The Senses

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					The Senses
                      The Senses
•   General senses of touch
    –   Temperature
    –   Pressure
    –   Pain
•   Special senses
    –   Smell
    –   Taste
    –   Sight
    –   Hearing
    –   Equilibrium
     Fool your sense of touch
• Cross your first and second fingers
• Touch your nose with your crossed
• It should feel as if you have two noses
• Your brain usually does not receive this
  kind of signal
  – it gets confused, thinks you must be feeling
   two separate things
          The Eye and Vision
• 70 percent of all sensory receptors are in
  the eyes
• Each eye has over a million nerve fibers
• The eye is a sphere about 1 inch in
• Only 1/6 of the eye is seen
  – Most of the eye is surrounded by bone &
    cushioned by fat
    Accessory Structures of the
• Eyelids
• Eyelashes
• Muscles

                             Figure 8.1b
    Accessory Structures of the
• Conjunctiva
  – Membrane that lines the eyelids
  – Connects to the surface of the eye & secretes
    mucus for lubrication
• Homeo Imbalance
  – Conjunctivitis =
    reddened irritated
    eyes. “Pinkeye” is
    the HIGHLY
    infectious form
    caused by bacteria
    or virus
    Accessory Structures of the
• Lacrimal apparatus
  – Lacrimal gland –
    produces diluted
    salt solution (tears)
  – Lacrimal canals –
    drains tears from
  – Lacrimal sac –
    provides passage
    of tears towards
    nasal cavity
                             Figure 8.1a
Properties of lacrimal fluid (AKA TEARS!)
    – Dilute salt solution which contains lysozyme an
      anti-bacterial protein
•   Protects, moistens, and lubricates the eye
•   Empties into the nasal cavity

•   Tear up for 2 reasons
• Nasolacrimal duct
  – empties tears
  into the nasal
  cavity (connects
  eye with nose)
  – Crying makes you
• Homeo Imbalance
  – A cold can cause the lacrimal duct to swell
    shut. This stops drainage of tears and you
    get watery eyes.
           Structure of the Eye
• The wall is composed of three tunics (layers)
   – Fibrous tunic –
     outside layer
   – Choroid –
   – Sensory
     tunic –
                                              Figure 8.3a
             The Fibrous Tunic
• Sclera
   – White connective tissue layer
   – “white of the eye”
• Cornea
   – Transparent “window”, allows for light to pass
   – Vulnerable to damage but, repairs itself easily
   – The only human tissue that can be
     transplanted without fear of rejection (no
     blood=no antibodies)
               Choroid Layer
• Blood-rich nutritive tunic
• Pigment dark in color prevents light from
• Modified interiorly into two structures
   – Cilliary body – smooth muscle, focuses lens
     for clear vision
   – Iris- smooth muscle, regulates amount of light
     that enters
       • Pigmented layer that gives eye color
       • Pupil – rounded opening in the iris
        Sensory Tunic (Retina)
• Contains millions of receptor cells called
  – Rods & Cones
• Signals pass from photoreceptors to retina
• Signals leave the retina toward the brain
  through the optic nerve
• Homeo Imbalance
  – Retinal Detachment: Retina separates from
    choroid. Retina cannot get nutrients and can
    die. Easily fixed with laser surgery.
  – Caused by violent motion of the head,
                 Blind Spot
• Photoreceptors cover the retina except
  where optic nerve leaves the eye.
  – This is the optic disk or blind spot
• Blind Spot Test
  – On your paper draw a dot about the size of a
    pea. Parallel to the dot and about 2 inches to
    the right make an X. Hold the image in front
    of you, cover your right eye, focus on the X
    and SLOWLY bring the image towards you.
    At some point the dot should disappear.
     Neurons of the Retina and
• Rods
  – Most are found towards the edges of the
  – Allow dim light & peripheral vision
  – all in gray tones
• Cones
  – Allow for detailed color vision
  – Densest in the center of the retina
              Cone Sensitivity
• There are 3 types of
  cones each sensitive to
  different wavelengths
• Total Color blindness is
  the result of lack all
  cone types. Partial is
  due to lack of 1 or 2
• Color Plates

