Lecture Material is adapted from Human Anatomy and Physiology Dr. Henrik Pallos THE SPECIAL SENSES
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Visual pathway to the brain and visual fields, inferior view. Both eyes Fixation point Optic tract: Fibers from lateral same side eye & Fibers from medial opposite eye Carries all the information from the same half of the visual field Suprachiasmatic nucleus Pretectal nucleus Lateral geniculate nucleus of thalamus Right eye Left eye Optic nerve Optic chiasma Optic tract Lateral geniculate nucleus Superior colliculus (sectioned) Uncrossed (ipsilateral) fiber Crossed (contralateral) fiber Optic radiation Superior colliculus Occipital lobe (primary visual cortex) The visual fields of the two eyes overlap considerably. Note that fibers from the lateral portion of each retinal field do not cross at the optic chiasma. Corpus callosum Photograph of human brain, with the right side dissected to reveal internal structures.
Visual Pathway To The Brain 1. Axons of retinal ganglion cells form optic nerve 2. Medial fibers of optic nerve decussate at optic chiasma 3. Most fibers of optic tracts continue to lateral geniculate body of thalamus 4. Fibers from thalamic neurons form optic radiation and project to primary visual cortex in occipital lobes
Visual Pathway Fibers from thalamic neurons form optic radiation Optic radiation fibers connect to primary visual cortex in occipital lobes Other optic tract fibers send branches to midbrain, ending in superior colliculi (initiating visual reflexes)
Visual Pathway A small subset of ganglion cells in retina contain melanopsin (circadian pigment) Respond directly to light stimuli and their fibers project to: Pretectal nuclei (involved with pupillary light reflexes) Suprachiasmatic nucleus of hypothalamus, timer for daily biorhythms
Depth Perception Both eyes view same image from slightly different angles Depth perception (three-dimensional vision) results from cortical fusion of slightly different images Requires input from both eyes
Visual Cliff
Visual Processing 1. Retinal cells split input into channels Color, brightness, angle, direction, speed of movement of edges (sudden changes of brightness or color) 2. Lateral geniculate nuclei of thalamus processes Depth perception, cone input emphasized, contrast sharpened 3. Primary visual cortex (striate cortex) raw vision Topographic representation of retina Neurons respond to dark and bright edges, and object orientation Provide form, color, motion inputs to visual association areas (prestriate cortices)
http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/v1/lgn-v1.html
Cortical Processing 4. Occipital lobe centers (visual association areas, anterior prestriate cortices) continue processing of form, color, and movement 5. Complex visual processing extends to other regions "What" processing identifies objects in visual field Ventral temporal lobe "Where" processing assesses spatial location of objects Parietal cortex to postcentral gyrus Output from both passes to frontal cortex Can directs movements based on visual input
Developmental Aspects Vision not fully functional at birth Babies hyperopic (farsighted) eyeball is shorter only gray tones eye movements uncoordinated, often one eye at a time tearless for 2 weeks By 5 th months: can follow moving objects, visual acuity is still poor By 3 rd year: depth perception, color vision well developed By 6 th year: emmetropic eyes developed By 8-9 th year: eye reaches its adult size
Developmental Aspects With age: lens loses clarity and discolors dilator muscles less efficient: pupils stay partly constricted As a result visual acuity drastically decreased by age 70 Lacrimal glands less active so eyes dry, more prone to infection Elderly are also risk for conditions that cause blindness Macular degeneration (progressive deterioration of macula lutea) glaucoma, cataracts, atherosclerosis, diabetes mellitus
Are the dots in between the squares white, black or grey? Is this picture still or moving? Are the lines paralell or crooked? Focus on the 4 dots in the middle of the picture for 30 seconds. Then look at a blank wall and see what you see or more importantly - who do you see? Maybe blink your eyes a few times to find out.
