neuro - reception
receptive fields
area in which stimulation leads to response of a particular sensory neuron
different for each sensory modality
e.g. surfaces areas for skin mechanosensation, range of directions for vision
adjacent receptive fields often overlap a lot
might receive input from many receptor cells
vary in size → smaller receptive fields give better resolution
larger = more sensitive, less resolution
e.g. can feel two points as separate more easily on your fingertips where receptive fields are smaller, than on the back of your hand
don’t want superprocessing all over body bc a lot of wasted energy
trade-off → sensitivity vs localisation
parts of the area can be excitatory, others inhibitory
foveal and extrafoveal receptive fields
bigger receptive fields collect more photons so they are more sensitive
small receptive field can localise where the stimulus is in the RF more easily, but collect fewer photons so are less sensitive
extrafoveal receptive fields:
circular with centre and surround
rods and cones
most common receptive fields in retina
on-centre receptive field → excitatory input from centre and inhibitory from surround
off-centre is opposite
diffuse light covering both centre and surround → no signal bc inhibitory and excitatory both stimulated and cancel each other out
foveal receptive fields
one receptor only
max resolution
only cones
no lateral inhibition / no centre surround
explains why Hermann grid illusion disappears when fixated → projected onto fovea
Hermann grid illusion
illusion due to retina receptive fields
see dots between squares, disappear when you focus on them
lateral inhibition → each receptor has negative input on neighbour ganglion cells
centre giving positive input (excitatory)
surround inhibition
less lit area gives weaker lateral inhibition
higher input at edge of lit area → bc lower inhibition
stronger inhibition at edge of darker area
overall → enhances perceived brightness at edge of bright area, darkens edge of dark area
this increase in contrast can help you see in more detail (contrast enhancement)
this happens when roads match diameter of centre of RF
strongest effect when exact match
why do the intersections disappear when fixated?
focusing → image protected on fovea centralis
highest density of receptors
only colour vision (see earlier)
RFs have no centre surround → just one receptor per ganglion so no lateral inhibition
optimised for resolution
no lateral inhibition = no contrast enhancement
stimulus intensity
stimulus intensity signalled by frequency of action potentials in a sensory nerve fibre
CNS needs modality (which sensory nerves are active) and intensity (frequency of impulses)
dynamic (measurement) range = central measurement of stimulus intensities, over which frequency of action potentials increases steadily
maintained discharge = region that sensor is not responsive, but still sends low rate of action potentials
saturation = further stimulus increases do not increase frequency of action potentials → max reached
info from two receptor cells → can stack to extend dynamic measurement range
e.g. A1 and A2 ultrasound sensor cells in moth ears, rods and cones in vision
stimulus detection theory
signal vs noise in a binary classifier
maintained discharge → even when there is no stimulus, sensory fibres still transmit action potentials at low frequency
varies over sensory fibres
when adequate stimulus at sufficient intensity → impulse frequency increases
CNS needs to be able to distinguish actual signal from noise of maintained discharge
discharge from stimulus and maintained discharge both vary around a mean
variances overlap → in this region CNS can’t tell whether there is a signal or not
threshold is exceeded when signal is moved further out of noise → little doubt there is a stimulus present
fewer false alarms/false negatives → increase intensity of signal to reduce overlap, reduce variation of maintained discharge to narrow response curves
binary classifiers
e.g. is this a predator or not?
