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A&P ch 16
| spinal gating | |
| pheromones | |
| tympanic reflex | |
| conductive vs. sensorineural deafness | |
| glaucoma | |
| photopupillary reflex | |
| Sensory input | is vital to the integrity of personality and intellectual function |
| Information communicated by the sense organs | rarely comes to our conscious attention • blood pressure, body temperature, and muscle tension |
| Sense organs initiate | somatic and visceral reflexes that are indispensable to homeostasis and to our survival |
| Sensation | a subjective awareness of the stimulus • most sensory signals delivered to the CNS produce no conscious sensation • filtered out in the brainstem • some do not require conscious awareness like pH and body temperature • sensory receptor: |
| sensory receptor: | a structure specialized 2 detect a stimulus •some receptors r bare nerve endings others r true sense organs |
| sense organs | nerve tissue surrounded by other tissues that enhance response to a certain type of stimulus •accessory tissues may include added epithelium muscle or connective tissue |
| receptor potential: | small, local electrical change on a receptor cell brought about by an initial stimulus • results in release of neurotransmitter or a volley of action potentials that generates nerve signals to the CNS |
| Transduction | the conversion of one form of energy to another • fundamental purpose of any sensory receptor • conversion of stimulus energy (light, heat, touch, sound, etc.) into nerve signals • sense organ, gasoline engine, light bulb are all transducers |
| Sensory receptors transmit four kinds of information: | modality, location, intensity, duration |
| Modality | type of stimulus or the sensation it produces • vision, hearing, taste • labeled line code: |
| labeled line code: | all action potentials are identical; each nerve pathway from sensory cells to the brain is labeled to identify its origin, and the brain uses these labels to interpret what modality the signal represents |
| location | encoded by which nerve fibers are issuing signals to the brain |
| receptive field: | area that detects stimuli for a sensory neuron • receptive fields vary in size: fingertip versus skin on back (two-point touch discrimination) |
| sensory projection: | brain identifies site of stimulation |
| projection pathways: | the pathways followed by sensory signals to their ultimate destination in the CNS |
| intensity | encoded in three ways • brain can distinguish intensity by: • which fibers are sending signals • how many fibers are doing so • how fast these fibers are firing |
| duration | how long the stimulus lasts • change in firing frequency over time |
| sensory adaptation: | if stimulus is prolonged, the firing of the neuron gets slower over time, and we become less aware of the stimulus |
| Classification of Receptors | by modality by origin of stimuli by distribution by adeaptation |
| Classification of Receptors by modality | • thermoreceptors, photoreceptors, nociceptors, chemoreceptors, and mechanoreceptors |
| Classification of Receptors by origin of stimuli | • exteroceptors: detect external stimuli • interoceptors: detect internal stimuli • proprioceptors: sense body position and movements |
| Classification of Receptors by distribution | • general (somesthetic) senses: widely distributed • special senses: limited to head • vision, hearing, equilibrium, taste, and smell |
| Classification of Receptors by adaptation | phasic receptor and tonic receptor |
| phasic receptor: | generate a burst of action potentials when first stimulated, then quickly adapt and sharply reduce or stop signaling even though the stimulus continues • smell, hair movement, and cutaneous pressure |
| tonic receptor: | adapt slowly, generate nerve signals more steadily • proprioceptors: body position, muscle tension, and joint motion |
| The General Senses | • receptors for the general senses are relatively simple in structure and physiology • consist of one or a few sensory nerve fibers and a spare amount of connective tissue • unencapsulated and encapsulated nerve endings |
| unencapsulated nerve endings | dendrites not wrapped in connective tissue |
| free nerve endings | • for pain and temperature • skin and mucous membrane |
| tactile discs | • for light touch and texture • associated with Merkel cells at base of epidermis |
| hair receptors | • wrap around base hair follicle • monitor movement of hair |
| Encapsulated nerve endings | • dendrites wrapped by glial cells or connective tissue • connective tissue enhances sensitivity or selectivity of response |
| tactile (Meissner) corpuscles | • light touch and texture • dermal papillae of hairless skin |
| Krause end bulbs | • tactile; in mucous membranes |
| lamellar (Pacinian) corpuscles | phasic • deep pressure, stretch, tickle, and vibration • periosteum of bone, and deep dermis of |
| bulbous (Ruffini) corpuscles: | tonic • heavy touch, pressure, joint movements, and skin stretching |
| table 16.1 | |
| Somatosensory Projection Pathways | from receptor to final destination in the brain, most somesthetic signals travel by way of three neurons |
