sensory physiology Flashcards
1
Q
accommodation of vertebrate camera eye
A
- adjustment of lens for near or far vision
- near vision = ciliary muscle contracts, slack suspensory ligaments, more spherical and refractive lens
- far vision = relaxed ciliary muscles, taught suspensory ligaments, flat and weakly refractive lens
2
Q
photoreceptors
A
- rods = more sensitive, widely distributed, low light vision (black and white_
- cones = 3 kinds, short (blue), medium (green) and long (red) wavelength
3
Q
rhodopsin
A
- visual pigment in rods
- embedded in membraneous discs
- contains retinal (vitamin A derivative) and opsin (protein) and a G-protein coupled receptor activated by light
4
Q
phototransduction cascade
A
- absorption of light shifts rhodopsin from cis to trans isomer
- activates G-protein transducin
- transducin activates cGMP phosphodiesterase
- cGMP broken down, can no longer activate Na+ channels
- Na+ channels close, photoreceptor is hyperpolarised
- neurotransmitter glutamate stops being released
5
Q
bipolar cells
A
- sit behind photoreceptors
- have excitatory or inhibitory receptors for glutamate (light)
- form processing cells, light on and light off channels
- indicate increases and decreases in light intensity
6
Q
centre surround organisation
A
- allows retinal ganglion cells to transmit information about contrast in the visual field
- bipolar cells are excited by photoreceptors in middle more than photoreceptors on outside
- sensitive to edges, picks out features from image
7
Q
horizontal cells
A
- connect neighbouring locations in retina
- can be excited by light in receptive field but inhibited by light from edges, creating contrast
8
Q
amacrine cells
A
further tune responses from bipolar cells e.g. selectivity for movement
9
Q
retinal ganglion cells
A
- closest to light in cascade
- different types with different properties
10
Q
optics in very simple organisms
A
non directional photoreceptors in skin capture light intensity
11
Q
shallow pit eyes
A
- shallow pits with photoreceptors in
- allows comparison of light intensity in different directions
12
Q
pinhole eye
A
small hole acts as a lens to focus light on retina and create a picture
13
Q
examples of eyes with refracting lens
A
- vertebrate camera eye
- eye with many lenses in series, often seen in aquatic organisms to cope with refraction
14
Q
example of convergent evolution in camera eyes
A
- fish have photoreceptors at back of eye
- octopus have photoreceptors at front of eye
- both achieve focus by moving the position of the lend instead of changing its shape
15
Q
diversity in number of photopigments
A
- most mammals are dichromats (2 photopigments, no long wave photoreceptor for red)
- humans (and some old world primates) are trichromats (S,M,L)
- reptiles and birds are tetrochromats (5)
- many organisms have a UV sensitive pigment
16
Q
why have mammals lost cone photoreceptors over time
A
- cones are useful in high light conditions
- many mammals became nocturnal/crepuscular in Jurassic period, so was no longer needed
17
Q
how to organisms see colour
A
the relative balance of excitation and inhibition from photoreceptors with different photopigments
18
Q
compound eyes
A
- found in invertebrates
- contains hundreds/thousands of ommatidia
- optimised for temporal over spatial acuity
19
Q
compound eyes - ommatidia
A
- division of compound eye with its own light focusing lens
- each captures light from small portion of visual field - makes up pixels
- light is focused through the lens on to the rhabdom and photopigments are stimulated
20
Q
compound eyes - temporal over spatial acuity
A
- optimised for seeing details in time
- invertebrates have high critical fusion frequencies as they have many lenses
- smaller lenses mean more defraction, so low spatial resolution
21
Q
rhabdom
A
contain rhabdomeres with microvili that contain photopigments
22
Q
enhancement and further processing of images in invertebrates
A
- occurs in optic lobe in brain (rather than in the retina like in vertebrates)
- contain neuropils where there are synapses between neurons; lamina, medulla and lobular
23
Q
classification of sensory receptors by role
A
- exteroreceptors monitor external environment
- interoreceptors monitor internal environment
- proprioreceptors monitor movement and position of limbs and body parts in space
24
Q
how a receptor responds to constant stimulation
A
- many slow down rate of action potentials
- phasic (quickly) at receptors where a change in stimulus is what is important e.g. touch/pressure
- tonic (slowly) at receptors where constant stimulus is what is important e.g. pain, position
25
sensory transduction
the way in which a sensory neuron gets excited by stimuli
26
classification of sensory receptors by structure
- special senses have specialised receptors in head e.g. taste, smell vision, hearing, equilibrium
- general senses have simple receptors, e.g. somatic sensations (skin), visceral sensations (organs)
27
mechanoreceptive hairs in vertebrates
- have stereocilia
- synapse to sensory hair
- when stereocilia are mechanically deflected, protein bridges between them open ion channels, exciting the hair cell
28
lateral line system in fish and amphibians
- 'pits' or 'canal' along each side of organism with stereocilia embedded in gelatinous culpula (neuromast)
- detects vibration, movement and pressure gradients in surrounding water
- surrounding water moves into lateral line system, diverting culpula and therefore depolarising hair cells