Chemical senses 1. Smell: Olfaction 2. Taste: Gustation Chemoreceptors respond to chemicals in aqueous solution Smell receptors: airborne chemicals dissolved in fluids coating nasal membranes Taste receptors: food chemicals dissolved in saliva
Olfactory receptors. Olfactory epithelium Olfactory tract Olfactory bulb Nasal conchae Route of inhaled air
Olfactory receptors. Olfactory tract Olfactory gland Olfactory epithelium Mucus Mitral cell (output cell, 2 nd order) Glomeruli Olfactory bulb Cribriform plate of ethmoid bone Filaments of olfactory nerve Lamina propria connective tissue Olfactory axon Olfactory stem cell Olfactory sensory Neuron (1 st order) Supporting cell Dendrite Olfactory cilia Route of inhaled air containing odor molecules
Specificity of Olfactory Receptors Humans can distinguish ~10,000 odors ~400 "smell" genes active only in nose 1. Each encodes unique receptor protein Protein responds to one or more odors 2. Each odor binds to several different receptors 3. Each receptor has one type of receptor protein Pain and temperature receptors also in nasal cavities
Physiology of Smell Gaseous/volatile odorant must enter nasal cavity Odorant must dissolve in fluid of olfactory epithelium Activation of olfactory sensory neurons Dissolved odorants bind to receptor proteins in olfactory cilium membranes
Smell Transduction Odorant binds to receptor activates G protein G protein activation camp (second messenger) synthesis camp Na + and Ca 2+ channels opening Na + influx depolarization and impulse transmission Ca 2+ influx olfactory adaptation Decreased response to sustained stimulus
Olfactory transduction process. Slide 6 1 Odorant binds to its receptor. Odorant Adenylate cyclase G protein (G olf ) Receptor camp camp Open camp-gated cation channel GDP 2 Receptor activates G protein (G olf ). 3 G protein 4 Adenylate 5 camp opens activates cyclase converts a cation channel, adenylate ATP to camp. allowing Na + and cyclase. Ca 2+ influx and causing depolarization.
Olfactory Pathway Olfactory receptor cells synapse with mitral cells in glomeruli of olfactory bulbs Axons from neurons with same receptor type converge on given type of glomerulus Glomerulus: single aspect of odor Each odor activates a unique set of glomeruli Mitral cells amplify, refine, and relay signals Olfactory bulb: Amacrine granule cells release GABA to inhibit mitral cells Only highly excitatory impulses transmitted
The Olfactory Pathway Impulses from activated mitral cells travel via olfactory tracts to piriform lobe of olfactory cortex Some information to frontal lobe Smell consciously interpreted and identified Some information to hypothalamus, amygdala, and other regions of limbic system Emotional responses to odor elicited Sympathetic response: danger Parasympathetic response: digestion Protective reflexes: sneezing, choking
McGraw Hill Anatomy and Physiology
Human Pheromones No clear evidence that human body odors affect sexual behaviour. Evidence: sweat and vaginal secretion affect other s sexual physiology Woman s apocrine sweat influence other women s menstrual cycle Dormitory effect : absence of men, synchronized menstrual cycle Presence of men: ovulating (close to it) woman vaginal secretion contains copulin pheromones Can raise testosterone level in males
Noma http://noma.dk/food-and-wine/
Taste Buds and the Sense of Taste Receptor organs are taste buds Most of 10,000 taste buds on tongue papillae On tops of fungiform papillae On side walls of foliate and vallate papillae Few on soft palate, cheeks, pharynx, epiglottis
Structure of a Taste Bud 50 100 flask-shaped epithelial cells of 2 types Gustatory epithelial cells taste cells Microvilli (gustatory hairs) are receptors Three types of gustatory epithelial cells One releases serotonin; others lack synaptic vesicles but one releases ATP as neurotransmitter Basal epithelial cells dynamic stem cells that divide every 7-10 days
Basic Taste Sensations There are five basic taste sensations 1. Sweet sugars, saccharin, alcohol, some amino acids, some lead salts 2. Sour hydrogen ions in solution 3. Salty metal ions (inorganic salts) 4. Bitter alkaloids such as quinine and nicotine; aspirin 5. Umami amino acids glutamate and aspartate Prof. Kikunae Ikeda 1864-1936 1908
Basic Taste Sensations Possible 6th taste ( oleogustus ) Growing evidence humans can taste long-chain fatty acids from lipids Perhaps explain liking of fatty foods http://chemse.oxfordjournals.org/content/early/2015/07/02/chemse.bjv036.short?rss=1 http://chemse.oxfordjournals.org/content/early/2015/07/02/chemse.bjv036.full.pdf+html
