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111 Cards in this Set
- Front
- Back
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Visual System
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One of the most important special senses in human and other mammals
In addition to audition, vision is needed for human communication Detects and interprets photic stimuli Visible light photic stimuli are electromagnetic waves between 400 and 750 nM long |
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Layers of eye
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Sclera
Cornea Choroid Retina |
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Sclera
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avascular (light impeded), dense, white, opaque protective coat covers 85%
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Cornea (Layer)
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avascular (light impeded), covers 15%, lined by a thin tear film
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Choroid
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vascular
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Retina
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1. neuronal layer
2. outer pigmented layer - absorb light |
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Cornea (Transparent)
Aqueous Humor (Transparent) |
Has refractive power - (change in direction or bending of light rays)
AH- has refractive power as well |
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Vitreous Homor (Transparent)
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90% volume of eye
structural support shock absorber |
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Last transparent part of eye
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Retina
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Cornea - general info
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Is the clear tissue at the front of the eye
Protective barrier Serves as the main refractive element of the visual system, directing incoming light through the lens for precise focusing on the retina. Refractive power is measured in diopters 2/3 of the 59 diopters of refractive power of the eye - ability to bend light A normal cornea is round, with even curves from side to side and top to bottom. |
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Lens
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focus incoming images into the retina
1/3 refractive power avascular transparent elastic convex anterior and posterior sides |
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Accommodation
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The ability increase the lens refractive power
Zonules are radial ligaments that connects the lens to the ciliary body contraction of the muscles in the ciliary body |
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Contraction of the muscles in the ciliary body
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relaxes the lens ligaments
lens become spherical, convex and thicker lens refractive power increases shape for near vision contraction controlled by parasympathetic nerve signals - gives ability to bend light more |
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Presbyopia
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Loss in power of accommodation
Eye remains focused on distant objects Wears bifocal glasses Upper segment for far-seeing Lower segment for near-seeing (reading) |
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Lacrimal system:
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lacrimal gland - produces tears
puncta and tear sac - collects tears nasolacrimal duct - empties tears into the nasal cavity Disorder: dry eyes |
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Tears - composition
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98% H2O,
1.5% NaCl potassium albumin glucose lysozymes immunoglobulin |
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Tears - function
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wet and protect cornea and conjunctiva
cleans and provides nutrients to cornea protects against infection |
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Conjunctiva
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A thin layer of mucous membrane that lines the outer surface of eye and the anterior surface of the eyelids.
Disorders: conjunctivitis (inflammation of the conjunctiva) bacteria, virus, chlamydia, allergens |
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Aqueous humor
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Fluid
Produced by ciliary process epithelium Na,K-ATPase ion carriers co-transporters Plasma Provides nutrients to lens and cornea (glucose) b/c avascular |
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Na,K-ATPase Function
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Na,K-ATPase
localized in the plasma membrane of the cell. See pg 8 |
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What regulates Na, K-ATPase?
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Acetylcholine and NO
See pg 8 |
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Aqueous humor outflow
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Trabecular meshwork
Schlemn’s canal (under trabecular meshwork) |
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Cellular mechanisms of Aqueous humor Regulation
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Agents that decrease cell volume increase the rate of aqueous humor outflow:
-Nitric oxide & cGMP Agents that disrupt the actin cytoskeleton increases aqueous humor outflow. -Ouabain |
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If trabecular meshwork is clogged
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Build up of pressure
The spaces in meshwork get smaller as pressure increases |
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Intraocular pressure
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Rates of secretion of aqueous humor
Rates of outflow of aqueous humor Improper regulation of IOP is a risk factor for glaucoma |
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Receptor and Neuronal Function of the Retina
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Light captured by rods and cones and sent to horizontal cells. Then synapse with rods and cones or bipolar cells that synapse with rods and cones. Biploar cells synapse with amacrine and ganglion cells. Axons of ganglion cells from optic nerve that take signal from eye to brain.
