Chapter #15: Special Senses Flashcards
What are the special senses?
-Special senses are any of the senses with special sensory receptors
-Receptor cells are localized in the head only
What are the five special senses?
1) Vision (dominant special sense, most used)
2) Olfaction (Smell)
3) Gustation (Taste)
4) Hearing
5) Equilibrium (balance and orientation)
The Anatomy of the Eye: Accessory structures
1) Conjunctiva: transparent mucous membrane
2) Palpebrae (eyelids)
3) Lacrimal Apparatus
4) Extrinsic Eye Muscles
Conjunctiva: transparent mucous membrane
-Function: produce lubricating mucus
-Palpebral conjunctiva: portion that covers the inner eyelids
-Bulbar conjunctiva: portion that covers anterior surface of eye (except cornea)
Palpebrae (eyelids)
-Muscles that allow eyelids to open or close:
1) Orbicularis oculi: encircles the eye
-closes eye when contracts
2) Levator palpebrae superioris
-associated with upper eyelid
-when contracted, upper eyelid opens
-Lacrimal caruncle on medial portion-sebaceous and sweat glands here produce oily secretion
-prevents dry eye, why you usually have crusties in your eye in the morning
Lacrimal Apparatus
-Function: production and drainage of tears, protection of eyes
-Tears contain lysozyme, lubricate eye surface
-Enhanced tear production washes away foreign bodies in eye, lysozyme kills bacteria & other pathogens
-Composed of:
A) Lacrimal glands: produces and releases dilute saline solution (tears)
B) Lacrimal canaliculi: drains tears from eye surface at medial portion of eye
C) Nasolacrimal duct: drains tears from lacrimal canaliculi into nasal cavity
Extrinsic eye muscles
-Function: allows movement of eye in the orbit
-All muscles attach to the sclera of the eye
Six extrinsic eye muscles
1) Superior rectus
2) Inferior rectus
3) Lateral rectus
4) Medial rectus
5) Superior oblique
6) Inferior oblique
Function of each extrinsic eye muscles
1) Superior rectus - elevates eye and turns it medially
2) Inferior rectus - depresses eye and turns it medially
3) Lateral rectus - moves eye laterally
4) Medial rectus - moves eye medially
5) Superior oblique - depresses eye and turns it laterally
6) Inferior oblique - elevates eye and turns it laterally
Extrinsic eye muscles functions
-Rectus muscles pull eye in direction indicated by name of muscle
-Superior & inferior rectus muscles also pull the eye medially when they contract
-Oblique muscles either elevate or depress the eye and turn it laterally
The Anatomy of the Eye: The Eyeball (3 layers)
1) The Fibrous Layer
2) The Vascular Layer
3) Retina
The Fibrous Layer
-outermost coat of the eye with 2 regions
A) Sclera: the “whites of the eyes”
-Functions: gives eyeball shape, provides sturdy anchor for extrinsic muscles
B) Cornea: transparent layer at the most anterior region of the eye
-Functions: allows light to enter eye, bends light as it passes
-Supplied with many pain receptors
-High regenerative & repair capacity
-No blood vessels, no immune system supply
The Vascular Layer
-middle coat of the eye with 3 regions
A) Choroid
B) Ciliary body
C) Iris
Choroid
-part of the vascular layer
-well-vascularized layer, dark in color
-Blood vessels here nourish surrounding layers of the eye
-Dark in color-absorbs light - important because the darker the color, the more light is absorbed and it prevents light from bouncing around the inside of your eye
Ciliary Body
-part of the vascular layer
-structure that encircles the lens
-Composed of 3 regions:
-Ciliary muscle: smooth muscle bundles that control lens shape
-Causes the lens to flatten or bulge
-Ciliary processes: secrete aqueous humor
-Suspensory ligaments: extend from ciliary processes to lens
-Functions: Holds lens in place, transmits tension from ciliary muscle to lens
Iris
-part of the vascular layer
-the colored portion of the eye
-Color depends on amount of melanin
-Pupil: central opening that lets light enter the eye
-Smooth muscle layers of iris allows for constriction or dilation of pupil
A) Sphincter pupillae: when contractedpupil contricts
B) Dilator pupillae: when contracted-pupil dilates
Retina
-innermost layer of the eye
-This layer contains all photoreceptors of the eye
-Two layers present:
A) Pigmented layer
B) Neural layer
Pigmented layer
-part of the retina
-lies against choroid
-Pigment here absorbs light
-Phagocytes here help with photoreceptor renewal
Neural layer
-part of the retina
-innermost layer of retina
-Contains photoreceptor cells
-Rods: used for dim light and peripheral vision
-Most numerous
-Found mostly on outer edges of retina
-Cones: used for bright light and high-resolution color vision
-Found mostly in fovea centralis and macula lutea
-Also contains bipolar cells and ganglion cells
-Both used to generate action potentials in response to light stimuli
Other structures associated with the retina
-Optic disc: point at which the optic nerve exits the back of the eye
-No photoreceptors found here- ”blind spot”
-Macula lutea: area where other structures are displaced-photoreceptors receive direct light
-Fovea centralis found at center of macula lutea
-Contains only cones-provides extremely detailed color vision
-Is only 1/1000th of the total visual field
What effect does the macula lutea have on vision?
