ch 12 anatomy senses

middle ear (tympanic cavity)

an air filled space in temporal bone in the temporal bone that separates the outer and inner ears it is bounded by the tympanic membrane laterally and the inner ear medially and houses three small bones called AUDITORY OSSICLES

endorphins

another group of neuropeptides with pain suppressing morphinelike actions found in pituitary gland and regions of nervous system

perception

the way the brain interprets this information

olfactory receptor cells

these cells and their membrane receptor molecules, sense odors receptor cells are chemoreceptors sensitive to chemicals dissolved in liquids

general senses

those with receptors widely distributed throughout the body, including skin, various organs, and joints

reflex sympathetic dystrophy

form of neuropathic pain that causes an intense burning sensation in a hand or foot even if the extremity is paralyzed of has been amputated

refraction

light rays must bend to be focused in this phenomenon convex lens= causes light ways to converge concave lens= light waves diverge

rhodopsin

light sensitive pigments in RODS that decomposes when they absorb light energy this is visual purple , and it is embedded in membranous discs stacked in these receptor cells opsin- colorless protein that rhodopsin molecules breaks down into in the presence of light

taste receptors

like olfactory receptors, rapidly undergo sensory adaptation resulting loss of taste can be avoided by moving bits of food over the surface of the tongue to stimulate different receptors

anosmia

loss of olfactory receptors

pain inhibiting biochemicals

released in the posterior horn are neuropeptides called enkephalins and amine serotonin enkephalins can suppress both acute and chronic pain impulses therefore can relieve strong pain sensations as much as morphine and other opiate drugs do serotonin stimulates other neurons to release enkephalins

static equilibrium

the organs of SE are in the vestibule, a bony chamber, between the semicircular canals and the cochlea the membranous labyrinth inside the vestibule consists of two expanded chambers-- a UTRICLE and a SACCULE the larger utricle communicates and is continuous with the saccule and membranous portions of the semicircular canals the saccule in turn communicates with the cochlear duct MACULA- small patch of hair cells and supporting cells on its wall when the head is upright, the hairs of the macula in the utricle project vertically, while those in the saccule are horizontal in both the utricle and saccule, the hairs contact a sheet of gelatinous material (otolithic membrane) that has crystals of calcium carbonate (otoliths) embedded on its surface/ these particles add weight to the sheet making it more responsive to changes in position the hair cells which are the sensory receptors have dendrites of sensory neurons wrapped around their bases/ these neurons are associated with the vestibular portion of the vestibulocochlear nerve gravity stimulates the hair cells to respond/ this usually happens when the head forward backward or to one side movements tilt mass of one or more maculae and material sags and hairs bend

the transfer of vibrations through matter produces:

sound these vibrations travel in waves, much like ripples on the surface of a pond/ the higher the wave the louder the sound the more waves per second, the higher the frequency, or pitch of sound vibrating vocal folds(cords) in the larynx produce sounds of the human voice the auricle of the ear helps collect sound waves traveling through air and directs them into external acoustic meatus after entering the tube the meatus, the sound waves pass to the end of the tube and alter the pressure on the tympanic membrane

5 types of sensory reseptors are recognized, based on their sensitives to specific stimuli:

1. CHEMORECEPTORS- respond to changes in the concentration of chemicals/ type of receptor is associated with senses of smell and taste/ chemoreceptors in internal organs detect changes in blood concentrations of o2, hydrogen ions, glucose, and other chemicals 2. PAIN RECEPTORS- also called nociceptors respond to tissue damage/triggering stimuli includes exposure to excess mechanical, electrical, thermal, or chemical radiation 3. THERMORECEPTORS- sense temp change 4. MECHANORECEPTORS- are of several types and sense mechanical forces by detecting change changes that deform receptors /they include a number of receptors in skin that respond to physical contact, several receptors in in the ear that provide balance and vibrations form sound proprioceptors- sense changes in the tensions of muscles and tendons baroreceptors- also called pressorecptors/ in certain blood vessels detect changes in BP stretch receptors- in the lungs sense degree of inflation 5. PHOTORECEPTORS- in the eyes respond to light energy of sufficient intensity

pain impulses that originate from tissues of the head reach the brain on sensory fibers of the :

5th, 7th, 9th, and 10th cranial nerves

6 extrinsic muscles of eye :

