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…..

2. Ampullae of Lorenzini – passive electroreception

Scyliorhinus (catshark)

Kalmijn 1971

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

http://dolphindrivehunting.wordpress.com/research/dolphin-vocalisation/

Whales use sound for both communication and navigation. Q: Which audiogram reflects use of sound in communication? In navigation?

Houser et al. 2001

Bauman-Pickering Et Al. 2010Echolocating dolphins