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LECTURE 13 - OUTLINE
Sensory Systems
2. Mechanosensory systems
1. Overview
- neuromasts
- lateral line system
3. Electrosensory systems
- electroreceptive organs
- electrolocation
BIOL 4340 – Lecture 13 - 1
OVERVIEW
- ancient system present in all fishes (& larval amphibians)
- a series of mechanoreceptive organs* in the skin
- not present in amniotes (e.g. reptiles, aves & mammals)
- ancient system found in agnathans/gnathostomes
- electroreceptive organs in the skin (derived from*)
- absent from (1) living hagfishes (2) most teleost fishes
Octavolateralis system
1. Mechanosensory system
2. Electrosensory system
3. Auditory/vestibular system
- inner ear structure found in all vertebrates
- static equilibrium; linear & angular acceleration; hearing
- living tetrapods; middle & external ears for airborne sound
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scales
lateral line canallateral line pore
nerve
muscle
- jelly-like structure
enclosing hair cells
cupula
hair cells with
sensory cilia
LATERAL LINE SYSTEM - 2030
BIOL 4340 – Lecture 13 - 3
neuromast
HAIR CELLS
Hair Cell
Supportive Cell
Kinocilium
Stereocilli
Hair Bundle
Efferent nerve ending
Afferent (sensory) nerve ending
Hair cell = receptor cell
- 1 long kinocilium
- a beveled cluster of 15 – 30
(up to 150!) stereocilli
- sustentacular cells
- morphologically polarized
- afferent neurons transmit
information to the CNS
- efferent neurons transmit
information from the CNS
- tonic receptors; movement
alters polarization state –
modulates discharge rateBIOL 4340 – Lecture 13 - 4
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scales
lateral line canallateral line pore
nerve
muscle
NEUROMASTS
*1. Hair cells (sensory)
2. Supporting (sustentacular) cells
3. Mantle cells (outer rim)
4. Neurons
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NEUROMASTS
Canal neuromast (CN)
Superficial neuromast (SN)
- freestanding skin neuromast
- can occur raised or in pits
- SNs usually smaller than CNs
- inverse relationship between SNs & CNs
- neuromast in fluid-filled canal
of lateral line system
cupula
hair cell
support cell
epidermis
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NEUROMASTS
: pores of lateral line canal/s
: free neuromasts
Variations of lateral line canal systems
1. Number
2. Placement and branching pattern
3. Canal widthfunctional implications yet to be elucidated
4. Number size and placement of pores
5. Inter-animal variationBIOL 4340 – Lecture 13 - 7
NEUROMASTS
: pores of lateral line canal/s
: free neuromasts
Squalus acanthias
Sphyrna lewini
distribution of pit organs in dogfish & hammerhead shark
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Ampullary Organ
ELECTRORECEPTIVE ORGANS
ampullary opening
ampullary canal
ampullareceptorcells
support cells
- canal and tube filled with K+ richmucopolysaccharide “jelly”
- jelly has properties of electricalcapacitor
- typical of chondrichthyans
- ampullae of Lorenzini (disc. 1678)
skin surface
- tonic receptors; electrical stimulus alters discharge rate
(a) +ve inc. neural discharge
(b) -ve dec. neural discharge
BIOL 4340 – Lecture 13 - 9
Ampullary Organ
ELECTRORECEPTIVE ORGANS
ampullary opening
ampullary canal
ampullareceptorcells
- canal and tube filled with K+ richmucopolysaccharide “jelly”
- jelly has properties of electricalcapacitor
- typical of chondrichthyans
- ampullae of Lorenzini (disc. 1678)
Sensory cell of ampullary organ
- kinocilium only, no stereocilia
- no efferent innervation of cell
skin surface
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ELECTRORECEPTIVE ORGANS
Dorsal view Ventral view
- restricted to the cephalic region
- passive electrolocation
: ampulla of Lorenzini : pit organ : lateral line
- mucous/temperature/salinity??
- detect weak electric currentsgenerated by prey
e.g. cardiac muscle contraction
Lower limit of detection*
Hammerhead shark (Sphyrna lewini)
% orientations
70% at <0.1 µV cm-1
40% at <0.01 µV cm-1
- arrangement of organs varies
*Kajiura & Holland (2002) Electroreception in… …sharks. J Exp Biol 205:3609-3621 BIOL 4340 – Lecture 13 - 11
ELECTRORECEPTIVE BEHAVIOUR
Passive electrolocation of prey organisms
Kalmijn (1971) The electric sense of sharks and rays. J Exp Biol 55: 371-383
- ampullae of Lorenzini determined to be electroreceptors
- do sharks make significant use of these fields?
- are there electric fields in the natural habitat that can be detected?
Plaice (Pleuronectes platessa)
- feeding response intensified by odourCatshark (Scyliorhinus canicula)
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Passive electrolocation of prey organisms
- ampullae of Lorenzini determined to be electroreceptors
- do sharks make significant use of these fields?
- are there electric fields in the natural habitat that can be detected?
Agar Chamber - allow electric field to emanate
- dissect mechanism by eliminating optical, chemical,
mechanical or electrical stimuli
- attenuate other stimuli
ELECTRORECEPTIVE BEHAVIOUR
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Passive electrolocation of prey organisms
- sharks exhibited identical behaviour pattern as previously observed
- clearly no need for visual cues
Olfaction?
- bait bag: sharks exhibited food seeking behaviour at outlet tube
ELECTRORECEPTIVE BEHAVIOUR
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Passive electrolocation of prey organisms
- sharks exhibited identical behaviour pattern as previously observed
- clearly no need for visual cues
Mechanical?
- agar chamber covered with thin layer (10 µm) of polyethylene plastic
- ignored plaice inside agar chamber
ELECTRORECEPTIVE BEHAVIOUR
BIOL 4340 – Lecture 13 - 15
Passive electrolocation of prey organisms
- buried electrodes simulating the bioelectric field of a plaice
- elicited a robust and specific natural feeding response
- presented with the option of electrode or bait
- ignored bait and attacked electrode
ELECTRORECEPTIVE BEHAVIOUR
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Neuromast
MECHANO/ELECTRORECEPTIVE ORGANS
Neuromast Ampullary organCharacteristic
Distribution head, tail, trunk head
Receptor cell hair cell (kinocilium + stereocilli)
modified hair cell (kinocilium only)
Peripheral termination
afferent & efferent afferent only
Function mechanoreception electroreception
Stimulus water movement DC & low freq. AC
Role “distance touch” e.g. orientation, coordination of swimming, escape
electrolocationelectrodetection
Ampullary Organ
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