EXTRINSIC MUSCLES- arise in bones of the orbit and are inserted by broad tendons on the eye's outer surface each one is associated with a primary action: 1. SUPERIOR RECTUS- rotates eye upward and toward the midline 2. INFERIOR RECTUS- rotates downward and toward midline 3. MEDIAL RECTUS- rotates toward midline 4. LATERAL RECTUS- rotates away from midline 5. SUPERIOR OBLIQUE- rotates downward and away from midline 6. INFERIOR OBLIQUE- rotates the eye upward and away from the midline have fewest muscle fibers(5-10) enabling very precise movement STRABIMUS- person whose eyes are not coordinated well enough to align

taste cells for each 5 taste sensations are in all areas of the tongue, but:

are distributed such that each sensation seems to arise most strongly from a particular region sweet stimulus peaks at tip of tongue whereas responsiveness to sour is greatest at the margins of the tongue and to and to bitter at back / salt is are widely distributed

hearing receptor cells

are epithelial cells, but respond to stimuli somewhat like neurons when a receptor cell is at rest =polarized when its hair cells bend, selective ion channels open and its cell membrane depolarizes = membrane becomes more becomes more permeable to calcium ions receptor cell has no axon or dendrites but it does have neurotransmitter- containing vesicles in the cytoplasm near its base as calcium ions diffuse into the cell some of these vesicles fuse with the cell membrane and release neurotransmitter to the outside which then stimulates the dendritic ends of nearby sensory neurons and in response their axons conduct impulses along the cochlear branch of the vestibulcochlear nerve (cranial nerve VIII) to the brain

projection

at the same time that sensation forms, the cerebral cortex interprets it as coming from receptors being stimulated this process ,which is closely related to perception, is called this bc the brain projects the sensation back to apparent source allows person to pinpoint region of stimulation this way we perceive that the eyes see an apple, the nose smells it, and the ears hear the crunch into it

sensory adaptation

brain prioritizes the sensory input it receives, or all incoming information would be over whelming for example: Until this sentence prompts you to think about it, you are unaware of the pressure of clothing against skin or background noise the ability to ignore unimportant stimuli is called this peripheral adaptation- decreased response to a particular stimulus central adaptation- decreased response along CNS pathways leading to sensory regions of cerebral cortex once adaptation occurs to a particular stimulus, a sensation will only occur if strength of stimulus changes

outer (external ear)

consists of all the structures that face the outside these include an outer, funnel-like structure called the AURICLE(pinna), EXTERNAL ACOUSTIC MEATUS an S-shaped tube that leads inward for about 2.5 cm, and the tympanic membrane (eardrum) the meatus terminates with the tympanic membrane

sense of taste derives from:

combinations of chemicals binding specific receptor cells this takes place on taste hair surfaces binding of chemicals alters membrane polarization, generating impulses on nearby sensory nerve fibers

auditory tube (Eustachian tube)

connects each middle ear to the throat tube allows air to pass btw the tympanic cavity and the outside of the body by way of the throat(nasopharynx) and mouth helps maintain equal air pressure on both sides of the tympanic membrane/ necessary for normal hearing function of auditory tube becomes noticeable during rapid change in altitude/ as person descends from a high altitude air pressure on the outside of tympanic membrane steadily increases and may push membrane inward out of its normal position, impairing hearing when the air pressure difference on the sides of the tympanic membrane is great enough some air may force its way up through the auditory tube into middle ear/ this equalizes the pressure on both sides of the tympanic membrane, which moves back into its regular position, causing a popping sound tube is usually closed by valve like flaps in the throat, which may inhibit air movements into the middle ear swallowing, yawning, or chewing aid in opening the flaps and can hasten equalization of air pressure

pain receptors (nociceptors)

consist of free nerve endings not in nervous tissue of brain deficiency of blood flow is ischemia thus leading to a deficiency of oxygen called hypoxia this results in a muscle cramp pain receptors adapt very little if at all// once it is activated it may continue to send impulses into the CNS for some time