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Neuronal Retina
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central to the visual process
light absorbed by photoreceptors rods – black/white cones - color converted to electrical signal in a process called phototransduction. |
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CONES
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Light sensitive portion of cone – cone pigment
High density of cones in the fovea (located in the macula lutea) Detect color vision Three types of cones respond to the blue, green and red portions of the visible electromagnetic spectrum |
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RODS
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A visual pigment called rhodopsin traps light retinal (vitamin A-derived pigment) and opsin
Rhodopsin Is a membrane protein |
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Rhodopsin
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Contains a chromophore called 11-cis retinal which is covalently bound to opsin
Photon capture converts 11-cis-retinal to all-trans retinal Opsin is activated Metarhodopsin II – activated rhodopsin |
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Metarhodopsin II
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Relays activating changes to the G protein, transducin
GTP binds to transducin α subunit Activates phosphodiesterase (PDE) PDE degrades cGMP to GMP The decrease in cGMP concentration leads to closure of cyclic-nucleotide-gated (CNG) channels |
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Effects of Metarhodopsin II
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resulting in two effects:
a decrease in Ca2+ influx hyperpolarization of the membrane potential Lowered [Ca2+]i concentration disinhibits guanylate-cyclase-activating protein (GCAP), leading to activation of guanylate cyclase (GC) and resynthesis of cGMP. Light that is not absorbed by rhodopsin is absorbed by retinal pigment melanin (keeps light from scattering) |
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Optic Nerve
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Primary Visual Center of Brain
axons of the retinal ganglion cells form the optic nerve |
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Visual Cortex
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located in the occipital lobe neuronal circuitry provides for visual sensation and perception
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Re-formation of Rhodopsin
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all-trans retinal revert to 11-cis form conversion catalyzed by retinal isomerase
Vitamin A in cytoplasm of rods and pigment of retinal Reduced sensitivity to light – deficiency in vitamin A |
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Re-formation of Rhodopsin
(cont) rod vision, light adaptation, dark adaptation |
Rod vision adapted for night and low-level illumination
Light adaptation - decreased sensitivity to light bright light causes concentrations of photosensitive chemicals in rods and cones to be reduced sensitivity of eye to light also reduced Dark adaptation increase in light sensitive pigments remains in darkness retinal and opsin combine also vitamin A is converted into retinal |
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Errors of Refraction
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The refractive process is similar to the way a camera takes a picture.
The cornea and lens in your eye act as the camera lens. The retina is similar to the film. If the image is not focused properly, the film (or retina) receives a blurry image |
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Hyperopia
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(farsightedness )
decreased refractive power eyeball too short distant objects are clear, and close-up objects appear blurry images focus on a point beyond the retina corrected with convex lens |
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Myopia
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(nearsightedness)
refractive surfaces have too much refractive power the eye is too long faraway objects appear blurry because they are focused in front of the retina affects over 25 percent of all adult Americans. corrected with concave lens |
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Astigmatism
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uneven curvature of the cornea
blurs and distorts both distant and near objects. the cornea is shaped more like the back of a spoon, curved more in one direction than in another. light rays to have more than one focal point and focus on two separate areas of the retina, distorting the visual image. Two-thirds of Americans with myopia also have astigmatism. |
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Refractive errors
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are usually corrected by eyeglasses or contact lenses.
refractive surgeries are becoming an increasingly popular option. |
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Cataracts
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lens opacity (does not allow the transmission of light)
most common cause of visual loss treated with lens replacement (surgery) |
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RETINAL DEFECTS
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Color blindness – confuse or mismatch colors
Retinitis Pigmentosa - degeneration of the retinal photoreceptors Diabetic Retinopathy – 3rd cause of blindness involves thickening of the retinal capillary walls, hemorrhages, formation of fragile blood vessels Treatment - Scatter laser treatment helps to shrink the abnormal blood vessels |
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Age-related macular degeneration (AMD)
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is a disease associated with aging that gradually destroys sharp, central vision.
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Wet AMD
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abnormal blood vessels behind the retina start to grow under the macula.
