Special Senses

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evlymenwilliams
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197870
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Special Senses
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2013-03-03 17:01:45
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special senses
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vision, hearing, smell, taste,
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  1. Vision and Light
    • •Vision - perception of light emitted or reflected from objects in the environment
    • •Visible light
    • •electromagnetic radiation with wavelengths from 400 to 750 nm
    • •must cause a photochemical reaction to produce a nerve signal
    • •radiation below 400 nm; energetic, kills cells
    • •radiation above 750 nm; too little energy to cause photochemical reaction
  2. Image Formation: Refraction, Accomodation, and Constriction
    • •Refraction
    • •Bending of light rays
    • •Accommodation
    • •Change in the shape of the lens
    • •Constriction
    • •Change in the size of the pupil
  3. PRINCIPLE OF REFRACTION
    • •Speed of light in a vacuum 3 X 10 5 km/s
    • •Slows down in air, water, glass, other mediums
    • •When light rays strike a surface at an angle the rays are bent
    • •Refractive index – the ability of a medium to slow down light rays relative to air (1.0)
  4. OPTICAL COMPONENTS
    • •Structures refract light to focus on retina
    • •cornea
    • •transparent cover on anterior surface of eyeball
    • •aqueous humor
    • •serous fluid posterior to cornea, anterior to lens
    • •lens
    • • changes shape to help focus light
    • •rounded with no tension
    • •flattened due to pull of suspensory ligaments
    • •vitreous humor
    • •jelly fills space between lens and retina
  5. REFRACTION
    • Bending of light rays occurs when light passes through substance with different refractive index at any angle other than 90 degrees
    • •refractive index of air is arbitrarily set to n = 1
    • •refractive index
    • •cornea is n = 1.38
    • •lens is n = 1.40
    • •Cornea refracts light more than lens does
    • •due to shape of cornea
    • •lens becomes rounder to increase refraction for near vision
  6. EFFECTS OF CORRECTED LENSES
    • •Hyperopia - farsighted (eyeball too short)
    • •correct with convex lenses
    • •Myopia - nearsighted (eyeball too long)
    • •correct with concave lenses
  7. Astigmatism
    irregularities in the curvature of lens and cornea leading to blurred vision.
  8. ACCOMMODATION OF LENS
    • •Change in the shape of the lens to bring an object in focus
    • •Ciliary muscles contract
    • •Suspensory ligaments relax
    • •Decreasing diameter of ciliary body
    • •Allowing lens to become more rounded (convex)
    • •Near point accommodation - closest point for an object in visual field while remaining in focus
  9. Presbyopia
    • "old vision"
    • •Decreased ability to accommodate with age due to decreased flexibility of lens
    • •Leads to difficulty reading and doing close handiwork
    • •bifocals
  10. CATARACTS
    • clouding of lens
    • •aging, diabetes, smoking, and UV light
  11. Glaucoma
    Aqueous Humor:

    • Produced by ciliary body, flows to posterior chamber through pupil to anterior chamber - reabsorbed into canal of Schlemm
    • •Glaucoma
    • •death of retinal cells due to elevated pressure within the eye
    • •obstruction of scleral venous sinus
    • •colored halos and dimness of vision
  12. DRUGS TO TREAT GLAUCOMA
    • •Tonometry - to screen for glaucoma by measuring intraocular pressure and to permit evaluation of glaucoma
    • • -pneumatic tonometry consists of the electronic measurement of pressure after a short burst of gas strikes the cornea

    • •Cholinergic drugs - to produce miosis (constriction of the pupil) in the treatment of glaucoma. They reduce intraocular pressure by increasing the outflow of fluid from the anterior chamber of the eye.
    • • Carbonic anhydrase inhibitors - lower intraoccular pressure by inhibiting the formation of fluid
    • • Beta blocking agents - lower intraoccular pressure by reducing aqueous humor production; block the action of epinephrine and norepinephrine.
