Audition

I. Sound
   1. hertz (wave length/sec or frequency) conveys pitch
       a. pure sounds have only a single frequency
   2. decibels (amplitude of wave) conveys loudness
 

II. the ear
   1. external ear (pinna)
   2. middle ear (tiny bones or ossicles)
   3. inner ear (mostly cochlea)
      A. fluid filled tunnel contains receptors (transduction)
      B. oval window
      C. basilar membrane & tectorial membrane (hair cells between)
 

III. theories of hearing pitch
   1. place theory (for high frequencies)
      A. specific frequencies vibrate specific areas of  basilar mem.
   2. Frequency theory (for low frequencies)
      A. pitch corresponds to the rate of basilar membrane vibration
      B. volley principal
 

IV. deafness
   1. ossicles become fused
   2. hair cells become damaged (with loud noise)
   3. brain damage
   4. prenatal problems or disorders of childhood
 

V. how do we perceive sources of sound?
   1. the loudness & timing of sounds reaching each ear
   2. also, we use our eyes
 

VI. auditory pathway
   1. hair cells synapse on axons of the auditory nerve
   2. lower brainstem (medulla)
   3. auditory thalamus: medial geniculate nucleus (MGN)
   4. auditory cortex (auditory map)
 

VII. a 5-6 mo. old fetus can hear and see
 
 

Somatic Senses (touch, temperature, pain, kinesthesia)

I. touch
  1. physical stimuli are mechanical (deformation of skin)
     A. receptors in the skin have long axon which reach into the spinal cord
     B. dermatomes
  2. intensity depends on firing rate & number of neuron stim.
  3. most sensitive areas of skin have more cortex devoted
  4. location of touch is coded by spatial info (maps in cortex)
 

II. pain
  1. people who are insensitive to pain experience injuries
  2. limbic system as well as cortex receive pain info.
  3. neural mechanisms seem to be able to block pain (gate theory)
  4. we appear to have analgesics neurotransmitters (endorphins & anandamides)
  5. substance P (a neurotransmitter) increases pain sensitivity
    A. capsaicin: found in hot peppers
 

III. temperature (two types of receptors respond to changes in temp.)
  1. some receptors respond to warmth others coolness
  2. adaptation occurs
 

IV. Chemical Senses
   1. Gustation
       A. physical stimuli are chemicals dissolved in saliva
       B. receptors are taste cells that are found in taste buds
         a. they synapse on cranial nerve axons which carry the signal to the nucleus of the solitary
             tract (medulla).  The signal is then sent to other brain areas
       C. there are 4 primary taste (bitter, sweet, sour, salty)
       D. to some degree this is innate (4 mo. fetus prefer sugar)
       E. sensory adaptation (when food sits on a single spot)

   2. Olfaction
      A. physical stimuli are chemicals dissolved in nasal mucus
      B. receptors (cilia) in olfactory epithelium
        a. these synapse synapse on the olfactory bulb (olfactory cranial nerve)
        b. olfactory bulb axons extend to cerebral cortex & limbic system
      C. adaptation occurs
      D. pheromones (chemicals that communicate)

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