anything focused on the macula lutea will be seen very clearly
Why can’t we “see” the blind spot?
primary visual cortex fills in the blank
The Lens
-biconvex, transparent, flexible structure in the eye
-Function: used to bend light as it enters the eye
-Anterior portion covered with lens epithelium
-Functions: coordinates metabolic activities of lens, provides more cells for lens fibers
-Bulk of lens thickness made up by lens fibers
-Fibers are laid down over lifetime, old fibers not broken down
If overtime, old fibers are never broken down, how is this a disadvantage?
-causes lens to become much more thick as time goes by
-won’t bend light the same
-thicker = loses its flexibility to change the shape of the lens
-this is why vision becomes worse as you age
-ex. cataracts
Internal Chambers & Fluids of the Eye
-Anterior segment: segment found in front of the lens
-Contains aqueous humorwatery fluid
-Functions: supplies nutrients and oxygen to structures in the front of the eye & removes waste
-Aqueous humor is continuously drained and produced
-Posterior segment: segment found behind the lens
-Contains vitreous humorjelly-like fluid
-Functions: transmits light, stabilizes the lens from the posterior side, holds the retina in place, & contributes to intraocular pressure
-Vitreous humor lasts a lifetime
Wavelengths & Light
-Human eyes only respond to electromagnetic radiation in the visible light spectrum (400-700 nm)
-Most of what we see is light reflecting off a surface & entering the eye
-Color of particular objects caused by what wavelengths are absorbed & what are reflected
-Ex: green grass reflects green wavelength, absorbs all others
-White-all wavelengths of light reflected
-Black-all wavelengths of light absorbed
Refraction of Light
-Light travels at a constant speed through a single medium (gas, liquid, solid)
-Speed changes in different densities
-Refraction occurs when a light wave passes through a boundary from one medium and into another medium with a different density
Through what medium does light travel the fastest? Slowest?
fastest = gas
slowest = solid
What happens to the light wave?
-light in water/liquids travels at a different speed (straw looks bent)
-Ex: a straw in a glass of water looks bent
Refraction of light in human body
-In the human body-the cornea and the lens refract light as it enters the eye
-Light rays bend so they converge at a single point-the focal point -But the real image is upside down & reversed
Focusing Light on the Retina
Light is bent 3 times as it enters the eye:
1) Cornea
2) Anterior surface of lens
3) Posterior surface of lens
-The cornea is mostly responsible for bending light
-But it cannot change shape
-The lens is used to fine-tune refractionforms clear image
-Lens can change shape to change refractory power of lens
What does refractory power mean?
-the ability of the lens to bend light
-high = bend light more
-low = bend light less
Changing Lens Shape
-Use of ciliary muscles and suspensory ligaments around lens
-Relaxation of ciliary muscle = increased tension in suspensory ligaments
-Effect: suspensory ligaments are pulled tight
-Contraction of ciliary muscle = decreased tension in suspensory ligaments
-Effect: suspensory ligaments go slack
What effect does relaxing ciliary muscles have on lens shape? How does this affect refractory power?