take input along many different sensory dimensions
total performance of a classifier can be measured and compared using Receiver Operating Characteristic (ROC)
to get to ROC, move threshold from far right to far left and plot true positive rate over false positive rate
more overlap = more ROC approaches straight line
perfect overlap → classifier is not better than a random guess
trigger stimuli
specific features of high importance to animal
e.g. clicks and crackles of predators in undergrowth → much more effective at triggering responses in auditory cortex than a continuous pure tone
‘grandmother cell’ → respond to facial features for recognition
stimulus intensity and detection threshold
threshold stimulus = lowest level that is detected in half the cases
not constant → depends on factors such as fatigue, context and practise
detecting differences in signal intensity → Weber’s law
increased stimulus intensity = increased magnitude of change in stimulus required to generate a just noticeable difference
one spoon in one hand and two in the other → easy to feel difference
ten in one hand and eleven in the other → same absolute difference but much harder to feel difference
Weber-Fechner law
Fechner was Weber’s student → extended the law
gives relationship between subjective threshold stimulus and suprathreshold stimulus (stimulus large enough to produce an action potential)
incorporates the fact that different individuals have different sensitivities
threshold magnitude = stimulus intensity required for an action potential in that particular individual
Stanley Stevens modified formula:
stimulus specificity
receptors have evolved to be optimally sensitive to their respective adequate stimulus
inadequate stimuli that are very strong can elicit sensory perception
e.g. gentle pressure on closed eyes → see stars
these visual phenomena are called pressure phosphenes
‘phenomenon of seeing light without light entering the eye’
brain can only make sense of stimuli by knowing which receptors are stimulated
motor and sensory regions of human primary cortex
large area for sensory input processing
primary areas → direct input
association areas → meaningful perceptual representation
located next to respective sensory areas
motor areas → create motor function
Metin and Frost 1989 study on hamsters
rerouted nerve fibres in new-born hamsters
retinal ganglion cells → thalamic somatosensory nucleus (in the brain) instead of the visual cortex
hamsters tested when adult → visual stimulation caused response in somatosensory neurons, but in a way characteristic of the visual cortex
suggests the cortical areas in the visual and somatosensory pathways perform similar transformations on input
info going in determines what cortex becomes → plasticity
sensory maps
receptive fields are arranged into two dimensional arrays → except olfactory system
described as sensory maps
spatial relationships of these arrays are maintained in the central nervous system
somatosensory map
parts of sensory surface of most biological importance, where greatest discrimination of sensory input is required → disproportionately large areas of the sensory map in the cortex
due to smaller and more numerous receptive fields from more important sensory areas + increased complexity of neuronal connectivity
sensory homunculus is most famous illustration of this
sized in relation to the areas parts of the body are given in the brain
these areas are more biologically important
such a scary guy
equivalent map in motor cortex
tonotopic map
when unrolled, the cochlea of the inner ear has certain areas that respond to certain sound frequencies
mapped exactly the same way in auditory cortex in brain
starts at low frequencies and goes to high frequencies
linear in humans but some animals are auditory specialists → more complex
auditory fovea
because horseshoe bats are Doppler specialists, they need to be able to discriminate frequencies around their call frequencies very well
auditory fovea = large section of inner ear cochlea dedicated to the range around their call frequency
gives very good frequency resolution
example for evolution of receptive fields → frequency selectivity of inner ear
tonotopic and chronotopic maps in bats
high frequency resolution of auditory fovea also found in auditory cortex
large area dedicated to discriminating very narrow frequency band around the call frequency
example of a specialised tonotopic map
small frequency range disproportionately represented in map
also found in katydids and mole rats (different frequency ranges)
adjacent → chronotopic maps of echo delay = object distance
very important for bats → green region = delay cued neurons
right echo delay → certain neurons spike
massive auditory cortex in relation to brain size (compared to humans)
retinotopic map
outside world projected onto specific cortex area → make processing easier
chemoreception
biological reception of chemical stimuli
mediated by receptors stimulated by chemical substances → chemoreceptors that fall into two categories
olfaction = scent perception, airborne
gustation = taste, direct contact
what is a chemical stimulus?
every chemical compound → extremely diverse
inorganic:
salts
other ions e.g. metal
contact receptors → taste
organic:
extremely diverse
used for communication
origins
early unicellular organisms
find food by chemical gradient
diffused chemical compounds the food will exude
avoid/find others by excretions
oldest communication
taste vs flavour
everyday experience of taste is actually flavour
flavour = combination of taste, olfaction, and the somatosensory perception of the food or drink
olfaction → from volatile food molecules that reach the nasal cavity through the back
somatosensory → e.g. texture and pain
all contribute to what we call taste generally
taste
function = test food before ingestion
perceived through taste buds in oral cavity
chemical has to be water soluble to reach taste bud
six ‘primary’ tastes in humans:
salty → organic salts e.g. NaCl
sour → acids e.g. vinegar
sweet → carbohydrates and amino acids e.g. glucose
bitter → alkaloids, often poisons e.g. quinine
umami (”delicious”) → amino acids, mainly L-glutamate
“metallic” → unclear
we know we can sense metal in our mouth but we don’t know how we pick it up
note → spicy is not a taste but somatosensation → pain
mechanisms of primary tastes
each taste cell has specific receptors in its microvilli
bitter, sweet and umami → specific receptor proteins
G-protein coupled receptors
sour → H+ ions interact with ion channels to depolarise the membrane
salty → Na+ ions pass through voltage gated Na+ ion channels to depolarise membrane
