Sensory Systems

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Sensory Systems

• Sensation is the detection of changes in the
  internal or external environment
• Perception is the interpretation of sensations
• Each unique type of sensation is a sensory
  modality

• Sensory neurons carry information for only one
  sensory modality
• The general senses are both the somatic senses
  and the visceral senses
• The special senses are the sense modalities of
  vision, hearing, smell, taste, and
  balance/equilibrium

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Sensory Receptors

• Sensation usually involves 4 events
• Stimulation of a sensory receptor
• Transduction of the stimulus
• Generation of nerve impulses
• Integration of sensory input
• Sensory receptors can be classified by structure

• Free nerve endings are bare dendrites, which
  produce generator potentials
• Encapsulated nerve endings are enclosed in
  special structures
• Special receptor cells synapse with sensory
  neurons to produce receptor potentials

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The Five Senses
Vision
Hearing
Taste
Smell
Touch
Temperature Pain Balance Stretch Acceleration Pres
sure Texture Vibration Tickle Itch Etc.
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Sensory Receptors Sensory Modalities
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Sensory Receptors
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Sensory Receptors
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Sensory Receptors
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Sensory Receptors
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Sensory Receptors
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Sensory Receptors
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Temperature

• Thermoreceptors are free nerve endings
• There are two basic thermal sensations cold and
  warm
• Cold receptors mostly synapse with large
  myelinated A fibers
• Warm receptors mostly synapse with small
  unmyelinated C fibers
• Hot sensations activate both warm and cold
  receptors, and pain receptors

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Pain

• Nociceptors are free nerve endings
• There are two basic types of pain
• Fast pain is carried by large myelinated A fibers
• Fast pain is sometimes known as sharp, piercing,
  pricking, emergency pain
• An example of fast pain would be a knife cut or
  stab wound
• Slow pain is carried by small unmyelinated C
  fibers
• Slow pain is sometimes known as dull, aching,
  throbbing, burning, or reminding pain
• An example of slow pain would be a toothache, or
  the day after an ankle sprain

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Olfactory Epithelium

• 1 square inch of membrane holding 10-100 million
  receptors
• Covers superior nasal cavity and cribriform plate
• Odorants bind to receptors
• Na channels open
• Depolarization occurs
• Nerve impulse is triggered

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Adaptation Odor Thresholds

• Adaptation decreasing sensitivity
• Olfactory adaptation is rapid
• 50 in 1 second
• Complete in 1 minute
• Low threshold
• Only a few molecules need to be present
• Methyl mercaptan added to natural gas as warning
• Hyposmia decreasing ability to smell
• 50 over age 65
• 75 over age 80
• Cigarette smoking
• Anosmia cannot smell

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Gustatory Sensation Taste

• Taste requires dissolving of substances
• Five classes of stimuli sour, bitter, sweet,
  salty, umami
• Other tastes are a combination of the five
  taste sensations plus olfaction
• There may be a sixth taste bud, perhaps fatty
• Vallate papillae contain 100 - 300 taste buds
• Fungiform papillae contain 5 taste buds each
• Filiform papillae contain tactile receptors but
  no taste buds
• 10,000 taste buds found on tongue, soft palate
  larynx

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Physiology of Taste

• Receptor potentials developed in gustatory hairs
  cause the release of neurotransmitter that gives
  rise to nerve impulses
• Complete adaptation in 1 to 5 minutes
• Thresholds for tastes vary among the 5 primary
  tastes
• Most sensitive to bitter (poisons)
• Least sensitive to salty and sweet

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Vision

• More than half the sensory receptors in the human
  body are located in the eyes
• A large part of the cerebral cortex is devoted to
  processing visual information
• Eyeball is about 1 inch in diameter
• Over 80 of the eyeball is enclosed in the orbit

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Lacrimal Apparatus

• About 1 ml of tears produced per day
• Spread over eye by blinking
• Contains bactericidal enzyme lysozyme

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Tunics (Layers) of Eyeball

• The eye is constructed of three layers
• Fibrous Tunic(outer layer) sclera cornea
• Vascular Tunic (middle layer) choroid,
  ciliary body, iris, lens
• Nervous Tunic(inner layer) retina

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Cavities of the Interior of Eyeball

• Anterior cavity (anterior to lens)
• Filled with aqueous humor
• Produced by ciliary body
• Continually drained
• Replaced every 90 minutes
• Two chambers
• Anterior chamber between cornea and iris
• Posterior chamber between iris and lens
• Posterior cavity (posterior to lens)
• Vitreous chamber filled with vitreous body
  (jellylike)
• Formed once during embryonic life
• Floaters are debris in vitreous of older
  individuals

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Muscles of the Iris

• Constrictor pupillae (circular) are innervated by
  parasympathetic fibers while Dilator pupillae
  (radial) are innervated by sympathetic fibers
• Response varies with different levels of light

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Electromagnetic Spectrum
Its not exactly correct, but you can get a rough
approximation by thinking of violet as 400 nm,
green as 500 nm, yellow as 600 nm, and red as 700
nm.
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Photoreceptors Rods Cones

• Rods rod shaped
• Shades of gray in dim light
• 120 million rod cells
• Shapes movements
• Distributed along periphery
• Cones cone shaped
• Sharp, color vision
• 6-8 million
• Fovea of macula lutea
• Densely packed region
• At exact visual axis of eye
• Sharpest resolution (acuity)

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Pathway of Nerve Signal in Retina