Inner tunic

consists of RETINA, which contains the visual receptor cells (photoreceptors)/ nearly transparent sheet of tissue is continuous with the optic nerve in the back of the eye and extends forward as the inner lining of the eyeball/ it ends just behind the margin of the ciliary body /thin and delicate but its structure is complex, including retinal pigment epithelium, neurons, nerve fibers, and limiting membranes there are five major groups of retinal neurons/ the nerve fibers of three of these groups are: the PHOTRECEPTORS, BIPOLAR NEURONS, and GANGLION CELLS/ they provide a direct pathway for impulses triggered in the photoreceptors to the optic nerve and brain nerve fibers of the other two groups of retinal cells: HORIZONTAL CELLS and AMACRINE CELLS/ they pass laterally between retinal cells / these cells modify the pattern of impulses conducted on the fibers of the direct pathway MACULA LUTEA- in the central region od the retina is a yellowish spot called this and it occupies about 1 square mm FOVEA CENTRALIS- depression in center of macula lutea that is in the region of the retina that produces the sharpest vision OPTIC DISC- just medial to the fovea centralis is an area called this / here nerve fibers from the retina leave the eye and become parts of the optic nerve / referred to as blind spot of eye bc it lacks receptor cells space enclosed by lens, ciliary body, and retinas the largest compartment of the eye called the POSTERIOR CAVITY / it is filled with jellylike transparent fluid called VITREOUS HUMOR, which with some collagen fibers comprise the VITREOUS BODY

light must pass through what to get to photoreceptors:

cornea, aqueous humor, lens, vitreous humor, and several layers of retina

to be tasted a chemical must:

dissolve in saliva, which is a watery fluid surrounding the taste buds salivary glands supply this fluid

visual accessory organs

each eye, lacrimal gland, and associated extrinsic muscles are hours in the orbital cavity of the skull EYELID- composed of four layers-- skin, muscle, connective tissue, and conjunctiva/ skin of eyelid is the thinnest of the body orbicularis oculi--muscle that moves the eyelid// fibers encircle the opening between the lids and spread out onto the cheek and forehead// muscle acts as sphincter that closes the lids when it contracts levator palpebrae superioris - muscle of eyelid// fibers arise in roof of the orbit and are inserted in the connective tissue of the upper lid// when contracted upper lids raise and eye opens connective tissue layer contains modified sebaceous glands that secrete an oily substance that keeps lids from sticking together CONJUNCTIVA- is a mucous membrane that lines the inner surfaces of the eyelids and folds back to cover the anterior surface of the eyeball except for its central portion (cornea)/ in eyelids=thick/ on eyeball= thin / freely movable and transparent LACRIMAL APPARATUS- consists of lacrimal gland which secretes tears , and a series of ducts which carry tears to nasal cavity / the gland is in the orbit superior and lateral to the eye / tears secreted continuously and spread medially across eye two small ducts (superior and inferior canaliculi) collect tears and their openings (puncta) can be seen on medial borders of the eyelids fluid then moves into the LACRIMAL SAC which lies in a deep groove of the lacrimal bone an then to nasolacrimal duct that empties into nasal cavity lysozyme-gladular cells of conjunctiva secrete tearlike liquid with antibacterial proteins reducing risk of eye infections when a person cries parasympathetic nerve fibers conduct motor impulses to the lacrimal glands

taste cells (gustatory cells)

each taste bud includes a group of modified epithelial cells and function as sensory receptors each of our 10,000 taste buds 50 to 150 taste cells interwoven among and wrapped around the taste cells is a network of sensory fibers whose ends closely contact the receptor cell membranes stimulated receptor cell triggers an impulse which is conducted along a nearby fiber into the brain

basilar membrane

extends from the bony shelf of the cochlea and forms the floor of the cochlear duct it has many thousands of elastic fibers and becomes thinner from the base of cochlea to its apex vibrations entering the perilymph at the oval window travel along the scala vestibuli and pass through the vestibular membrane to enter the endolymph of the cochlear duct where they move the basilar membrane after passing through the bm, the vibrations enter the perilymph of the scala tympani, and movement of the membrane covering the round window dissipates their force into the air in the tympanic cavity

special senses

have more specialized receptors and are confined to structures in the head, such as eyes and ears

cerebral cortex interprets:

information from receptor cells that travel along sensory fibers

inner (internal) ear

inner ear is a complex system of intercommunicating chambers and tubes called a LABYRINTH each ear has two such regions -- bony labyrinth and membranous labyrinth bony(osseous) labyrinth- is a cavity within the temporal bone membranous labyrinth- tube that lies within the bony labyrinth and has similar shape between the bony and membranous labyrinth is a fluid called PERILYMPH, secreted by cells in the wall of the bony labyrinth ENDOLYMPH- in the membranous labyrinth is a slightly different fluid called this parts of the labyrinths include a COCHLEA that functions in hearing and three SEMICIRCULAR CANALS that provide a sense of equilibrium VESTIBULE- bony chamber between the cochlea and the semicircular canals, houses membranous structures that serve both hearing and equilibrium

salt receptors

ionized inorganic salts mainly stimulate these receptors quality of sensation depends upon the type of positively charged ion that it releases into a solution such as Na + (table salt)

tympanic membrane

is a semitransparent membrane covered by a thin layer of skin on its outer surface and by mucous membrane on the inside has an oval margin and is cone shaped, with the apex of the cone directed inward the tympanic membrane vibrates back and forth in response in response to sound waves, reproducing the vibrations of the sound-wave source

