Special senses V: lateral line, electroreception, echolocation

Question 1

lateral line: features

Answer 1

• series of visible pores along body of aquatic animals
• detect movement, vibration, pressure gradients in surrounding water
• important for orientation, predatory behaviour, defence, rheotaxis (behavioural orientation to water current) and social schooling
• uses neuromasts (mechanoreceptors)

Question 2

lateral line: neuromasts- name two types

Answer 2

• superficial

- canal

Question 3

lateral line: neuromasts- superficial

Answer 3

• located on surface of the
  skin
• external

Question 4

lateral line: neuromasts- canal

Answer 4

• subdermal

- located within water filled canals beneath skin connected to exterior via series of pores

Question 5

lateral line: neuromasts- features

Answer 5

• comprises of group of mechanoreceptive hair cells
• each hair cell has numerous fine hairs (stereocilia) arranged in size order
• hairs covered by flexible cupula
• similar to crista ampullaris and cupula in semicircular canals of ear

Question 6

lateral line: neuromasts- mechanism

Answer 6

• water movement displaces cupula, deflecting the hairs
• movement of hairs towards kinocilium = depolarisation and increase in NT release
• movement of hairs away from kinocilium = hyperpolarisation (decrease NT)
• hair cells occur in pairs, oppositely aligned to aid direction sensitivity

Question 7

lateral line: afferent pathway

Answer 7

• hair cells release NT onto primary afferent nerve terminals
• APs transmitted along afferent lateral line neurons via CN VIII to spinal cord and medulla
• higher order processing and sensory integration occurs in telencephalon

Question 8

lateral line: efferent pathway

Answer 8

• efferent neurons located in medulla send processes to contact neuromasts
• inhibit synaptic transmission when swimming to prevent reception of self generated stimulation of lateral line

Question 9

electroreception: features

Answer 9

• ability to detect electric fields
• evolved from mechanosensory lateral line
• mainly found in animals from aquatic environments

Question 10

electroreception: names types

Answer 10

• passive

- active

Question 11

electroreception: passive

Answer 11

• detect weak electric fields generated by other animals

- primarily used for prey detection, predator avoidance, finding conspecifics

Question 12

electroreception: active

Answer 12

• produce electric field and detection of disturbances in the field
• communication and object detection

Question 13

electroreception: bioelectric fields

Answer 13

• weak dipole electric fields surround live animals
• ion leakage from mouth, gills, anus
• modulated by ventilatory movements or other rhythmic movement

Question 14

electroreception: eg

Answer 14

• crustaceans and elasmobranchs produce up to 50mV
• teleosts produce up to 500mV
• electrical signals differ in frequency and amplitude

Question 15

electroreception: passive

Answer 15

• ampullary organ (ampullae of Lorenzini)
• alveoli lined with sensory epithelium (SE) connected to exterior via conductive jelly filled canal
• each receptor cell in sensory epithelium has single kinocilium projecting into the lumen
• receptor cells respond to differences in voltage btw apical surface and basal surface
• 5-12 afferent nerves receive input from 1000s of receptor cells

Question 16

electroreception: stimulus localisation

Answer 16

• ampullary organs arranged in cluster means basal voltage (VREF) is same within cluster but apical voltages are different depending on position of stimulus
• afferent nerves project to brain in parallel channels to provide directional info

Question 17

electroreception: stimulus localisation- unstimulated

Answer 17

• steady discharge of APs

Question 18

electroreception: stimulus localisation- positive voltage

Answer 18

• decrease in NT and decrease neural firing

Question 19

electroreception: stimulus localisation- negative voltage

Answer 19

• increase in NT and increase in neural firing

Question 20

electroreception: shark deterrents

Answer 20

• they are highly sensitive to electric fields
• threshold sensitivity (1 microvolt)
• strong electric fields deter
• 3-10 V
• effective distances 0.2m-1.2m

Question 21

electroreception: mammals eg

Answer 21

• platypus
• echidna
• dolphin

Question 22

eg. Guiana dolphin

Answer 22

• vibrissal crypts on rostrum of dolphin
• 2-10 crypts on each side
• benthic feeding, ‘crater feeding’ where electroreception may help them find buried prey

Question 23

eg. Guiana dolphin vibrissal crypts

Answer 23

• similar to ampullary electroreceptors in others, have lumen and afferent nerve bundle
• detect electric fields w vibrissal crypts

Question 24

electroreception: active- features

Answer 24

• emit electric field produced by electrocytes (modified mm cells) arranged in columns
• CNS stimulation causes simultaneous depolarisation of electrolytes
• each column insulated and voltage is summed

Question 25

electroreception: active- eg. electric eel

Answer 25

• 6000 electrocytes

- 10V -> 720V max

Question 26

electroreception: active- diversity of waveforms

Answer 26

• of electric field allows communication in weak electric fish: sex recognition, find shoal, warn conspecifics
• must differentiate from electric field of conspecifics of others

Question 27

electroreception: active- tuberous organ

Answer 27

• tuned to specific electrical freq or amplitudes

- beneath epidermis, no canal

Question 28

electroreception: pathways- afferent

Answer 28

• same as lateral line
• AP transmitted along afferent electrosensor neurons via CN VIII to spinal cord/ medulla
• high order processing and sensory integration in telencephalon

Question 29

electroreception: pathways- efferent

Answer 29

• lack this pathway
• remove biopotentials created by animal itself via inhibitory connections in brain removing common mode signal (bioelectric field of self)

Question 30

echolocation: features

Answer 30

• emit high freq sounds into env to detect echoes reflected of surrounding objects
• time delay and intensity of echo provide info on distance, direction
• auditory system
• foraging and navigation

Question 31

echolocation: eg bats

Answer 31

• vocalise through lynx
• ultra sound range inaudible by humans
• modified basilar membrane (within cochlea) enlarged to suit echolocation freq

Question 32

echolocation: eg. bulldog bats

Answer 32

• communication, differ sex, btw colonies, individuals

- will adjust sound freq and duration when approaching prey

Question 33

echolocation: eg. cetaceans

Answer 33

• vocalise through nasal sacs
• melon focuses vocalisations
• high freq don’t travel far in water (5-200m)
• returning echoes received: fatty tissue (lower jaw) then relayed to mid and inner ear
• high sensitivity

Question 34

echolocation: pathways

Answer 34

• ear -> auditory nn -> pons -> inf colliculus -> thalamus (MGN) -> auditory cortex (temporal lobe)
• similar to humans but highly specialised

Question 35

echolocation: pathways distinct cortical areas

Answer 35

• neurons specialised for computing:
• target range (pulse-echo delay, FM-FM)
• target velocity (Doppler shift)
• insect wing flutter (fast doppler modulations)

Question 36

echolocation: humans

Answer 36

• visually impaired humans

- sonar tech (medical ultrasound, mapping sea floor)