Sensory Biology Flashcards
1
Q
what is the mind-body problem?
A
how do mental properties (thoughts and feelings), arise from physical properties (biochemical and electric signals)
2
Q
In order for an organism to detect and respond to these physical stimuli, what must they be?
A
Collected (at the boundary between the external environment and the internal environment (the cell membrane)
Transduced into messages within the organism, which it can respond to (chemical and electrical signals)
3
Q
why is Fluidity is of significance in sensory systems?
A
because proteins are shuttled in the plane of the membrane to relay signals (e.g. G-protein signal transduction)
4
Q
what do Most membrane-bound proteins?
A
project all the way through the bilayer from the extracellular to the intracellular space (these are called integral proteins)
5
Q
what does the intramembranous domain constist?
A
alpha-helical segments, of mostly hydrophobic amino acid residues
6
Q
what is fundamental to sensory systems?
A
Conformational changes in membrane proteins.
7
Q
what does a stimulus at a biomembrane result in?
A
a protein changing shape (initial detection of the stimulus), which results in a membrane potential (transduction of the signal)
o This process allows the organism to sense and respond to the stimulus
8
Q
What is an overview of how receptor proteins allow cellular responses to occur?
A
o Receptor protein í activation signal í effector molecule
o Release of second messenger í cellular response
9
Q
What is the most important type of receptor molecule? What is it
A
the 7TM (seven transmembrane) receptor. They make seven passes through the membrane, therefore have seven transmembrane domains. - Large superfamily of proteins: 2% of the mammalian genome codes for them
10
Q
What do the intracellular loops of GPCRs provide?
A
recognition surfaces for specific G-proteins.
11
Q
what is desensitisation and what part of GPCRs are involved?
A
occurs when a receptor is overexposed to its agonist and becomes unresponsive. phosphorylation sites on the c-terminal are involved in desensitisation
12
Q
when is sensitivity of a GPCR restored after sensory adaptation?
A
o Sensitivity is restored when the tail is dephosphorylated again by phosphatase enzymes in the cytosol.
13
Q
what type of activity does the α subunit of GPCRs have? What does this mean?
A
GTPase activity - its attached GTP is soon hydrolysed to GDP, switching the mechanism off again by changing its conformation back to the deactivated form.
14
Q
What happens after the effector molecule is activated?
A
Classes of effector molecules include cyclase enzymes, phospholipases, phosphodiesterases and membrane channels. o They give rise to the second messengers including cyclic-AMP, inositol triphosphate (IP3), diacyglycerol (DAG) and the Ca2+ ion. Adenylyl cyclases (ACs) catalyse the formation of the second messenger cAMP.
Activation of the effector protein phospholipase C-β, results in the formation of two second messengers
15
Q
what does A stimulated GPCR results in the activation OF?
A
membrane-embedded PLC-β (which is the effector molecule), which reacts with PIP2, to produce the second messengers IP3 and DAG
16
Q
WHAT DOES DAG DO?
A
DAG activates PKC when the Ca2+ concentration of the cytosol rises
17
Q
what are the different types of channels in a membrane and how are they activated?
A
Some channels are activated directly by environmental change, others are activated by binding of ligands (ligand-gated ion channels LGICs), others by a change in voltage across the membrane (voltage-gated ion channels VGICs).
…result in a receptor potential
18
Q
what is the difference between the tertiary + quaternary structure of TRP channels?
A
The tertiary structure involves six transmembrane domains (s1-s4 and s5 and s6)
The quaternary structure consists of four of these 6TM subunits, grouped around a central pore
19
Q
what happens When a ligand attaches to binding sites on the channel?
A
the channel opens and cations flow along their gradients. Selectivity filters (charged amino acids lining the pore of the channel) can select the ions that pass.
20
Q
How are voltage gated ion channels activated?
A
by changes in membrane potential, and they differ in the ions that they allow to pass (K+, Cl-, Ca2+ and Na+). o Any change in potential gradient, results in conformational change in membrane bound voltage-sensitive proteins.
21
Q
What causes the inactivation of the voltage gated ion channels; NA+ channels?
A
o The inactivation is due to the intracellular segment between domains III and IV blocking the channel.
o The three conformations of this channel are: closed, open and inactivated
22
Q
why does Electric current flows between these two points. in the membrane?
A
The cytoplasm and the extracellular fluid are ionic solutions ( they conduct electric currents).
o Depolarising the membrane at a certain point creates a voltage difference between that point and the membrane a small distance away.
23
Q
what happens when the sensitive ending of the neurosensory cell is stimulated?
A
depolarisation of the membrane occurs, which spreads by a local circuit, until it reaches a region of the cell membrane populated by the voltage-gated Na+ channels
- If the depolarisation reaches a threshold value, the Na+ channels are opened, and an action potential is initiated
- The action potential propagates to the central nervous system (CNS).
- Because the initial depolarisation does not occur in a separate cell, it is sometimes called a generator potential.
24
Q
what are the are different biophysical causes for adaptation in different systems?
A
o E.g. it is a result of the methylation of receptor transducer proteins in bacterial chemosensitivity
o In animal G-protein systems it is a result of phosphorylation which occurs on the cytosolic C terminus
25
Why is the The refractory period of great importance in sensory signalling?
because it restricts the frequency at which impulses can travel down a sensory fibre - there can be no further action potentials while the Na+ gates remain closed.