-makes lens flatter, lower refractory power
What effect does contracting ciliary muscles have on lens shape? How does this affect refractory power?
makes lens rounder (bulges), higher refractory period
Focusing Light: Distant Vision
-The far point of vision: point at which the lens no longer needs to change shape to focus light
-In normal eye ~20 feet
-Ciliary muscles are relaxed
Why does the lens not need to change shape?
-human eyes have evolved for distant vision
-When looking at distant object - light rays entering eye are nearly parallel (really easy to focus)
-Cornea & lens can easily bend light to focus it on retina
When ciliary muscles are relaxed, is the lens flatted or bulged?
-flattened because you do not need to do a lot of work
-lens flattens for distant vision
Focusing Light: Close Vision
-The near point of vision: closest point to face that still allows clear vision
-In normal eye 4 inches
-The closer an object is to the face - the more divergent the light rays as they enter the eye
-3 processes must occur for close vision
Does the lens have to work harder to bend divergent light rays? Why or why not?
yes because you need to get light rays to come together, need more refractory power (bulge)
What are the 3 processes that must occur for close vision?
1) Accommodation of the lens: contraction of ciliary muscles
2) Constriction of pupils
-Effect: prevents divergent rays from entering eye
3) Convergence of eyes: medial rotation of the eyeballs
-Effect: keeps object focused on foveae
-The closer the object, the more the eyes must converge
What effect does accommodation have on the lens?
bulge
What would happen if divergent light rays enter the eye?
it starts to bounce around in the eye and cause blurry vision
Photoreceptors: Functional Anatomy
-Two photoreceptors: rods and cones
-Anatomy (of both):
-Outer segment: embedded in pigmented layer of retina
-Contain photopigments (visual pigments) folded into discs
-Photopigments replaced throughout life -Inner segment: embedded in the neural layer of retina
Rods
-Sensitive to light
-used in dark conditions
-Only one visual pigment in rods - no color vision
-Converging pathways - several rods all synapse on a single ganglion
What effect does several rods synapsing at a single ganglion have on visual acuity?
Primary visual cortex - brain can’t tell exactly which rod was stimulated which creates a blurry picture
Cones
-Low sensitivity
-used in light conditions
-Single cone has 1 of 3 (red, green, or blue) visual pigments - color vision
-Each cone synapses on its own ganglia
What effect does each cone synapsing on its own ganglia have on visual acuity?
when a cone is stimulated, your brain knows exactly which cone was activated
Phototransduction
-Definition: Process of converting light energy into a graded receptor potential that begins when a photoreceptor catches light
-Remember: there are 3 cells involved in light processing
-Photoreceptor cells: create graded potential in response to incoming light stimuli
-Bipolar cells: create either IPSP or EPSP -Ganglion cell: generate action potential that is propagated along the optic nerve
Information Processing: The Retina
-In the dark - photoreceptor ion channels are open
-Result: receptor is depolarized to -40 mV
-In the light - photoreceptor ion channels close
-Result: receptor is hyperpolarized to -70 mV
-This process uses a G-protein (transducin) signaling system
-11-cis-retinol absorbs light & becomes all-trans retinol
Light Adaptation
-Retina adjusts to varying amounts of light entering the eye
-Light adaption: dark to light conditions
-In the dark: rod vision dominates
-In the light
-Rods bombarded with stimuli - ”white light” occurs
-Rods “turned off” & cones “turned on”
-Adaptation to bright light takes ~60 seconds
-Highest visual acuity & color vision reached in ~5 minutes
Is retinal sensitivity high or low during light adaptation?
high
What happens to retinal sensitivity when in the light?
low because there’s lots of light and you do not want a super sensitive retina
Dark Adaptation
-Dark Adaptation: occurs when we move from light to dark conditions
-In the light - cone vision dominates
-In the dark
-Sudden lack of light causes a temporary loss of vision
-Cones “turn off,” rods “turn on”
-Adaptation to dark takes up to 30 minutes
Is retinal sensitivity high or low in the dark?
low
What happens to retinal sensitivity in the dark?
must adapt, retinal sensitivity will increase
The Pathway to the Visual Cortex
-Optic nerve exits the back of the eye
-Optic chiasm: location where medial fibers from each optic nerve cross over to other hemisphere
-Lateral fibers do not cross over
-Optic tracts continue to the visual cortex
-Each eye also receives visual input from the other side of the body
Each optic tract
1) Carries fibers from the lateral portion of the eye on the same side
2) Carries fibers from the medial portion of the eye of the opposite side
3) Contains all information from the same half of the visual field
How does each eye receive visual input from the other side of the body?