all change receptor potential
receptor cell synapses with a sensory neuron to relay the message to the central nervous system
taste buds
different animals have very different numbers of taste buds → e.g. humans have 9,000, cows have 25,000, chickens only have 24
high diversity even in humans
consist of several receptor cells → with specialised microvilli located in taste pores
microvilli detect dissolved chemicals → leads to activation of receptor cells
arranged in papillae
in oral cavity → tongue, soft palate and upper oesophagus
only the oral cavity ones give us conscious info → oesophagus ones don’t
four types of papillae on mammalian tongue
circumvallate
foliate → short vertical folds
fungiform → like circumvallate but no wall
filiform → all over tongue, for mechanoreception, no taste buds
all areas of the tongue are sensitive to all tastes → but to a different degree
some individuals have the inherited ability to taste certain bitter compounds
percentage differs between ethnic groups and sexes
supertasters → more sensitive to a wide range of oral stimuli
higher density of fungiform papillae
~25% of people in Western populations
prefer to put more salt in food to wash out bitterness
modality
labelled line principle → info on which fibre is active gives info on what taste is being experienced
across-fibre pattern theory → sensory information can be conveyed by altering the temporal pattern of action potentials, among multiple responding nerve fibres
most likely to be labelled line principle
olfaction
information about chemical composition before contact
most important sense for many organisms
wide range of compounds → so wide range of receptors
important in communication
hormones → within organisms
pheromones → between organisms of the same species
allomones → between organisms of different species
olfactory receptors in vertebrates and invertebrates
actual receptor looks identical → not the case for any other senses
primary cells → have their own axon
rather than synapsing with a cell that does the action potential business
shows it’s a really old sense → from before split between vertebrates and invertebrates
insects → pore in exoskeleton so fluid in contact with air
how does olfaction work?
fluid covering olfactory epithelium ‘catches’ volatile molecules
interact with receptor proteins in ciliary segment of receptor cells
generate electric response in receptor cells
receptor cells project to olfactory bulb in brain
protrusion that makes contact with bone
glomeruli collect / sort responses from similar receptors
all of the fibres from the same type of receptor project into one glomerulus
two different olfactory systems in mammals
all mammals have standard main olfactory epithelium (MOE)
receptor cells in MOE connect to glomeruli in main olfactory bulb (MOB)
vomeronasal (Jacobson’s) organ is a second system
mainly for pheromones
in oral cavity → need to breathe air in over palate to sense
links to accessory olfactory bulb (AOB)
longer route
ungulates, felids and other mammals
associated with behaviour called flehming
lost in primates
odorant receptor (OR) genes
900-1000 OR genes → by far the largest gene superfamily in mammals
same in all mammals
GPCRs
approx 50 locations over all chromosomes
large fraction can be deactivated
humans have 50% deactivated
most new world monkeys have <20% deactivated
except howler monkey → only new world monkey with trichromatic vision
dichromats = red/green blind
primates with trichromatic colour vision have a higher fraction of deactivated OR genes than dichromats
no longer rely heavily on olfaction
if you can see better you don’t need to be able to smell as well → relationship between different senses
olfactory adaptation
receptor adaptation → after continuous exposure to an odorant the receptors stop responding to the odorant and detection ceases
cognitive habituation → psychological / neuronal process by which, after long-term exposure to an odorant, one is no longer able to detect that odorant
like not knowing what your house smells like, unless you go away for ages
not at receptor level → higher
chemotaxis
qualities of chemical communication
directionality → unlike with light and sound, direction of particle does not equal direction to source
hard to tell where the chemical compounds are coming from
speed → very slow, minutes to days
e.g. compared to milliseconds to sound
temporal pattern → lost within a short distance from sender
can’t tell the temporal pattern easily
oldest sense but not great, hence evolution of other senses
transmission of chemical signals
chemical stimuli are transmitted in 3 different types of molecular movement:
diffusion
in completely still environment → slow spread
laminar flow
air flowing over a surface → faster higher up and slower over surface
turbulent flow
windy, lots of directions
chemotaxis
movement in response to chemical gradient
in an aquatic turbulent/laminar field:
klinotaxis → sequential sampling from several locations
detect, move a bit and detect again
zigzag in and out of plume of chemicals
works with a single receptor
tropotaxis → simultaneous comparison from separate receptor organs
e.g. antennae → compare left and right input to know which direction to go
rheotaxis → follow current
chemotaxis in moths:
pheromone male attraction
males have large feathery antennae → maximise surface area so more sensitive to female moth pheromones
females have thin antennae
beat wings while resting to stream air through antennae
once it picks up the pheromone scent → zigzags against air current and follows scent upwind
if loses scent → fly perpendicular to air current searching for pheromone trail
efficient at finding source in high turbulence
Catania 2013 → stereo sniffing for navigation to an odour source in mammals
moles tested in complete darkness on ability to find prey just by scent
one nostril blocked → veer off to opposite side
towards unblocked stronger input
differential signal essential for directional sniffing
plastic tubes in nostrils → curved to point out to side
uncrossed → normal behaviour
crossed → longer search time
evidence for directional olfaction
basics of electroreception
electroreception = biological ability to perceive natural electrical stimuli
electric field → field lines between two dipoles
dipoles = equal but opposing charges
field lines go from positive to negative dipole
field line density → shows field strength
charged particles in a field → accelerate following field lines towards opposite charge dipole
travels along field lines rather than just straight towards charge
what is electroreception good for?
