Sensory Systems

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Sensory Systems
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Cell Structure

• Cells of the sensory and nervous system derive
  embryonically from the ectoderm.
• Like epithelial cells, they are polar, having one
  end that is specialized for secretion.
• There are a diversity of neurons, sensory, motor,
  interneurons, and neuroendocrine

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Sensation Reflex

• Sensory cells and neurons are part of the
  peripheral nervous system, while the central
  nervous system is composed of the spinal cord and
  brain.
• Certain sensory situation demand a quick response
  and thus only involve one interneuron in the
  spinal cord without the involvement of the CNS.

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Sensory Information

• The relay of stimulus can result in either
  excitation or inhibition.
• In the knee jerk reflex the quadriceps is
  excited and contracts, while the hamstring is
  inhibited and relaxes.

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Categories of Sensation

• Somatic Senses are those that are distributed
  throughout the body (soma). These include the
  touch senses of touch, heat, cold, and pain.
• Special Senses are more localized in distribution
  and are associated with a particular sensory
  organ smell (nose), taste (nose), hearing
  (ears), and vision (eyes)

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Types of Sensory Receptors

• Somatic Senses
• Mechanoreceptors - mechanical energy
• Thermoreceptors - infared energy
• Nociceptors/Pain Receptors - tissue damage
• Special Senses
• Chemoreceptors chemical energy
• Mechanoreceptors - mechanical energy
• Electromagnetic/Photoreceptors visible and
  ultraviolet light

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Touch

• The sense of touch is mitigated through mechano,
  thermo, and pain receptors.
• Merkel disk receptors, Meissner corpuscles,
  Ruffini receptors, and Pancinian corpuscles are
  responsible for this sense and are categorized
  based on their depth and responsiveness
  (superficial or deep, and slow and rapid firing).
  Superficial sensory cells have free endings
  while deep sensory cells are encapsulated.

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Touch Transduction
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• Inhibitory mechanisms highlight the distinction
  between highly stimulated sensory cells and their
  neighbors
• This creates greater discrimination or acuity.

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Taste

• Taste buds have a pore through which fluids
  contact the surface of receptor cells. The
  receptors end in hair-like extensions containing
  receptors that respond to particular chemicals
  (sweet, sour-acids, salty, bitter-alkaloids).

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Taste Transduction
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Smell or Olfaction

• Olfactory receptors are similar to taste
  receptors in having hair-like ciliated endings
  that contain receptors for water soluble of
  volatile substances.
• The limbic system, located in the middle of the
  cerebral hemisphere, is associated in emotion and
  memory.

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Smell Transduction
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Taste Transduction

• Transduction animation
• Sensory cells communicate to the parietal lobe
  for integration.

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The Ear

• The ear is often segregated into outer, middle,
  inner components.
• The outer ear is composed of the pinna and inner
  channel.
• The middle ear contains the eardrum and ear
  bones.
• The inner ear is where the cochlea is found.

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The Cochlea

• The cochlea contains fluid and is bordered by the
  oval and round windows.
• Wave of pressure begin in the vestibular canal
  and proceed to tympanic canal.
• The basilar membrane of the cochlear duct is
  variable in its response to different
  frequencies.
• When it basal membrane vibrates relative to the
  static tectorial membrane hair cells in the organ
  of Corti are stimulated.

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Vestibular Apparatus Dynamic Equilibrium

• The vestibular apparatus senses both dynamic and
  static equilibrium.
• It is composed of 3 semicircular canals
  positioned in the x, y, and z planes, each having
  a ampulla at its base.
• When the head accelerates or rotates fluid is
  displaced and causes the gelatinous cupula to
  move and stimulate sensory hair cells.

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Vestibular Apparatus Static Equilibrium

• At the base of the vestibular apparatus are bulbs
  called the utricle and saccule.
• When you start or stop moving, movement of the
  underlying membrane causes stimulation of hairs
  cells projecting in to the less mobile calcium
  carbonate otoliths.

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Vision

• Photoreceptors are found in the retina and
  include both rods and cones (color), most dense
  at the fovea.
• Both interneurons and blood capillaries service
  the photoreceptors from front.
• The interneurons are transferred through the
  optic nerve (blindspot).

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The Outer Eye

• The outer eye is formed by the cornea, aqueous
  humor, iris, pupil, and the lens and its ciliary
  muscles.
• The cornea is the on the outer surface of the eye
  and it helps to focus light. Cataracts occur
  when there is cloudy vision caused when
  transparent lens proteins change such they no
  longer transmit light effectively (fried eggs).

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Visual Accommodation

• Visual accommodation occurs through the
  adjustment of the lens.
• To focus on distant objects the ciliary muscles
  relax and allow the lens to flatten and moving
  the focal point further back.
• To focus on near objects the ciliary muscles
  contract and cause the eye to bulge, shortening
  the focal point.

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The Middle Eye

• The middle portion of the eye is composed of the
  liquid vitreous humor.
• In Glaucoma, excess liquid accumulates in the eye
  putting pressure on the eyes blood vessels so
  that they may collapse and no longer be able to
  service the retinal neurons.

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The Inner Eye Sensory Transduction
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