Special senses V: lateral line, electroreception, echolocation Flashcards
lateral line: features
- 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)
lateral line: neuromasts- name two types
- superficial
- canal
lateral line: neuromasts- superficial
- located on surface of the
skin - external
lateral line: neuromasts- canal
- subdermal
- located within water filled canals beneath skin connected to exterior via series of pores
lateral line: neuromasts- features
- 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
lateral line: neuromasts- mechanism
- 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
lateral line: afferent pathway
- 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
lateral line: efferent pathway
- 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
electroreception: features
- ability to detect electric fields
- evolved from mechanosensory lateral line
- mainly found in animals from aquatic environments
electroreception: names types
- passive
- active
electroreception: passive
- detect weak electric fields generated by other animals
- primarily used for prey detection, predator avoidance, finding conspecifics
electroreception: active
- produce electric field and detection of disturbances in the field
- communication and object detection
electroreception: bioelectric fields
- weak dipole electric fields surround live animals
- ion leakage from mouth, gills, anus
- modulated by ventilatory movements or other rhythmic movement
electroreception: eg
- crustaceans and elasmobranchs produce up to 50mV
- teleosts produce up to 500mV
- electrical signals differ in frequency and amplitude
electroreception: passive
- 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
electroreception: stimulus localisation
- 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
electroreception: stimulus localisation- unstimulated
- steady discharge of APs
electroreception: stimulus localisation- positive voltage
- decrease in NT and decrease neural firing
electroreception: stimulus localisation- negative voltage
- increase in NT and increase in neural firing
electroreception: shark deterrents
- they are highly sensitive to electric fields
- threshold sensitivity (1 microvolt)
- strong electric fields deter
- 3-10 V
- effective distances 0.2m-1.2m
electroreception: mammals eg
- platypus
- echidna
- dolphin
eg. Guiana dolphin
- vibrissal crypts on rostrum of dolphin
- 2-10 crypts on each side
- benthic feeding, ‘crater feeding’ where electroreception may help them find buried prey
eg. Guiana dolphin vibrissal crypts
- similar to ampullary electroreceptors in others, have lumen and afferent nerve bundle
- detect electric fields w vibrissal crypts
electroreception: active- features
- 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
electroreception: active- eg. electric eel
- 6000 electrocytes
- 10V -> 720V max
electroreception: active- diversity of waveforms
- of electric field allows communication in weak electric fish: sex recognition, find shoal, warn conspecifics
- must differentiate from electric field of conspecifics of others
electroreception: active- tuberous organ
- tuned to specific electrical freq or amplitudes
- beneath epidermis, no canal
electroreception: pathways- afferent
- 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
electroreception: pathways- efferent
- lack this pathway
- remove biopotentials created by animal itself via inhibitory connections in brain removing common mode signal (bioelectric field of self)
echolocation: features
- 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
echolocation: eg bats
- vocalise through lynx
- ultra sound range inaudible by humans
- modified basilar membrane (within cochlea) enlarged to suit echolocation freq
echolocation: eg. bulldog bats
- communication, differ sex, btw colonies, individuals
- will adjust sound freq and duration when approaching prey
echolocation: eg. cetaceans
- 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
echolocation: pathways
- ear -> auditory nn -> pons -> inf colliculus -> thalamus (MGN) -> auditory cortex (temporal lobe)
- similar to humans but highly specialised
echolocation: pathways distinct cortical areas
- neurons specialised for computing:
- target range (pulse-echo delay, FM-FM)
- target velocity (Doppler shift)
- insect wing flutter (fast doppler modulations)
echolocation: humans
- visually impaired humans
- sonar tech (medical ultrasound, mapping sea floor)