generally underwater bc water is better conductor than air
absence of sufficient light
electrolocation → detecting, identifying and localising objects
electrocommunication → others in the environment can’t listen in
nocturnal animals
murky waters
buried prey
bioelectricity
cell membranes are good insulators → separate charges on either side of membrane
allows electropotential gradients to form
this is the basis of all neuronal activity
in our bodies → neuronal activity creates dipoles
all action potentials, nervous activity and brain activity produce dipoles
muscle activity also produces dipoles - e.g. heartbeat + respiration muscles
animals are constantly emitting electric fields
who uses electroreception?
most non-teleosts:
Agnatha, Elasmobranchii, Holocephali, Chondrostei, Polypteri, Dipnoi
some teleosts:
Siluriformes - catfishes
Gymnotiformes - knifefishes
Mormyriforms - elephant nose fishes
Xenomystinae - African knifefishes
weird looking fish bc of electroreception requirements
amphibian larvae
platypus and echidnas
weird nose/mouth parts for electroreception
Guiana dolphin - Czech-Damal et al 2012
receptor physiology
leak channels mean every cell is sensitive to changes in electric fields
electroreceptor cells do not have their own axon → synapse with an underlying sensory neuron
current flows into cell body following field lines
change in receptor membrane potential → response to current
receptor connected with synapse to afferent fibre
receptor potential → postsynaptic action potentials in afferent fibre
hasn’t happened many times but pretty easy to turn cells into electroreceptors
electroreceptive organs
lampreys
epidermal end buds → 3-30 sensor cells
microvilli → containing leak channels
underwater so good conductance
pretty basic design
chondrichthyes (cartilaginous fishes)
ampullae of Lorenzini
open ended mucus-filled ducts with ampulla (sensors) at base
conductive jelly in channels
duct more conductive than surrounding tissue
field line direction determines response strength
if perfectly aligned with duct →strong signal, ions accelerated all the way along
response is directional
ampullae run in different directions so if a certain duct gives strong output, the field lines are going in that direction
teleost fishes
ampullary organs
short duct with ampulla at base (sensors)
not very common
tuberous organs
no duct - instead have plug of loosely packed epidermal cells
directionality like with ducts
covered in microvilli
more common
platypus
modified sweat glands
sweat is full of ions and ions are charged particles
free nerve endings
mammals have loads in skin → mechanoreception but can be modified for electroreception
~40,000 per platypus → in narrow stripes on bill
two types of electroreception
passive → pick up natural electrical stimuli (e.g. from brain and muscle activity)
just electroreceptive sensors needed
active → generate weak electrical signal (electrogenesis)
pick up changes in the electric field with electroreceptive sensors
passive electroreception
Guiana dolphins
receptors are derived from hairs
same basic design - conductive channel leading to free nerve endings
~10% false positive rate but generally good at sensing
sharks
bite an electric field in absence of prey
scanning behaviour → explains shape of hammerhead sharks - better sensing for finding buried prey
Kalmijn 1971 experiments:
small spotted catsharks bite buried fish
agar chamber blocks chemical signal - still attacked
neither chemical nor electric cues - no attack
electrostatic dipoles are attacked and preferred over bait
working range = 15cm
ray roost finding
rays can be trained into one of two alternative coral roosts
reversing electric field → swap to alternative roost
shows rays use electric fields to find their roosts
again preferred cue
active electroreception
generate an electrostatic field
objects in the field modify the field depending on their impedance
either conductive or resistive compared to medium
conductive → pulls in field lines
resistive → pushes field lines away bc they go where there is least resistance
electroreceptive organs in the skin pick up these changes
body surface is sensor
CNS interprets overall input
behaviour
side searching → keep head in same spot and rotate body → stop if notice change in field
not long range sense
reverse swimming before capture → keeping same distance from object where they can sense it
electrogenesis - diversity
electric organs have evolved 6 times independently in fishes
in different positions
clearly benefit and strong evolutionary pressure
strong electric fields → defence / prey stunning
electric eel → 300-650V to stun its prey
electrocyctes - derived from muscle or neuronal cells - 100-150mV each
many columns of rows of electrocytes to increase current further → stack lots of small volt cells to get very big voltage overall → long body so they can stack loads
weak electric fields → active electroreception
problem = noise by self-generated fields (muscles)
undulating locomotion → long fin, not using all body musculature to move
spatial separation → move electric organ away from main muscles
pulses and waves
two types of discharge that can be produced:
pulse → one action potential, producing one single click
wave → many action potentials, series of clicks, produces sine wave function that sounds like a constant tone
synchronisation
difficult to synchronise discharges of tens of thousands of electrocytes
different distance from brain = different arrival time of action potential
nerves take detours → all equal length
nerves with different propagation speeds → same arrival time despite different length
compensatory synaptic delay
jamming avoidance response
what happens if more than one fish in the same area?