  13. CONSTRICTION OF THE PUPIL
    • •Light enters the eyes through the pupils
    • •Pupillary constrictor - smooth muscle encircling the pupil
    • •parasympathetic stimulation narrows pupil
    • •Pupillary dilator - spokelike myoepithelial cells
    • •sympathetic stimulation widens pupil
    • •Active when light intensity changes or gaze shifts from distant object to nearby object
    • •photopupillary reflex -- both pupils constrict if one eye is illuminated (type of consensual reflex)
  14. NEAR RESPONSE
    • Allows eyes to focus on nearby object (that sends oblique light waves to eyes)
    • 1.convergence of eyes
    • •eyes orient their visual axis towards object
    • 2.constriction of pupil
    • •blocks peripheral light rays and reduces spherical aberration (blurry edges)
    • 3.accomodation of lens
    • •ciliary muscle contracts, lens takes convex shape
    • •light refracted more strongly and focused onto retina
  15. TUNICS OF THE EYEBALL
    • Fibrous layer - sclera and cornea
    • •Vascular layer - choroid, ciliary body and iris
    • •Internal layer - retina and optic nerve
  16. NONRECEPTOR RETINAL CELLS
    • •Bipolar cells (1st order neurons)
    • •synapse on ganglion cells
    • •large amount of convergence
    • •Ganglion cells (2nd order neurons)
    • •axons of these form optic nerve
    • •more convergence occurs (114 receptors to one optic nerve fiber)
    • •Horizontal and amacrine cells form connections between other cells
    • •enhance perception of contrast, edges of objects and changes in light intensity
  17. TEST FOR BLIND SPOT
    • •Optic disk = blind spot
    • •optic nerve exits posterior surface of eyeball
    • •no receptor cells
    • •Blind spot - use test illustration above
    • •close eye, stare at X and red dot disappears
    • •Visual filling - brain fills in green bar across blind spot area
  18. PHOTORECEPTOR CELLS
    • •Posterior layer of retina - pigment epithelium
    • •purpose is to absorb stray light and prevent reflections
    • •Photoreceptors
    • •rod cells (night - scotopic vision)
    • •outer segment - stack of coinlike membranous discs studded with rhodopsin pigment molecules
    • •cone cells (color - photopic vision)
    • •outer segment tapers to a point
  19. DETACHED RETINA
    • •Blow to head or lack of vitreous
    • •Blurry areas in field of vision
    • •Disrupts blood supply, leads to blindness
    • •How does a detached retina disrupt the blood supply to neural retina?
  20. VISUAL PIGMENTS
    • •Rod cells have rhodopsin
    • •has absorption peak at wavelength of 500 nm
    • •2 major parts of molecule
    • •opsin - protein portion
    • •retinal - a vitamin A derivative
    • •Cones contain photopsin
    • •opsin moieties contain different amino acids that determine wavelengths of light absorbed
    • •3 kinds of cones absorbing different wavelengths of light produce color vision
  21. RHODOPSIN BLEACHING/REGENERATION
    • •Rhodopsin absorbs light, converted from bent shape (cis-retinal) to straight (trans-retinal)
    • •retinal dissociates from opsin (bleaching)
    • •5 minutes to regenerate 50% of bleached rhodopsin
  22. GENERATING VISUAL SIGNALS
    • •Opsin is an enzyme
    • •Inactive when associated with cis-retinal
    • •In light trans-retinal disassociates from opsin making it active
    • •Activated opsin interacts with transducin to facilitate the breakdown of cGMP by phosphodiesterase
    • •Breakdown of cGMP will lead to closure of ligand gated Na clannels
  23. GENERATING VISUAL SIGNALS 2
    • In the light ligand gated Na channels are closed by the breakdown of cGMP
    • •Na influx ceases
    • •Decreasing glutamate release at distal synapse
    • •In the light there is a decrease in glutamate signaling on bipolar cells
  24. NIGHT VISION
    • •Rods sensitive – react even in dim light
    • •extensive neuronal convergence
    • •600 rods converge on 1 bipolar cell
    • •many bipolar converge on each ganglion cell
    • •results in high degree of spatial summation
    • •one ganglion cells receives information from 1 mm2 of retina producing only a coarse image
  25. NIGHT VISION
    • •Edges of retina have widely-spaced rod cells, act as motion detectors
    • •Covers a large area in visual field
    • •Small depolarization to very low levels of light in several rods can activate bipolar cell
    • •Images generated are not clear because these photoreceptors cover a large area and converge
  26. DAY VISION
    • Fovea contains only 4000 tiny cone cells (no rods)
    • •no neuronal convergence
    • •each foveal cone cell has "private line to brain"
    • •High-resolution color vision
    • •little spatial summation so less sensitivity to dim light
    • •Small depolarization in cones cannot activate bipolar cells because there is no additive effect
  27. COLOR VISION
  28.  