26
How does the diameter of the nerve fibre determine the rate of impulse propagation?
- As the diameter increases, the local circuits can spread further along the axoplasm, and open Na+ gates further away from the active region.
- Some invertebrates such as annelid worms and cephalopod molluscs have developed giant fibres, which allow rapid conduction in emergency reactions.
27
What do taste buds consist of?
consist of several receptor cells with
specialized microvilli located in
taste pores
Microvilli detect dissolved chemicals, leading to the activation of receptor cells.
Taste buds are arranged in papillae
28
why is taste a gate-keeper?
Function: test food before ingestion
Perceived through taste buds in oral cavity
Chemical has to be water soluble
Basic ‘primary’ tastes in humans
29
What is a chemical stimulus?
```
Every chemical compound - extremely diverse
Inorganic
salts
Other ions, including metal
contact receptors - taste
Organic based on carbon
extremely diverse
communication
```
30
What are the Mechanisms of primary tastes?
Each taste cell has specific receptors in its microvilli
Bitter, sweet and umami have specific receptor proteins (GPCRS)
sour H+ ions block ion channels
salty Na+ ions through Na+ gated ion channels
31
what are Tasters, nontasters and supertasters?
Tasters and nontasters - 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
32
What are the two different olfactory systems in mammals?
All mammals have the standard main olfactory epithelium (MOE)
Receptor cells in the MOE connect to glomeruli in the main olfactory bulb (MOB)
Vomeronasal (Jacobson’s) organ is a second system
Mainly for pheromones
Oral cavity
Links to accessory olfactory bulb
Flehming
Ungulates, felids and other mammals
33
How is olfaction detected?
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
Glomeruli collect/sort responses from similar receptors
Axel 2005 (Nobel lecture)
34
What is Olfactory adaptation
Sense of smell (like other senses) is a change detector
Receptor adaptation: after continuous exposure to an odorant the receptors stop responding to the odorant and detection ceases (biochemical)
Example: Walking into a bakery and can only smell fresh bread for a few minutes.
Cognitive habituation: The psychological/neuronal process by which, after long-term exposure to an odorant, one is no longer able to detect that odorant
Example: Going away, coming back and noticing how your house smells
35
What are Qualities of chemical communication?
Directionality: In contrast to light and sound, direction of particle ≠ direction to source
Speed: very slow, milliseconds for sound, minutes to days for chemical stimuli
Temporal pattern: lost within a short distance from sender
Summary: not great, hence evolution of other senses
36
what is flavour?
combination of the sense of taste (mediated by the specialised taste receptor cells in the mouth), olfaction (olfactory input through the back way into your nose, via the mouth), and the somatosensory perception of the food or drink - what it feels like, or its consistency
37
what are the basic primary tastes in humans?
```
o Salty (organic salts, e.g. NaCl table salt)
o Sour (acids, e.g. vinegar)
o Sweet (carbohydrates and amino acids, e.g. glucose)
o Bitter (alkaloids, often poisonous, e.g. quinine)
o Umami "delicious" (amino acids, L-glutamate and aspartate)
o "Metallic" (status unclear)
```
38
What is electroreception?
"Electroreception is the biological ability to perceive natural electrical stimuli."
39
What is a dipole and do humans have one?
Equal but opposing charges e.g. a positive charge, with an opposing negative charge, separated in space.
Yes: Cell membranes are fantastic insulators : They separate charges on either side of the membrane, allowing electropotential gradients to form - which is the whole basis of receptor potentials, action potentials, and all neuronal activity.
40
What is electroreception used for ?
o Absence of sufficient light - can replace vision: if light absent animals have diff sensory modalities to find out (Animals often rely on electroreception when there is not enough light - it helps to replace vision)
Electroreception can be used for:
o Electrolocation (detecting, identifying and localising objects)
o Electrocommunication
41
What animals is electroreception found in?
Find electrolreception in:
o Nocturnal animals
o animals living in conditions with low visibility like murky waters and deep sea,
o can be used to penetrate into a substrate to find buried prey
o (find hidden prey buried under a substrate) E.g. hammerhead shark finds prey buried in the sand
42
What are the 2 types of electroreception?
a) Passive electroreception - e.g. in hammerhead sharks
o Pick up existing natural electrical stimuli
o Just electroreceptive sensors needed - The sensory equipment is all that is needed- they are only sensing electric fields from other organisms
b) Active electroreception. - generate a weak electrical signal: electrogenesis (creating your own electric field)
o Electroreceptive sensing organs are still needed to sense the electric fields
o But they also need an organ to create an electric signal
o These organisms generate, and then pick back up their electric signals with electroreceptive sensors
o They pick up changes in their self-generated electric fields, which occur by the presence or absence of objects in the field -
o E.g. Electric eel
o (This is a similar concept to echolocation, but with electric fields)
43
Who uses electroreception?
o Most non-teleosts
o Agnatha, Elasmobranchii, Holocephali, Chondrostei, Polypteri, Dipnoi
o Some teleosts:
o Siluriformes (catfishes)
o Gymnotiformes (knifefishes)
o Mormyriforms (elephant nose fishes)
o Xenomystinae (african knifefishes)
o Amphibian larvae
o Platypus & Echidnas (Pettigrew 1999)
o Guiana dolphin (Czech-Damal et al. 2012)
44
Receptor physiology - how the receptors work?