blood raise the macula from its normal place at the back of the eye early symptom of wet AMD is that straight lines appear wavy. |
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Dry AMD
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light-sensitive cells in the macula slowly break down
blurred central vision blurred spot in the center of your vision. Treatment include: argon laser photocoagulation of extrafoveal choroidal neovascularisation (CNV) and photodynamic therapy of selected sub-foveal CNV |
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Understanding IOP regulation
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is important in identifying potential treatments for individuals with high IOP and glaucoma
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Glaucoma
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Optic neuropathy
characterized by: optic disk cupping (increasing in size and depth) as result of axonal loss visual field loss - area in which objects can be seen while the eye is focused on a central point. |
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Hearing
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EARS:
The external ear, the middle ear, and the cochlea of the inner ear are concerned with hearing. The receptors for hearing are hair cells in the cochlea. Level of sound is measured in decibels sound pressure level or dB SPL |
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Structures of the Ear
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See pg 2
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Outer ear
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Auricle –
corrugated surface acts as a reflector that collects sounds from different directions and frequency captures the mechanical energy (sound) focus mechanical energy External Auditory Meatus transmits the mechanical energy to the tympanic membrane (eardrum) |
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Structures in the middle ear
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See pg 3
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Middle ear
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The middle ear is an air-filled cavity in the temporal bone
The auditory (eustachian) tube connects the middle ear to the nasopharynx The three auditory ossicles, the malleus, incus, and stapes, are located in the middle ear . The malleus manubrium, (handle of the malleus) head short process The incus interacts with the head of the stapes. The stapes (foot plate )is attached to the walls of the oval window. |
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The inner ear: tubes of the cochlea
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See pg 4
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Cochlea
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The cochlear portion is a coiled tube
Throughout its length, the basilar membrane and Reissner's membrane divide the cochlea into three chambers or scalae: **scala vestibuli scala media **scala tympani **contain perilymph and communicate with each other at the apex of the cochlea through a small opening called the helicotrema |
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Cochlea cont
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The scala vestibuli ends at the oval window
The scala tympani ends at the round window The scala media contain endolymph |
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Basilar membrane
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Fibrous membrane
Length of the fibers increase progressively from the oval window to the helicotrema Diameter of the fibers decrease progressively from oval window to the helicotrema High-frequency resonance occur near the oval window Low-frequency resonance occur at the helicotrema |
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Organ of Corti
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See pg 5
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Organ of Corti cont
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Located on the basilar membrane
contains the hair cells, which are the auditory receptors. outer hair cells inner hair cells Tectorial membrane cover the rows of hair cells |
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Organ of Corti cont
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The axons of the afferent neurons that innervate the hair cells form the auditory (cochlear) division of the eighth cranial nerve.
The processes of the hair cells are bathed in endolymph Basilar membrane is relatively permeable to perilymph in the scala tympani and the bases of the hair cells are bathed in perilymph. |
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Function of the external ear
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The external ear funnels sound waves to the external auditory meatus .
The external auditory meatus funnels sound waves to the tympanic membrane (eardrum). |
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Function of the middle ear
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Air filled cavity
The tympanic membrane receives sound from the external auditory meatus The tympanic membrane transmits sounds to the ossicles; malleus, incus and stapes Ossicles conducts sounds to the cochlea |
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Function of the inner ear
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Fluid filled cavity
Converts mechanical sound into electrical signals Hair cells located in organ of Corti generates nerve impulses in response to vibration |
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Sound waves
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A is the record of a pure tone.
B has a greater amplitude = louder C greater frequency = higher pitch D is a complex wave that is regularly repeated= musical sound E have no regular pattern= noise |
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Sound
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Sound is produced when vibrations of the molecules in the external environment strike the tympanic membrane.
Level of sound is measured in decibels sound pressure level or dB SPL. The waves travel through air at a speed of approximately 344 m/s (770 mph) at 20 °C at sea level (1450 m/s at 20 °C in fresh water and is even greater in salt water). The loudness of a sound is correlated with the amplitude of a sound wave. |
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Sound (cont)
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The pitch of a sound is correlated with the frequency (number of waves per unit of time).
Sound waves that have repeating patterns are perceived as musical sounds Harmonic vibrations (overtones) that give the sound its characteristic timbre (quality). Aperiodic nonrepeating vibrations cause a sensation of noise |
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Tympanic Reflex
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Loud sounds initiate a reflex contraction called tympanic reflex.
Contraction of the tensor tympani and stapedius decreases sound transmission. Its function is protective, preventing strong sound waves from causing excessive stimulation of the auditory receptors. |
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Sound Transmission
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Sound waves produce pressure changes on the external surface of the tympanic membrane
In response to the pressure changes the tympanic membrane moves in and out. The motions of the tympanic membrane are imparted to the malleus. The malleus moves and transmits the vibrations to the incus. |
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Sound Transmission (cont)
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The incus moves and transmits vibrations to the stapes. Movements of the stapes vibrates along the oval window against the fluid in the scala vestibuli.
The basilar and tympani membranes move in the same direction, so a shearing motion bends the hairs. The hairs of the inner hair cells are not attached to the tectorial membrane, but they are apparently bent by fluid moving between the tectorial membrane and the underlying hair cells. |
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Sound Transmission (cont)
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The inner hair cells are the primary sensory cells that generate action potentials in the auditory nerves.