Basic Taste Sensations Taste likes/dislikes have homeostatic value Guide intake of beneficial and potentially harmful substances Umami: protein intake Sweet: carbohydrate intake Salty: minerals Sour: Vitamin-C or spoiled food (protective) Bitter: many natural poison is alkaloids, protective
Physiology of Taste To taste, chemicals must Be dissolved in saliva Diffuse into taste pore Contact gustatory hairs
Activation of Taste Receptors Binding of food chemical (tastant) depolarizes taste cell membrane neurotransmitter release Initiates a generator potential that elicits an action potential Different thresholds for activation Bitter receptors most sensitive All adapt in 3-5 seconds; complete adaptation in 1-5 minutes
McGraw Hill Anatomy and Physiology
McGraw Hill Anatomy and Physiology
McGraw Hill Anatomy and Physiology
Taste Transduction Gustatory epithelial cell depolarization caused by Salty taste due to Na + influx (directly causes depolarization) Sour taste due to H + (by opening cation channels) Unique receptors for sweet, bitter, and umami coupled to G protein gustducin Stored Ca 2+ release opens cation channels depolarization neurotransmitter ATP release
Gustatory Pathway Cranial nerves VII and IX carry impulses from taste buds to solitary nucleus of medulla Impulses then travel to thalamus and from there fibers branch to Gustatory cortex in the insula Hypothalamus and limbic system (appreciation of taste) Vagus nerve transmits from epiglottis and lower pharynx
McGraw Hill Anatomy and Physiology
The gustatory pathway. Gustatory cortex (in insula) Thalamic nucleus (ventral posteromedial nucleus) Pons Solitary nucleus in medulla oblongata Facial nerve (VII) Glossopharyngeal nerve (IX) Vagus nerve (X)
Role Of Taste 1. Triggers reflexes involved in digestion 2. Increase secretion of saliva into mouth 3. Increase secretion of gastric juice into stomach 4. May initiate protective reactions Gagging Reflexive vomiting
Influence of other Sensations on Taste Taste is 80% smell Thermoreceptors, mechanoreceptors, nociceptors in mouth also influence tastes Temperature and texture enhance or detract from taste VISUAL!
Homeostatic Imbalances of the Chemical Senses Anosmias (olfactory disorders) no smell Most result of head injuries and neurological disorders (Parkinson's disease) Uncinate fits olfactory hallucinations Olfactory auras prior to epileptic fits Irritation of olfactory pathway Taste disorders less common Receptors are served by 3 nerves Infections, head injuries, chemicals, medications, radiation for CA of head/neck Chemical senses few problems occur until fourth decade, when these senses begin to decline Odor and taste detection poor after 65
The Ear: Hearing and Balance Three major areas of ear 1. External (outer) ear hearing only 2. Middle ear (tympanic cavity) hearing only 3. Internal (inner) ear hearing and equilibrium Receptors for hearing and balance respond to separate stimuli Are activated independently
Structure of the ear. External ear Middle ear Internal ear (labyrinth) Auricle (pinna) Helix Lobule External acoustic meatus The three regions of the ear Tympanic membrane Pharyngotympanic (auditory) tube
External Ear Auricle (pinna) composed of Helix (rim); Lobule (earlobe) Funnels sound waves into auditory canal External acoustic meatus (auditory canal) Short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands Transmits sound waves to eardrum
External Ear Tympanic membrane (eardrum) Boundary between external and middle ears Connective tissue membrane that vibrates in response to sound Transfers sound energy to bones of middle ear
Middle Ear (Tympanic Cavity) A small, air-filled, mucosa-lined cavity in temporal bone Flanked laterally by eardrum Flanked medially by bony wall containing: oval (vestibular) window round (cochlear) window
Middle Ear Epitympanic recess superior portion of middle ear Mastoid antrum Canal for communication with mastoid air cells Pharyngotympanic (auditory) tube connects middle ear to nasopharynx Equalizes pressure in middle ear cavity with external air pressure
Structure of the ear. Oval window (deep to stapes) Entrance to mastoid antrum in the epitympanic recess Malleus (hammer) Auditory ossicles Incus (anvil) Stapes (stirrup) Tympanic membrane Semicircular canals Vestibule Vestibular nerve Cochlear nerve Cochlea Round window Pharyngotympanic (auditory) tube Middle and internal ear
Otitis Media Middle ear inflammation Result of sore throat Especially in children Shorter, more horizontal pharyngotympanic tubes Most frequent cause of hearing loss in children Most treated with antibiotics Myringotomy to relieve pressure if severe
