Special Senses

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Special Senses

• Chapter 12

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Special Senses
Receptor Stimulus Info Provided
Taste Chemical Taste buds identify specific chemicals
Smell Chemical Olfactory cells detect presence of chemicals
Pressure Mechanical Movements of the skin or changes in the body surface
Proprioceptors Mechanical Movement of the limbs
Balance (ear) Mechanical Body movement
Outer ear Sound Signals sound waves
Eye Light Signals changes in light intensity, movement and colour
Thermoregulators Heat Detect the flow of heat
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Sensory Receptors

• A stimulus is a form of energy
• Sensory receptors are another form of energy
• Taste receptors (tongue) convert chemical energy
  into a form of electrical energy (action
  potential)
• Light receptors (eye) convert light energy into
  electrical energy
• Balance receptors (ear) convert gravitational or
  mechanical energy into electrical energy
• Sensory adaptation occurs once you have adjusted
  to a change in the environment
• Ex when you no longer hear the clock ticking

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Taste Human Tongue

• Human taste receptors are centralized within the
  taste buds of the tongue
• Once dissolved, chemical stimulate receptors
  within taste buds which will send a message to
  the brain for interpretation

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Smell The Nose

• Chemicals in the air combine with receptor ends
  on olfactory cells (in nasal cavity) to create an
  action potential
• Chemicals with specific shapes gain access to
  specific receptor sites to combine with
  complementary receptors
• The impulse is carried to the front of the brain
  for interpretation
• Sense of taste and smell work together
• Clogged nasal passages reduce effectiveness of
  olfactory cells

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Vision The Eye

• Composed of 3 layers
• Sclera
• Choroid Layer
• Retina

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The Eye
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Sclera

• Outer white covering of the eye, supports and
  protects the eyes inner layers
• Front is covered by a transparent tissue that
  reflects light toward the pupil
• Cornea
• Requires oxygen and nutrients
• Is not supplied with blood vessels
• Oxygen is absorbed from gases in tears
• Nutrients are supplied by the aqueous humor which
  also refracts light

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Choroid Layer

• Middle layer of the eye
• Pigments prevent scattering of light by absorbing
  stray light
• Many blood vessels in this layer
• Toward the front is the iris
• Composed of thin circular muscle
• Muscle controls the size of the pupil opening
  (center of the iris)

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The Retina

• Innermost layer of the eye
• Composed of 3 different layers
• Light sensitive cell layer
• Rods photoreceptors used for viewing in dim
  light
• Cones photoreceptors that identify colour,
  packed densely at the back of the retina in area
  called the fovea cetralis (center of the retina)
• Once these cells are excited, the nerve message
  is passed on to.
• Bipolar Cells
• Relays message to
• Optic Nerve
• Carries impulse to Central Nervous System
• Blind Spot is the area where the optic nerve
  attaches to the retina, it contains no rods or
  cones (hence blind)

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Other Structures

• Lens
• Focuses the image on the retina and is found
  immediately behind the iris
• Ciliary Muscles
• Alter the shape of the lens
• Vitreous Humor
• Large chamber behind the lens
• Contains jelly-like material that maintains the
  shape of the eyeball, permits light transmission
  to the retina

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Focusing an Image

• Light rays pass through the cornea and through
  the lens which bends the light toward the retina
• As the light is bent, the object is projected on
  the fovea centralis of the retina, upside down
  yet interpreted by the brain right side up
• To focus
• Far away objects
• Ciliary muscles relax and lens flattens
• Close objects
• Ciliary muscles contract and lens becomes round
• This is called accommodation

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Eye disorders

• Glaucoma
• Ducts that drain the aqueous humor from the front
  of the eye become blocked resulting in pressure
  that ruptures blood vessels and leads to a lack
  of oxygen to the eye
• Cataracts
• Grey/white spots on the lens caused by break down
  of the lens. This prevents light from entering
  the eye
• Astigmatism
• Uneven curvature of part of the cornea causing
  images to be projected short of the retina and in
  the wrong spot leading to.
• Myopia
• Being nearsighted means you can see things close
  up but not far away
• Light rays fall in front of the retina instead of
  on the photoreceptors in the retina
• Hyperopia
• Being farsighted mean you can see things far away
  but not close up
• Light rays fall behind the retina
• Colour Blindness
• Due to a lack of cones, usually red and green
  cones
• Diabetic Retinopathy
• Capillaries to the retina burst spilling blood
  into the vitreous fluid, can also lead to retinal
  detachment
• Macular Degeneration
• Cones are destroyed due to thickened choriod
  vessels