3 AUDITORY OSSICLES:

malleus, incus, stapes attached to the walls of the tympanic cavity by tiny ligaments and are covered by mucous membrane bridge the tympanic membrane and the inner ear, transferring vibrations between these parts specifically the malleus is attached to the tympanic membrane, helping to maintain its conical shape/ when tympanic membrane vibrates the malleus vibrates in unison with it the malleus vibrates the incus, and the incus passes the movement on to the stapes ligaments hold the stapes to an to an opening in the wall of the tympanic membrane called the OVAL WINDOW vibration of the stapes, which acts like a piston at the oval window, transfers vibrations to a fluid within the inner ear vibrations of fluid stimulate the hearing receptors in addition to transferring vibrations, the ossicles form a lever system that helps increase(amplify) the force of the vibrations as they pass from the tympanic membranes to the oval window bc ossicles transfer vibrations from large surface of tympanic membrane to much smaller are of oval window, the vibrational force strengthens as it travels from outer to inner ear /result is pressure at oval window is 22 times greater than that which sound waves exert on the tympanic membrane

proprioceptors

mechanoceptors that send info to the CNSabout body position and the length and tension of skeletal muscle lamellated corpuscles function as pressure receptors in joints the other main proprioceptors are stretch receptors: muscle spindles and Golgi tendon organs MUSCLE SPINDLES- located throughout skeletal muscles/ each spindle consists of several small, modified skeletal muscle fibers(intrafusal fibers) enclosed in a connective tissue sheath each intrafusal fiber has near its center a specialized nonstriated region with the end of a sensory nerve fiber wrapped around it/ striated portions of the intrafusal fiber contract to keep the spindle taut at different muscle lengths thus if the whole muscle is stretched , the muscle spindle is also stretched, triggering sensory impulses on its nerve fibers/ these sensory fibers synapse in the spinal cord with lower motor neurons leading back to the same muscle/ in this way, stretch of the muscle spindle triggers impulses that contract the skeletal muscle of which it is a part this action is called a STRETCH FLEX, opposes the lengthening of the muscle and helps maintain desired position of limb GOLGI TENDON ORGANS- are in tendons close to their attachments to muscles/ each GTO connects to a set of skeletal muscle fibers and is innervated by a sensory neuron/have high thresholds and increased tension stimulates them /sensory impulses from them produce a reflex that inhibits contraction of the muscle whose tendon they occupy / therefore GTO stimulate a reflex with an effect that is opposite of a stretch reflex

taste cells are:

modified epithelial cells and divide continually snd differentiate into new taste cells functions for only about three days before it is replaced

middle ear has 2 small skeletal muscles attached to the auditory ossicles which are:

muscles controlled by a reflex TENSOR TYMPANI is inserted on medial surface of the malleus and is anchored to the cartilaginous wall of the auditory tube/ when it contracts, it pulls the malleus inward/ maintains tension on tympanic membrane/ this is important bc loose tympanic membrane would not be able to effectively transmit vibrations to ossicles STAPEDIUS is attached to the posterior side of the stapes and the inner wall of the tympanic cavity/ it pulls the stapes outward when it contracts

olfaction adaptation

olfaction undergoes this very rapidly so the intensity of an odor drops about 50 percent within a second following stimulation within a minute receptors may become almost insensitive to a given oder which is why we get used to a smell if we've been around it for an extended period of time olfactory receptor neurons are the only nerve cells in direct contact with outside environment therefore prone to damage basal cells along basement membrane of olfactory epithelium regularly divide and yield cells that replace lost neurons which makes the neurons unusual in that they are replaced when damaged

olfactory pathways

once olfactory receptor cells are stimulated, impulses conducted along their axons through tiny openings in cribriform plates of ethmoid bone these fibers which collectively form the first cranial nerve synapse with neurons located in the enlargements of the OLFACTORY BULBS which are structures that lie on either side of crista Galli of the ethmoid bone in the olfactory bulbs, the sensory impulses travel along the OLFACTORY TRACTS to portions of limbic system(brain center for memory and emotions) olfactory cortex- main interpreting area for olfactory impulses and are deep within the temporal lobes and at bases of the frontal lobes, anterior to hypothalamus

