1
Q
List the components of photoreceptors
A
- vertebrate rods and cones –> light hyperpolarises
- ciliary line –> the photoreceptive part of the cell derived from a modified cilium - Invertebrate retinula cells –> light depolarises
- rhabdomere line –> the photoreceptive membranes derived from the cell body
2
Q
Describe the processes that occur during vertebrate phototransduction when it is dark
A
- Na+ and Ca2+ ion channels kept open by high levels of cGMP
- photoreceptor is depolarised increasing transmitter release but these receptors do not produce APs
3
Q
Describe the processes that occur during vertebrate phototransduction when it is light
A
- light activates transducin to break down cGMP into GMP
- ion channels close hyperpolarising the cell and reducing transmitter release
4
Q
Describe visual processing in lower vertebrates
A
- reptiles, amphibians and fish have small rudimentary forebrains
- no visual processing in forebrain - take place in the visual part of the midbrain (optic tectum)
5
Q
Describe avian vision and behaviour
A
- foveal base acts to create a telephoto system
- when birds dives the head faces forward but the visual axis is at an angle
- due to this they fly along a curved path to keep prey image in the medial fovea
6
Q
Describe the processes that occur during invertebrate phototransduction when it is light
A
- light activates phospholipase C to break down PIP2 to IP3 and DAG
- this opens ion channels in the membrane causing the photoreceptor to depolarise but there are no APs
7
Q
Describe the photoreceptors present in invertebrates
A
marine worm and flat worm
- rhabdome
- pigment cell
box jelly fish
- ‘cornea’
- pigment cell
- rhabdome
- pigment granules
8
Q
What are compound eyes?
A
- present in insects and crustacea
- made up of photoreceptor units each with its own lens
- bulbous shape can provide nearly all round vision
- receptor units in different parts of the eye can have different properties
- first appeared in the pre-cambrian anomalocaris
9
Q
Describe the visual system in flies
A
- use polarised light for navigation and colour vision to find flowers
- the visual system is tuned to recognise such features as movement, looming, visual field slippage
10
Q
What are simple eyes (ocelli)?
A
- present in spiders and insects
- smaller than compound eyes
- many receptors under a single lens
- insects with compound eyes usually have 3 simple eyes arranged in a triangular position
- when flying, these eyes act as a horizon path detector to maintain a stable flight path
11
Q
Describe the cuttle fish visual subterfuge
A
- male displays to female to encourage her to mate
- side of body facing her shows male patterning
- could attract rival mates who would try to compete
- so other side of body shows female patterning
12
Q
Describe how infra-red vision in snakes works
A
- only works because snake body temp is much lower than mammalian prey so the receptor is kept cool
- part of the somatosensory system and does not receive signals from the eyes
- the infrared vision of the pit organ maps onto the optic tectum so that the two types of information are superimposed
- the trigeminal nerve is the main sensory nerve to the face
13
Q
How do we detect sound?
A
sound is detected because it sets up vibrations in the eardrum (tympanic membrane) and amplified by the movement of the ear ossicles in the middle ear
14
Q
Describe the features of the organ of corti (the hearing organ)
A
- tectorial membrane
- hair cells
- basilar membrane
- nerve cells (spiral ganglion)
15
Q
What is tonotopy?