Ear Ossicles Three small bones in tympanic cavity: 1. Malleus 2. Incus 3. Stapes Suspended by ligaments and joined by synovial joints Transmit vibratory motion of eardrum to oval window Tensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to hearing receptors
The three auditory ossicles and associated skeletal muscles. View Superior Malleus Incus Epitympanic recess Lateral Anterior Pharyngotympanic tube Tensor tympani muscle Tympanic Stapes Stapedius membrane muscle (medial view)
Break Auditory transduction http://youtu.be/petrigtenoc Organ of Corti http://youtu.be/1je8wdujkv4 http://irp.nih.gov/our-research/research-in-action/high-fidelity-stereocilia/slideshow Figure 6: Different diameters and slopes of cochlear turns to illustrate individual variations of the human cochlea (with permission of Helge Rask-Andersen, Uppsala, Sweden). http://openi.nlm.nih.gov/detailedresult.php?img=3200995_cto-04-04-g-006&req=4
Two Major Divisions of Internal Ear 1. Bony labyrinth Tortuous channels in temporal bone Three regions: 1. Vestibule 2. Semicircular canals 3. Cochlea Filled with perilymph similar to CSF 2. Membranous labyrinth Series of membranous sacs and ducts Filled with potassium-rich endolymph
Membranous labyrinth of the internal ear. Temporal bone Semicircular ducts in semicircular canals Anterior Posterior Lateral Cristae ampullares in the membranous ampullae Utricle in vestibule Saccule in vestibule Stapes in oval window Facial nerve Vestibular nerve Superior vestibular ganglion Inferior vestibular ganglion Cochlear nerve Maculae Spiral organ Cochlear duct in cochlea Round window
Vestibule Central egg-shaped cavity of bony labyrinth Contains two membranous sacs 1. Saccule is continuous with cochlear duct 2. Utricle is continuous with semicircular canals These sacs House equilibrium receptor regions (maculae) Respond to gravity and changes in position of head
Semicircular Canals Three canals (anterior, lateral, and posterior) that each define ⅔ circle Lie in three planes of space Membranous semicircular ducts line each canal and communicate with utricle Ampulla of each canal houses equilibrium receptor region called the crista ampullaris Receptors respond to angular (rotational) movements of the head
Membranous labyrinth of the internal ear. Temporal bone Semicircular ducts in semicircular canals Anterior Posterior Lateral Cristae ampullares in the membranous ampullae Utricle in vestibule Saccule in vestibule Stapes in oval window Facial nerve Vestibular nerve Superior vestibular ganglion Inferior vestibular ganglion Cochlear nerve Maculae Spiral organ Cochlear duct in cochlea Round window
The Cochlea A spiral, conical, bony chamber Size of split pea Extends from vestibule Coils around bony pillar (modiolus) Contains cochlear duct, which houses spiral organ (organ of Corti) and ends at cochlear apex
Anatomy of the cochlea. Helicotrema at apex Modiolus Cochlear nerve, division of the vestibulocochlear nerve (VIII) Spiral ganglion Osseous spiral lamina Vestibular membrane Cochlear duct (scala media)
The Cochlea Cavity of cochlea divided into three chambers 1. Scala vestibuli abuts oval window, contains perilymph 2. Scala media (cochlear duct)-membranous labyrinth contains endolymph 3. Scala tympani terminates at round window; contains perilymph Scalae tympani and vestibuli are continuous with each other at helicotrema (apex)
The Cochlea The "roof" of cochlear duct is vestibular membrane External wall is stria vascularis secretes endolymph "Floor" of cochlear duct composed of Bony spiral lamina Basilar membrane, which supports spiral organ The cochlear branch of nerve VIII runs from spiral organ to brain
Anatomy of the cochlea. Vestibular membrane Osseous spiral lamina Tectorial membrane Cochlear duct (scala media; contains endolymph) Stria vascularis Spiral organ (Corti) Basilar membrane Scala vestibuli (contains perilymph) Scala tympani (contains perilymph) Spiral ganglion
Tectorial membrane Hairs (stereocilia) Outer hair cells Anatomy of the cochlea. Inner hair cell Afferent nerve fibers Supporting cells Fibers of cochlear nerve Basilar membrane
Properties of Sound Sound is Pressure disturbance (alternating areas of high and low pressure) produced by vibrating object Sound wave Moves outward in all directions Illustrated as an S-shaped curve or sine wave
Air pressure Sound: Source and propagation. Area of high pressure (compressed molecules) Wavelength Area of low pressure (rarefaction) Crest Trough Distance Amplitude A struck tuning fork alternately compresses and rarefies the air molecules around it, creating alternate zones of high and low pressure. Sound waves radiate outward in all directions.