o Current flows into cell body following field lines
o Electroreceptor cells do not have their own axon, they make a synapse with an underlying sensory neuron
o If the membrane potential of the cell changes, it will be transmitted through the synapse, and be turned into action potentials in the afferent sensory fibre
o In electroreceptors, a change in the external field causes a change in the membrane potential
o There are leak channels in the bottom and the top of the cell, so any external charge following an electric field line can move freely through the cell
o By entering the cell, a charge causes the polarity of the cell inside to change E.g. if a negative charge is following an external field line, the cell becomes more negatively charged when it is inside, or less negatively (more positively) charged when it moves out of the cell again
o The receptor potential of the cell can therefore change (in response to current) because of this charges that are following external field lines
o So an external field induces a current through the cell í This changes the receptor potential of the cell --> Receptor connected with synapse to afferent fibre --> turned into action potentials by the afferent nerve fibre --> postsynaptic action potentials in afferent fibre
45
Electroreceptors in lampreys?
o Electroreceptive organs in the lamprey are grouped in epidermal end buds (3-30 sensor cells per end bud)
o Microvilli at the top of the receptor cells contain the leak channels, which allow the electric current to pass through
o Leak channels are essential for this mechanism to work, because the charges need to be able to flow through the cells
o Afferent fibres make synapses with the receptor cells underwater
46
Electroreceptor in Cartilaginous fishes (Chondrichthyes)?
The electroreceptive organs in a skate are in the form of lines of dark pores on the ventral side near the mouth
o Ampullae of Lorenzini
o mucus filled ducts, with an opening or pore to the external and a sensory receptor at the base
47
Electroreceptors in Teleost fishes (Teleostei)?
There are two types of electroreceptor organs in teleosts
1. Ampullary organs consist of
o A short duct which opens to the external of the body with ampulla at the base - where the receptor cells with their microvilli and leak channels are
o The receptor cells synapse with the nerve cells and relay the message to the CNS
o The duct here gives directionality to this receptor, similarly to the ampullae of Lorenzini in the skate
o Not common
2. Tuberous organs are the more common type of electroreceptor in teleosts
o plug instead of a duct
o The plug is made of loosely packed epidermal cells which are highly electrically conductive
o The plug channels the field lines down to the receptor cells, and again gives the structure directionality
o The sensory cells are covered in microvilli, and they synapse with an afferent nerve fibre
48
Electroreceptors in Platypus (Monotremata)?
o Modified mucous glands w/ free nerve endings.
o The mucus gland is in the dermis of the skin of the platypus
o A canal leads out to the exterior of the animal
o In its original use as a mucous gland, secretions would have been released on to the epidermis, they have been turned to a different modified use as an electroreceptor here
o They pick up any currents that pass down the mucus filled canal, again giving a certain level of directionality
o Nerve cells at the base relay impulses to the CNS
o These receptor cells have different evolutionary starting points, but always use the same principle - an electroreceptor and a guidance structure or channel for directionality.
o Every platypus has about 40,000 of these modified mucus glands, mostly on the bill in narrow stipes.
49
How do rays find roost?
o Orientation and navigation by electrolocation
o Experimenters trained rays to find one of two alternative 'roosts' - which were artificial dipoles created by electrodes
o Then they switched the dipoles (flipped them so they were opposite to what they had been before)
o The rays swap to the alternative roost that is in a different location but now has the same electric dipole as the original one they ere trained to recognize
--> Roost finding based on electric fields.
50
What is the basis of active electroreception?
This is the basis of active electroreception -
o The field line density is higher if there is a more conductive object in the field
o The field line density is lower if there is a more resistive object in the field
o The fish can compare the field lines around its own body before objects are there, and after they distorted the field lines,
o The fish can feel the differences in the electric field density (electric field strength) at those areas on its body, because its body is covered in electroreceptive organs specifically for this purpose
o So fish who want to do active electroreception, cover their bodies with electroreceptors and then wait for any changes to happen, which are indicative of something being there inside their electric field.
o Their whole body surface is the sensor
51
Electroreception in Knifefishes?
Active electrolocation - behaviour - Lanoo + Lanoo 1993
o Knifefishes
o Side searching behavior when looking for prey
o Leave their head in one place, and move their tail around in a sweeping motion
o If there is a prey item nearby, it will at some point come in close enough range to the searching tail of the fish that it is detected
o Once they have found a prey item, they switch to this reverse swimming behaviour
o The Daphnia in the diagram is in range to be detected
o The fish swims backwards, keeping it in range alongside their body
o When it is in front of their head (where they also have electroreceptors) they can eat it
o This is a very short-range system, but it is good enough for catching small planktonic prey like Daphnia which are very hard to detect otherwise
52
What is electrogenesis? (compare with electroreception)
The production of electricity (or the transfer of electrons) in the tissues of a living organism.
vs Electroreception simply means the ability to detect electrical currents.
53
Give examples of different kinds of electrogenesis uses and what is one of the problems+solution in one of the uses?