-The lens flips/reverses the image
-Therefore:
1) Medial portion of eye receives input from temporal part of the visual field
2) Lateral portion of eye receives input from medial part of the visual field
Fibers in the pathway to the visual cortex
-Most fibers in optic tracts synapse with neurons at lateral geniculate nucleus of thalamus
-These fibers then project to primary visual cortex
-Other fibers travel to:
1) Superior colliculi: visual reflex center that controls extrinsic eye muscles; ability to follow a moving object in space (in midbrain)
2) Pretectal nuclei: mediates pupillary response to light; helps with constricting and dilating pupils (in midbrain)
3) Suprachiasmatic nucleus: sets biorhythms; change light intensities of day and night (in hypothalamus)
Depth Perception
-Each eye has a visual field of ~170 degrees
-Complete visual fields of left & right eye overlap
-Both eyes “see” what is in this area of overlap, creates 2 images
-Visual cortex combines two images to create depth perception
-Importance: depth perception allows us to locate objects in space
-If one eye is lost or not used, depth perception is lost
Chemoreceptors
respond to stimuli dissolved in solution (we won’t smell of it’s not dissolved in solution)
Olfactory receptors
-receptors found in olfactory epithelium
-Location: roof of nasal cavity
-Contains 3 cell types:
1) Olfactory sensory neurons
2) Supporting cells
-function is to support olfactory sensory neurons
3) Olfactory stem cells
Olfactory Cilia
-hair-like projections found in olfactory epithelium
-Function: increase receptive surface area of neuron
-Mucus surrounding cilia dissolves airborne odorants
What would happen to sense of smell without mucus?
we would not be able to smell, in order to smell anything the chemical must dissolve in mucus
Axons structures
-Axons of multiple sensory neurons bundled together to form filaments of the olfactory nerve
-Filaments travel through ethmoid bone via cribiform formamen
-In brain, axons synapse with olfactory mitral cells of olfactory bulb
-Site of synapse forms glomeruli
Longevity of Olfactory Sensory Neurons
-Superficial location = prone to destruction
-Life span of olfactory sensory neuron is 30-60 days (if they are healthy)
-Olfactory stem cells replace damaged/destroyed neurons
How are olfactory sensory neurons destroyed?
-strong chemical smells
-can rip off easily, hard sneeze
Why is it important that olfactory stem cells replace damages or destroyed neurons?
you would lose your sense of smell if olfactory stem cells didn’t replace & specialize
Two things must take place for sensation of smell to occur
1) Activation of sensory neurons
A) Odorant in gaseous state dissolves in epithelium
B) Odorant binds receptor proteins in olfactory cilium membrane
2) Transduction of smell: binding creates a graded potential, strong graded potential generates action potential
-Transduction involves G-protein
-Na+ influx depolarizes olfactory sensory neuron - creates receptor potential -Ca2+ influx causes adaptation, decreased response to sustained odorant stimulus
Pathway to the Olfactory Cortex
-In olfactory bulb: olfactory sensory neurons synapse with mitral cells
-Graded potential at olfactory sensory neuron creates action potential at mitral cells
-Impulses flow from olfactory bulb via olfactory tract
-Information from olfactory tract takes 1 of 2 pathways:
-1) Sent to olfactory cortex: smell consciously interpreted/identified
-2) Sent to limbic system: smell elicits an emotional response
-Activation of sympathetic or parasympathetic system
-Activation of protective reflexescoughing, sneezing
Gustation
-Chemoreceptors found on taste buds
-Most located on papillae of tongue
-3 types of papillae:
1) Fungiform papillae: found all over tongue, contain 1-5 taste buds each
2) Vallate papillae: found at back of tongue, have many taste buds each
3) Foliate papillae: found on side of tongue, taste bud number varies with age
Each taste bud has two types of epithelial cells
1) Gustatory epithelial cells
2) Basal epithelial cells
Gustatory epithelial cells
-receptor cells for taste
-Gustatory hairs:microvilli projecting from tips of gustatory epithelial cells
-Function: receptor membrane of gustatory epithelial cells
-Sensory dendrites wrap around gustatory hairs
-Function: forms first part of pathway to the brain
Basal epithelial cells
-stem cells
-Function: replace lost/damaged gustatory epithelial cells
-Taste buds replaced every 7-10 days
Why is it necessary to replace lost of damaged gustatory epithelial cells?