Properties of Sound Waves Frequency Number of waves that pass given point in given time Pure tone has repeating crests and troughs Wavelength Distance between two consecutive crests Shorter wavelength = higher frequency of sound
Properties of Sound 1. Pitch Perception of different frequencies Normal range 20 20,000 hertz (Hz) Most sensitive 1500-4000 Hz Higher frequency = higher pitch 2. Quality Tone- single frequency: pure but bland Most sounds mixtures of different frequencies Richness and complexity of sounds (music)
Properties of Sound 3. Amplitude Height of crests Amplitude perceived as loudness Subjective interpretation of sound intensity Normal range is 0 120 decibels (db) Severe hearing loss with prolonged exposure above 90 db Amplified rock music is 120 db or more Gunshot 140dB, single energy, more dangerous
Pressure Pressure Frequency and amplitude of sound waves. High frequency (short wavelength) = high pitch Low frequency (long wavelength) = low pitch 0.01 0.02 0.03 Time (s) Frequency is perceived as pitch. High amplitude = loud Low amplitude = soft 0.01 0.02 0.03 Time (s) Amplitude (size or intensity) is perceived as loudness.
Transmission of Sound to the Internal Ear 1. Sound waves vibrate tympanic membrane 2. Ossicles vibrate and amplify pressure at oval window 3. Cochlear fluid set into wave motion 4. Pressure waves move through perilymph of scala vestibuli Auditory transduction http://youtu.be/petrigtenoc
Transmission of Sound to the Internal Ear 1. Waves with frequencies: below threshold of hearing travel through helicotrema and scali tympani to round window 2. Sounds in hearing range: go through cochlear duct vibrating basilar membrane at specific location, according to frequency of sound
Auditory ossicles Pathway of sound waves and resonance of the basilar membrane. Slide 6 Malleus Incus Stapes Cochlear nerve Oval window Scala vestibuli Helicotrema 4a Scala tympani 2 3 4b Cochlear duct Basilar membrane 1 Tympanic membrane Round window Route of sound waves through the ear 1 Sound waves vibrate the tympanic membrane. 2 Auditory ossicles vibrate. Pressure is amplified. 3 Pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli. 4a Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells. 4b Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells.
Resonance of the Basilar Membrane 1. Fibers near oval window short and stiff Resonate with high-frequency pressure waves 2. Fibers near cochlear apex longer, more floppy Resonate with lower-frequency pressure waves This mechanically processes sound before signals reach receptors
Pathway of sound waves and resonance of the basilar membrane. Basilar membrane High-frequency sounds displace the basilar membrane near the base. Medium-frequency sounds displace the basilar membrane near the middle. Low-frequency sounds displace the basilar membrane near the apex. Fibers of basilar membrane Base (short, stiff fibers) Apex (long, floppy fibers) 20,000 2000 200 Frequency (Hz) Different sound frequencies cross the basilar membrane at different locations. 20
Excitation of Hair Cells in the Spiral Organ Cells of spiral organ Supporting cells Cochlear hair cells One row of inner hair cells: auditory message Three rows of outer hair cells: increase responsiveness of the inner hair cells by contracting/stretching & protecting inner hair cells from damage Have many stereocilia and one kinocilium Afferent fibers of cochlear nerve coil about bases of hair cells
Tectorial membrane Anatomy of the cochlea. Inner hair cell Hairs (stereocilia) Outer hair cells Afferent nerve fibers Supporting cells Fibers of cochlear nerve Basilar membrane Organ of Corti http://youtu.be/1je8wdujkv4
Excitation of Hair Cells in the Spiral Organ Stereocilia Protrude into endolymph Longest enmeshed in gel-like tectorial membrane Sound bending these toward kinocilium Opens mechanically gated ion channels Inward K + and Ca 2+ current causes graded potential and release of neurotransmitter glutamate Cochlear fibers transmit impulses to brain
