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Comparative animal physiology > sensory physiology > Flashcards

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
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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
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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
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4
Q

phototransduction cascade

A
  1. absorption of light shifts rhodopsin from cis to trans isomer
  2. activates G-protein transducin
  3. transducin activates cGMP phosphodiesterase
  4. cGMP broken down, can no longer activate Na+ channels
  5. Na+ channels close, photoreceptor is hyperpolarised
  6. neurotransmitter glutamate stops being released
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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
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6
Q

centre surround organisation

A

allows retinal ganglion cells to transmit information about contrast in the visual field

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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
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8
Q

amacrine cells

A

further tune responses from bipolar cells e.g. selectivity for movement

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9
Q

retinal ganglion cells

A
  • closest to light in cascade
  • different types with different properties
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10
Q

optics in very simple organisms

A

non directional photoreceptors in skin capture light intensity

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11
Q

pinhole eyes

A
  • shallow pits with photoreceptors in
  • allows comparison of light intensity in different directions
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12
Q

pinhole eye

A

small hole acts as a lens to focus light on retina and create a picture

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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
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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
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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
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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
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17
Q

how to organisms see colour

A

the relative balance of excitation and inhibition from photoreceptors with different photopigments

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18
Q

compound eyes

A
  • found in invertebrates
  • contains hundreds/thousands of ommatidia
  • optimised for temporal over spatial acuity
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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
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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
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21
Q

rhabdom

A

contain rhabdomeres with microvili that contain photopigments

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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
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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
Q

sensory transduction

A

the way in which a sensory neuron gets excited by stimuli

26
Q

classification of sensory receptors by structure

A
  • 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
Q

mechanoreceptive hairs in vertebrates

A
  • have stereocilia
  • synapse to sensory hair
  • when stereocilia are mechanically deflected, protein bridges between them open ion channels, exciting the hair cell
28
Q

lateral line system in fish and amphibians

A
  • ‘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
Q

semicircular canals - vertebrate inner ear

A
  • 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
Q

otolith organs - vertebrate inner ear

A
  • 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
31
Q

otolith organs in lower vertebrates

A
  • e.g. fish, amphibians
  • also detect sound and vibration as they don’t have cochlea
32
Q

weberian apparatus

A
  • in some fish
  • transfers vibration from swim bladder to inner ear
33
Q

mechanoreceptive hairs in arthropods

A
  • suspended in socket
  • vibrates and tugs on end of sensory neuron, opening ion channels
34
Q

statocysts (arthropods)

A
  • 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
Q

outer ear - terrestrial vertebrates

A
  • external pinna and auditory canal
  • collects sound waves and channels them into the middle ear, which converts them into fluid vibrations
36
Q

middle ear - terrestrial vertebrates

A
  • 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
Q

ossicles

A
  • 3 small bones in middle ear
  • malleus (hammer)
  • incus (anvil)
  • stapes (stirrups)
38
Q

inner ear - terrestrial invertebrates

A
  • semicircular canals
  • cochlea (only mammals have true cochlea, birds and crocodilians have a straight cochlear duct)
39
Q

cochlear

A
  • vestibular and tympanic canal contain endolymph fluid
  • organ of corti = basiliar membrane between vestibular and tympanic canal and tympanic membrane
40
Q

basiliar membrane

A
  • 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
Q

organ of corti

A
  • 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
Q

arthropod ‘ears’

A
  • filliform sensilla (hairs) on body detect particle movement in surroundings
  • different to vertebrate ears that detect pressure waves
43
Q

tympanic ears

A
  • 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
44
Q

Olifaction

A
  • smell
  • long range chemoreception
  • chemical stimulus = odorant
45
Q

olifaction in vertebrates

A
  • receptor cells are olifactory neurons containing cilia, short lifespan (months)
  • odorant molecule dissolved in mucus
46
Q

olifactory transduction cascade

A
  • odorant receptor protein embedded in membrane of neuron (many receptor types)
  • involves a G protein and second messenger
47
Q

gustation

A
  • taste
  • close range/contact chemoreception
  • chemical stimulus = tastant
48
Q

gustation in vertebrates

A
  • specialised epithelial receptor cells (lifespan ~10 days) containing microvili that project into taste pore
  • basal cells in taste pore generate receptor cells
49
Q

salt and sour tastants

A
  • 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
Q

sweet, bitter and umami tastants

A
  • specialised receptors activate G proteins (G protein coupled receptors)
  • influence ion channels via second messengers
51
Q

olifaction and gustation in insects

A
  • fluid filled sensilla with chemoreceptors at base (bypasses exoskeleton cuticle)
  • gustatory hairs have a terminal pore
  • olifactory hairs are porous along length
52
Q

electroreception

A
  • 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
Q

examples of organisms that use eklectroreception

A
  • 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
Q

magnetoreception

A
  • 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
55
Q
A

Comparative animal physiology (8 decks)

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