The Senses

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The Senses
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The Senses

• General senses of touch
• Temperature
• Pressure
• Pain
• Special senses
• Smell
• Taste
• Sight
• Hearing
• Equilibrium

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Fool your sense of touch

• Cross your first and second fingers
• Touch your nose with your crossed fingertips
• 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

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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 diameter
• Only 1/6 of the eye is seen
• Most of the eye is surrounded by bone cushioned
  by fat

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Accessory Structures of the Eye

• Eyelids
• Eyelashes
• Muscles

Figure 8.1b
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Accessory Structures of the Eye

• Conjunctiva
• Membrane that lines the eyelids
• Connects to the surface of the eye secretes
  mucus for lubrication

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• Homeo Imbalance
• Conjunctivitis reddened irritated eyes.
  Pinkeye is the HIGHLY infectious form caused by
  bacteria or virus

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Accessory Structures of the Eye

• Lacrimal apparatus
• Lacrimal gland produces diluted salt solution
  (tears)
• Lacrimal canals drains tears from eyes
• Lacrimal sac provides passage of tears towards
  nasal cavity

Figure 8.1a
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• 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

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• Nasolacrimal duct empties tears into the nasal
  cavity (connects eye with nose)
• Crying makes you sniffle

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• Homeo Imbalance
• A cold or allergies can cause the lacrimal duct
  to swell shut. This stops drainage of tears and
  you get watery eyes.

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Structure of the Eye

• The wall is composed of three tunics (layers)
• Fibrous tunic outside layer
• Choroid middle layer
• Sensory tunic inside layer

Figure 8.3a
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The Fibrous Tunic

• Sclera
• White connective tissue layer
• white of the eye
• Cornea
• Transparent window, allows for light to pass
  through
• Vulnerable to damage but, repairs itself easily
• The only human tissue that can be transplanted
  without fear of rejection (no bloodno antibodies)

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Choroid Layer

• Blood-rich nutritive tunic
• Pigment dark in color prevents light from
  scattering
• 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

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Sensory Tunic (Retina)

• Contains millions of receptor cells called
  photoreceptors
• Rods Cones
• Signals pass from photoreceptors to retina
• Signals leave the retina toward the brain through
  the optic nerve

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• 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, genetics

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• The seven bones that articulate to form the
  orbit.yellow Frontal bonegreen Lacrimal
  bonebrown Ethmoid boneblue Zygomatic
  bonepurple Maxillary boneaqua Palatine
  bonered Sphenoid bone

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• Anatomy of eye activity!
• Eye coloring sheet
• Cow eye dissection!

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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.

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Neurons of the Retina and Vision

• Rods
• Most are found towards the edges of the retina
• Allow dim light peripheral vision
• all in gray tones
• Cones
• Allow for detailed color vision
• Densest in the center of the retina

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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
  types.
• Color Plates

Figure 8.6
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Color Plates

• Ishiharas color plates

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Lens

• Biconvex crystal-like structure
• Held in place by a ligament attached to the
  ciliary body

Figure 8.3a
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• The lens divides the eye into 2 segments or
  chambers
• Homeo Imbalance
• Cataracts Occur as we age. The lens becomes
  hard and opaque

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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

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• 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!

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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
  floaters)

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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
  accommodation
• As objects come closer the lens bulges

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Images Formed on the Retina

• The image on the retina is reversed, upside-down
  and smaller

Figure 8.10
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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 retina
• Farsightedness- you can see far away but not
  close up. Picture focuses behind retina.

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• http//video.about.com/vision/LASIK-Eye-Surgery.ht
  m

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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 eyes
• Allows for binocular vision depth perception

Figure 8.11
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• http//www.peteducation.com/article.cfm?c171797
  aid1596

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The Ear

• Houses two senses
• Hearing
• Equilibrium (balance)

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Anatomy of the Ear

• The ear is divided into three areas
• Outer (external) ear (Hearing)
• Middle ear (Hearing)
• Inner ear (Hearing Balance)

Figure 8.12
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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
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The Middle Ear or Tympanic Cavity

• 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 membrane
• The auditory tube connecting the middle ear with
  the throat
• Allows for equalizing pressure (popping of ear)
• This tube is otherwise collapsed

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• 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.

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Bones of the Tympanic Cavity

• The 3 bones in the cavity collectively called the
  Ossicles.
• Smallest bones in the body
• 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
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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 endolymph

Figure 8.12
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Inner Ear or Bony Labrynth

• 3 subdivisions
• Cochlea
• Vestibule
• Semicircular canals

Figure 8.12
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Organs of Hearing

• Organ of Corti
• Located within the cochlea
• Contain receptors hair cells
• Above and below cochlear duct contain perilymph.
  Sound waves set this fluid into motion.

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• Waves hit the basilar membrane the hairs on it
  are bent by the movement of the gel-like
  tectorial membrane above them.
• Cochlear nerve attached to hair cells transmits
  nerve impulses to auditory cortex on temporal
  lobe

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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

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Static Equilibrium- at rest

• Maculae receptors in the vestibule
• Report on the position of the head in respect to
  gravity
• 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 cells
• 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

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Function of Maculae
Figure 8.13ab
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Dynamic Equilibrium

• Occur in the Semicircular canals. Orientated in
  3 planes so no matter the movement, it is
  detectable.
• 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 cap)
• Drag and motion of the endolymph is transmitted
  to the brain

Figure 8.14c
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neat

• 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.

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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
  chemicals
• Both senses complement each other and respond to
  many of the same stimuli

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Olfaction The Sense of Smell

• Olfactory receptors are in the roof of each nasal
  cavity
• Neurons with long cilia (hairs) covered in mucus
• Chemicals dissolve into mucus are detected
• 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

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Olfactory Epithelium
Figure 8.17
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The Sense of Taste

• Taste buds house taste receptor organs
• Most are on the tongue (10K)
• Few on soft palate cheeks

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The Tongue and Taste

• The tongue is covered with projections called
  papillae. Give tongue its 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 papillae

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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

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Anatomy of Taste Buds
Figure 8.18
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Taste Sensations

• Sweet receptors
• Sugars
• Sour receptors
• Acids
• Bitter receptors
• Alkaloids
• Salty receptors
• Metal ions

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• http//www.pbs.org/wgbh/nova/body/tongue-taste.htm
  l
• Tour of the tongue web interactive
• http//www.pbs.org/wgbh/nova/body/science-picky-ea
  ters.html
• The science of picky eaters (1245)
• http//www.pbs.org/wgbh/nova/body/bitter-taste.htm
  l
• Genetically modified mouse that cannot taste
  bitter

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Jelly Belly Lab

• What if you couldnt smell? Would you REALLY
  taste the world around you?

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• http//www.youtube.com/watch?v38PGB9dcr4c
• Perspective on the 5 senses