Auditory Pathways to the Brain Impulses from cochlea pass 1. via spiral ganglion 2. to cochlear nuclei of medulla From there, impulses sent 3. To superior olivary nucleus Via lateral lemniscus to 4. Inferior colliculus (auditory reflex center) From there, impulses pass 5. to medial geniculate nucleus of thalamus, then 6. to primary auditory cortex Auditory pathways partially decussate so that both cortices receive input from both ears
The auditory pathway. Medial geniculate nucleus of thalamus Primary auditory cortex in temporal lobe Inferior colliculus Lateral lemniscus Superior olivary nucleus (ponsmedulla junction) Midbrain Cochlear nuclei Vibrations Vibrations Medulla Vestibulocochlear nerve Spiral ganglion of cochlear nerve Bipolar cell Spiral organ
Auditory Processing Pitch: perceived by impulses from specific hair cells in different positions along basilar membrane Loudness: detected by increased numbers of action potentials that result when hair cells experience larger deflections Localization of sound depends on relative intensity and relative timing of sound waves reaching both ears
Homeostatic Imbalances of Hearing 1. Conduction deafness Blocked sound conduction to fluids of internal ear Impacted earwax, perforated eardrum, otitis media, otosclerosis of the ossicles 2. Sensorineural deafness Damage to neural structures at any point from cochlear hair cells to auditory cortical cells Typically from gradual hair cell loss Single explosively loud sound Prolonged exposure to high intensity sounds (headset, earphones on maximum volume)
Treating Deafness Cochlear implants for congenital or age/noise cochlear damage Convert sound energy into electrical signals Inserted into drilled recess in temporal bone So effective that deaf children can learn to speak
Homeostatic Imbalances of Hearing Tinnitus Ringing or clicking sound in ears in absence of auditory stimuli Usually a symptom, not a disease Due to cochlear nerve degeneration, inflammation of middle or internal ears, side effects of aspirin
Symphony No. 5 Fate knocks at the door!" https://upload.wikimedia.org/wikipedia/commons/e/ee/beet5mov1bars1to5.ogg
Torres Del Paine, Chile, 2014
Equilibrium and Orientation Vestibular apparatus Equilibrium receptors in semicircular canals and vestibule 1. Vestibular receptors: monitor static equilibrium 2. Semicircular canal receptors: monitor dynamic equilibrium
Maculae Sensory receptors for static equilibrium One in each saccule wall and one in each utricle wall Monitor the position of head in space necessary for control of posture Respond to linear acceleration forces NOT rotation Contain supporting cells and hair cells Stereocilia and kinocilia are embedded in the otolith membrane studded with otoliths (tiny CaCO 3 stones)
Maculae 1. Maculae in utricle: respond to horizontal movements and tilting head side to side 2. Maculae in saccule: respond to vertical movements Hair cells synapse with vestibular nerve fibers
Activating Maculae Receptors Hair cells release neurotransmitter continuously Movement modifies amount they release Bending of hairs in direction of kinocilia Depolarizes hair cells Increases amount of neurotransmitter release More impulses travel up vestibular nerve to brain
Activating Maculae Receptors Bending away from kinocilium Hyperpolarizes receptors Less neurotransmitter released Reduces rate of impulse generation Thus brain informed of changing position of head
The effect of gravitational pull on a macula receptor cell in the utricle. Otolith membrane Kinocilium Stereocilia Receptor potential Depolarization Hyperpolarization Nerve impulses generated in vestibular fiber When hairs bend toward the kinocilium, the hair cell depolarizes, exciting the nerve fiber, which generates more frequent action potentials. When hairs bend away from the kinocilium, the hair cell hyperpolarizes, inhibiting the nerve fiber, and decreasing the action potential frequency.