consuming solid food scrapes off epithelial cells
Taste has six basic modalities
1) Sweet: produced by most sugars, alcohols, some amino acids, lead salts
2) Sour: produced by acids
3) Salty: produced by metal ions (inorganic salts)
4) Bitter: produced mostly by alkaloids, some nonalkaloid
5) Umami: produced by amino acids glutamate & aspartate
6) Long-chain fatty acids: produced by presence of lipids
-most substances produce a combination of these tastes
-single taste cell responds to only 1 modality
-all areas of tongue can detect all taste modalities
Two processes must occur for perception of taste to take place
1) Activation of taste receptors
2) Transduction of taste
Activation of taste receptors
-Chemical tastant must dissolve in saliva
-Tastant binds gustatory epithelial cellgraded potential occurs
-Neurotransmitter release to sensory dendrite elicits action potential
Transduction of taste
-different mechanisms affect how we taste
A) Salty: Na+ influx through Na+ channels directly depolarizes gustatory epithelial cell
B) Sour: H+ acts intracellularly to open ion channels
C) Bitter/sweet/umami: G-protein gustducin activation leads to opening of ion channels to depolarize membrane
Pathway to the Gustatory Cortex
-Facial nerve carries information from anterior 2/3 of tongue
-Glossopharyngeal nerve carries information from posterior 1/3 of tongue
-Most fibers synapse at solitary nucleus in medulla, travel to primary gustatory cortex
-Others travel to limbic system & hypothalamus
What does the limbic system and hypothalamus provide with the sensation of taste?
emotional responses to what we consume, I like this or I don’t like this, appreciation for what we taste
Importance of taste
-Taste likes & dislikes have homeostatic value
-“Cravings” usually mean we are short on a macronutrient, ion, etc.
-Ex: Cravings salt supplies body with minerals (sodium)
-Ex: Craving sweets supplies body with carbohydrates (glucose)
-Some tastes indicate spoiled food (extreme sour) or poison (extreme bitter)
How is the indication of spoiled food or poisonous food important for homeostasis?
prevent you from getting sick or dying; survival value
Three major regions of the ear
1) External ear
2) Middle ear
3) Inner ear
External ear
-External acoustic meatus: tube extending from auricle to tympanum
-Function: Allows sound to pass to deeper regions of ear
-Tympanic membrane (tympanum): thin membrane that divides outer ear from middle ear
-Function: vibrates in response to sound waves
Middle Ear
-3 auditory ossicles
A) Malleus: largest and most lateral
-Attaches to tympanum laterally
-Attaches to incus medially
B) Incus: middle bone
-Attaches to malleus on one side, stapes on opposite side
C) Stapes: smallest bone
-Attaches to oval window
Function of 3 ossicles
-Sound conduction
-vibrate in response to incoming sound waves: transmit sound from tympanum to inner ear
-Muscles associated with bones:
-Tensor tympani & stapedius: contract in response to extreme sound vibrations
Why are the tensor tympani & stapedius important?