| first-order neuron | afferent neuron•from body, enter dorsal horn of spinal cord via spinal nerves • from head, enter pons & medulla via cranial nerve • touch, pressure, and proprioception on large, fast, myelinated axons • heat and cold on small, unmyelinated, slow fibers |
| second-order neuron | • decussation to opposite side in spinal cord, medulla, or pons • end in thalamus, except for proprioception, which ends in cerebellum |
| third-order neuron | thalamus to primary somesthetic cortex of cerebrum |
| Projection pathways for pain | • two main pain pathways to brain, and multiple subroutes |
| nociceptor | stimulates secondorder nerve fiber |
| substance P | is neurotransmitter at this synapse |
| second-order fiber | transmits signal up the spinothalamic tract or spinoreticular tract to the thalamus |
| thalamus | relays the signals through third-order neurons to the cerebral cortex where one becomes conscious of the pain |
| pain | discomfort caused by tissue injury or noxious stimulation, and typically leading to evasive action |
| nocieptors | two types providing different pain sensations; fast pain and slow pain |
| fast pain | travels myelinated fibers at 12 to 30 m/s • sharp, localized, stabbing pain perceived with injury |
| slow pain | travels unmyelinated fibers at 0.5 to 2 m/s • longer-lasting, dull, diffuse feeling |
| somatic pain | from skin, muscles, and joints |
| visceral pain | from the viscera • stretch, chemical irritants, or ischemia of viscera (poorly localized) |
| referred pain: | pain in viscera often mistakenly thought to come from skin or other superficial site •results from convergence of neural pathways in CNS •brain assumes visceral pain is coming from skin•brain cannot distinguish source •heart pain felt in shoulder or arm |
| gustation | (taste): sensation that results from action of chemicals on taste buds • 4,000 taste buds mainly on tongue • inside cheeks, and on soft palate, pharynx, and epiglottis |
| lingual papillae | filiform, foliate, fungiform, vallate (circumvallate) |
| filiform | no taste buds • important for food texture |
| foliate | no taste buds • weakly developed in humans |
| fungiform | • at tips and sides of tongue |
| vallate | (circumvallate) • at rear of tongue • contains one-half of all taste buds |
| taste buds | • all taste buds look alike • lemon-shaped groups of 40 to 60 taste cells, supporting cells, and basal cells |
| taste cells | have tufft off apiicall miicroviilllii (taste hairs) that serve as receptor surfface ffor taste molleculles |
| taste pores | pit in which the taste hairs project; to be tasted, molecules must dissolve in saliva and flood the taste pore |
| taste hairs | are epithelial cels, not neurons • synapse wiith and rellease neurotransmiiters onto sensory neurons at theiir base |
| basal cells | • stem cellls that repllace taste cellls every 7 to 10 days |
| supporting cells | resemblle taste cellls wiithout taste haiirs, synaptiic vesiiclles, or sensory rolle |
| 5 primary sensations | salty, sweet, sour,butter, umami |
| salty | produced by metal ions (sodium and potassium) |
| sweet | associated with carbohydrates and other foods of high caloric valuev |
| sour | acids ex; citrus fruits |
| bitter | associated with spoiled foods and alkaloids such as nicotine, caffeine, quinine, and morphine |
| umami | “meaty” taste of amino acids in chicken or beef broth |
| how is taste influenced | is influenced by food texture, aroma, temperature, and appearance |
| mouthfeel | detected by branches of lingual nerve in papillae |
| regional differences in taste sensations on tongue | tip is most sensitive to sweet, edges to salt and sour, and rear to bitter |
| activate second-messenger systems | • sugars, alkaloids, and glutamate bind to receptors which activates G proteins and second-messenger systems within the cell |
| depolarize cells directly | • sodium and acids penetrate cells and depolarize directly |
| two mechanisms of action: | activate second-messenger systems and depolarize cells directly; either mechanism results in release of neurotransmitters that stimulate dendrites at base of taste cells |
| olfactory mucosa | contains 10-20 million olfactory cells, which are neurons, as well as epithelial supporting cells & basal stem cells • mucosa of superior concha, nasal septum, and roof of nasal cavity covering about 5 cm2 • on average 2,000 to 4,000 odors distinguished |
| olfactory cells | • are neurons shaped like little bowling pins • head bears 10 to 20 cilia called olfactory hairs that have binding sites for odorant molecules and are nonmotile • lie in a tangled mass in a thin layer of mucus • basal end of each cell becomes the axon |
| olfactory cells part 2 | axons collect into small fascicles &leave cranial cavity through cribriform foramina in the ethmoid bone •fascicles are collectively regarded as cranial nerve I •only neurons in body directly exposed to the external environment • have a lifespan of only 6 |
| odorant molecules | bind to membrane receptor on olfactory hair; • activate G protein & cAMP system •opens ion channels for Na+ or Ca2+ •depolarizes membrane& creates receptor potential •action potential travels to brain •olfactory receptors adapt quickly due to synaptic inh |