axons of ganglion cells in retina leaves the eyes forming the :

optic nerve right optic tract= fibers from nasal half of left eye and temporal half of right eye left optic tract= fiber from nasal half of right eye and temporal half of left eye

ear

organ of hearing has outer(external), middle, and inner(internal) sections in addition to making hearing possible, the ear provides the sense of equilibrium

olfactory organs

organs appear as yellowish brownish masses within pinkish mucous membrane cover upper parts of the nasal cavity, superior nasal conchae, and a portion of the nasal septum olfactory receptor cells are bipolar neurons surrounded by columnar epithelial cells / neurons have knobs at the distal ends of their dendrites covered with hairlike cilia odorant molecules are chemicals that stimulate olfactory receptor cells /dissolved partially in nasal cavity around cilia then bind to receptor proteins on cilia to be detected odorant molecule depolarizes olfactory receptor cells and thereby generating action potentials if depolarization reaches threshold

sensation of pain being when

pain impulses reach the level of thalamus- that is before they even reach the cerebral cortex however cerebral cortex must judge intensity of pain and location/ also responsible for emotional and motor responses to pain

visceral pain

pain receptors are the only receptors in viscera whose stimulation produces sensation pain receptors in organ respond differently to stimulation than ones in surface tissues

external acoustic meatus

passes into the temporal bone near this opening , hairs guard the tube the opening and tube are lined with skin that has many modified sweat glands called CERUMINOUS GLANDS, which secrete wax(cerumen) hairs and wax help keep large foreign objects, such as insects, out of the ear

diminished senses are often one of the first signs of significant aging

presbycusis- hearing loss due to degeneration of nerve pathways to the brain / may affect ability to understand speech floaters- specks of tiny dense clumps of gel like deposits presbyopia- inability to read small print up close as one gets older /loss of elasticity in lens glaucoma- develops in the eyes as a person ages when the rate of aqueous humor formation exceeds the rate of its removal/ excessive fluid pressure tonometer- tool used to measure eye pressure cataract- lens or capsule slowly becomes cloudy opaque and bicolored adding yellow tinge to sight

sensation

raw form in which sensory receptors send info to the brain

visceral senses

receptors in internal organs include lamellated corpuscles and free nerve endings ex of info these receptor convey= sense of fullness after eating and discomfort of intestinal gas

middle ear infection(otitis media)

red bulging tympanic membrane caused by bacteria reaching middle ear from nose or throat instrument used called otoscope

photoreceptors of the eye are modified neurons of 2 distinct types:

rods- have long thin projections at their terminal ends cones- have short blunt projections retina- has about 100 million rods and 3 million cones rods and cones occupy a deep layer of the retina closely associated with a layer of retinal pigment epithelium/ projections extend into the pigmented layer and contain light sensitive visual pigments retinal pigment epithelium(STORES VITAMIN A) absorbs light that the receptors do not absorb only stimulated when light reaches them rods are hundreds of times more sensitive than are cones / rods provide more vision in dim light / rods = black and white and more general outlines /cones = color and sharp images fovea centralis in macula luteas lacks rods but has densely packed cones

touch and pressure senses

senses of touch and pressure derive from 3 types of receptors /as a group these receptors sense mechanical forces that deform or displace tissues. These receptors include: FREE NERVE ENDINGS- simplest receptors, common in epithelial tissue, where they lie between epithelial cells/ responsible for sensation of itching TACTILE (MEISSNER'S) CORPUSCLES- small, oval masses of flattened connective tissue cells in connective tissue sheaths/ Two or more sensory fibers branch into each corpuscle and end within it as tiny knobs/ tactile corpuscles are abundant in hairless areas of the skin such as lips, fingertips, nipples, palms, and external genital organs/ provide fine touch, such as distinguishing two points on the skin, where an object touches to judge its texture LAMELLATED (PACINIAN) CORPUSCLES- relatively large, ellipsoidal structures composed connective tissue fibers and cells/ common in deeper dermal tissues of the hands, feet, penis, clitoris, urethra and breasts and also in the connective tissue capsules of synovial joints / heavier pressure and stretch stimulate lamellated corpuscles and also detect vibrations in tissues

