PHYSIOLOGY

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PHYSIOLOGY

• Sensory Systems

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Gustatory Receptors

• Taste or Gustation
• The sensation following the stimulation of oral
  chemoreceptors
• Chemoreceptors are surrounded by supporting cells
• Chemoreceptors are shed every 10-14 days and are
  renewed by division of the supporting cells.

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Tastes

• Four basic tastes
• Sweet
• Glucose, fructose, amino acids
• Sour
• H concentrations
• Salty
• Na concentration
• Bitter
• Quinine, caffeine, nicotine, strychinine, etc.
• Umami
• Produced by compounds like monosodium glutamate
• Not a classic taste

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Gustatory Transduction

• Chemicals enter the pores of taste buds and react
  with the gustatory hairs
• Chemicals may open sodium gates directly or may
  stimulate membrane receptors and G proteins and
  the second messenger system

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Olfaction

• Olfactory cells lie in a specialized region in
  the roof of the nasal cavity
• The olfactory epithelium
• Odors combine to produce depolarization and
  impulse activity
• 80 of taste is smell
• Olfactory neurons are bipolar neurons

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Olfactory Receptors

• Supporting cells secrete mucus
• Continual degeneration and replacement of neurons
• Every 60 days
• Basal cells differentiate into olfactory neurons

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Olfaction

• Humans can detect about 104 different smells
• Odiferous compounds are mainly organic
• Containing 3-20 carbon atoms
• Odiferous compounds reach the olfactory
  epithelium, aided by sniffing
• The molecules must dissolve in the mucus layer
  (water soluble) to react with the receptors on
  the olfactory cilia

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Odorant receptors

• One receptor per olfactory neuron
• 1000 different receptors
• cAMP system is used for smells

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Glomeruli

• Olfactory neurons synapse with the olfactory bulb
  in regions called glomeruli
• From the olfactory bulb to the temporal lobe
• Each olfactory neuron synapses with only one
  glomerulus
• Each glomerulus receives input from several
  thousand olfactory neurons in the epithelium
• Each glomeruli receives input from neurons
  expressing the same receptor

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Disorders of smell and taste

• Anosmia
• Inability to detect odors
• Ageusia
• Inability to detect tastes
• Uncinate Fits
• Hallucinations of smell

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Vision
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Functional Anatomy of the Eye

• Three peripheral layers
• Tough fibrous outer layer
• Sclera and cornea
• Middle layer
• The choroid or pigmented layer
• Absorbs light rays
• Inner neural layer
• The retina

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Vitreous Humor

• In the posterior chamber of the eye
• Used to
• Maintain the shape of the eye
• Holds the retina in place
• Produced in the fetal stage of development

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Aqueous Humor

• Produced by the ciliary muscles into the anterior
  chamber of the eye
• Drains into the canal of Schlemm or Scleral
  Venous Sinus
• ½ teaspoon is produced per day and this much
  drains per day
• Clog of the canal may cause Glaucoma

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Constriction of the Pupil

• Miosis
• Results in a better depth of focus
• Light rays pass only through the central part of
  the lens
• Sympathetic Nervous System
• Dilator control
• Mydriasis
• Parasympathetic Nervous System
• Constrictor control
• Pupils are consensual

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Lenses

• Concave
• Light bends outward
• Convex
• Light bends inward

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Lens Focuses Light on the Retina

• Light passes through the cornea and lens prior to
  striking the retina
• Light must refract
• Focal Point
• The single point where the rays converge
• Focal Length
• Distance from the center of a lens to its focal
  point

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Vision Problems

• Hyperopia
• Far-sightedness
• The focal point falls behind the retina
• Myopia
• Near-sightedness
• The focal point falls in front of the retina
• Astigmatism
• Caused by a cornea and/or lens that is not
  perfectly dome shaped

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Convergence

• The eye muscles pull eyes so that both eyes see
  one fused image

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Accommodation

• The process by which the eye adjusts the shape of
  the lens to keep objects in focus
• Presbyopia
• Hardening of the lens with age due to addition of
  layers to the lens
• Focused at Infinity
• The lens is pulled flat by tension in the
  ligaments
• Close Up
• The lens rounds up after the ciliary muscles
  contract and the suspensory ligaments relax

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Eye

• Optic Disc
• Axons of the ganglion cells all form the optic
  nerve
• The optic nerve leaves the eye at the optic disc
• No rods or cones at the optic disc
• Blind spot

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Rods and Cones

• Rods
• More numerous than cones by a ratio of 201
• Function well in low light
• Nighttime vision
• Cones
• High-acuity vision
• Color vision during the daytime
• High levels of light

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Light

• Each cone contains visual pigments that are
  excited by different wavelengths of light
• Visual pigment
• Bound to cell membranes of dendrites
• The transducers that convert light energy into a
  change in membrane potential
• Rods
• Visual pigment is rhodopsin

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Cones

• Red, green, blue, yellow(?) cones
• Each cone type is stimulated by a range of light
  wavelengths but is most sensitive to a particular
  wavelength
• Colorblindness
• Lack of cones
• X-chromosome

