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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

BIOL 4340 – Lecture 13 - 2

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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

BIOL 4340 – Lecture 13 - 5

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

BIOL 4340 – Lecture 13 - 13

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

BIOL 4340 – Lecture 13 - 17