


Blepharitis : Blepharitis Inflammation of the eyelid margins


Causalgia : Causalgia Persistent, burning pain usually associated with injury to a limb Also called complex regional pain syndrome.Most common between ages 40-60. Diagnosis through observation, thermography, and radiography.Treatment includes physical therapy, corticosteriods, local anesthetic, vasodilaters and antidepressants.


Conjunctivitis : Conjunctivitis Inflammation of the conjunctiva Viruses, bacteria, irritating substances (shampoo, dirt, smoke, pool chlorine), sexually transmitted diseases (STDs) or allergens (substances that cause allergies) can all cause conjunctivitis. Pink eye caused by bacteria, viruses or STDs can spread easily from person to person but is not a serious health risk if diagnosed promptly; allergic conjunctivitis is not contagious.


Diplopia : Diplopia Double vision


Emmetropia : Emmetropia Normal condition of the eyes; eyes with no refractive defects.


Enucleation : Enucleation Removal of the eyeball


Exophthalmos : Exophthalmos Abnormal protrusion of the eyes Associated with hyperthyroidism and Grave’s disease. In the case of Graves Disease, the displacement of the eye is due to abnormal connective tissue deposition in the orbit and extraocular muscles (Epstein et al, 2003) which can be visualized by CT or MRI. If left untreated, exophthalmos can causes the eye lids to fail to close during sleep leading to corneal damage. The process that is causing the displacement of the eye may also compress the optic nerve or ophthalmic artery leading to blindness


Hemianopsia : Hemianopsia Defective vision affecting half of the visual field


Hyperalgesia : Hyperalgesia Heightened sensitivity to pain Caused by injury, or allergic/inflammatory reaction. One unusual cause is platypus venom (venomous ankle spurs)


Iridectomy : Iridectomy Surgical removal of part of the iris Treatment for one type of glaucoma where the iris sags and blocks normal drainage.


Iritis : Iritis Inflammation of the iris Also called anterior uveitis. It is the 3rd leading cause of blindness in the developed world. White blood cells are shed into the anterior chamber of the eye in the aqueous humor. These cells can accumulate and cause adhesions between the iris and the lens. Iritis is associated with over 90 different pathogens and autoimmune disorders. Some treatments include antibiotics and steroids.


Keratitis : Keratitis Inflammation of the cornea Symptoms include pain, and profuse tearing. Can be caused by infection, trauma, dry eyes, UV exposure, contact lens over-wear, degeneration. Herpes simplex keratitis


Labyrinthectomy : Labyrinthectomy Surgical removal of the labyrinth


Labyrinthitis : Labyrinthitis Inflammation of the labyrinth Usually caused by a viral infection, occasionally bacterial. Symptoms include reduced hearing or distortion, ringing in the ear, dizziness, imbalance, nausea and vomiting. Often follows the common cold. Viral form improves on its own within a few weeks. Anti-nausea medication can be prescribed.


Meniere’s Disease : Meniere’s Disease Inner ear disorder that causes ringing in the ears, increased sensitivity to sounds, dizziness, and hearing loss Meniere’s disease is a problem with the inner ear, the part of the ear responsible for balance as well as hearing. When you have Meniere’s disease, too much endolymph (fluid) backs up in the canals, a condition called endolymphatic hydrops. Extra fluid causes pressure to build up, so the canals swell and can’t work right. This leads to problems with the ear’s hearing and balance systems.


Neuralgia : Neuralgia Pain resulting from inflammation of a nerve or a group of nerves. Trigeminal neuralgia


Neuritis : Neuritis Inflammation of a nerve Optic neuritis Optic neuritis is acute visual loss owing to demyelination of the optic nerve. It may be an isolated autoimmune condition or part of multiple sclerosis. Fortunately, vision recovers to normal or near normal in over 90% of patients within six months. No treatment improves those chances.


Otitis media : Otitis media Inflammation of the middle ear Bacterial or viral infection occurs in the fluid buildup af