1. Electric organs in different positions
2. Evolved six times independently in fishes
í clearly a benefit and a strong evolutionary pressure
3. Strong electric fields (electric eel, catfish, torpedo ray, stargazer)
o For stunning prey, or in defense
4. Weak electroreception
o For prey localisation + communication
5. Problem
o These fish produce electric fields themselves via their neuron activity, action potentials, muscle activity - which interferes with their electroreception í noise by self generated fields
6. Solutions:
o Reduce muscle activity as much as possible
o Keep the body still - many move just by using a long undulating fin
o Move the electroreceptive organs away from the rest of their body where their own electric field is less strong
54
What are electrocyte cells?
o 'Batteries' in fish are electrocyte cells
o Electrocytes are modified cells derived from muscle cells or nerve cells + are under neuronal control.
In order to produce specific clicks, or sine wave functions, electrocyte discharges must be perfectly synchronized.
55
What are the 2 types of electrical discharge of electrogenesis?
There are two types of discharge that can be produced
1. Electric pulses -are one action potential, producing one single click
2. Wave type discharges are a series of clicks (many action potentials)
o This produces a sine wave function of sound - tonal sound
o The wave type discharge sounds like a constant tone with a certain pitch
(from Albert and Crampton 2005)
56
How do organisms make sure that the synapses to the electrocyte cells all arrive at the same time, despite their being different distances away?
o Nerves take detours to make them all the same length
o Axons with different propagation speeds E.g. thicker nerves carry signals faster
o Compensatory synaptic delay: At the synapse itself - some of the synapses have a delay before they respond to an action potential arriving
57
EOD (Electric Organ Discharge) Behaviour - pulse- & wave-type_ explain
Pulse electric discharge - elephant nose fish
o When the ball enters the water, the clicks increase
o This is typical scanning behavior
Waveform example - knifefish
o Constant tone
o Note the locomotion - it holds its body still and just uses the undulating motion of the ventral fin to move around
58
Explain the Jamming avoidance response (JAR)
o What happens if more than one fish is in the same area? - adding conspecifics
o Increase in pulse rate
o Change in wave frequency
o Aggressive behaviour
o Pulse type - elephant nose fish: Greatly increased clicking rate, Aggressive interaction
o Waveform - knifefish: They separating their pitches, and change the pitch - the tones resonate; Communicating - aggressive interaction
o Reasons for EOD changes in the presence of conspecifics
o Communication
o Potential jamming avoidance response JAR! - avoid their two signals jamming
59
Explain bioelectric crypsis and give an animal example
o Cuttlefish do not have electrolocation or electrogenesis capabilities
o But, they use a form of bioelectric camouflage to avoid being eaten by electrolocating sharks. (Sharks use electroreceptive organs on their head and nose to locate and catch their prey).
o Cuttlefish FREEZE when they sense sharks are in the area: switch off all muscle (reduces the amount of electrical activity in their tissues) and brain activity
o stop any electric field they are emitting, and this effectively hides them from the sharks electrolocation Electric camouflage!
o Prevents detection by electric signals
60
What are are the two types of mechanosensitive channel in e.coli? what are their structures? How do they open?
Large –conductance channels (MscL)• five subunits of a small two transmembrane protein , grouped around a central water filled pore
Small-conductance channels (MscS): larger, 3 transmembrane proteins, seven subunits around a pore
OPEN BY TWISTING IN RESPONSE TO STRETCH
61
how do stretch channels play a role in osmoregulation in bacteria?
* Fresh water (e.g rain) causes cells to swell - water molecules flow into the cell via osmosis
* This risks the cell bursting, so stretch channels open in response to the pressure of the expanding cell
* Solutes can then flow out, to counteract the osmotic stress by making the water concentration gradient less steep.
62
How is there mechanical continuity between the outer cuticle of c.elegans, the receptor in the membrane of the receptor neuron, and the microtubules inside the receptor neuron?
. Elegans has six touch receptor neurons in its body
• These are filled with bundles of microtubules.
• The touch receptor channels are found in the membrane of the touch receptor neurons.
• A linking protein joins the receptor channel to the microtubules inside the neuro
• Another linking protein joins the receptor channel to the cuticle of the worm
63
What are the types of invertebrate sensilla? why are they needed?
Insects and spiders have a hard chitinous exoskeleton
• Because the surface is not flexible, sensory endings develop internally in the muscles, or externally in the exoskeletal joints of the appendages
Hair (trochoid sensilla)
Campaniform sensilla
Scolopidia (in chordotonal organs)
64
What do sheath cells do? what insect sensilla are they involveD in?
Sheath cells secrete fluid and nutrients into sensilla sinus
Insect trichoid sensilla
Cuticular projection (projection of the cuticular)
• Containing one or more neurosensory cells (own axon – no synapse)
• Supporting sheath cells surround the neurosensory cell
o Innermost - thecogen cell
o Middle - tricogen cell
o Outer - tormogen cell
65
How does movement of the hair in an insect produce a response? how is this directional?
via trochoid sensilla:
Movement of the hair
• Stretches dendrite membrane
• Opens strectch activated ion channels
• This causes an influx of cations, which depolarises the membrane
Movement in one direction depolarises the membrane
• Movement in the opposite direction hyperpolarises the membrane
• This gives the sensilla directional sensitivity - important in detecting which direction body parts, air or substrate are moving in.
66
How are campaniform sensilla stimulated?
• Neurosensory cell lies under the dome
• The dendrite forms a tubular body in the cupola
• Deformations of the exoskeleton depress the dome, which compresses the tubular body.