-prevent damage to these 3 bones
-if a sound is too loud you can split the bones if these muscles were not here
Other structures associated with the middle ear
-Oval window and round window: small openings in middle ear
-Pharyngotympanic tube: runs from middle ear to nasopharynx (of throat)
-Function: opening of tube equalizes pressure in the middle ear
-Importance: tympanic membrane only vibrates if pressure is equal on either side
Inner ear
-innermost portion of ear with 2 subdivisions
A) Bony labyrinth
B)) Membranous labyrinth
-The cochlea
Bony Labyrinth
-part of the inner ear
-system of channels that weave through the temporal bone
-The bony labyrinth is the cavity inside the bone
-Filled with perilymph: fluid similar to CSF
-Function: surrounds & supports the membranous labyrinth
Membranous labyrinth
-membranous sacs and ducts found within the bony labyrinth
-Filled with endolymph: fluid similar to ICF
-Function: surrounds sensory cells in ear: transmits sound & allows for balance/equilibrium
The Cochlea
-spiral chamber of the inner ear
-Innermost portion is membranous, external portion is bony
-Divided into 3 chambers: scala vestibuli, scala tympani, scala media
-Cochlea ends blindly at helicotrema
-Function: produces nerve impulses in response to sound vibrations
Parts of the Cochlea
1) Scala vestibuli
2) Scala tympani
3) Scala media
Scala vestibuli
part of bony labyrinth that begins at oval window
Scala tympani
-part of bony labyrinth that ends at round window
-Vestibuli + tympani are continuous, ”meet” at helicotrema
Scala media (cochlear duct)
-part of membranous labyrinth
-Vestibular membrane: wall that divides s. media from s. vestbuli
-Stria vascularis: secretes endolymph
-Basilar membrane: forms floor of scala media
The spiral organ of the scala media
-Receptor region of cochlea with two cell types:
1) Cochlear hair cells
-One row of inner hair cells
-Three rows of outer hair cells
-Cochlear nerve fibers wrap around hair cells
2) Supporting cells: support hair cells
Sound
-Sound is a mechanical wave: results from vibration of particles of medium through which sound wave is traveling
-Sound waves produced by compressions and rarefactions
-Compression: air molecules are pushed together
-Rarefaction: air molecules spread apart
-Sounds waves are alternating waves of compressions and rarefactions
-Air molecules travel outward from sound source
-Sound waves travel in one direction
-Sound waves decrease in strength with distance
-Speed at which sound travels is constant within a given medium
What medium does sound travel fastest? Slowest?
sound travels fastest through a solid and slowest through a gas
Frequency (pitch)
-number of sound waves that pass a point in a given period
-Wavelength: distance between crests of a given sound wave
-Shorter wavelength = higher frequency
-Human hearing frequency range: 20-20,000 Hz -Tone: sound consisting of a single frequency
Amplitude
-height of crests for a given sound wave
-Denotes loudness of sound
-Look at difference in height between crest/trough for given sound wave
-Human hearing: 0 dB-120 dB
-Above 120 dB: sound is painful
-Hearing loss occurs from prolonged exposure to 90+ dB
Transmission of sound to the inner ear takes the following path
1) Sounds waves vibrate the tympanic membrane
2) Malleus vibrates in response to tympanum
3) Movement of oval window causes perilymph of scala vestibuli to move
4) Once perilymph is set in motion, one of 2 paths can be taken
Step #2: Malleus vibrates in response to tympanum
-Incus & stapes also vibrate
-Stapes transmits vibrations to the oval window in middle ear
Step #3: Movement of oval window causes perilymph of scala vestibuli to move
-Perilymph moves in pressure waves toward helicotrema
-Round window acts as a pressure valve to allow perilymph movement
Step #4: Once perilymph is set in motion, one of 2 paths can be taken
A) Helicotrema path: low frequency (<20 Hz) pass completely around helicotrema to round window
B) Basilar membrane path: sounds waves transmitted through scala media
-Pressure waves vibrate basilar membrane: stimulates hair cells in spiral organ
-Stimulation of hair cells generates action potential
Does the helicotrema path lead to sound perception?
no because the pressure wave is so weak that it does not stimulate the basilar membrane at all
Basilar membrane
-“tuned” to specific frequencies in specific areas
-Why? Fibers in basilar membrane differ in length & elasticity from oval window - helicotrema
-Near oval window: fibers short & stiff
-Near helicotrema: fibers long & loose
What frequency do the short and stiff fibers respond to? Why?
high frequency, hit them with lots of sound waves
What frequency do the long and loose fibers respond to? Why?
low frequency
Sound Transduction
-Movement of basilar membrane stimulates inner hair cells
-Inner hair cells have hair-like projections called stereocilia
-Tallest stereocilia embedded in tectorial membrane
-Stereocilia joined by tip links
-Tip links connect to mechanically gated ion channels - pulling tip links opens ion channels
When basilar membrane is at rest
-Some tip links open: small amount of ion flow
-Inner hair cell slightly depolarized
When stereocilia pivot toward tallest hair
-Tip links open: all ion channels open
-K+ and Ca2+ enter inner hair cell
-Inner hair cell depolarizes: creates receptor potential
-Neurotransmitter from inner hair cell released to cochlear nerve - action potential
When stereocilia bend toward shortest hair
-Tip links close
-K+ and Ca2+ no longer enter inner hair cell
-Inner hair cell hyperpolarizes
-Neurotransmitter no longer released
What is the role of outer hair cells?
