Structure and Function: Sensory Systems

  1. Characteristics of living mammals (*diagnostic)

    1. Skeletal features
      1. Skull

        1. CNS: foramen magnum
        2. Vision: orbits, zygomatic arch
        3. Smell: rostrum, turbinal bones
        4. Hearing: external auditory meatus, auditory bullae

      2. Three ossicles in middle ear* (malleus, incus, stapes)

    2. Soft tissues
      1. Hair*
      2. Scent glands (deer scent glands, dik-dik antorbital gland)
      3. Pinnae* (not all mammals)
      4. Large, convoluted brain
      5. Corpus callosum* connects brain hemispheres (except monotremes and marsupials)

  1. Sensory systems
    1. Vision
      1. Tapetum lucidum - creates eye shine

      2. Rods and cones

    2. Hearing
      1. Range of human hearing
      2. Ultrasound (frequency >20,000 Hz)
      3. Infrasound (frequency <20 Hz)

      Elephant infrasound (from 1:16-3:27)

    3. Taste
    4. Olfaction
    5. Touch
    6. Electroreception
      video of platypus foraging

  1. Case Studies
    1. Hearing in kangaroo rats
      1. Video of kangaroo rate evading a snake bite
      2. Auditory bullae are bigger than braincase
      3. Big tympanic membrane (as can be seen from the enlarged auditory meatus
      4. Long malleus
      5. Small stapes
      6. Results in transformer ratio of 97:1 (compared to human 18:1)

    2. Echolocation - video of prey capture
      * These online resources require an Adobe Shockwave Player plug-in. Click here to download. You browser may not allow this, so I've recorded the demonstrations on an old computer using my phone - sorry for the poor quality, but they're wonderful demonstrations and they are soon to be lost.

      1. Bat echolocation using ultrasound*

        1. How it works Biosonar demonstration*
        2. Impedence
        3. Delay and range

          • Types* (Fig. 12.6)

            1) Frequency modulated (FM) - for determining fine details
            2) Constant frequency (CF) - for determining change in relative distance
            How do these calls change as the bat approaches its prey?

        1. Associated morphological specializations

          1) nose leaves
          2) complex faces
          3) big ears with tragus
          4) alterations in cranial structure (Fig. 12.15)

          5) middle ear specializations
      1. Dolphin echolocation
        dolphin sonar demonstration*

        1. Production of clicks*
        2. Focusing of clicks through melon
          Dissected melon and computed tomography of melon
        3. Reception by the lower jaw
        4. Some sound reception by the teeth? May help with localization of sound
        5. Reception by the middle ear