Transcript Inner Ear

Sensory Systems
Sound, Lateral line, Electroreception, etc.
Chapter 6
Mechanoreception
• Mechanoreception in fishes is largely involved in
the detection of motion of water.
• Facilitates:
“hearing”
“balance”
“touch/feel” “gravity detection”
• System is divided into two basic components:
inner ear
lateral line
Inner ear structure
& function
• Pars superior semicircular canals
– 3 canals arranged in
three dimensions (x, y, z
axes)
– contain viscous fluid
– canal lined w/ hair cells
– detects position and
movement (inertia)
Inner Ear: Otolith
• Otolith organs
– Within each chamber is a suspended otolith
• Composed of CaCO3 and protein
• Used in determining growth rate
– Translucent (mineral) – slow growth
– Opaque (organic) – fast growth
– Daily rings – rapid growing fish
• Shape is species specific
• Highly resistant to digestion
micrograph of anglefish ootoliths
Weberian Apparatus - enhanced sensitivity of
hearing
• Found only in Ostariophysi
(minnows, catfishes, characins)
• Modified pleural ribs first four
vertebrae
• Sound waves impinge on swim
bladder and make it vibrate
• Swim bladder vibrations
transmitted mechanically by
W.A. to otolith
Sound Production by fishes
• Stridulatory (grinding) mechanisms
–
–
–
–
pharyngeal teeth (grunts)
spine erection and locking (catfish, triggerfish)— “popping”
skull grinding against vertebrae (seahorses)
resonance of grinding by swim bladder for more harmonics (clicks
and scratches become croaks and grunts)
• Swim bladder sounds
–
–
–
–
resonation of stridulatory sounds (catfish)
belching or gulping – physostomes (remember pneumatic duct)
“strumming” - rubbing muscles against side of swim bladder
“whistles” - muscles pull against wall of swim bladder to cause
vibrations
More sounds…
• Hydromechanical - low roar
-caused by rapid water displacement
• due to undulation or turning
• noise from turbulent flow, e.g. in fast
swimming
– especially used by schooling fish
http://www.marine.usf.edu/bio/fishlab/fish_sound_production.htm
Different Fish Sounds…
Obeta “Creaking”
Barge (topsail catfish)
Seacat
Toadfish pulse!!
“Grunt” “Drumming”
http://www.physorg.com/news157224812.html
Acoustic-lateralis system in fishes
“the lateral line”
“The feeling IS mutual...”
Only works in water! (Surprise!)
Important for:
Detecting prey
Avoiding predators
Schooling
Interpret surroundings
• Locations:
–
–
–
–
Lateral (side) canal
Supraorbital (above eye) canal
Infraorbital (below eye) canal
Hyomandibular (lower jaw)
canal
Neuromast—group
of hair cells bundled
together
Cupula—
gelatinous
sheath over cilia
of hair cells in
neuromast
Hair cell—cilia on
exposed surface of cell
Basic funcional unit of
lateral line.
Structure of Lateralis Canals
• Epidermal tunnel
• Pores open from canal to
skin surface
• Neuromasts distributed
within tunnel
• Fluid in tunnel is more
viscous than water;
therefore, more resistant
to flow
Structure of Lateralis Canals
• Movement of water
outside fish causes
displacement of fluid in
canal
• Canal fluid motion
causes bending of
neuromast, firing of hair
cells, triggers message to
CNS
• Sensitive to low freq.
(10 - 200 Hz)
More on lateral line...
• Primitive fish = lateral line possesses multiple
branches
• Modern fish = reduced to single line along the side
of the body and isolated pores on the head
• In sharks: lateral line present, but not obvious on
the side of the body
Sometimes water and electricity DO mix...
Why do fish need electricity?
• Electrical currents are carried with great efficiency
• Salt content of water also helps.
• Water advantageous!