• Compression of the tubular body results in a membrane depolarisation in the dendrite, and ultimately an action potential relaying the signal to the CNS via the axon.
Elliptical domes are most sensitive to compression along their short axis: These structures are therefore directional
67
what are Scolopodia? how are they activated?
stretch receptors of Chordotonal organs o Movements of internal structures move the attached cap cell, which mechanically deforms the dendrite and results in a depolarisation
68
what are Trichobothria?
• Hair sensilla of spiders (trichobothria) - one of the most sensitive mechanoreceptors known: very slender hairs found on the bodies of spider, especially on the legs, No more than 10 um diameter.
• Base of the hair is embedded in a specialised socket
Four neurosensory cells in the socket
o Dendrites of the neurosensory cells attach though an extremely thin (0.5 um) membrane
• The neurosensory cells are very sensitive to any movement of this membrane
69
Why can trichobothria detect low amounts of energy
o The amount of mechanical energy needed for a response in a spider trichobothria, is in only just higher than the energy we see in all particles due to their random motion and collisions with nearby particles (Brownian motion)
• They can detect movements of particles that are only just larger than those that occur due to random motions
70
How do whip slides use tricobothria?
prey detection, but for communication as well
• the first pair of legs are modified into sensory palps – they are are not used for walking
• These are the antenniform legs: • The vibrations that they use create particularly strong responses in the trichoborthria receptors on oponents walking leg joint
• They are using the excitation of these trichobothria to communicate
71
What are the two mechanoreceptors insects have for sound detection?
hair sensilla - near field sounds that are transmitted by air particles.(Johnston's organ, acoustic sensilla on the cerci, sensory hairs on the bodies of some moth caterpillars). AND tympanic organs which respond to sound pressure waves: far field sounds
72
what are some of the fast adapting mechanoreceptors of vertebrates? (Respond only during the initial pressure on the skin)
1. Hair follicle receptor (hair skin, sensory nerve endings: meshwork at base of folicle, respond to movement of the hair)
2. Pacinian corpuscles (non hairy + hairy skin), deeper layers of skin, small oval structures with connective tissue surrounding nerve fibre, slippage of layers creates pressure stimulus
3. Messner's corpuscle (non-hair skin, nerve endings surrounded by connective tissue capsule, connected to epithelium: mechanical linkage between skin + organ)
73
what are some slow adapting mechanical receptors in vertebrates? (Respond constantly throughout the displacement )
Merkel cells: Lie just beneath the epidermis, Large irregular nucleus, with microvilli projecting into the epidermal cells. . The sensory neuron at the base is expanded into a disk. Respond to sudden displacements of skin
Ruffini endings - in deep layers of the dermis - Network of fine sensory neuron endings in a connective tissue capsule - Sensory axon breaks into a network of fine endings - Respond to constant displacement of skin
both in hairy + non hair skin
74
How does Mechanical deformation of the stereocilia occurs due to vibrations and pressure changes caused by sound occur and lead to a response?
• Movement of the stereocilia opens K+ gated channels in the membrane
• K+ floods in, which results in a membrane depolarization
• Synapse with a sensory neuron
• The response depends on the direction that the stereocilium is moves
o Deflection toward the kinocilium results in a depolarisation by opening K+ channel
o Deflection away from the kinocilium results in a hyperpolarisation by closing K+ channels
• These are therefore directional receptors
75
what is a proposed model for the hair cell mechanics?
* Polypeptide links attach to ion channels
* The ion channels are attached to microfilaments in the stereocilia
* When the stereocilia are deflected by sound, the links between them pull open the ion channels (K+ in depolarisaton)
* But the ion channels slip down the membrane, because they are attached to the microfilaments inside the stereocilia
* This takes the tension from the polypeptide links off of the ion channels, and they close again
* The response stops
* When the sound stops, the stereocilia bend back to their resting position
* This again puts tension on the ion channels from the polypeptide links
* But the ion channels slip back up the membrane, because they are attached to the microtubules
* The tension is released again and the response ends
This could be why you get a response at the beginning and the end of the sound in a rapidly adapting system, but it falls to zero in the middle
76
What are fish otoliths? what do the do
hair cells in inner ear of fish
Ottoliths:
• Crystals of calcium carbonate ‘ear stones’
• Press down on on hair cells with gravity
• A system to detect linear acceleration of the head.
• Movement of head = movement of otoliths Bends hair cells with movement Information on acceleration and position of fish
• Otoliths are inside the inner ear
• They make contact with the hair cells
o When the head is moved forward or backwards or up or down, the movement of the otoliths presses on the stereocilia of the hair cells, and bends them in different directions depending on the movement
o When the head is stationary, gravity causes them to weigh down on the underlying hair cells.
77
what are particle detectors? What do they do?
hair-like structures and are found in arthropods: move when they are exposed to moving particles –the mass movements of particles that occur in the near field (close to the sound source
78
How are particle detectors able to discriminate frequencies and be very sensitive?
* Long hairs amplify any displacement, so they can be very sensitive to small displacements
* Long hairs oscillate with low frequencies, and small hairs oscillate with high frequencies, so they are able to discriminate frequencies
79
What are the two vectors than an incident sound wave is broken down into by particle detectors? Which is important for localisation of sound?
o Vertical component (force)
o Horizontal component (force)
o A vertical force on a hair will not displace it, but the horizontal component does –> it bend the hair over
• The displacement of the hair, and therefore the strength of the signal, depends on the angle that the incident sound wave is coming from
• Insects can therefore use the strength of the signal to work out where the sound has come from
80
What is the problem with localisation of sound by particle detectors? How is this overcome?