                                 Figure 8.6
             Color Plates
• Ishihara’s color plates
• Biconvex crystal-like structure
• Held in place by a ligament attached to the
  ciliary body

                                         Figure 8.3a
• The lens divides the eye into 2 segments
  or chambers
• Homeo Imbalance
  – Cataracts: Occur as we age. The lens
    becomes hard and opaque
   Internal Eye Chamber Fluids
• Aqueous humor
  – Watery fluid found in chamber between the
    lens and cornea
  – Maintains intraocular pressure
  – Provides nutrients for the lens and cornea
• Homeo Imbalance
  – If the aqueous humor cannot drain, pressure
    in the eye increases dramatically.
  – This leads to glaucoma, which will become
    painful and possibly lead to loss of sight.
  – Early detection is key since a lot of damage
    can be done w/o pain.
    • The machine that blows on your eye!
   Internal Eye Chamber Fluids
• Vitreous humor
  – Gel-like substance behind the lens that fills
    the eyeball
  – Lasts a lifetime and is not replaced (can be
            Lens Accommodation
•   Light is bent or refracted
    as it enters the eye
•   The lens changes shape
    so that the light is
    focused on the retina
•   The ability to focus on
    objects closer is called
•   As objects come closer
    the lens bulges
   Images Formed on the Retina
• The image on the retina is reversed,
  upside-down and smaller

                                         Figure 8.10
  Vision Problems
• Perfect vision is called
  emmetropia or
  “harmonious vision”
• Nearsightedness- you
  can see up close but
  not far away. Picture
  focuses in front of
• Farsightedness- you
  can see far away but
  not close up. Picture
  focuses behind retina.
• http://video.about.c
                 Visual Pathway
• Optic nerve: carry
  impulses from retina to
  brain, bundled at the
  posterior of the eyeball
• Part of each optic
  nerve crosses at the
  optic chiasma
   – Each side of brain
     receives info from both
   – Allows for binocular
     vision & depth
     perception                   Figure 8.11
Predator   Prey
• Say the color of the fonts
                   The Ear
• Houses two senses
  – Hearing
  – Equilibrium (balance)
             Anatomy of the Ear
• The ear is
  divided into three
   – Outer (external)
     ear (Hearing)
   – Middle ear
   – Inner ear
     (Hearing &
                                  Figure 8.12
                 The External Ear
Structures of the external ear
   – Pinna (auricle)- collects and
     directs sound waves into the
     auditory canal
   – External auditory canal-short
     chamber in the temporal bone.
     The walls are covered in
     ceruminous glands which
     produce earwax (cerumen).
   – Tympanic membrane- end of
     external ear. Vibrates when
     sound hit it.
                                     Figure 8.12
       The Middle Ear or Tympanic
• Air-filled cavity within the
  temporal bone
• Two tubes are associated
  with the inner ear
   – The opening from the
     auditory canal is covered
     by the tympanic
   – The auditory tube
     connecting the middle ear
     with the throat
       • Allows for equalizing
         pressure (popping of ear)
       • This tube is otherwise
• Homeo Imbalance
  – Otitis Media-Inflammation of the middle ear is
    a common result of a sore throat. In acute
    forms the eardrum bulges and becomes
    inflamed. Fluid needs to be drained with a
    semi-permanent ear tube and antibiotics. If
    untreated it can lead to hearing loss.
     Bones of the Tympanic Cavity
• The 3 bones in the
  cavity collectively called
  the Ossicles.
• Smallest bones in the
   – Malleus (hammer)
   – Incus (anvil)
   – Stapes (stirrup)
• Transfer and amplify
  the vibration from the
  ear drum to the fluid in
  the inner ear!
                               Figure 8.12
     Inner Ear or Bony Labyrinth
• Maze of bony
  chambers in the
  temporal bone behind
  the eye socket.
• The chambers are
  filled with perilymph
  fluid (plasma-like)
• Suspended in the
  perilymph are fluid
  filled sacs called
                              Figure 8.12
     Inner Ear or Bony Labrynth
• 3 subdivisions
   – Cochlea
   – Vestibule
   – Semicircular