The outer hair cells increase the amplitude and clarity of sounds. Prestin is a membrane protein (the motor protein of outer hair cells) |
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Sound Transmission (cont)
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Cochlea transduces sound energy into electrical signals and sends them to the brain
Hearing begins: The hair cells in the organ of Corti generate changes in membrane potential proportional to the direction and distance the hair moves. Electrical signals are sent via the nerve fibers |
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Uncoiled cochlea and flow of stimulus energy
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See Pg
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Frequency resonance of basilar membrane
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See Pg
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Central Pathway
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Nerve fibers from the spiral ganglion of Corti enter the cochlear nuclei and synapse
Second-order neurons pass to the opposite side of the brain stem From there, auditory impulses pass by various routes to the: inferior colliculi medial geniculate body auditory cortex. The primary auditory cortex is Brodmann's area 41. |
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Auditory cortex (AC)
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Discriminate different sound pitches and patterns of sound (AC)
Detect direction of sound (AC) Meaning of sound (AAC) |
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Deafness
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Conductive (conduction) deafness
impaired sound transmission in the external or middle ear impacts all sound frequencies. |
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causes of conduction deafness
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are plugging of the external auditory canals with wax (cerumen) or foreign bodies,
otitis externa (inflammation of the outer ear, "swimmer's ear") otitis media (inflammation of the middle ear) causing fluid accumulation ( in the inner ear) |
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Sensorineural deafness
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is most commonly the result of loss of cochlear hair cells
problems with the cochlear nerve or within central auditory pathways. It often impairs the ability to hear certain pitches while others are unaffected. |
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Causes of Sensorineural deafness
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Aminoglycoside antibiotics such as streptomycin and gentamicin obstruct the mechanosensitive channels in the hair cells and can cause the cells to degenerate
Damage to the outer hair cells by prolonged exposure to noise Tumors of the eighth cranial nerve Audiometer-used to determine hearing disabilities |
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Olfactory epithelium
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Receptor cells for smell sensation are olfactory cells
Olfactory sensory neurons are embedded within the olfactory epithelium These neurons project axons to the olfactory bulb of the brain. |
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Cell types in olfactory epithelium
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There are three cell types:
olfactory sensory neurons supporting cells (sustentacular) Secretes mucus that bathes the odorant receptors on the cilia and provides the appropriate molecular and ionic environment for odor detection. basal stem cells Produce new olfactory sensory neurons |
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Olfactory sensory neuron: dendrite
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Dendrite
projects into the nasal cavity terminates in a knob containing 10 to 20 cilia Odorants bind to specific odorant receptors on the cilia initiate a cascade of events leading to generation of action potentials in the sensory axon. |
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Olfactory sensory neuron: axon
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A single axon projects from each neuron to the olfactory bulb.
The axons of the olfactory sensory neurons pass through the cribriform plate and enter the olfactory bulbs. |
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Odorant receptor
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See Pg
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Signaling mechanism
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See Pg
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Odorant receptors
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The olfactory system mediates discrimination of more than 10,000 different odors.
The genes code for about 1000 different types of odorant receptors All the odorant receptors are coupled to heterotrimeric G proteins. Odorant molecule binds to its receptor |
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Odorant receptors (cont)
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The G protein subunits (a, b, g ) dissociate.
The a-subunit activates adenylate cyclase to catalyze the production of cAMP, Open cation channels - causing an inward-directed Ca2+ current. This produces the graded receptor potential, which then leads to an action potential in the olfactory nerve. |
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Basic neural circuits in the olfactory bulb
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Note that olfactory receptor cells with one type of odorant receptor project to one olfactory glomerulus (OG) and olfactory receptor cells with another type of receptor project to a different olfactory glomerulus.
CP, cribriform plate; PG, periglomerular cell; M, mitral cell; T, tufted cell; Gr, granule cell. |
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Olfactory Bulbs
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In the olfactory bulbs
olfactory glomeruli - axonal synapse of the olfactory sensory neurons with primary dendrites of the mitral cells and tufted cells Axons of mitral cells and tufted cells go into the olfactory cortex |
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Olfactory Bulbs (cont)
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periglomerular cells- are inhibitory neurons connecting one glomerulus to another
granule cells have no axons and make reciprocal synapses with the lateral dendrites of the mitral and tufted cell the mitral or tufted cell excites the granule cell by releasing glutamate, granule cell inhibits the mitral or tufted cell by releasing GABA. |
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Regions of the Olfactory Cortex
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The axons of the mitral and tufted cells pass through the lateral olfactory stria to terminate on dendrites of pyramidal cells:
Anterior olfactory nucleus Olfactory tubercle Piriform cortex Amygdala – emotional response Entorhinal cortex - memories Then to the frontal or orbitofrontal cortex -discrimination of odors |
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Vomeronasal Organ
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Vomeronasal organ in olfactory epithelium of rodents and various other mammals
perception of odors that act as pheromones. sensory neurons project to the accessory olfactory bulb and from there primarily to areas in the amygdala and hypothalamus concerned with reproduction and ingestive behavior. Vomeronasal input has major effects on these functions. |
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Vomeronasal Organ (cont)
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The vomeronasal organ has about 100 G protein-coupled odorant receptors that differ in structure from those in the rest of the olfactory epithelium.