general senses

senses whose sensory receptors are widespread, associated with skin, muscles, joints, and viscera these senses can be divided into 3 groups: 1.EXTERORECPTIVE CELLS- associated wth changes at body surface/ include the senses of touch, pressure, temp, and pain 2. INTEROCEPTIVE SENSES-(visceroreceptive) associated with changes in viscera ( blood pressure stretching blood vessels, an ingested meal stimulating pH receptors in small intestine, and so on) 3.PROPRIOCEPTIVE SENSES- associated with changes in muscles and tendons and in body position

taste pathways

sensory impulses from taste receptor cells in the anterior two- thirds of the tongue travel on fibers of the facial nerve(VII) impulses from taste receptors in the posterior one-third of the tongue and in back of mouth pass along the glossopharyngeal nerve (IX) impulses from base of the tongue and pharynx travel on vagus nerve (X) These cranial nerves conduct impulses into medulla oblongata then impulses ascend to the thalamus and are directed to the gustatory cortex of the cerebrum, located in the insula

sensation occurs when:

sensory neurons reach threshold and the resulting action potentials cause the brain to become aware of that sensory event pain is a sensation

Dif between sensory receptors and membrane receptor

sensory receptors may be as small as the individual cell or as large as complex organs such as eye or ear/ sensory receptor respond to sensory stimuli membrane receptors are molecules such as proteins and glycoproteins on the cell membranes/ they enable cells such as olfactory receptor cells to respond to specific molecules

stereoscopic vision

simultaneously perceives distance, depth ,height, and width of objects requires vision of two eyes visual cortex interprets the two images and as a result the perception of a single object is seen in three dimensions

taste buds

special organs of taste resemble orange sections and associate on the surface of the tongue with tiny elevations called PAPILLAE are also scattered in roof of mouth, linings of the cheeks, and the walls of the pharynx structure is somewhat spherical with an opening called a TASTE PORE on its free surface tiny projections (microvilli), called TASTE HAIRS protrude from the outer ends of the taste cells and jut through the taste pore /these taste hairs are the sensitive parts of the receptor cells

special senses

special senses are those whose sensory receptors are part of large, complex sensory organs in the head. these senses and their respective organs include the following smell- olfactory organs taste- taste buds hearing equilibrium -ears sight-eyes

the feeling of equilibrium (balance) derives from two senses--

static equilibrium -organs associated with this sense the position of the head, maintaining stability and posture when the head and body are still dynamic equilibrium - the organs of this detect motion and aid in maintaining balance when the head and body suddenly move or rotate

sour receptors

stimulated by acids intensity is roughly proportional to the concentration of the hydrogen ions in the substance being tasted

five primary taste sensations :

sweet, sour, salty, bitter, and umami each of the many flavors we experience results from one of the primary sensations or from a combination of them way we experience flavors may also reflect the concentration of chemicals as well as the sensations of smell, texture(touch), and temperature spicy food may trigger pain receptors causing a burning sensation salts and acids act through specific ion channels sensations of bitter, sweet, umami include specific membrane receptors

umami

taste long recognized in Japan/ word means delicious arises from binding of certain amino acids, including glutamic acid and aspartic acid to specific receptors flavor enhancer monosodium glutamate(MSG) used in many prepared foods is formed from glutamic acid and also stimulates umami receptors

tympanic reflex

tensor tympani and stapedius muscles are the effectors in this reflex is elicited in about 1/10th of a second after a loud, external sound reflex contracts the muscles, and the malleus and stapes move as a result the bridge of ossicles in the middle ear becomes more rigid, reducing its effectiveness in transferring vibrations to the inner ear reduces pressure from loud sounds that might otherwise damage the hearing receptors ordinary vocal sounds also elicit the tympanic reflex, such as when a person speaks or sings this action muffles the lower frequencies of such sounds, improving the hearing of higher frequencies, which are common in human vocal sounds

determination of eye color

the amount and distribution of melanin in the irises and the density of tissue in the body of the iris determine eye color blue or green eyes= when melanin is present only in epithelial cells on the iris's posterior surface, the iris reflects more colors of light gray eyes= same distrubution of melanin is denser in the body of the iris brown eyes= when melanin is within the body of the iris as well as in the posterior epithelial covering

outer tunic

the anterior 6th of the outer tunic bulges forward as the CORNEA ,the windows of the eyes/ helps focus entering light rays/ largely composed of connective tissue with a thin layer of epithelium sclera- cornea is continuous with this/ the white portion of the eye/ makes up posterior 5/6th of the outer tunic and is opaque sue to many large disorganized collagen and elastic fibers/ protects eye and is an attachment for extrinsic muscles optic nerve-- in back of the eye this nerve and blood vessels pierce the sclera/the dura mater that encloses these structures in continuous with sclera