-Fibers that wrap around outer hair cells are efferent
-Outer hair cells can change the flexibility of the basilar membrane
Two functions:
1) Increases responsiveness of inner hair cells
2) Protection: outer hair cells stiffen in response to loud sound
Does the basilar membrane move more easily or less easily to increase responsiveness of inner hair cells? Why?
easier to move basilar membrane = easier to stimulate inner hair cells
What happens to the basilar membrane? How does this protect our sense of hearing?
you can rip inner hair cells or break membrane, after hair cells make basilar membrane more stiff to decrease damage when sounds are loud
Pathway to the Primary Auditory Cortex
-Fibers from cochlear nerve project to superior olivary nucleus
-Pass through thalamus, project to primary auditory cortex
-Some fibers are contralateral, others are ipsilateral
-Each auditory cortex receives information from both ears
Auditory Processing
-Pitch: impulses from specific hair cells interpreted as specific pitch
-Multiple frequencies stimulate multiple parts of basilar membrane simultaneously
-Loudness: louder sounds = more movement of fluid in cochlea
-Larger waves of fluid = more movement of basilar membrane, more deflection of inner hair cells
-Localization of sound: intensity and timing localize sound source
-If intensity & timing are identicalabove, below, in front, or behind
-If intensity & timing are differentleft or right side
Equilibrium
-Two structures responsible for equilibrium:
1) Vestibule
2) Semicircular Canals
Vestibule
-most central portion of bony labyrinth of inner ear
-Contains 2 membranous sacs
A) Saccule: continuous with the cochlea
B) Utricle: continuous with semicircular canals -Both sacs contain maculae receptors
-Function: respond to linear acceleration & head position
Semicircular Canals
-System of three fluid-filled canalseach canal lies in different plane of space
-Anterior, posterior, and lateral
-Semicircular duct passes through each canal
-Ampullae: swelling at the end of each duct with receptor crista ampullares
-Function: respond to rotational movement
Maculae Anatomy
-Flat patch with supporting cells + hair cells (stereocilia, kinocilia)
-Base of hair cells supplied by vestibular nerve
-Tips of stereocilia and kinocilia embedded in otolith membrane
-Otolith membrane: jelly-like base with small otolith stones embedded in membrane
-Otoliths are dense
Sensation of movement
-Otoliths are densecauses membrane to move in response to head movement
-Movement of otolith membrane bends hair cells
-Bending toward kinociliumhair cells depolarize
-Bending away from kinociliumhair cells hyperpolarize
Utricle vs Saccule
-In utricle: maculae are horizontal, hair cells are vertical
-In saccule: maculae are vertical, hair cells are horizontal
**Maculae only respond to changes in head position
Cristae Ampullares Anatomy
-Contains hair cells and supporting cells
-Ampullary cupula: gel that surrounds hair cells
-Vestibular nerve fibers supply hair cells
Sensation of Rotational Movement
-Endolymph flows through canals in opposite direction as rotational movement
-Hairs deflected: depolarization occurs, increased neurotransmitter released
-Consistent speed of rotation: endolymph travels at same speed as rotation
-Hair cells not stimulated
-Stop rotating: endolymph flows in opposite direction
-Hair cells hyperpolarize: less neurotransmitter released
Pathway to Vestibular Nuclei or Cerebellum
-Information sent directly to reflex centers of brain stem
-Impulses travel to 1 of 2 destinations:
1) Vestibular nuclei: major integrative area for balance
-Also receives visual & somatic receptors
-Vestibular nuclei sends impulses to brain stem: information used to correct body position
2) Cerebellum
-Function: coordinates skeletal muscle activity and muscle tone to maintain head position, posture, balance