A
- because how far the travelling wave travels depends on frequency, there is a tonopic relationship (position codes frequency) that is seen throughout all the auditory pathways
- tonotopy is maintained all the way to the brain
16
Q
Describe how insects hear
A
- the ‘ear’ (tympanum) is in the leg
- the tympanum plays the same role as the eardrum in vertebrates that vibrates more than the normal cuticle
- crista acoustica, auditory neurone
17
Q
Describe how bats utilise ultrasound pulses
A
- bats use echolocating calls for navigation and catching prey
- call frequencies are typically 25-100kHz
- when hunting they can detect insect wing movements as well as judging how far away they are
- moths use auditory systems to detect predators
18
Q
Describe the hearing organ of a mosquito (johnston’s organ)
A
- only male mosquitos use hearing to detect females
- airborne vibrations detected by the entire antenna –> detected by the jonston’s organ at the base of the antenna
- active processes in the sensory neurone amplify the signal
19
Q
List the five types of taste sensation
A
- sweet
- salt
- bitter
- sour (acid)
- umami (glutamate)
20
Q
Describe the sensory transduction for salt and acid
A
- taste cells for salt and acid have channels for Na+ and H+ ions
- they depolarise the cell, opening Ca2+ channels, causing transmitter release
21
Q
Describe the sensory transduction for bitter, sweet and umami
A
- have a G-protein coupled receptor that bind to molecules causing ion channels to open, triggering transmitter release
22
Q
Describe olfactory transduction
A
- binding of odour molecules causes a G protein subunit to stimulate adenylyl cyclase
- increases levels of cAMP which opens ion channels in the cell membrane causing it depolarise which causes an AP
23
Q
Describe olfaction in invertebrates
A
- simple system in which ion channel is opened by binding an odour molecule
- chemosensory receptor molecules lie on outer membranes of cilia
24
Q
Describe the structure of a bee brain
A
- sensory integration centres (mushroom bodies)
- contain glomeruli
25
Describe the features present in skin sensation
naked ending - pain, temp
hair follicle ending - hair movement
merkel's endings - sustained pressure, mapping of texture and shape
meissner's ending - touch
paicinian corpuscle - vibration
ruffini ending - shear stress
26
What are proprioceptors?
Receptors monitoring muscles and joints
- muscle spindles
- golgi tendon organs
- joint receptors
27
Describe how muscle spindles work
- when the muscle is stretched, the sensory axon in the spindle responds
- when the signal reaches the spinal cord, the alpha motorneurons contract the muscle
- so gamma motor neurons fire and the spindle contracts, restoring its responsiveness
28
What are golgi tendon organs?
- monitor stretch in tendons
- responsible for our awareness of the relative positions of different parts of the body
29
What are joint receptors?
these endings in the capuscle and the supporting ligaments of joints give sensations of pain and discomfort when the joint is moved beyond its range of normal movement
30
Describe the role of touch/wind sensitive hairs in invertebrates
- mediated by mechanosensory hairs
- important in maintaining flight movements
31
Describe proprioreceptors in insects and crustacea
- as the fumur rotates upwards, its surface contacts the hair plate on the coxa indicating that it can travel no further
- campaniform sensillae - depressions with a floor of very thin cuticle which monitor distortion of the insect skeleton
32
What is the chordontal organ?
- lies inside the exoskeleton and is a stretch receptor
- when the joint is flexed, different sensory neurons detect the position of the joint and speed of the movement
33
What is the muscle receptor organ?
- present in crustaceans
- formed from small accessory muscles that are supplied by the same nerve cells that control the power muscles
- analogous to the muscle spindle
- monitors tail flips used for escape
34
What are the ampullae of lorenzini?
- found on sharks and rays - detect electric fields associated with muscle activity in potential prey species
- also detect temp
- sensory nerve endings lie at base of pit filled with conductive gel
- prey can be detected even when not visible
35
Describe how fish communicate by electric signals
- electric fields generated by modified muscle cells
- electric receptors generally very similar to ampullae of lorenzini
- producing electric discharge is energetically expensive
- can be detected by some predators
- signal amplitude therefore kept low except during feeding and social interaction
36
Describe the 3 possible theories to explain how birds can detect magnetic fields
1. electroreceptors activated by moving through a magnetic field - birds dont seem to have these
2. detection based on magnetic metal crystals if they were present in nerve cells - magnetite granules present around beak but not in neurones
3. magnetic sense linked to vision as is only present when birds are under full spectrum white light - current favoured theory is that the magnetic field alters the spin state if high energy electrons generated when photopigments absorb light energy
Structure and function of living organisms
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