Direction confounded with loudness (if the sound is louder, it has more energy and displaces the hair more as well)
Solution:
• Insects overcome this by having many particle detectors or trichoid sensilla in different locations and angles on their body (many sensilla in different directions)
• The combined information disentangles differences that are due to direction from the overall loudness of the signal
81
What are tympani ears? (Pressure detectors are tympanal ears)
• Sensitive to the pressure component of sound, which can travel over much longer distances than the particle component– used for Far field sounds
• A tympanum is stretched over a closed cavity, with a sensory cell inside, coupled to the tympanum
• Incident sound wave pressure bends the tympanum: it moves in + out
The coupled sensory cell records the movements and converts them into neural impulses
82
How do mammals and small animals / insects overcome the fact there is no inherent directionality in pressure detectors?
Mammals use a directional pinna (external ear) – usally two
o The direction with the maximum received signal amplitude is likely to be the direction of the sound source
o Ridges and folds reflect sounds of different wavelengths
Two pressure detector ears can provide directional information
INSECTS/ SMALL ANIMALS use pressure differential detectors: sound wave can reach both sides of tympanum
o As long as the two sound waves are out of phase when they reach the tympanum, the tympanum will be bent towards the side with the lowest pressure.
o The tympanum is displaced when the pressure is different between the opposite sides
Directionality is related to the angle of incidence of the sound wave
83
how is the directionality of pressure differentially related to the angle of incidence of the sound wav?
o If a sound wave travels straight into one side of the tube, the force on the tympanum will be greatest, because sound reaches that side first
o If a sound wave arrives perpendicular to the tube, the force on the tympanum will be zero because the pressure that arrives at each side of the membrane is exactly the same – it has travelled the same distance down each side of the tube to arrive at the tympanum
84
What are the differences in ear structure between primitive jawless fish + jawed fish:
Jawed fish: 2 fluid filled chambers: semi circular canals at right angles + two others: UTRICULUS + SACCULUS which form the membranous labyrinth (The Laguna is an outgrowth of the sacculus which will eventually form the cochlea in higher vests)
Jawed fish: • An extra semi-circular canal in the membranous labyrinth of the inner ear
• three semi-circular canals set at right angles to each other. This structure is conserved in all of the jawed vertebrates
85
How can the swim bladder increase hearing sensitivity?
o In-between the inner ear and the swim bladder, the anterior vertebrae have been modified to form connecting bones called the Weberian ossicles.
o The Weberian ossicles connect the swim bladder to the sacculus of the membranous labyrinth, via two other chambers called the sinus impar and the endolymphatic canal
o Vibrations picked up by the air inside the swim bladder, are transmitted via the Weberian ossicles to the sacculus of the inner ear where they can be detected
o This amplifies the signal because air inside swim bladder is less dense to particles vibrate with greater amplitude than surrounding tissues or water
86
What is the structure of the ear in reptiles?
The lagena (on its way to becoming the cochlea) has become attached to the walls of the surrounding cavity so that three distinct canals are formed
• The middle canal is called the cochlear duct
• It has an underlying membrane called the basilar membrane with rows of hair cells lying on it (see lecture 5)
• The hair cells are covered by a gelatinous membrane called the tectorial membrane
• The tectorial membrane is key in detecting the vibrations due to sound
• The middle ear still has a columella to conduct vibrations from the tympanum to the membranous labyrinth of the inner ear.
The beginnings of an auditory meatus: the tympanic membrane is depressed beneath the body surface– so the entrance to the ear looks like a hole
It is not thought that reptiles can discriminate between frequencies.
87
What gives mammals excellent frequency of discrimination? What gives them sound localisation?
The organ of Corti.
| Localisation: large + highly moveable pinna
88
What happens when pressure waves (sound) impinge on the tympanic membrane?
the vibration is transmitted, via the auditory ossicles, to the oval window.
·The pressure changes are then transmitted into the fluid filled cochlea As the membrane covering the oval window moves inward, the pressure in the scala vestibuli ↑ and this vestibular membrane is forced downwards
—> This ↑ pressure in the scala media until this forces the basilar membrane to move downwards
—> ↑ pressure in the scala tympani & results in a bowing outwards another membrane called the round window. The pressure waves are therefore transmitted through the cochlea, and different frequencies are detected by the hair cells running the length of the basilar membrane
89
What are the two mechanisms responsible for frequency discrimination in the cochlea?
1. Volley theory: Cochlear nerve fibres phase lock to the sound frequencies
2. Place theory: The basilar membrane increases in width from the round window end to the apex of the cochlea (helicotrema)
90
What do fish + other aquatic organisms have a problem with in sound + hearing? How do they overcome this?