    • •Primates have well developed color vision
    • •nocturnal vertebrates
    • have only rods
    • •Cones named for absorption
    • peaks of photopsins
    • •blue cones peak sensitivity at 420 nm
    • •green cones peak at 531 nm
    • •red cones peak at 558 nm (orange-yellow)
    • •Color perception based on mixture of nerve signals
  29. COLOR BLINDNESS
    • •Hereditary lack of one photopsin
    • •red-green is common (lack either red or green cones)
    • •incapable of distinguishing red from green
    • •sex-linked recessive (8% of males)
    • • Usually Ishihara plates are used to test color vision.
  30. VISUAL ACUITY
    Snellen eye chart-visual acuity 20/20, 20/40, 20/15
  31. OPHTHALMOSCOPIC EXAM OF EYE
    • •Direct evaluation of blood vessels
    • •Ophthalmoscopy – used to detect retinal changes associated with hypertension, diabetes mellitus, atherosclerosis, and increased intracranial pressure
    • •-an ophthalmoscope is used to examine the interior of the eyeball, with or without the use of dilating drops
  32. STEREOSCOPIC VISION (STEREOPSIS)
    • Depth perception - ability to judge distance to objects
    • •requires 2 eyes with
    • overlapping visual fields
    • •panoramic vision has eyes
    • on sides of head (horse)
    • •Fixation point
    • •farther away requires image focus medial to fovea
    • •closer results in image focus lateral to fovea
  33. VISUAL PROJECTION PATHWAY
    • Bipolar and ganglion cells in retina - 1st and 2nd order neurons (ganglion cell axons of form CN II)
    • •Hemidecussation in optic chiasm
    • •1/2 of fibers cross over so that images of all objects in left visual field fall on right half of each retina
    • •each side of brain sees what is on side where it has motor control over limbs
    • •3rd order neurons in lateral geniculate nucleus of thalamus form optic radiation to 1 visual cortex where conscious visual sensation occurs
    • •Few fibers project to superior colliculi and midbrain for visual reflexes (photopupillary and accommodation)
  34. PITCH AND LOUDNESS
    • Pitch - frequency vibrates specific parts of ear
    • •hearing range is 20 (low pitch) - 20,000 Hz (cycles/sec)
    • •speech is 1500-4000 where hearing is most sensitive
    • •Loudness – amplitude; intensity of sound energy
  35. THE EAR
    • •The subdivisions of the ear are:
    • •Outer ear - Collects sound waves and passes them to tympanic membrane via external auditory canal
    • •Middle ear - Contains the tympanic membrane and the ossicles; conducts sound waves into inner ear
    • •Inner ear - Composed of the bony labyrinth and the membranous labyrinth; Contains the receptors for hearing and equilibrium
    • THE EAR
  36. SPIRAL ORGAN
    • Cochlear duct separated from
    • •scala vestibuli by vestibular membrane
    • •scala tympani by basilar membrane
    • Spiral organ (organ of corti)
    • •Stereocilia of hair cells attach to gelatinous tectorial membrane
    • •Inner hair cells
    • •hearing
    • •Outer hair cells
    • •adjust cochlear responses to different frequencies
    • •increase precision
  37. COCHLEAR HAIR CELLS
    • •Stereocilia of IHCs
    • •bathed in high K+
    • •creating electrochemical gradient
    • •tips embedded in tectorial membrane
    • •bend in response to movement of basilar membrane
    • •pulls on tip links and opens ion channels
    • •K+ flows in – depolarization causes release of neurotransmitter
    • •stimulates sensory dendrites at base
  38. SENSORY CODING
