The Special Senses

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The Special Senses
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Objectives

• List and describe the major forms of special
  senses.
• Identify the location, the structure, and
  function of the special sense organs.
• a. Tactile
• b. Gustation
• c. Olfactory
• d. Visual
• e. Auditory

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Tactility Touch

• Specialized nerve receptors are located in the
  dermal layers of the skin which are sensitive to
  pressure associated with touch, heat, cold, and
  pain. These are specially modified sensory
  neurons called receptors. There are also
  receptors in muscle tissue which detect
  stretching, force of contraction and the
  stretching of tendons.

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Skin Receptors

• Skin
• I. Free nerve endings
• a. Nocireceptors Temperature, mechanical
  (pain
• itching, tickle, stretching) Dermis
• b. Merkel discs Light pressure, mechanical
  (discriminative touch) Dermis
• c. Root hair plexus Hair movement, mechanical
  
• Dermis
• II. Encapsulated Nerve Endings
• a. Meissners corpuscle light pressure
  mechanical, Located in hairless areas, palms
  or hands and soles of feet. (discriminative
  touch, vibrations.) Dermis
• b. Ruffinis corpuscle mechanical, thermal
  (rough and persistent touch)
• Dermis
• c. Krauses corpuscle mechanical, thermal
  (touch, low frequency vibrations) Dermis of
  mucus membranes
• e. Pacinian corpuscle Deep pressure,
  mechanical (deep pressure, stretch, and high
  frequency vibrations) Dermis of skin and joint
  capsules

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Skin Receptors
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Muscle Receptors

• Muscle
• I. Encapsulated nerve endings
• a. Muscle spindles stretch, mechanical, sense
  of muscle length, all skeletal muscle
• b. Golgi tendon receptors stretch mechanical,
  muscle tension

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Gustation Taste

• Taste buds
• a. Most are located on the tongue, some are
  located within other areas of the mouth.
• b. Papillae small elevated projections on
  the tongue
• c. Fungiform, circumvallate, and foliate
  contain taste buds.
• d. Filiform are sensitive to touch
• e. Gustatory cells are specialized receptors
  located on each taste bud (50-125 per taste bud)
  which have special hair like projections which
  are sensitive various chemicals which act as
  stimuli for various taste sensations.
• f. The gustatory nerves are connected by the
  cranial nerves to the medulla oblongata, which
  relays the message to the thalamus and then to
  the gustatory center of the brain where the
  stimulus is interpreted.
• g. Gustation and olfactory are closely
  associated to produce the sensation of taste.

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Gustation Taste
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Olfactory Smell

• Sensory cells are located in the epithelial
  lining of the mucous membrane of the nose.
• Olfactory neural chemoreceptors have specialized
  cilia which detect the presence of specific
  chemicals within the air we breath.
• Basal cells are germinative cells which regularly
  replace the olfactory neruons.
• The neuron are connected to the olfactory bulb
  which when stimulated sends a message to the
  olfactory center of the brain where the smell is
  interpreted.

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Olfactory Smell
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Auditory (Hearing) and Balance

• The ear is a duel organ, not only is responsible
  for the sense of hearing but also it functions as
  the organ of balance.
• The sensation of balance and hearing are both
  associated with specialized receptors with
  hair-like mechanoreceptors (hair cells).
• The ear is divided into three major regions
• a. External Pinna or auricle and auditory
  canal
• b. Middle Tympanic membrane (eardrum) and
  auditory ossicles ( malleus (hammer), incus
  (anvil) and stapes (stirrup)
• c. Inner Semicircular canals and vestibular
  nerve (balance) and the cochlea and round or
  oval window and the cochlear nerve (sound)

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Auditory (Hearing) and Balance
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Auditory (Hearing)

• Pinna is designed to capture sound vibrations and
  channel them into the auditory canal.
• The tympanic membrane transfers the sound
  vibrations to the auditory ossicles of the middle
  ear.
• The auditory ossicles then transfer the
  vibrations to the round window of the cochlea.
• Within the cochlea is the organ of Corti where
  the hair cells are located. Each respond to a
  different frequency of vibration.
• The cochlea have canals which are filled with
  fluid, which surrounds the Organ of Corti.
• When the fluid is stimulated by vibrations from
  the round window, the fluid transfers the
  vibrations to the hair cells, which then
  transfers the message to the auditory center of
  brain for interpretation through the acoustic
  nerve

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Balance
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Balance
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Vision

• The eye is the organ of vision.
• It converts light energy into electrical nerve
  impulses which are then interpreted by the brain
  as sight.
• The lens of the eye focus light on the retina.
• The retina contain specialized nerve receptors
  sensitive to light intensity (rods) and
  wavelengths or colors of light (cones).
• The optic nerve then carries the message to the
  brain where it is interpreted as sight in the
  visual center of the occipital lobes.

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Eye Structure
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Retina Structure
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Common Refraction Disorders