•
•
•
•
Prey detection
Navigation
Communication
Defense
Electric Field Production by Fishes
• Electric field produced by modified muscle cells
(electrocytes) - often much of body musculature
• Electrocytes are disc-shaped and stacked in columns
• Stimulation of electrocytes causes depolarization of
cells - small electric current
- stack of cells functions
like batteries in series
Uses of electroreception
• Prey detection
...detect electromagnetic field produced by
prey...
• extremely sensitive: voltage gradient of
0.01 - 0.1 microvolts/cm,
...or detect prey distortion of self-induced
field from Electric Organ Discharge
(EOD)
Uses of electroreception
• Navigation
– detect distortion of self-induced field from normal body
functions by moving through another electromagnetic
field, including Earth’s – Chondrichthyes
– Slight movement of magnetite crystal in skull against hair
cells – similar to otolith function
- some Osteichthyes
Electrolocation
Uses of electroreception
• Communication
– Electrical signals are species-specific
– Used to signal species, sex, size, maturation state,
location, distance, individual recognition, courtship,
dominance, warnings, etc.
– Modify pulse frequency, voltage, field shape as part
of the “vocabulary” for communication
Examples:
Mormyrids-elephantfish
Gymnotids-knifefishes
Siluriformes-catfish
Rajidae-skates
Chondrichthyes-sharks
Sensory organs used in electroreception
• Ampullary organs (low frequency detection)
– ampullae of Lorenzini in sharks (Chondrichthyes),
lungfishes (Sarcopterygii), sturgeons (Actinopterygii)
– pit organs in some teleosts (catfish, knifefish,
elephantfish)
– gel-filled canal (conductive)
– lining of canal with closely-spaced, flattened, highresistance cells (no gaps - no current leakage)
– receptor cells at base of ampule - depolarization
causes Ca2+ flux, causing release of neurotransmitter
to sensory neuron
Ampullae of Lorenzini trivia...
• Canal varies in length relative to the salinity of the
environment
-Saltwater elasmobranchs = long canals
-Freshwater elasmobranchs = short canals
Sensory organs used in electroreception
• Tuberous organs
– detect only high frequency & low voltage AC fields
– found in fishes that produce Electric Organ Discharge
(EOD):
• knifefishes (Gymnotidae)
• elephantfishes (Mormyridae)
Types of Electric Fields
• Weak electric fields (EOD-induced) (millivolts)
– require intricate coordination - enlarged portion
of cerebellum (metencephalon)
– used for communication, prey detection
Black ghost knifefish, Apteronotus albifrons
Electric fish
•Gymnotiforms
S. America (L)
•Mormyriforms African (R)
•Found in muddy or “black”
water
•Note long tail in both
groups
Types of Electric Field
• Strong electric fields (EOD-induced)
– 10’s to 100’s of volts (stunning)
torpedo rays (20 - 50 volts)
electric catfish (300 volts)
electric eel* (500 volts!)
*Enough to knock a human unconscious
or at least flatten you out...
Vision in Fishes
3-dimensional vision in a dim, dense, filtered environment
Eye of southern flounder: courtesy of David Mowery
Main Challenges...
• Water density-absorbs light differently than does the
atmosphere - e.g. parallax at surface (bends light)
• Water is a dim medium due to high absorptive
capacity - 10% or more lost in first meter of clear lake
water
• Water absorbs long wavelength (low frequency) more
readily than short wavelengths
• red drops out in shallow water
• blue penetrates to greatest depths
• Lense specializations:
– spherical shape
Visual adaptations...
FOCUS
– protruding position ACUITY
• moveable position, off-center
NEAR- AND FARSIGHTED!
Adaptations for vision in water
• Retinal specializations:
– High density of rods—good in low light
– Choroid gland maintains elevated O2
levels in fish retinal tissue (rete mirabile)
– Shallow species have more cones (why??)
Rods and cones work
together to provide maxium
visual accuity over a maximum
range of light conditions.
– Specialized pigments for blue end of
spectrum
– Tapetum lucidum reflective, enhances low
light vision
Smell (Olfaction)
Taste!!
Fish tast buds are located on: head, mouth
Sometimes...all over body for catfish!