Special Senses

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Chapter 15
Special Senses
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Ear Notes
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Definitions

• Pinna Elastic cartilage
• Tympanic membrane eardrum
• Ear ossicles malleous, incus, stapes
• Two membranes in inner ear oval window, round
  window
• Eustachian tube connects ear to throat
• Function equalize pressure

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Inner Ear

• Labyrinth
• Bony
• Cochlea Hearing
• Vestibule Balance
• Semicircular canals Balance
• Membranous
• Lymphs
• Endolymph
• In membranous labyrinth
• Perilymph
• Space between membranous and bony labyrinth

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Hearing

• Organ of hearing
• How we hearhappens within the cochlea

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Effect of Sound Waves on Cochlear Structures
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Hearing Process

• Waves move perilymph
• Perilymph moves vestibular membrane that moves
  endolymph
• Endolymph moves tectorial membrane which moves
  the hair cells
• Hair cells send impulse to nerves the brain
• Sound waves leave through round window

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Auditory Function

• Vibrations produce sound waves
• Volume or loudness number of hairs stimulated
• Pitch Function of wave frequency

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Balance

• Static
• Evaluates position of head relative to gravity
• Detects linear acceleration and deceleration

• Kinetic
• Evaluates movements of head
• 3 semicircular canals
• Ampulla
• endolymph moves when head moves

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Semicircular Canals

• Contain fluid and hair
• Movement moves fluid hairs
• Sends impulse to brain

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Ear Disorders ?

• Tinnitus
• Ringing, clicking, whistling in ear due to
  disorders in middle or inner ear
• Motion sickness
• Dysfunctions caused by stimulation of
  semicircular canals during motion
• Otitis Media
• Infections in the middle ear
• Earache
• Results from otitis media, dental abscesses, TMJ
  pain

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The Eye
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Structure of the Eye

• Layers and coats
• Fibrous Tunic Outer
• Scleratough, white, outer portion maintains
  shape,
• protects internal structures, provides muscle
  attachment
• point continuous with cornea
• Corneatransparent portion of anterior eye
  avascular bends refracts light
• Vascular Tunic Middle
• Choroidmiddle layer blood vessels darkly
  pigmented
• Ciliary bodyholds ciliary muscles (smooth)
  attached to lens w/ suspensory ligaments to
  control lens shape
• Lens- transparent bioconvex
• Iriscolored, smooth muscle ring with the pupil
  in the middle controls light entering pupil

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Structure of the Eye Continued

• RetinaInner
• Retina-incomplete, innermost layer nervous layer
  (contains neurons sensitive to light)
• Rods (black white)
• Cones (color)
• Fovea Centralis/Macula lutea- where light is
  focused see fine images (area of greatest
  acuity)
• Optic disc (no photoreceptor cells) AKA Blind Spot

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Cavities (compartments) in the Eye

• Anterior cavitybetween the lens and cornea
• Filled with aqueous humorclear, watery fluid
• Helps maintain intraocular pressure
• Glaucomatoo much intraocular pressure due to too
  much aqueous humor ?
• Posterior cavitybehind the lens and posterior
  portion of the eye
• Filled with vitreous humorsoft, gelatin-like
  substance
• Helps with intraocular pressure to prevent
  collapse

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Muscles of the Eye

• Extrinsic eye muscleskeletal muscles that move
  the eyeball
• Intrinsic eye musclesmooth muscles in the
  eyeinvoluntary
• Iris
• Ciliary body

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Accessory structures

• Eyebrows eyelasheskeep some foreign particles
  out of eye
• Eyelidshelp with lubrication
• Conjunctiva-mucus membrane lining the lid
• (AKA Pink eye (conjunctivitis) caused by an
  infection or irritation ?
• Closes from outside to in/ top to bottom

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Lacrimal Apparatus

• Lacrimal apparatus
• Lacrimal Gland Produces tears to moisten,
  lubricate, wash
• Lacrimal Canaliculi
• Collects excess tears
• Punctum
• Lacrimal Sac
• Nasolacrimal duct
• Opens into nasal cavity

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? Concept Review ?

• What are the 3 main layers of the eye?
• -sclera, choroid, retina
• What are the 3 accessory structures and describe
  their function?
• -eyebrows, eyelashes, eyelids (protection
• lubrication)
• Where are tears formed and where do they go?
• -lacrimal gland, nasalacrimal duct

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How we see (4 main steps)Formation of Vision on
the Retina

• 1. Refraction of light rays
• cornea, aqueous humor, lens, vitreous humor
• 2. Accommodation of lens
• Increase in curvature to achieve greater
  refraction on near objects
• Emmetropia Normal resting condition of lens
• Far vision 20 feet or more from eye
• Near Vision Closer than 20 feet
• 3. Constriction of pupil
• Iris contracts to limit the amount of light that
  enters the eye

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How we see ContinuedFormation of Vision on the
Retina

• 4. Convergence of eyes
• Light must hit the same spot of the retina on
  both eyes to see only one object
• Both eyes are directed on the object at the same
  angle
• Single binocular vision seeing one object with
  two eyes

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Eye Disorders ?

• Myopia Nearsightedness
• Focal point too near lens, image focused in front
  of retina
• Hyperopia Farsightedness
• Image focused behind retina
• Presbyopia
• Degeneration of accommodation, corrected by
  reading glasses
• Astigmatism Cornea or lens not uniformly curved
• Strabismus Lack of parallelism of light paths
  through eyes

• Retinal detachment
• Can result in complete blindness
• Glaucoma
• Increased intraocular pressure by aqueous humor
  buildup
• Cataract
• Clouding of lens
• Macular degeneration
• Common in older people, loss in acute vision
• Diabetes
• Dysfunction of peripheral circulation

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The Mouth
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Sense of Taste

• Specific sense organ TASTE BUDS
• Located on projections of tongue called papillae

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Structure of a Taste Bud

• Gustatory cellcontain tiny, cilia-like gustatory
  hairs
• Taste poreopening in the papillae that is bathed
  in saliva
• The chemicals of food must dissolve in the
  saliva to stimulate the hairs to start an
  impulse.

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Primary Tastes
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The Nose
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Sense of Smell

• Olfactory organs
• Sensory hairs
• Olfactory cells
• Olfactory nerves
• Olfactory bulb
• Olfactory tract

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Smelling

• Substance must be
• Able to become a gas
• Water soluble or very small
• Lipid soluble (to get into membrane)

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Effects of Aging on the Special Senses

• Slight loss in ability to detect odors
• Decreased sense of taste
• Lenses of eyes lose flexibility
• Development of cataracts, macular degeneration,
  glaucoma, diabetic retinopathy
• Decline in visual acuity and color perception