| hydrophilic | diffuse through mucus |
| hydrophobic | transported by odorant-binding protein in mucus |
| olfactory cells synapse | in olfactory bulb • on dendrites of mitral and tufted cells • dendrites meet in spherical clusters called glomeruli • each glomeruli dedicated to single odor because all fibers leading to one glomerulus come from cells with same receptor type |
| hearing | a response to vibrating air molecules |
| equillibrium | : the sense of motion, body orientation, '7balance • both senses reside in the inner ear, a maze of fluid-filled passages and sensory cells • fluid is set in motion and the sensory cells convert this motion into an informative pattern of action potentials |
| sound | any audible vibration of molecules • a vibrating object pushes on air molecules • in turn push on other air molecules • air molecules hitting eardrum cause it to vibrate |
| pitch | our sense of whether a sound is “high” or “low” • determined by the frequency: cycles per second, or hertz (Hz) • human hearing range is 20 to 20,000 Hz • infrasonic frequencies below 20 Hz• ultrasonic frequencies above 20,000 Hz • speech is 1,500 to 5 |
| loudness | the perception of sound energy, intensity, or amplitude of the vibration • expressed in decibels (dB) • prolonged exposure to sounds > 90 dB can cause damage 16-24 |
| ear | has three sections: outer, middle, and inner ear • first two are concerned only with the transmission of sound to the inner ear • inner ear: vibrations converted to nerve signals |
| outer ear | a funnel for conducting vibrations to the tympanic membrane |
| auricle | (pinna) directs sound down the auditory canal • shaped and supported by elastic cartilage |
| auditory canal | passage leading through the temporal bone to the tympanic membrane |
| external acoustic meatus | slightly S-shaped tube that begins at the external opening and courses for about 3 cm |
| guard hairs and cerumen | • guard hairs protect outer end of canal • cerumen (earwax): mixture of secretions of ceruminous and sebaceous glands and dead skin cells |
| middle ear | located in air-filled tympanic cavity in temporal bone tympanic membrane (eardrum) closes inner end of auditory canal that vibrates freely in response to sound • innervated by sensory branches of the vagus and trigeminal nerves; highly sensitive to pain |
| tympanic cavity | is continuous with mastoid air cells • space only 2 to 3 mm wide between outer and inner ears • contains auditory ossicles |
| auditory tube | (eustachian) tube connects middle-ear cavity to nasopharynx • equalizes air pressure on both sides of tympanic membrane • normally flattened and closed, and swallowing and yawning opens it • allows throat infections to spread to the middle ear |
| auditory ossicles | malleus, incus, and stapes; • malleus: attached to inner surface of tympanic membrane • incus: articulates in between malleus and stapes • stapes: footplate rests on oval window (inner ear begins) |
| stapedius and tensor tympani muscles | attach to stapes and malleus otitis media tympanostomy |
| inner ear: baby labyrinth | passageways in temporal bone |
| membranous labyrinth: | fleshy tubes lining bony labyrinth; • filled with endolymph: similar to intracellular fluid • floating in perilymph:similar to cerebrospinal fluid |
| abyrinth: | vestibule and three semicircular ducts |
| cochlea | organ of hearing • winds 2.5 coils around a screwlike axis of spongy bone, the modiolus • threads of the screw form a spiral platform that supports the fleshy tube of the cochlea; has three fluid-filled chambers separated by membranes |
| scala vestibuli: | superior chamber • filled with perilymph • begins at oval window and spirals to apex |
| scala tympani: | inferior chamber • filled with perilymph • begins at apex and ends at round window • secondary tympanic membrane: membrane covering round window |
| scala media | (cochlear duct): triangular middle chamber • filled with endolymph • separated from: • scala vestiboli by vestibular membrane • scala tympani by thicker basilar membrane |
| spiral organ | (organ of Corti): acoustic organ that converts vibrations into nerve impulses |
| Spiral organ | (organ of Corti) has epithelium composed of hair cells and supporting cells • hair cells have long, stiff microvilli called stereocilia on apical surface • gelatinous tectorial membrane rests on top of stereocilia |
| spiral organ has | four rows of hair cells spiraling along its length •inner hair cells: single row of about 3,500 cells • provides for hearing • outer hair cells: three rows of about 20,000 cells • adjustsresponseof cochlea to different frequencies • increases precision |
| tympanic membrane | • has 18 times area of oval window • ossicles concentrate the energy of the vibrating tympanic membrane on an area 1/18 that size • ossicles create a greater force per unit area at the oval window and overcome the inertia of the perilymph |
| vibration of ossicles | causes vibration of basilar membrane under hair cells • as often as 20,000 times per second • hair cells move with basilar membrane |
| stereocilia of outer hair cells | • bathed in high K+ fluid, the endolymph creating electrochemical gradient • outside of cell is +80 mV and inside of cell is near −40 mV • tip embedded in tectorial membrane |