• Their body tissues are a very similar density to the surrounding water
• So they have a similar acoustic impedance to the water
• The sound energy is absorbed into their body well and not much is reflected as it passes from the water to the fish
• This means the entire body vibrates with the sound wave, leaving no differential movements of body parts to stimulate the sensory cells
Otoliths: The increased density of the otoliths compared to the surrounding tissues, increases the sensitivity by increasing the mechanical displacement of the stereocilia, and amplifying the response
91
What is seismic communication in fruogs?
an detect vibrations in the substrate
• They have an opercularis muscle in the shoulder
• This connects the skeleton of each shoulder to a thin cartilaginous disk called the operculum, which lies over the oval window of the inner ear on that same side of the body
• Vibrations in the substrate propagate up through the forelimbs, and travel through the opercularis muscle, to be conducted into the inner ear
Thought to be used in communication
92
How do owls improve sound localisation and signal intensity?
The feathered head is disc shaped to increase signal intensity and provide forward directionality in the horizontal plane
To improve sound localisation in the vertical plane some species of barn owl have one ear opening set above the median plane, and one set below
• This asymmetry generates intensity differences between the two ears, depending on the vertical location of the sound: creates intensity differences depending on vertical location of sound
• They can build up an accurate 3d map of sound sources in their brain
• Birds often have an air cavity joining their two middle ears – making their ears pressure differential detectors and increasing their localisation abilities
93
Why do marine mammals need dense capsules? What are they?
Tissues have similar acoustic impedance to water (little differential movement of parts tocreate s signal
• Cetaceans: Dense capsules surrounding inner and middle ear (simiar to tooth enamel).
o Each ear capsule suspsended in air cavity of foarm: air prodives acoustic isolation because it is less dense than other tissues.
o Acoustic isolation increases sensitivity as it allows sounds to be amplified
• Fatty tissue capsules instead of tympana
94
What is localisation blur? What does it refer to?
related to the just noticeable difference and the Weber-Fechner law
(Weight example : easy to tell the difference between 1 kg and 1.5 kg, but very difficult to tell the difference between 20 kg and 20.5kg
·The just noticeable difference in stimulus increases with the stimulus intensity (logarithmic relationship))
localisation blur refers to
• The smallest possible change of position of the sound source, that produces a just-noticeable change of position of the auditory event.
• The amount the position of the sound source has to be changed, to be recognised as a change by 50% of the experimental subjects (psychometric function curve)
95
Where do we most accurately localise sounds?
* We can localise sounds most accurately in the forward direction.
* The lower limit for the localisation blur is about 1⁰
* At 90⁰ to the direction that the subject is facing in, the localisation blur is about three to 10 times as big as for the forward direction.
* So we are not as good at localising sounds that come from the side
96
what were the results of an experiment on persistance?
When the switching speed of the speaker is slow, the subjects hear the noise coming from the appropriate places
• When the switching speed is increased, the subjects only hear the sounds oscillating between the left and right sides of their head
• When the switching speed is increased even further, the subjects just hear diffuse auditory event in the middle of their head.
The brain is only able to process changes in auditory events at a certain rate
Persistence is shorter when the sound source alternates from left to right than when it alternates from front to rear
97
why are the ridges and folds in the mammalian pinna important in sound localisation?
alter the sound waves as they enter the ear canal
• There are resonant frequencies associated with the human pinna – eigenfrequencies (Shaw and Teranishi, 1968)
• Turns spatial attributes of the sound into temporal and spectral attributes, which can be decoded by the brain into information on the location of the sound source
• Path lengths to the ear canal depend on the angle of incidence of the sound and the distance from the source
• Sound will enter the ear canal directly (red line) And also via different paths (blue line), where it is reflected off ridges in the pinna
* The difference between path lengths depends on the direction of incidence
* If the sound had arrived from a different location, the path lengths would have been different due being reflected off different folds and ridges
98
What are interaural transfer functions?
| how do these change with different angles from the source?
the differences between sound signals at the two ears
• When the incident angle is 0⁰ or 180⁰, there are no differences in sound signals between the two ears
• At other angles of incidence sound reaches the ear on the near side sooner, and is stronger.
• Differences in intensity between the two ears depend the distance of the sound source
• Differences in arrival time, or phase, between the two ears does not depend on distance.
99
How do interaural time differences change? What are they best for? why?
time differences vary depending on the frequency of the sound
Interaural time differences are best used for localising low frequencies
• For lower frequencies, phase delays between sound waves between the two ears are easily determined (unless the wavelength is so long that it just bends around the head)
• For high frequencies the differences in phase delays are more difficult to decode, - the phase differences are too small and many wavelengths fit in-between the ears
100
Why do broadband sounds contain more information?
* Broadband sounds comprise of different spectral components that are made up of different frequencies (and therefore wavelengths). They are much more common in nature than narrowband or pure tone signals.
* The different components will be out of phase by different amounts for a particular time delay. The auditory system has to be able to evaluate the different spectral components of a sound individually with respect to their interaural time differences. Our auditory system is very good at this.
* Broadband sounds that include a large range of different frequencies therefore provide more directional information based on the interaural time differences than a narrowband signal or a pure tone
101
why are some sounds hard to locate with interaural time differences? what is an example of this?
* Some signals don’t have a clear start and end point, they have a gradual and slow increase in amplitude and then a slow gradual decrease,
* It is very hard to judge when they actually started
* Some animals use this to their advantage to conceal the ITD cues from a predator
* Warning calls are often very difficult to find the starting point of – they have a slowly rising starting amplitude
102
How do Interaural intensity differences depend on the frequency of the sound?
an animals head is larger than the wavelength of the sound, the ear closer to the sound will receive sound at a higher intensity than the ear furthest away
• There is an acoustic shadow created by the head, which makes the sound much quieter on that side
• If the animals head is smaller than the wavelength of the sound, both ears will receive the same sound amplitude because the sound wave will just bend around the head and there is no acoustic shadow
• Interaural intensity differences work better for high frequency sounds because these have shorter wavelengths and produce more of an acoustic shadow
103
What is the compensation factor?