    • Vigorous vibrations excite more inner hair cells over a larger area
    • •triggers higher frequency of action potentials
    • •brain interprets this as louder sound
    • •Pitch depends on which part of basilar membrane vibrates
    • •at basal end, membrane narrow and stiff
    • •brain interprets signals as high-pitched
    • •at distal end, 5 times wider and more flexible
    • •brain interprets signals as low-pitched
  39. BASILAR MEMBRANE FREQUENCY RESPONSE
    Notice high and low frequency ends
  40. COCHLEAR TUNING
    • •Increases ability of cochlea to receive some sound frequencies
    • •Outer hair cells contract reducing basilar membranes freedom to vibrate
    • •fewer signals from that area allows brain to distinguish between more and less active areas of cochlea
  41. TYMPANIC REFLEX
    • •Tensor tympani muscle
    • •Tenses eardrum
    • •Stapeduis muscle
    • •Reduces movement of stapes
    • •Make up tympanic reflex
    • •Muffles transfer of sound waves to inner ear
  42. TYMPANIC REFLEX 2
    • •Works for loud sounds that gradually build up
    • •Thunder
    • •Dampens our speech allowing us to hear others when we speak
    • •Not effective for sustained loud noises
    • •Breaks sterocilia
    • •Irreversible hearing loss
  43. AUDITORY PROJECTION PATHWAY
    • •Spiral ganglion formed by cell bodies of sensory neurons
    • •Axons form cochlear nerve portion of CN VIII (vestibulocochlear)
    • •Synapse in cochlear nuclei (near pons)
    • •Second order neurons pass superior olivary nucleus (pons)
    • •compares sounds from both sides to identify direction Binaural hearing
    • •Cochlear tuning
    • •Tympanic reflex
  44. AUDITORY PROJECTION PATHWAY 2
    • •Inferior colliculus helps
    • •locate origin of sound
    • •process fluctuations in pitch during speech
    • •produce startle response; head turning to loud sound
    • •Third order neurons from inferior colliculus go to thalamus
    • •Fourth order neurons to cerebral cortex
  45. DISORDERS ASSOCIATED WITH HEARING
    • •Deafness
    • •Sensorineural-death of hair cells
    • •Continued exposure to lound noise
    • •Conduction-disruption of sound wave transmission to inner ear
    • •Damaged ear drum
    • •Otosclerosis- fusion of ossicles to each other or fusion of stapes to oval window
    • •Ottis media- middle ear infection common in children due to short horizontal auditory tubes
    • •Fluid accumulates in tympanic cavity
    • •Myringotomy- cutting eardrum and inserting small drainage tube
    • •Audiometry
    • •test to evaluate an individual’s hearing acuity
    • While in a soundproof room an individual uses earphones to listen for sounds produced by an audiometer
  46. EQUILIBRIUM
    • •Control of coordination and balance
    • •Receptors in vestibular apparatus
    • •semicircular ducts contain crista
    • •saccule and utricle contain macula
    • •Static equilibrium – perceived by macula
    • •perception of head orientation
    • •Dynamic equilibrium
    • •perception of motion or acceleration
    • •linear acceleration perceived by macula
    • •angular acceleration perceived by crista
  47. STATIC EQUILIBRIUM
    • •Saccule and Utricle
    • •Contain macula
    • •hair cells with stereocilia and one kinocilium buried in a gelatinous otolithic membrane
    • •otoliths add to the density and inertia and enhance the sense of gravity and motion
  48. DYNAMIC EQUILIBRIUM
    • Semicircular canals
    • •Contains crista ampullaris
    • •Consists of hair cells buried in a mound of gelatinous membrane (one in each duct)