pain pathways

the axons(fibers) that conduct impulses away from pain receptors are of two main types: fast pain fibers- (also knows as A-delta fibers) are myelinated/ conduct impulses rapidly, at velocities up to 30 meters per second/ these impulses are associated with immediate sensation of sharp pain typically originates in local area of skin/ continues after pain-producing fiber stop slow pain fibers- (C fibers) are unmyelinated/ conduct impulses more slowly than fast pain fibers at velocities up to 2 meters per second/ impulses cause a delayed, dull, aching pain sensation that may be widespread and difficult to pinpoint/ such pain may continue after the original stimulus ceases/ although immediate pain is usually sensed as coming from the surface, delayed pain is felt in deeper tissues as well as in the skin/ visceral pain impulses are generally carried on C fibers dual sensation = result of a usual event that stimulates pain receptors in both fast and slow pain fibers/ sharp pricking pain then dull aching pain sensation/ more intense and may worsen over time

dynamic equilibrium

the bony semicircular canals lie at right angles and occupy 3 different planes of space two of them, the ANTERIOR CANAL and POSTERIOR CANAL are oriented vertically whereas the third LATERAL CANAL is horizontal AMPULLA- in perilymph of each bony canal is a membranous semicircular duct that ends in a swelling called this / ampullae communicate with the utricle of the vestibule an ampulla contains a ridge that crosses the tube and houses a sensory organ crista ampullaris- each of these organs are called this// has a number of sensory hair cells and supporting cells the hairs of the hair cells extend upward into a dome shaped mass called a CUPULA// hair cells connected at bases to dendrites of neurons when head or torso moves so does semicircular canals but the fluid inside the membranous ducts remain stationary due to inertia cupula bends in opposite direction of head and hairs bend with it moving hairs stimulate neurons and impulses are conducted to the brain parts of cerebellum are important in interpreting impulses form semicircular canals

perception occurs when:

the brain interprets those sensory impulses realizing you've stepped on a tack is perception

structure of the eye

the eye is a hollow, spherical structure about 2.5 cm in diameter 3 distinct layers: an outer fibrous tunic, a middle vascular tunic , and an inner nervous tunic

iodopsins

the light sensitive pigments of cones are similar to rhodopsin in that they are composed of retinal combines with a protein in the rods; the protein however differs than that in rods the three sets of cones in the retina all contains an abundance of one of the 3 different visual pigments: erythrolabe- pigment that is most sensitive to red light chlorolabe- most sensitive to green light cyanolabe- most sensitive to blue light if all three types are stimulated then light is perceived as white, and if none are stimulated then it is seen as black people who lack a cone type are color blind

cochlea

tube shaped a bit like snail shell, coiled a bony core, the MODIOLUS a thin bony shelf (SPIRAL LAMINA) extends out from the core and coils around it within the tube a portion of the membranous labyrinth in the cochlea in the COCHLEAR DUCT(scala media) runs inside the tube opposite of the spiral lamina, and together these structures divide the tube into upper and lower compartments the upper compartment called the SCALA VESTIBULI, leads from the oval window to the apex of the spiral the lower compartment called the SCALA TYMPANI extends from the apex of the spiral to a membrane-covered opening in the wall of the inner ear the tympanic cavity, called the ROUND WINDOW these compartments form the bony labyrinth of the cochlea and they are filled with perilymph at the apex of the cochlea, beyond the tip of the cochlear duct, a small opening, the HELICOTREMA, connects the perilymph in the upper and lower compartments and allows the fluid pressures in them to equalize cochlear duct ends as a closed sac at the apex of the cochlea/ the duct is separated from from the scala vestibuli by a VESTIBULAR MEMBRANE (Reissner's membrane) and from the scala tympani and from the scala tympani by a BASILAR MEMBRANE

most sensory neurons are:

unipolar neurons portion of neuron associated with dendrites ,called peripheral process , functions like an axon because of this ch 12 calls neuron processes that bring sensory information to CNS "sensory fibers" or "afferent fibers" no matter the type of neuron

sweet receptors

usually stimulated by carbohydrates but a few inorganic substances, including some salts of lead and beryllium, also elicit sensations

bitter receptors

variety of chemicals stimulates these including many organic compounds inorganic salts of magnesium and calcium produce bitter sensations too extreme sensitivity to bitter tastes is inherited 25 types of bitter receptors have been identified alkaloids - group of bitter compounds of medical interest, which include a number of poisons such as strychnine, nicotine, and morphine spitting out of bitter substances may be a protective mechanism

