SENSES 1

• General senses


  Often exist as individual cells or receptor units, widely distributed throughout the body
• Special senses

  Large and complex organs, localized grouping of specialized receptors
• Sensory receptor types


  • Encapsulated
  • Unencapsulated ("free" or "naked")
• Classification by type of stimuli required to activate receptors


  • Photoreceptors (light)
  • Chemoreceptors (chemicals)
  • Pain receptors (injury) (nociceptors)
  • Thermoreceptors (temperature change)
  • Mechanoreceptors (movement or deforming of capsule)
  • Proprioceptors (position of body parts or changes in muscle length or tension)
• Sensory pathways

  • All sense organs have common functional characteristics: 1) Able to detect a particular stimulus, 2) Stimulus is converted into a nerve impulse, 3) Nerve impulse is perceived as a sensation in the central nervous system (CNS)
• General sense receptors


  • Free nerve endings (pain, temperature, crude touch)
  • Tactile (Meissner) corpuscles (fine touch, vibration)
  • Bulbous (Ruffini) corpuscles (touch, pressure)
  • Lamellar (Pacini) corpuscles (pressure, vibration)
  • Bulboid corpuscles (Krause end bulbs) (touch)
  • Golgi tendon receptors (proprioceptors)
  • Muscle spindles (proprioceptors)

  
• Eyes

  • Composed of an optical component that focuses the visual image on the receptor cells, and a neural component that transforms the visual image into a pattern of graded and action potentials

  
• Parts of the eye

  • Sclera
  • Cornea
  • Conjunctiva
  • Choroid
  • Lens
  • Retina
  • Aqueous humor
  • Vitreous humor

  
• Visual pathway

  Impulse travels from rods and cones through bipolar and ganglionic layers of retina, nerve impulse leaves eye through optic nerve, visual interpretation occurs in visual cortex of cerebrum
• Protective mechanisms of the eye

  • Eyelids and eyelashes, tears and lacrimal gland
• Light processing in the eye

  Amount of light entering eye controlled by iris, eye refracts light to focus image on retina

  
• Accommodation

  Strength of lens depends on shape, regulated by ciliary muscle
• Phototransduction


  Photoreceptors convert light stimuli into neural signals
• Rods and cones

  Rods provide indistinct gray vision at night, cones provide sharp color vision during the day
• Color vision and adaptation

  • Color vision depends on ratios of stimulation of three cone types, eyes can vary in sensitivity through dark and light adaptation

  
• Visual information processing

  Visual information modified and separated before reaching visual cortex, thalamus and visual cortex elaborate visual message
• Cone types

  • Each cone type is most effectively activated by a particular wavelength of light in the range of color indicated by its name
• The sensitivity of the eyes can vary markedly through dark and light adaptation
• Visual information is modified and separated before reaching the visual cortex
• Thalamus and visual cortex


  Elaborate the visual message
• Monocular zone


  Portion of the visual field associated with only one eye

  
• Binocular zone


  Where left and right visual fields overlap
• The ear functions in hearing and in equilibrium and balance
• Mechanoreceptors

  Receptors called mechanoreceptors
• Parts of the ear

  • External
  • Middle
  • Inner
• Sound waves

  Traveling vibrations of air molecules
• Hearing

  Neural perception of sound energy
• Sound characteristics

  • Pitch (tone)
  • Intensity (loudness)
  • Timbre (quality)
• External ear


  • Auricle (pinna)
  • External auditory canal
• Middle ear

  • Ear ossicles (malleus, incus, stapes)
  • Auditory (eustachian) tube
• The middle ear bones convert tympanic membrane vibrations into fluid movements in the inner ear
• Inner ear

  • Bony labyrinth filled with perilymph
  • Membranous labyrinth filled with endolymph
  • Receptors for balance in the semicircular canals are called cristae ampullaris
• Cochlea

  Pea-sized, snail-shaped, "hearing" portion of the inner ear
• Organ of Corti

  Sense organ for hearing in the cochlea
• Hair cells in the organ of Corti

  Transduce fluid movements into neural signals
• Inner hair cells

  Role in hearing
• Outer hair cells


  Role in hearing
• Equilibrium

  • Static - sense of gravity
  • Dynamic - sense of speed and direction of movement
• Vestibular nerve


  Carries nerve impulses from the equilibrium receptors of the vestibule
• Deafness is caused by defects in either conduction or neural processing of sound waves