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Photoreceptors

• Light passes the ganglion cells and does not
  stimulate them
• Ganglion cells have action potentials
• Light passes the bipolar cells and does not
  stimulate them
• Bipolar cells only have graded response
• Light is the ligand for either rods or cones
• This depends on the kinetic energy of the light

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Photoreceptors

• Photoreceptors in the retina transduce light
  energy into electrical signals
• The Fovea Centralis
• The point on which light focuses

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Phototransduction

• Rhodopsin
• Opsin plus 11cis retinal
• Purple and kinked in shape
• Visual pigment for rods
• When activated by as little as one photon of
  light the 11cis retinal can be bleached
• Bleaching
• Light Changes 11 cis retinal to all trans retinal
• All trans retinal is clear and a straight chain

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Phototransduction

• When a rod is in darkness
• Rhodopsin is not active
• cyclicGMP levels in the rod are high
• Sodium channels are open
• Depolarization of the rod

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Phototransduction

• Kinetic Energy of light transforms 11 cis retinal
  to all trans retinal
• All trans retinal and Opsin separate
• Opsin moves horizontally in the membrane and
  binds with transducin
• Transducin is a G protein
• Transducin binds to phosphodiesterase
• PDE converts cGMP to GMP
• Sodium gates close

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Binocular Vision

• Visual Field
• Each ganglion cell receives signals from a
  particular area of the retina
• Binocular Zone
• Where the visual fields overlap
• Provides 3-D Vision
• Medial aspect crosses over
• Lateral aspect stays on same side of the brain

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Ear

• Outer Ear
• Pinna
• Collects sound waves
• Ear Canal
• Sends sound waves to tympanic membrane
• Tympanic Membrane
• Ear Drum
• Vibrates at the same frequency and amplitude as
  the original wave

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Middle Ear

• Eustachian Tube
• Normally collapsed
• Opens transiently to equlibrate middle ear
  pressure and atmospheric pressure
• Ossicles
• Used to amplify the original sound wave by as
  much as 20X on the oval window
• Malleus
• Incus
• Stapes

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Sound

• Frequency
• The number of waves that pass a particular point
  in a second
• The longer the wave lengths the lower the
  frequency
• The units of frequency is Hertz
• The higher the frequency the higher the pitch of
  the sound

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Sound

• Amplitude
• The height of the wave
• Amplitude is measured in decibels
• The higher the amplitude the louder the sound

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Inner Ear

• Cochlea
• Scala vestibuli
• Top canal
• Filled with Perilymph
• Scala Media
• Middle canal
• Cochlear duct
• Contains neurons for hearing
• Filled with Endolymph
• Organ of Corti
• Scala tympani
• Bottom canal
• Filled with Perilymph

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Cochlear Duct

• Tectorial Membrane
• Dendritic hairs are embedded in the tectorial
  membrane
• Basilar Membrane
• Supporting cells are embedded in the basilar
  membrane
• Supporting cells surround auditory neurons

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Sound Transduction

• Sounds waves become mechanical vibrations, then
  fluid waves, then chemical signals and finally
  action potentials

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Phonotransduction

• First Transduction
• Sound waves strike the tympanic membrane and
  become vibrations
• The sound wave energy is transferred to the three
  bones of the middle ear, which vibrate

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Phonotransduction

• Second
• The stapes is attached to the membrane of the
  oval window
• The Stapes strikes the oval window and increases
  the force of the original wave 20X
• Vibrations of the oval window creates waves in
  the perilymph at the same frequency and amplitude
  as the original sound wave
• Third
• The fluid waves push on the flexible tectorial
  and basilar membranes of the cochlear duct.
• Hair cells bend and release neurotransmitter

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Phonotransduction

• Fourth
• Neurotransmitter is released, creating action
  potentials that travel through the cochlear nerve
  to the brain
• Energy from the waves transfers across the
  cochlear duct is dissipated at the round window

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Organ of Corti

• The bending or shearing of the neurons indicates
  pitch and loudness
• The bending of the neurons in the first third of
  the neuron signals high pitch sounds to the brain
• The bending of neurons in the first and second
  third of the neuron signals medium pitch sounds
• The bending of neurons in the first, second and
  third part of the cochlea signals a low pitch
  sound to the brain

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The Organ of Corti

• The higher the amplitude of the wave the more the
  kinetic energy
• The high amplitude waves cause a greater shearing
  force which opens more sodium gates
• The more sodium gates that open the more the
  action potentials
• This creates a louder sound

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Equilibrium
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Equilibrium

• Static Equilibrium
• Little to no movements
• Uses the vestibular region of the inner ear
• Dynamic Equilibrium
• Greater body movements
• Uses the semicircular canals

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Static Equilibrium

• The Vestibular Apparatus senses Linear
  Acceleration
• Vestibular Apparatus
• Two saclike otolith organs
• The utricle and the saccule
• The sensory receptors of the utricle and saccule
• The maculae
• The macula consists of a gelatinous mass known as
  the otolith membrane
• Otolithic crystals are embedded in the membrane
• Made of calcium carbonate crystals
• Shearing or bending of the dendrites sends
  signals to the brain

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Dynamic Equilibrium

• Semicircular Canals sense rotational acceleration
• Endolymph within the semicircular canals are in
  three different planes
• Endolymph moves and moves the gelatinous cupula
  to activate receptor cells

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