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.
• Permits
“hearing” “balance”
“touch/feel” “gravity detection”
• System is divided into two basic components:
inner ear
lateral line
• Sensory hair cells -basic unit (sensory apparatus)
Inner ear structure & function
• Pars superior - semicircular
canals
– 3 canals arranged in three
dimensions (x, y, z axes)
– filled with viscous fluid
– inner walls lined with naked
hair cells
– function to detect position and
movement (inertia)
– input integrated with input
from utricle organ (utriculus lapillus) for balance
Inner ear structure & function
• Pars superior semicircular canals
– 3 canals arranged in
three dimensions (x, y, z
axes)
– filled with viscous fluid
– inner walls lined with
naked hair cells
– function to detect
position and movement
(inertia)
– input integrated with
input from utricle organ
(utriculus - lapillus) for
balance
Inner Ear of Fishes
Lateral View. SC=
Semicircular
Canals, U=
Utriculus,
UO=Utricular
Otolith or Lapillus,
M=Macula,
SU=Sulcus,
S=Sacculus,
SO=Saccular
Otolith or Sagitta,
L=Lagena,
LO=Lagenar Otolith
or Asteriscus.
Modified from
Popper and Coombs
(1982).
Inner Ear: Otolith
• Pars inferior - otolith organs
– Three chambers, arranged anterior
to posterior, filled with viscous fluid.
– Within each chamber is a suspended
otolith
– inner walls of chambers lined with
naked hair cells
• 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)
• Apparatus is made of
modified pleural ribs of first
four vertebrae
• Sound waves impinge on
swim bladder and make it
vibrate
• swim bladder vibrations
transmitted mechanically by
W.A. to pars inferior
Sound Production by fishes
• Stridulatory (grinding) mechanisms
–
–
–
–
pharyngeal teeth (grunts)
spine erection and locking (catfish, triggerfish)
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
Ability to make sounds by fishes
• Hydromechanical sound production - low roar
– analogous to air rush associated with passing
train
– caused by rapid water displacement
• due to undulation or turning
• noise from turbulent flow, e.g. in fast
swimming
– especially used by schooling fish
Acoustic-lateralis system in fishes
“the lateral line”
“The feeling IS mutual...”
Only works in water! (Surprise!)
Senses movement of
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
Kinocilium—long, serves
as trigger
Stereocilia–shorter graded,
serve to condition
kinocilium for being
triggered
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 in
water due to density and salt content, water makes an
excellent medium for this action.
• Used not only in prey detection, navigation, and
communication, but has been modified for defensive
purposes in several species.
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)
Sensory organs used in electroreception
• Tuberous organs
– bud-shaped swelling in epidermis
– receptor cells constantly depolarized by self-induced
EOD, causing release of neurotransmitter to sensory
neuron
– detects changes in EOD-induced field by change in
the frequency of sensory impulses to brain PHASIC receptor
Types of Electric Fields
• Weak electric fields (EOD-induced)
– require intricate coordination - enlarged portion
of cerebellum (metencephalon)
– measure in millivolts/cm
– used for communication, prey detection
Black ghost knifefish, Apteronotus albifrons
Electric fish
•Gymnotiforms in S. America (L)
•Mormyriforms in Africa (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...
Wave vs pulse EOD species
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??)
– 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!