    • •Orientation causes ducts to be stimulated by rotation in different planes

    • As head turns, endolymph lags behind, pushes cupula, stimulates hair cells
    • •After 30 sec endolymph catches up and hair cells no longer stimulated
  49. EQUILIBRIUM PROJECTION PATHWAYS
    • •Hair cells of macula and semicircular ducts synapse on vestibular nerve
    • •Fibers end in vestibular nucleus in pons and medulla
    • •Then to thalamus
    • •Finally relayed to cerebral cortex for awareness of position and movement
  50. DISORDERS ASSOCIATED WITH EQUILIBRIUM
    • •Meniere’s Syndrome
    • •May lead to deafness and a loss of equilibrium
    • •Accumulation of excessive endolymph in the inner ear
    • •Vertigo
    • •Sensing motion when at rest
    • •Unsual movement of endolymph in inner ear
    • •Motion Sickness
    • •Characterized by nausea and vomiting
    • •Brought about by repetitive angular, linear or vertical movement
  51. Chemical Senses-Taste
    • Gustation-Sensation of taste
    • -results from action of chemicals on taste buds
    • Lingual Papillae
    • -filiform (no taste buds)
    •    important for texture
    • -foliate (no taste buds)
    • -funigorm
    •    at tip and sides of tongue
    • -Vallate (circumvallate)
    •     at rear of tongue
    •     contains half of taste buds
  52. Physiology of Taste
    • Molecules must dissolve in saliva
    • 5 Primary Sensations-throughout tongue
    • 1. Sweet-tip
    • 2. Salty-Lateral margins
    • 3. Sour-Lateral margins
    • 4. Bitter-posterior
    • 5. Umami-taste of amino acids (MSG)

    • Influenced by food texture, aroma, tempurature, and appearance
    • -mouthfeel -dectected by lingual nerve in papillae
    • Hot pepper stimulates free nerve endings (pain)
  53. Physiology of Taste (Mechanisms of Action)
    • activate 2nd messenger systems
    • -sugars, alkaloids, and glutamates bind to receptors depolarize cells directly
    • -sodium and acids penetrate cells
  54. Projection Pathways for Taste
    • Innervation of taste buds
    • -facial nerve (VII) -anterior 2/3 of tongue
    • -glossopharyngeal nerve (IX)-posterior 1/3
    • -vagus nerve (X)- palate, pharynx, epiglottis
    • To medulla
    • To hypothalamus and amygdala
    • -activate autonomic reflexes eg salivation, gagging, vomiting
    • To thalamus, then postcentral gyrus of cerebrum
    • -conscious sense of taste
  55. Chemical Sense-Smell
    • Olfactory mucosa
    • -contains receptor cells for olfaction
    • -highly sensitive up to 10,000 odors
    • -on 5cm2 of superior concha & nasal septum
  56. Olfactory Epithelial Cells
    • Olfactory Cells
    • -olfactory hairs neurons with 20 cilia: bind molecules in thin layer of mucus
    • -axons pass through cribrifrom plate, survive 60 days
    • -Supporting cells
    • -Basal Cells
  57. Physiology of Smell
    • Molecules bind to receptor on olfactory hair
    • -hydrophilic -diffuse through mucus
    • -hyrdophobic-transport by odorant-binding protein
    • Activate G protein and cAMP system
    • Opens ion channels for Na or Ca ions (creates receptor potential)
    • Action potential travels to brain
    • Receptor adapt quickly -due to synaptic inhibition in olfactory bulbs
  58. Olfactory Pathway
    • Olfactory cells synapse in olfactory bulb
    • -on mitral and tufted cell dendrites
    • -in spherical clusters called glomeruli (each glomeruli dedicated to single odor)

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