• Light penetrates retina
• Rods cones transduce light into action
  potentials
• Rods cones excite bipolar cells
• Bipolars excite ganglion cells
• Axons of ganglion cells form optic nerve leaving
  the eyeball (blind spot)
• To thalamus then the primary visual cortex

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Visual Processing in Retina

• The layers of cells (bipolar, amacrine,
  horizontal, ganglion) in the retinal process
  information before it leaves the eye
• For example, the presence of center-on and
  center-off fields enhances contrast

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Pathway of Nerve Signal to the Brain

• Medial optic fibers cross at the optic chiasm
• Lateral optic fibers remain on the same side of
  the brain
• Thus both sides of the brain get information from
  both eyes

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Refraction by the Cornea Lens

• Image focused on retina is inverted reversed
  from left to right
• Brain learns to work with that information
• 75 of refraction is done by cornea, the rest is
  done by the lens
• Light rays from gt 20 are nearly parallel and
  only need to be bent enough to focus on retina
• Light rays from lt 6 are more divergent need
  more refraction
• extra process needed to get additional bending of
  light is called accommodation

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Correction for Refraction Problems

• Emmetropic eye (normal)
• Can refract light from 20 ft away
• Myopia (nearsighted)
• Eyeball is too long from front to back
• Glasses concave
• Hypermetropic (farsighted)
• Eyeball is too short
• Glasses convex (coke-bottle)
• Astigmatism
• Corneal surface wavy
• Parts of image out of focus

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Physiology of Vision

• Photopigments undergo structural changes upon
  light absorption
• Retinal is the light absorbing part of all visual
  photopigments
• All photopigments involved in vision contain a
  glycoprotein called opsin and a derivative of
  vitamin A called retinal

• There are four different opsins
• A cone contains one of three different kinds of
  photopigments so there are three types of cones
• Permit the absorption of 3 different wavelengths
  (colors) of light
• Rods contain a single type of photopigment
  (rhodopsin)

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Cone Absorption Spectra
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Color Blindness

• Color blind individuals are missing one or more
  types of opsin
• As a result they may see some colors, but not the
  full range
• Red/Green Color Blindness is the most common type
• Sex-linked X chromosome
• Defect in L or M cone
• Blue/Yellow Color Blindness is fairly rare
• Not a sex linked chromosome
• Defect in S cone

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Afterimages

• Staring at one color saturates the receptors
• When the color is removed, the receptors undergo
  hyperpolarization
• The receptors for the opponent color are
  highlighted by comparison
• As a result, we see an afterimage consisting of
  the opponent colors

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Structural Dissimilarity(Anatomy)
Functional Equivalence (Physiology)
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Animal Vision

• Some animals, such as birds and bees, can see in
  the UV range of the electromagnetic spectrum
• A flower may have a bullseye visible only in UV
  light
• This guides the pollinator to the area with the
  pollen

• What we see (visible light)

• What a bee sees (UV light)

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Special Animal Senses

• Some animals, such as rattlesnakes, can see in
  the infrared range of the spectrum
• Rattlesnakes have special heat sensors located in
  pits between the eye and nostril (loreal pits)
• They can detect differences in temperature as
  small as several thousandths of a degree

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Physics of Sound

• Sound waves are disturbances of air molecules
• Like all waves they can be characterized by
  frequency (pitch), wavelength, amplitude
  (loudness)

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Physics of Sound
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Physics of Sound
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Anatomy of the Ear

• Outer ear (auricle, external auditory canal,
  tympanic membrane)
• Middle ear (auditory ossicles, auditory tube)
• Inner ear (cochlea, semicircular canals)

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External Middle Ear

• External ear
• Auricle directs sounds into the ear
• Auditory canal 1 in
• Ceruminous glands
• Perforated eardrum
• Middle ear
• Air filled cavity in the temporal bone
• Malleus attached to tympanic membrane
• Mechanical transmission of sound
• Auditory tube equalizes pressure

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Inner Ear

• Bony labyrinth
• Cochlea
• Semicircular canals
• Vestibule
• Lined with periosteum, filled with perilymph
  (like CSF)
• Membranous labyrinth
• Sacs and tubules inside the bony labyrinth
• Filled with endolymph
• Utricle saccule

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Inner Ear Cochlea

• Cochlea
• Scala vestibuli ends at oval window
• Scala tympani ends at round window
• Helicotrema connects the two
• Cochlear duct (scala media)
• Vestibular membrane separates cochlear duct from
  scala vestibuli
• Basilar membrane separates cochlear duct from
  scala tympani

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Inner Ear Semicircular Canals

• Semicircular canals
• Arranged at approximately right angles (3 axes of
  space)
• End of each canal has swelling known as an
  ampulla
• Lateral semicircular canal is horizontal
• Other two semicircular canals are vertical

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Hearing

• Air waves, tympanic membrane, ossicles, oval
  window, endolymph
• Fluid vibrations cause basilar membrane to
  vibrate, which cause hair cells in spiral organ
  to brush against tectorial membrane
• Action potentials, carried by cranial nerve VIII
• High frequency sounds cause basilar membrane to
  vibrate near the base (narrow and stiff)
• Low frequency sounds cause basilar membrane to
  vibrate near apex (wide and flexible)

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Physics of Sound
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Animal Hearing
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Equilibrium

• Otoliths (calcium carbonate crystals)
• Static equilibrium (gravity)
• Macula receptors in utricle and saccule
• Hair cells in utricle and saccule
• Dynamic equilibrium (acceleration)
• Crista receptors in ampullae
• Tilting head causes otoliths to deflect hairs
• Action potentials in vestibular branch of cranial
  nerve VIII