increase in pulse rate
change wave frequency → e.g. one goes to higher frequency and one goes lower → higher frequency wins and the other one will go lower
aggressive behaviour
also important in radar, sonar and echolocation
bioelectric crypsis
cuttlefish use to avoid being eaten by sharks
switch off all muscle and brain activity → stops any electric field they are emitting
electric camouflage!
prevents detection by electric signals
reading
Bedore, C.N., Kajiura, S.M. and Johnsen, S., 2015. Freezing behaviour facilitates bioelectric crypsis in cuttlefish faced with predation risk. Proceedings of the Royal Society B: Biological Sciences, 282(1820), p.20151886.
selection pressures have influenced non-visual crypsis but the mechanisms are understudied
freezing behaviours (seen in wide range of taxa including cephalopods) is often accompanied with background pattern matching and visual displays
cephalopods (especially cuttlefish) are good for studying non-visual crypsis bc have a wide range of predators → many of which use non-visual senses while hunting/foraging
e.g. elasmobranchs can find prey using just electroreception
visual camouflage not necessarily effective → freezing might facilitate non-visual crypsis (of signals that are generate by movement)
like how voles freezing reduces auditory cues → hide better from owls
electric fields in aquatic animals comes from ion exchange at structures in direct contact with seawater
e.g. pumping water over gills
this study shows cuttlefish use a freeze response that reduces bioelectric signals from gills
also actively insulate ion-leaking structures in the presence of some predators
freezing reduced shark responsiveness to 30% and reduced detection distance by 5cm
parameters used may not exactly represent cuttlefish in natural habitat, were in experimental tank and didn’t have substrate to bury in → stresses animals which may affect data, however results suggest voltage was not affected by stress
Kalmijn, A.J., 1982. Electric and magnetic field detection in elasmobranch fishes. Science, 218(4575), pp.916-918.