29
semicircular canals - vertebrate inner ear
- evolution of lateral line system, detects rotation and angular acceleration
- stereocilia embedded in gelatinous cupula at base of canals, surrounded by endolymph fluid
- endolymph fluid moves as head rotates/accelerates, cupula bends in opposite direction
30
otolith organs - vertebrate inner ear
- utricle and saccule
- detects position with respect to gravity
- heavy calcium carbonate otoliths on top of gelatinous layer move in direction bend gelatinous layer downwards, bending sterecilia
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otolith organs in lower vertebrates
- e.g. fish, amphibians
- also detect sound and vibration as they don't have cochlea
32
weberian apparatus
- in some fish
- transfers vibration from swim bladder to inner ear
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mechanoreceptive hairs in arthropods
- suspended in socket
- vibrates and tugs on end of sensory neuron, opening ion channels
34
statocysts (arthropods)
- detects position with respect to gravity and acceleration
- statolith (concretion of calcium and sand grains) surrounded by ciliated receptor cells
- statolith excites different sensory hairs in statocyst depending on position
35
outer ear - terrestrial vertebrates
- external pinna and auditory canal
- collects sound waves and channels them into the middle ear, which converts them into fluid vibrations
36
middle ear - terrestrial vertebrates
- tympanic membrane (eardrum) separates outer from middle ear
- ossicles mechanically amplifies sound waves and transmits through vibrations
- oval window (membrane beneath stapes) increases pressure
- eustachian tube equalises pressure (connects to pharynx)
37
ossicles
- 3 small bones in middle ear
- malleus (hammer)
- incus (anvil)
- stapes (stirrups)
38
inner ear - terrestrial invertebrates
- semicircular canals
- cochlea (only mammals have true cochlea, birds and crocodilians have a straight cochlear duct)
39
cochlear
- vestibular and tympanic canal contain endolymph fluid
- organ of corti = basiliar membrane between vestibular and tympanic canal and tympanic membrane
40
basiliar membrane
- different regions vibrate maximally at different frequencies, separating sound into high and low frequencies
- end nearest round window is narrow and stiff, vibrating best at high frequencies
- other end is wide and flexible, vibrating best at low frequencies
41
organ of corti
- stereocilia embedded in tectorial membrane bend when basiliar membrane oscillate, depolarising the hair cells
- depolarisation of hair cells increases rate of neurotransmitter release, triggering the excitation of sensory neurons in the auditory nerve
42
arthropod 'ears'
- filliform sensilla (hairs) on body detect particle movement in surroundings
- different to vertebrate ears that detect pressure waves
43
tympanic ears
- present in some insects e.g. crickets, on front legs to detect direction of mating calls
- vibration sensitive membranes over air sacs
- sensory cells directly couples to tympanic membrane
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Olifaction
- smell
- long range chemoreception
- chemical stimulus = odorant
45
olifaction in vertebrates
- receptor cells are olifactory neurons containing cilia, short lifespan (months)
- odorant molecule dissolved in mucus
46
olifactory transduction cascade
- odorant receptor protein embedded in membrane of neuron (many receptor types)
- involves a G protein and second messenger
47
gustation
- taste
- close range/contact chemoreception
- chemical stimulus = tastant
48
gustation in vertebrates
- specialised epithelial receptor cells (lifespan ~10 days) containing microvili that project into taste pore
- basal cells in taste pore generate receptor cells
49
salt and sour tastants
- dissolve in saliva and directly interact with ion channels
- salt tastants are positively charged ions e.g. Na+
- sour tastants are H+
- pass into cell through amiloride-sensitive cation channels, initiating depolarisation
- H+ can also cause K+ leakage channels to close
50
sweet, bitter and umami tastants
- specialised receptors activate G proteins (G protein coupled receptors)
- influence ion channels via second messengers
51
olifaction and gustation in insects
- fluid filled sensilla with chemoreceptors at base (bypasses exoskeleton cuticle)
- gustatory hairs have a terminal pore
- olifactory hairs are porous along length
52
electroreception
- sensitivity to electrical field in medium around organism
- relies on modified neuromasts of lateral line system
- ampullary and tuberous electroreceptor types
- apical membrane has low electrical resistance, voltage changes in medium around animal able to directly affect cell
- basal membrane has high resistance, potential drop across membrane triggers depolarisation, releasing neurotransmitters
53
examples of organisms that use eklectroreception
- some sharks can pick up electrical information from prey muscle contraction
- some fish have modified muscle cells forming an electric organ that produces an electric field for monitoring external environment and communication
54
magnetoreception
- ability to detect magnetic field
- magnetic fields may be able to interfere with photoreceptors in organisms such as pigeons that use magnetic field for navigation because of deposits of magnetite in their sensory neurons
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