Linear acceleration
The Crista Ampullares (Crista) Sensory receptor for rotational acceleration One in ampulla of each semicircular canal Major stimuli are rotational movements Each crista has supporting cells and hair cells that extend into gel-like mass called ampullary cupula Dendrites of vestibular nerve fibers encircle base of hair cells
Location, structure, and function of a crista ampullaris in the internal ear. Crista ampullaris Endolymph Ampullary cupula Hair bundle (kinocilium plus stereocilia) Membranous labyrinth Crista ampullaris Fibers of vestibular nerve Hair cell Supporting cell Anatomy of a crista ampullaris in a semicircular canal Scanning electron micrograph of a crista ampullaris (200x) Section of ampulla, filled with endolymph Cupula Fibers of vestibular nerve Flow of endolymph At rest, the cupula stands upright. During rotational acceleration, endolymph moves inside the semicircular canals in the direction opposite the rotation (it lags behind due to inertia). Endolymph flow bends the cupula and excites the hair cells. Movement of the ampullary cupula during rotational acceleration and deceleration As rotational movement slows, endolymph keeps moving in the direction of rotation. Endolymph flow bends the cupula in the opposite direction from acceleration and inhibits the hair cells.
Activating Crista Ampullaris Receptors Cristae respond to changes in velocity of rotational movements of the head 1. Bending of hairs in cristae causes Depolarizations, and rapid impulses reach brain at faster rate 2. Bending of hairs in the opposite direction causes Hyperpolarizations, and fewer impulses reach the brain Axes of complementary semicircular ducts are opposite, one ampulla depolarize, one hyperpolarize Thus brain informed of rotational movements of head
Location, structure, and function of a crista ampullaris in the internal ear. Section of ampulla, filled with endolymph Cupula Fibers of vestibular nerve Flow of endolymph At rest, the cupula stands upright. During rotational acceleration, endolymph moves inside the semicircular canals in the direction opposite the rotation (it lags behind due to inertia). Endolymph flow bends the cupula and excites the hair cells. Movement of the ampullary cupula during rotational acceleration and deceleration As rotational movement slows, endolymph keeps moving in the direction of rotation. Endolymph flow bends the cupula in the opposite direction from acceleration and inhibits the hair cells.
Vestibular Nystagmus Strange eye movements during and immediately after rotation Often accompanied by vertigo As rotation begins eyes drift in direction opposite to rotation, then CNS compensation causes rapid jump toward direction of rotation As rotation ends eyes continue in direction of spin then jerk rapidly in opposite direction
Equilibrium Pathway to the Brain Equilibrium information goes to reflex centers in brain stem Allows fast, reflexive responses to imbalance Impulses travel to vestibular nuclei in brain stem or cerebellum, both of which receive other input Three modes of input for balance and orientation: 1. Vestibular receptors 2. Visual receptors 3. Somatic receptors
Neural pathways of the balance and orientation system. Input: Information about the body s position in space comes from three main sources and is fed into two major processing areas in the central nervous system. Vestibular receptors Visual receptors Somatic receptors (skin, muscle and joints) Cerebellum Central nervous system processing Vestibular nuclei (brain stem) Oculomotor control (cranial nerve nuclei III, IV, VI) (eye movements) Spinal motor control (cranial nerve XI nuclei and vestibulospinal tracts) (neck, limb, and trunk movements) Output: Responses by the central nervous system provide fast reflexive control of the muscles serving the eyes, neck, limbs, and trunk.
Motion Sickness Sensory input mismatches Visual input differs from equilibrium input Conflicting information causes motion sickness Warning signs are excess salivation, pallor, rapid deep breathing, profuse sweating Treatment with antimotion drugs that depress vestibular input
Homeostatic Imbalances Ménière's syndrome: labyrinth disorder that affects cochlea and semicircular canals Repeated attacks of vertigo, nausea, and vomiting Standing is difficult Maybe due to excessive endolymph production Maybe membrane rupture that allows mixing of endolymph and perilymph Antimotion drugs, low-salt diet, diuretics Removal of labyrinth when complete hearing loss
Developmental Aspects Newborns can hear but early responses reflexive Language skills tied to ability to hear well Congenital abnormalities common Missing pinnae, closed or absent external acoustic meatuses Maternal rubella causes sensorineural deafness
Developmental Aspects Few ear problems until 60s when deterioration of spiral organ noticeable Hair cell numbers decline with age Loud noise, disease, drugs Presbycusis occurs first Loss of high pitch perception Type of sensorineural deafness It is becoming more common in younger people!!
THE END
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