sensing body position - 

• lateral line system - helps fish sense objects from vibrations around them
  • mov’t in environment causes stereocilia (hair) on cupula membrane to move >> action potential >> messages sent to brain
  • bending of hair can have excitatory/inhibitive effects, depending on direction of bend
• statocyst - allows invertebrates to move themselves in respect to gravity
  • cilia embedded in calcium carbonate
  • cilia bends when position changes
• vestibular apparatus - saccule, utricle, semicircular canals used to determine position in vertebrates
  • similar to mechanism used in lateral line system
  • hair found in otolith membrane
  • utricle more sensitive to horizontal mov’t, saccule more sensitive to vertical mov’t
  • semicircular canals - gives sense of angular acceleration

ear - actually works better in water than air 

• outer ear - air vibrations travel through ear canal to eardrum (tympanic membrane)
• middle ear - contains 3 ossicles (small bones): malleus (hammer), incus (anvil), stapes (stirrup)
  • connected to throat by Eustachian tube to equalize air pressure
• inner ear - contains cochlea (contains cochlear duct)
  • vestibular/tympanic canal located on top/bottom of cochlear duct
  • all 3 chambers filled w/ fluid (vibrations >> fluid pressure waves)
  • organ of Corti - contains basilar membrane, hair cells, tectorial membrane
  • stimulation of hair cells >> action potential >> impulses interpreted as sound
  • different fiber lengths in basilar membrane >> different pitch
• sonar - direction of sound easily determined due to location of 2 ears
  • distance of sound hard to determine due to environment
  • echolocation - emitting sounds and using the time it takes for the sound to come back in order to determine location