The organ is not well developed in humans, There is evidence for the existence of pheromones in humans There is a close relationship between smell and sexual function |
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Primary sensations of smell
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Musky
Floral pepperminty pungent putrid |
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Adaptation
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Perception of the odor decreases and eventually ceases when continuously exposed.
rapid adaptation, or desensitization, mediated by Ca2+ acting via calmodulin on cyclic nucleotide-gated (CNG) ion channels. When the CNG A4 subunit is knocked out, adaptation is slowed. |
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Threshold for smell
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Minute quantity of stimulating agent in the air that can elicit a smell sensation
Methylmercaptan 1/25 trillionth of a gram is in milliliter of air (low threshold |
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Abnormalities in odor detection
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anosmia -inability to smell
hyposmia or hypesthesia -diminished olfactory sensitivity Due to nasal congestion damage to the olfactory nerves due to fractures of the cribriform plate tumors infections (such as abscesses). Alzheimer disease |
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Abnormalities in odor detection (cont)
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Aging - 75% of humans over the age of 80 have an impaired ability to identify smells
Hyperosmia - enhanced olfactory sensitivity Dysosmia - distorted sense of smell can be caused by sinus infections, partial damage to the olfactory nerves poor dental hygiene. |
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Primary sensations of taste
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Sour
Caused by acids; hydrogen ion concentration Salty Caused by sodium (cations) ion concentration Sweet Not caused by any one class of compound (sugars, glycols, alcohols, amino acids) Bitter _ Not caused by any one class of compound (alkaloids and organic substances containing nitrogen) Umami Food containing L-glutamate such as meat extracts and aging cheese. |
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Threshold for taste
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Humans sensitivity to:
Bitter > sour> sweet = salty |
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The salty taste:
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is triggered by NaCl.
Na+-selective channel called amiloride-sensitive epithelial sodium channel (ENaC). The entry of Na+ into the salt receptors depolarizes the membrane, generating the receptor potential. Other unknown receptors involved |
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Sour taste
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The sour taste is triggered by protons (H+ ions).
Protons enter the ENaCs The H+ ions block K+-sensitive channel. The fall in K+ permeability can depolarize the membrane. Hyperpolarization-activated cyclic nucleotide-gated cation channel (HCN), Other unknown mechanisms |
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Umami taste
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is due to activation of
metabotropic glutamate receptor (mGluR4). ionotropic glutamate receptors produces depolarization |
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Bitter taste
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is produced by a variety of unrelated compounds
Many of these are poisons bitter taste serves as a warning to avoid them. Receptors include: K+-selective channels. T2R family of receptors heterotrimeric G protein, gustducin. decreased cAMP increases the formation of inositol phosphates depolarization. Some bitter compounds are membrane permeable, quinine is an example. |
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Sweet taste
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Substances that taste sweet
T1R3 act via the G protein gustducin. sweet-responsive receptors act via cyclic nucleotides and inositol phosphate metabolism. |
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Taste receptors
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See Pg
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Taste buds located in papillae of the human tongue
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Papilla – nipple-shaped projection
3 major types Taste buds innervated by the chorda tympani branch of the facial nerve lingual branch of the glossopharyngeal nerve Ventral posterior medial nucleus of thalamus Gustatory cortex (anterior insula frontal operculum) |
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Cells in taste bud
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See Pg
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Neural pathway
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See Pg
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Abnormalities in taste
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Ageusia - absence of the sense of taste
Hypogeusia diminished taste sensitivity Causes: damage to the lingual or glossopharyngeal nerve. Neurological disorders certain infections (eg, primary amoeboid meningoencephalopathy) side effect of various drugs including cisplatin and captopril vitamin B3 or zinc deficiencies. Aging and tobacco abuse also contribute to diminished taste. |
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Abnormalities in taste (cont)
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Dysgeusia or parageusia - unpleasant perception of taste
causes a metallic, salty, foul, or rancid taste. temporary problem |