                             Figure 8.12
               Organs of Hearing
• Organ of Corti
   – Located within the
   – Contain receptors
     = hair cells
   – Above and below
     cochlear duct
     contain perilymph.
     Sound waves set
     this fluid into
– Waves hit the
  membrane & the
  hairs on it are
  bent by the
  movement of the
  gel-like tectorial
  above them.
– Cochlear nerve
  attached to hair
  cells transmits
  nerve impulses
  to auditory
  cortex on
  temporal lobe
         Mechanisms of Equilibrium
• Our brains compensate for
  disturbances in balance
  – This is a reflex that depends
    on sensory receptors with in
    the vestibule and semi-
    circular canals.
  – Receptors called vestibular
    apparatus is divided into 2
    functional parts: Static and
    dynamic equilibrium
      Static Equilibrium- “at rest”
• Maculae – receptors in the vestibule
   – Report on the position of the head in respect to
• Anatomy of the maculae
   – Each maculae is a patch of hair cells embedded in
     the otolithic membrane (gel-like)
   – Otoliths (tiny stones) float in the gel around the hair
   – Movements cause otoliths to roll and pull the gel
     which bends the hair cells (creates signal)
   – The information is sent via the vestibular nerve and
     then to the cerebellum
Function of Maculae

                      Figure 8.13a–b
                Dynamic Equilibrium
• Occur in the Semicircular
  canals. Orientated in 3 planes
  so no matter the movement, it is
• Responds to angular
  movements. When dancing or
  rocking on a boat it goes into
  over drive.
• Within each each semi-circular
  there is a region called:
   – Crista ampullaris: Tuft of hair cells
     covered by the Cupula (gelatinous
   – Drag and motion of the
     endolymph is transmitted to the
                                             Figure 8.14c
• When you hear the same tone…
  – Your auditory receptors tune it out (hum of air
    conditioning, car motor, etc)
  – BUT hearing is the last sense to leave our
    awareness when we fall asleep or receive
    anesthesia (or even when we die) and the first
    to come back as we awaken.
           You Have 2 Ears
• This is used to pinpoint the location of
• One ear gets the sound at a slightly
  different time than the other
• Clapping Activity
     Chemical Senses – Taste
           and Smell
• Both senses use chemoreceptors
  – Stimulated by chemicals in solution
  – Taste has four types of receptors
  – Smell can differentiate a large range of
• Both senses complement each other and
  respond to many of the same stimuli
    Olfaction – The Sense of Smell
•   Olfactory receptors are in the roof of each
    nasal cavity
    – Neurons with long cilia (hairs) covered in
    – Chemicals dissolve into mucus & are
•    Impulses are transmitted via the olfactory nerve
     and interpretation of smell is made in the brain
•   Smells create “smell snapshots” which are
    often linked with emotions.
    – Reaction to smell is rarely neutral
Olfactory Epithelium

                       Figure 8.17
            The Sense of Taste
•   Taste buds house taste receptor
    – Most are on the tongue (~10K)
    – Few on soft palate & cheeks
         The Tongue and Taste
•   The tongue is covered with projections
    called papillae. Give tongue it’s texture
    – Fungifiorm papillae – rounded projection
      with taste buds, most numerous
    – Circumvallate papillae – large papillae with
      taste buds, few in back
•   Taste buds are found on the sides of
       Structure of Taste Buds
• Gustatory cells are the receptors that
  respond to chemicals in saliva
  – Have gustatory hairs (long microvilli)
  – The long microvilli protrude through the taste
    pore and when stimulated, depolarize and the
    impulses go to the brain and you taste
Anatomy of Taste Buds

                        Figure 8.18
              Taste Sensations
• Sweet receptors
   – Sugars
• Sour receptors
   – Acids
• Bitter receptors
   – Alkaloids
• Salty receptors
   – Metal ions
           Jelly Belly Lab
• What if you couldn’t smell? Would you
  REALLY taste the world around you?

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