middle tunic

vascular tunic of eyeball (uveal layer) includes choroid coat, the ciliary body, and the iris CHOROID COAT is in the posterior 5-6ths of the globe of the eye, loosely joins the sclera/ blood vessels pervade the choroid coat and nourish surrounding tissues/ contains abundant pigment producing meloncytes that give it a brownish blackish appearance / melanin of these cells absorbs excess light and helps keep the inside of the eye dark CILIARY BODY-- which is the thickest part of the middle tunic, extends anteriorly and inward from the choroid coat and forms a ring within the front of the eye ciliary processes- radiating folds inn ciliary body ciliary muscles- groups of smooth muscle cells in ciliary body LENS- suspensory ligaments (many strong delicate fibers) extend inward fro the ciliary processes this transparent structure in place/ body of lens lacks blood vessels, lies directly behind the iris and pupil and is composed of specialized epithelial cells / largely composed of intracellular material/ quite elastic and can assume a globular shape // suspensory ligaments pull outward flattening the lens ACCOMMODATION- if tension on suspensory ligaments relaxes the elastic capsule rebounds and the lens surface becomes more convex/ this change occurs in the lens when the eye focuses to view a close object / ciliary muscles relax the suspensory ligaments / - lens thickens as ciliary muscles contract -lens thins as ciliary muscles relax lens fibers- specialized columnar epithelial cells that that are formed from the division of original layer of epithelium/ thickens lens slowly throughout life / more than 90 percent of proteins in a dense are lens crystallins which aggregate into these fibers/ these proteins provide transparency of lens/ \ IRIS-thin diaphragm mostly composed of connective tissue and smooth muscle // it is the colored portion of the eye from the outside / iris extends forward form periphery of ciliary body and lies between the cornea and lens // iris divides the space separating these parts called the ANTERIOR CAVITY// iris separates anterior and posterior chamber of anterior cavity AQUEOUS HUMOR- the epithelium on the inner surface of the ciliary body continuously secretes this watery fluid into the posterior chamber/ the fluid then circulates from this Chamber through the PUPIL( which is a circular opening in the center of the iris ), and into the anterior chamber / aqueous humor fills the space between the cornea and the lens providing nutrients and maintaining shape anterior scleral venous sinus (Canal of Schlemm)- aqueous humor fluid leaves the anterior chamber through veins and a special drainage canal called this/ its in the wall of the anterior chamber at the junction of the cornea and sclera smooth muscle cells of iris form 2 groups : circular set and radial set which control the size of the pupil through which light passes circular set (pupillary constrictor) -- acts as a sphincter and when it contracts the pupil gets smaller and intensity of light entering decreases radial set (pupil dilator)-when contracted the diameter of the pupil increases and the intensity of light entering increases

referred pain

visceral pain may feel as if it is coming from some part of the body other than the part being stimulated in this phenomenon ex: pain in heart may be referred to the left shoulder or the medial surface of the left upper limb/ pain in urogenital tract may be refereed to lower central region of abdomen or to the sides between ribs and the hip referred pain may derive from COMMON NERVE PATHWAYS that sensory impulses coming from both skin areas and from internal organs use during a heart attack the cerebral cortex may incorrectly interpret the source of the impulses as the shoulder left upper limb rather than heart

temperature receptors(thermoreceptors) include two groups of free nerve endings in the skin:

warm receptors- those that respond to warmer temperatures/most sensitive to temperatures above 77 degrees and become unresponsive at temp above 113 degrees( temp near and above 113 degrees can also trigger pain receptors, producing a burning sensation) cold receptors- those that respond to colder temperatures / most sensitive between temp 50 and 68 degrees/ temp dropping below 50 also trigger pain receptors, producing a freezing sensation both types of receptors rapidly adapt during intermediate temps

spiral organ (organ of Corti)

which contains about 16,000 hearing receptor cells, is on the superior surface of the basilar membrane and stretches from the apex to the base of the cochlea receptor cells called HAIR CELLS are in four parallel rows with many hairlike processes known as stereovilli (also called stereocilla) that extend into the endolymph of the cochlear duct above these hair cells is a TECTORIAL MEMBRANE, attached to the bony shelf of the cochlea/ it passes like a roof over the receptor cells, contacting the tips of their hairs the louder the sound= hair cells pushed upward against tectorial membrane

sensation depends on:

which region of cerebral cortex that receives the impulse