Hearing Transduction in hair cells Lateral-line system
Electroreception Vestibular and acoustic systems
Characteristics of sound Inner, middle, and outer ears
Sound for communication and navigation
cone density
Q: Why are cone and ganglion cell distributions similar?
Constructing a retinal map
blind spot
Q: How might differential sensitivity and acuity explain the distribution of rods and cones in the retina?
Q: Why can’t the cornea be used for accommodation in water?
Accommodation by dramatic changes in lens shape
Ecophysiology of vision 1) Terrestrial vs aquatic
Accommodation by anterior / posterior movement of the lens
Accommodation by having both terrestrial and aquatic accommodation systems
Frequent nocturnal adaptations heavy eyelid large eye size small rods densely packed rods tapetum lucidem increased corneal size
Ecophysiology of vision 2. nocturnal vs diurnal
Hall and Ross 2006
rod distribution
cone distribution
cones
rods
Q: which distribution of rods and cones is adaptive for nocturnal, and which for diurnal, animals (monkeys)?
Oilbird, Steatornis caripensis
Near sensing
olfaction
Hearing
Far sensing
vision
No tapetum lucidum
Small rods: 1,000,000/mm2
Multiple tiers of rods
….”enhance sensitivity at the expense of resolution [acuity].” Martin et al. 2004
Transduction in hair cells
1) External structure deflected
2) Deformation opens cation channels
3) Change in cell membrane potential
4) Inhibition or promotion of APs in the integrative cells that synapse with the transducing cell.
Hair cell development and occurrence
Placodes “sink” into the dermis (lateral line and ampullae of Lorenzini) or dermal bone (inner ear) during development.
1. Lateral line
3. Vestibular and acoustic systems of the inner ear
2. Ampullae of Lorenzini
Blinded fish can still school if their lateral line system is intact.
…or in linear canals beneath scales (many fish).
1. Hair cells of the lateral line system :
located superficially in frogs…..
3. Acoustic (hearing) and Vestibular (balance) systems
located in the INNER ear = a WATER-BASED system based on fluid movement and the deflection of hair cell cilia.
bony fish bird mammal
VV V
AA
Vestibular system
Hair cells in the semicircular canals detect angular movements of the head.
Hair cells in the maculae of the utricle and sacculus detect linear acceleration.
otoliths
“X”“Y”
Acoustic System Mechanical disturbances of the environment, transferred to the endolymph of the cochlea, are detected by hair cells.
Deflection of stereocilia during basilar membrane vibration
Nerve VIII
Central nervous system referrals of acoustic system action potentials are interpreted as sound.
Q: is “ringing in your ears” really sound?
Reflection
Refraction
Impedance mismatch
Acoustic impedance is a measure of pressure generated by sound waves. It varies with frequency and acoustic medium.
Impedance match
Impedance mismatch
At the air:water interface, less than 1% of the sound energy passes into the second medium
Ancestral (aquatic) ears: fish have inner ears http://ocr.org/sounds/fish/oyster-toadfish/
hyomandibular =stapes
sound
cusk eel
oyster toadfish
Q: By what route(s) do you predict that sound reaches the fish inner ear?
The middle ear is an amplification device
Inner ear middle ear environment
hyomandibular = stapes
ear drum = tympanum
sound
small cochlea
Terrestrial ears: amphibians, reptiles and birds have inner and middle ears
= spiracle
Q: Where is the impedance mismatch in a terrestrial ear?
Terrestrial ears: mammals have inner, middle, and outer ears.
The 3-ossicle mammalian ear converts tympanum displacements into smaller oval window displacements of higher force
Q: What problems arise when terrestrial mammals return to aquatic environments? Hearing in whales
Nummela et al. 2004
Q: Comparative audiograms: at what pitch/decibel ranges do these animals hear?
Q: What frequencies of sound would be most useful for navigation? Long distance communication?
Build your own audiogram at http://www.phys.unsw.edu.au/jw/hearing.html
Q: why is infrasonic pitch so useful for long distance communication?
Sound for communication
Many vertebrates communicate using sound that has a frequency too low for humans to hear.
Elephants generate low-frequency sound both vocally and seismically
Q: How does the received sound of an elephant rumble vary with increasing distance?
closest farthest
Q: Why would echolocating bats have specializations of the larynx and nose, as well as the ears?
Q: What wavelengths of sound are optimal for navigation?
Sound for navigation