Sensory perception (particularly sound)

  1. General considerations: sound
    1. perception is important feature of animal life
    2. what makes sounds?
      1. Prey or predators. Especially impt in visually limiting envts
      2. Mates. Much mating behavior is vibratory in fish
      3. Solid objects reflect back waves that can be detected for navigation
    3. Relevant properties of water
      1. Low compressibility and high density
        1. sensation of water displacement and turbulence: motion
        2. more energy required to generate sound, but it propagates farther and faster than in air
        3. properties of the sound field (drum illustration)
          1. illustrate by imagining vibrating drumhead. Two components of acoustic signal.
          2. particle displacement: velocity of molecules, back and forth: vector property.
          3. pressure wave, alternating compression and rarefaction: scalar property.
          4. these are out of phase, at least close to the source
          5. energy due to displacement higher than pressure near source but drops more rapidly
          6. Near field sound is displacement; far field sound is pressure wave
  2. Mechanoreception: sensing sound, flow, movement and gravity
    1. Octavolateralis system
      1. Definition: inner ear and lateral line system
      2. Used to be called acousticolateralis
        1. Believed functioned primarily in hearing
        2. Believed to be developmentally linked and homologous
        3. Now these beliefs in doubt, new name reflects innervation by 8th cranial nerve
      3. Common to both: neuromast organ, comprised of hair cells (handout)
        1. ciliary bundle, with
          1. kinocilium
          2. multiple stereocilia
        2. movement of kinocilium relative to stereocilia stimulates or inhibits nerve impulse
    2. The membranous labyrinth: the inner ear (handout; also fig 6.2, helfman et al.)
      1. Pars superior
        1. Functions in sensation of equilibrium, gravity
        2. Three semicircular canals, filled with endolymph
          1. Oriented as perpendicular planes in teleosts
          2. Reduced number in more primitive fishes
          3. Each canal has an ampulla, with a crista, made up of cupula and hair cells
          4. cupula moved by fluid in canal, stimulating hair cells. Direction-sensitive stimulus. Not a swinging door as once thought, more like a drumhead.
          5. Three planes of canals: sensitive to pitch, roll, yaw. Semicirc. Canals function in sensation of angular accelerations of head
      2. Pars inferior
        1. Three distinct chambers, each with otolith (in teleosts)
          1. utricule, containing the lapillus
          2. saccule, containing the sagitta
          3. lagena, containing the asteriscus
        2. each otolith lies on sensory macula, with hair cells
        3. Sensation of sound
          1. Fish tissue transparent to displacement waves: body moves with rest of water
          2. But heavier otoliths don’t move in synch, so hair cells stimulated
          3. Mostly sensitive to 'near field' sound
        4. also sensation of gravity and locomotion: in sum, linear accelerations
      3. Multifunction organs: not as clear separation of vestibular (orientation) and auditory functions.
      4. Experiments in function
        1. studies of nervous impulses using electrodes, in conjuction with stimuli
        2. extirpation of organ, and quantification of behavioral response, e.g., vestibular function: can tilt a fish by shining light from side. Can increase gravity in centrifuge.
    3. Elaborations of inner ear: the hearing specialist fishes
      1. Weberian apparatus in catfishes and minnows
        1. bones modified from first few vertebrae and processes
        2. connect swim bladder and labyrinth (transparency of 21-6, bond)
        3. swim bladder is transducer: gas compressible, pulsates
        4. this motion translated to lab. by apparatus
        5. fishes having this are much more sensitive to sound, esp in higher freqs (1000s of Hz)
        6. this has never really been tested. Removal of ossicles reduces sensitivity and bandwidth, but do ossicles move?
      2. Swim bladder extensions to inner ear: herring, tarpon, porgies, squirrelfish.
    4. Lateral line
      1. Neuromast organs (fig. 6.4, Helfman et al.)
        1. cupula, sense cells with hairs.
        2. water movement moves cupula, stimulating sense cells
        3. All fishes have some free neuromasts
        4. direction sensitive
      2. structure of lateral line canal
        1. canal pores open to envt
        2. neuromasts lie between pores
        3. endolymph in canal
        4. movement of lymph stimulates neuromasts
      3. Pattern of canal
        1. extent of canal indicates activity level: more active, more neuromasts in canal
        2. canal on head and body
      4. Functions
        1. over range of 10 Hz to 200 Hz: v. low frequencies
        2. obstacle detection
        3. feeding: localization of food, sensing predatory attack
        4. trunk lateral line impt in coordinating schooling behav.