• The auditory event is presented to a subject via headphones, and is displaced from the median plane by a time difference
• The signal is then returned to the median plane by only changing the intensity differences
• This is called the compensation factor, or the trading ratio
o This compensation factor depends on the amplitude or loudness of the signal
104
What do trading curves show? How do they change?
Trading’ experiments can be used to compare time and intensity differences between the two ears – is there an equivalent time difference to compensate for a particular intensity difference?
• These trading curves show the value of the interaural intensity difference which equates to a particular interaural time difference, in terms of equivalent sound lateralisation
• These change with signal amplitude: when signals are louder a greater sound intensity difference is necessary to compensate for a given interaural time difference --> The trading curves become less steep as the signal gets louder
105
Why do broadband sounds give us more information on the location of a sound source than narrowband or pure tone signals?
* Low-frequency components of the sound are localized on the basis of interaural time differences (clearer differences in phase delay between the wavelengths at the two ears)
* High-frequency components are localized on the basis of interaural intensity differences (acoustic shadow created by the head).
use this combination of cues
106
what are Interaural spectral differences ? what do they give us? how is this so?
- differences in the frequency content of the sounds that enter the two ears
* Give mammals unambiguous cues about where a sound source is coming from
* The pinna, due to its ridges and folds, leads the sound towards the ear drum on more than one pathway
* The direct pathway where the sound enters the ear canal directly and hits the ear drum
* Other pathways by which the sounds are reflected off structural elements of the pinna and enter our ears via different routes
* These different routes result in small delays between components of a sound arriving at the ear drum
* Our brains have learnt to interpret these signals
* The difference between the path lengths of the incident sound components varies systematically with the direction of sound incidence This results in interference between the components
107
What happens when two sound waves are superimposed on top of each other?
they will interact with either positive or negative interference
• Positive interference amplify each other
• Negative interference cancel each other out completely
• The interference patterns are frequency dependent
• Depending on the frequency (/wavelength) of the sound waves, some will interfere positively and some will interfere negatively
108
What are the types of spectral notches?
* Interference notches - correspond to frequencies where negative interference occurs
* Interference notches vary depending on direction of sound incidence, in a predictable systematic way
• Multipath propagation in the pinna – more than one copy of every sound reaches our eardrum. Interference between these multiple copies creates direction specific spectral notches
109
how do the calls of passerine birds changed in presence of perched predators and airbourne predators?
• For perched predators, they make themselves conspicuous by mobbing behaviour which attracts other bird’s attention to the predator; For airborne predators they dash for cover and hide
Chaffinches give a ‘chink’ call for perched predators, which provides abundant locational cues: want the call to be easily locatable because they are trying to attract other chaffinches to the predator to mob it
For an airborne predator, chaffinches give a very different, thin ‘seeet’ call, which is difficult to locate
The call is narrowband, at a constant pitch and it does not contain sharp discontinuities: avoids giving location cues to predators, but still communicates the presence of danger to other chaffinches, which take cover.
110
what are the properties of light waves?
1. The wavelength – units of length – distance between the two peaks
2. The amplitude of the wave - how intense + how bright the light actually is
3. The speed of the wave (c) units of speed length / time
4. The frequency of the wave (f) – units 1/ time
111
How many types of eyes are there? what are the types?
TEN TYPES
1. Eight types of compound eyes:
a. 3x superposition types
b. 5 apposition types
2. Two other types – mirror type eye (molluscs, scallops) + other invertebrates (spiders, cephalopods) have simple (Camera type) eyes.
112
What is a superposition eye?
n insect eye in which all light rays except those entering the central facet of a group of facets are intercepted.
“Superposition eyes produce real, erect images on a retina separated from the optical elements by a clear zone. In refracting superposition eyes, the optical elements may be lens cylinders or corneal lens/lens cylinder combinations. These act as inverting telescopes. “
113
What is an aposition eye?
form multiple inverted images, form multiple inverted images, the brain, with each eye typically contributing a single point of information. The typical apposition eye has a lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium.”
114
what are three types of apposition eyes?
Apposition eyes
a) refracting type apposition eye: facet + crystal in cone: refracts the light + focuses it down on the photoreceptor below
b) multi-surface eye: different densities of materials within these structures + it’s the densities + surfaces on cells and thus the refractions that causes the light to be focused on the cell below
c) graded structure; found in horshoe crabs: the lines show the points at which the density of the material is exacly the same.
115
What is the structure of the crustacean fused rhabdom?
Within the ommatidia, all the microvilli + photoreceptor cells overlap.
1. The microvilli are interdigitated
2. Typically seven cells make up the rhabdom
3. Pigent around the cells screen light between ommatidium
116
3 different types of superposition eyes?
3 different types of superposition eues
1. Telescope – moths
2. Mirror – shrimps / crabs – the crystalline cone is empty: just swuae open box, sides are silvered with guanine crystals + reflect light all the way down to the bottom.
3. Lens / mirror: hermit crabs