| stereocilium on inner hair cells | • single transmembrane protein at tip that functions as a mechanically gated ion channel •stretchy protein filament (tip link) connects ion channel of one stereo cilium to sidewall of next taller stereo cilium •tallest one is bent when basilar membrane ri |
| Sensory Coding | for sounds to carry meaning, we must distinguish between loudness and pitch |
| variations in loudness | (amplitude) cause variations in intensity of cochlear vibrations •soft sound produces relatively slight up&down motion of basilar membrane •louder sounds make basilar membrane vibrate more vigorously •triggers higher frequency of action potentials •brai |
| pitch | depends on which part of basilar membrane vibrates • at basal end, membrane attached, narrow and stiff • brain interprets signals as high-pitched • at distal end, 5 times wider and more flexible • brain interprets signals as low-pitched |
| sensory fibers begin | at the bases of hair cells • somas form the spiral ganglion around the modiolus • axons lead away from the cochlea as the cochlear nerve • joins with the vestibular nerve to form the vestibulocochlear nerve (cranial nerve VIII) |
| auditory projection pathway | each ear sends nerve fibers to both sides of the pons • end in cochlear nuclei; synapse with second-order neurons that ascend to the nearby superior olivary nucleus • superior olivary nucleus issues efferent fibers back to the cochlea |
| binaural hearing | comparing signals from the right and left ears to identify the direction from which a sound is coming • function of the superior olivary nucleus |
| inferior colliculi | ibers ascend to the inferior colliculi of the midbrain • helps to locate the origin of the sound, processes fluctuation in pitch, and mediates the startle response and rapid head turning in response to loud noise |
| third and fourth order neuron | • third-order neurons begin in the inferior colliculi and lead to the thalamus • fourth-order neurons complete the pathway from the thalamus to the primary auditory complex • involves four neurons instead of three unlike most sensory |
| primary auditory cortex | lies in the superior margin of the temporal lobe • siteofconscious perception of sound • because of extensive decussation of the auditory pathway, damage to right or left auditory cortex does not cause unilateral loss of hearing |
| equillibrium | coordination, balance, and orientation in three-dimensional space |
| vestibular apparatus | : constitutes receptors for equilibrium |
| • three semicircular ducts | • detect only angular acceleration |
| • two chambers | • anterior saccule and posterior utricle • responsible for static equilibrium and linear acceleration |
| static equilibrium: | the perception of the orientation of the head when the body is stationary |
| dynamic equilibrium: | perception of motion or acceleration |
| • linear acceleration: | change in velocity in a straight line (elevator) |
| • angular acceleration: | change in rate of rotation (car turns a corner) |
| macula | a 2 by 3 mm patch of hair cells and supporting cells in the saccule and utricle • macula sacculi: lies vertically on wall of saccule • macula utriculi: lies horizontally on floor of utricle |
| otoliths: | calcium carbonate–protein granules that add to the weight and inertia and enhance the sense of gravity and motion |
| • static equilibrium: | when head is tilted, heavy otolithic membrane sags, bending the stereocilia and stimulating the hair cells |
| • dynamic equilibrium: | in car, linear acceleration detected as otoliths lag behind, bending the stereocilia and stimulating the hair cells • because macula sacculi is nearly vertical, it responds to vertical acceleration and deceleration |
| rotary movements | detected by the three semicircular ducts • bony semicircular canals of temporal bone hold membranous semicircular ducts •each duct is filled w endolymph & opens up as a dilated sac (ampulla) next to the utricle • each ampulla contains crista ampullaris: |
| crista ampullaris | mound of hair cells and supporting cells |
| hair cells of | msacculi macula utriculi & semicircular ducts synapse on vestibular nerve;fibers end in complex of 4 vestibular nuclei on ea side of pons & medulla;nuclei receive input from ears;proces signals bout position/movement of body & relay info to 5 target areas |
| cerebellum: | integrates vestibular information into its control of head and eye movements, muscle tone, and posture |
| nuclei of oculomotor, trochlear, and abducens nerves | (CN III, IV, and VI) to produce vestibulo– ocular reflex: keeps vision fixed on distant object while walking |
| reticular formation: | thought to adjust blood circulation and breathing to postural changes |
| spinal cord: | descend through two vestibulospinal tracts of spinal cord and innervate extensor (antigravity) muscles |
| thalamus: | thalamic relay to cerebral cortex for awareness of position and motor control of head and body |
| 5 target areas | cerebellum, nuclei of oculomotor, trochlear, and abducens nerves , reticular formation, spinal cord, thalamus |
Created by:
sg109