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Vision The Nerve Impulse

• Begins with photoreceptors called rods (black and
  white) and cones (colour)
• Light stimulates rods/cones
• Bipolar cells are stimulated and transfer neural
  impulse to ganglion cells
• Axons of ganglion cells form the optic nerve
  which transmits an impulse to the occipital lobe
  of the brain
• See page 415 Fig 12.16

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Vision
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Vision p. 416
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Eye Dissection

• Eye dissection
• http//www.exploratorium.edu/learning_studio/cow_e
  ye/index.html
• Eye anatomy
• http//www.eschoolonline.com/company/examples/eye/
  eyedissect.html

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The EarHearing and Balance

• Chapter 12

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The Ear see p. 420
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Structures

• Outer Ear pinna, auditory canal
• Middle Ear tympanic membrane, ear ossicles,
  Organ of Corti, Eustachian tube
• Inner Ear Vestibule, Semicircular canals,
  cochlea

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Outer Ear

• Composed of
• the pinna
• the external ear flap that collects sound
• Auditory canal tube that carries sound waves to
  the eardrum
• Lined with sweat glands that produce earwax
• Earwax and hairs trap invading particles (dust,
  insects, bacteria) preventing them from entering
  the ear

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Middle Ear

• Tympanic Membrane (eardrum)
• Round, elastic structure that vibrates in
  response to sound waves
• Ossicles (3 small bones) each bone acts as a
  lever for the next as sound vibrations are
  received from the tympanum and amplified
• Malleus (the hammer)
• Incus (the anvil)
• Stapes (the stirrup)
• Concentrates vibrations into the oval window
• Eustachian Tube connects ear to throat, allows
  air pressure to equalize

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Inner Ear

• Cochlea coiled structure for hearing, is fluid
  filled
• Contains the Organ of Corti which is the organ of
  hearing when the oval window vibrates
• The basilar membrane moves up and down
• Hair cells move their stereocilia against the
  tectorial membrane
• Hair cells synapse with the auditory nerve which
  senses the bending of stereocilia and sends
  impulse to brain

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Inner Ear - Organ of Corti
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Sound

• Here is how it works
• http//www.sumanasinc.com/webcontent/animations/co
  ntent/soundtransduction.html

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Frequency Sound

• Hair cells distinguish frequency amplitude
• Frequency is waves that pass through specific
  point every second, measured in Hz (hertz)
• Frequency of speech 100-4000 Hz, we can hear
  between 20 20,000 Hz
• Hearing Loss results from damage to hair cells or
  damage to structures in middle or outer ear
• Amplitude is the intensity /volume of sound
• Louder noises (over 80 dB) put more pressure on
  hair cells which can destroy the stereocilia (
  see table 12.3 p 423)

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Inner Ear - Balance

• Semicircular Canals
• Mechanoreceptors to sense head and body rotation
• Consists of 3 fluid-filled loops arranged in 3
  different planes
• Base of each canal ends in a bulge containing a
  cupula
• Stereocilia stick into cupula and move when the
  head moves

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Inner Ear - Vestibule

• Made up of the utricle and saccule
• Both of these contain otoliths which are calcium
  carbonate granules lying over top of the hair
  cells
• When the head dips forward or back, gravity pulls
  on otoliths putting pressure on some hair cells
  which sends impulse to brain regarding head
  position

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Proprioreceptors

• Mechanoreceptor involved in coordination
• Found in muscles, tendons, joints
• Send info to brain regarding body position

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Home Entertainment ?

• Case Study Pain Relievers or Deadly
  Neurotoxins?
• Page 430, read and complete the 3 questions to
  hand in by next Tuesday (Feb 24)