dogfish and blue sharks showed feeding responses to dipole electric fields that mimic prey
stingrays can orient relative to electric fields produced by ocean currents
show these behaviours in very weak voltage gradients
mechanoreception
the detection of physical deformation in the body’s environment associated with pressure, touch, stretch, motion or sound
stretch-activated channels in E. coli
only mechanoreceptors known in molecular detail
two types of mechanosensitive channel
large-conductance channels (MscL)
two transmembrane protein
five subunits
central water-filled pore
small-conductance channels (MscS)
three transmembrane protein
seven subunits
more complex than MscL
open by twisting in response to stretch
relieve osmotic stress
e.g. rains → outside is more dilute → lots of water would flow in response to gradient → stretches cell so channels open
this relieves the pressure, also lose ions so reduce osmotic gradient
once pressure has been relieved → channel twists closed
stretch-mediated channels
twist open or closed kinda like a camera
mechanoreceptor channels in C. elegans
most well-known animal mechanoreceptor
body wall touch receptor
six subunit channel in membrane of touch receptor neurons
linked to:
neuron microtubules
outer cuticle of worm
six touch receptor neurons → filled with microtubules
use to avoid obstacles / swim away from predator things
arthropod mechanoreceptors
arthropod sensillum
hair (trichoid) sensilla (TS)
all over body, particularly at joints
campaniform sensilla (CS)
found at parts of body responsible for locomotion
measure tension in cuticle
base of hairs
scolopidia - in chordotonal organs
internal
insect trichoid sensillum
cuticular projection - containing one or more neurosensory cells
own axon - no synapse
supporting sheath cells surround neurosensory cell
thecogen
trichogen
tormogen
sheath cells secrete fluid and nutrients into sensillar sinus
as well as giving stability
movement of hair stretches dendrite membrane
opens ion channels
causes depolarisation or hyperpolarisation
directionality:
depolarisation or hyperpolarisation depending on direction of movement
campaniform sensillum
stretch of cuticle → pressure on dome → compresses tubular body → dendrite depolarisation → action potential in axon
can measure direction and magnitude of force
trichobothria of spiders
very slender hairs → especially on legs
for detection of air movement
very sensitive → close to physical limits of detection
can detect energy close to Brownian motion
like how with vision, you can’t get any more sensitive than one photon
can’t measure mechanosensory things in any more detail → nanometre displacements
Amblypygi - whip spiders
antenniform leg displays
legs that are for communication rather than walking
mid range communication
create vibrations that stimulate trichobothria on opponents walking leg joint
this is how they fight → basically wave aggressively at each other
arthropod sound detection
acoustic sensilla
near field sounds
tuned to breathing frequency oscillations
cockroach cerci
moth caterpillar hairs
spider sound localisation
chordotonal organs
within body cavity, joint articulations or base of antennae
stretch receptors made up of scolopidia
one or more neurosensory cells
dendrite ends with sensory cilium
cilium is enclosed by scolopale cells
top of scolopale enclosed by envelope/attachment cell and covered with cap cell
the cap cell attaches to internal structures
dendrite depolarises in response to movement
measuring direct movement of the bit of cuticle it’s attached to
Johnston’s organ = largest chordotonal organ found in insects
at base of antennae of most species
extremely sensitive to mechanical forces exerted on antenna
e.g. tuned to specific frequency of females’ flight
thousands of scolopidia - very complex
form ring around antennae
tympanal organ
far field sounds
on different parts of the body - evolved many times on widely diverse insect groups
predator avoidance
in most cases have evolved to have defences against echolocating bats
vertebrate mechanoreceptors
mammalian tactile receptors
slow adapting receptors → respond constantly throughout the displacement
Merkel cells
large irregular nucleus and microvilli
expanded sensory neuron right underneath epidermis
respond to sudden skin displacements
e.g. something pressing down on your skin
Ruffini endings
sensory neuron breaks into a network of fine endings
everywhere in skin
respond to constant skin displacement
fast adapting receptors → respond only during initial pressure on skin
hair follicle receptors
hairy skin
nerve endings around follicle base
respond to movements of the hair
when something touches the hair you perceive it as a change but then once it’s gone you’re not perceiving it any more
Pacinian corpuscles
non-hairy and hairy skin
layers of connective tissue
slippage of layers under pressure causes response
Meissner’s corpuscles
non-hairy skin
connective tissue attached to epithelium
respond to movement of skin
movement detection rather than pressure detection
hearing
hair cell is receptor for vertebrate hearing
stereocilia (hairs)
often with one kinocilium (one long hair and lots of shorter stereocilia hairs)
all linked with polypeptide threads
movement of the stereocilia opens K+ gated channels in the membrane
causing a receptor potential
synapse with sensory neuron
directional response
bend in one direction = depolarisation
bend in the other direction = hyperpolarisation
rapidly adapting response
polypeptide links attach to ion channels - pulls them open
ion channels attached to microfilaments in stereocilia
allows them to slip down the membrane (so they don’t break)
removes tension on them from the linkages
ion channels close
response stops
fish otoliths
hair cells in inner ear of fish
crystals of calcium carbonate
press down on hair cells with gravity
higher density so doesn’t just move with fish
movement of head = movement of otoliths
bends hair with movement
information on acceleration and position
e.g. can use to find upright swimming position
human ampullae
one ampulla for each semi-circular canal
each rotation direction
cupula with embedded hair cells
endolymph mechanical inertia deforms cupula
results in neuromast receptor potential
e.g. endolymph moves differently to rest of you / to the air
detects rotational acceleration
prolonged rotation at the same velocity results in endolymph moving at same speed as canal
sudden stop → endolymph keeps moving
false impression of rotation in opposite direction
disrupts balance
like when you spin an egg and the inside keeps spinning longer