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Brain Function and Malfunction > Sensory systems > Flashcards

Sensory systems Flashcards

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1
Q

What are sensory systems for?

A

awareness of environment
protection of harm
conscious control

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2
Q

What are exteroreceptors used for?

A

receptors for external stimuli

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3
Q

examples of exteroreceptors

A

photoreceptors, hair cells, olfactory receptors, skin receptors eg mechanoreceptors
taste receptors

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4
Q

proprioceptors

A

muscle reflexes and body position

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5
Q

central organisation of senses

A

project to cerebellum with branch to cortex via thalamus

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6
Q

what projection does not pass through thalamus before cortical area?

A

olfactory

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7
Q

perceptual threshold

A

brain decides what is necessary to fully perceive eg selective hearing

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8
Q

meissners corpuscles

A

sensitive touch/tapping

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9
Q

ruffinis corpuscles

A

touch and pressure

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10
Q

merkels discs

A

touch

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11
Q

pacinian corpuscle - where are they found?

A

subcut tissue in palms of hands and soles of feet, genitals, GIT

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12
Q

pascinian corpuscles respond to?

A

vibration or tickle

rapidly acting mechanoreceptors

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13
Q

how do pascinian corpuscles work?

A

Compression of the intricate sheath of concentric connective tissue lamellae triggers the single nerve ending in the clear central space of the receptor organ

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14
Q

tonic receptors

A

slowly adapting receptors respond for duration of stimulus

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15
Q

phasic receptors

A

rapidly act to a constant stimulus and turn off

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16
Q

meissners corpuscles are found where?

A

subepidermal location in hands, feet, forearm, tip of tongue

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17
Q

where are merkel cells found?

A

basal layer of the skin

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18
Q

what are merkel cells?

A

free nerve endings that terminate in discs

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19
Q

what are merkel cells associated with in most mammals?

A

whiskers

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20
Q

hair root nerve endings

A

rapidly adapting a delta fibres

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21
Q

where are thermoreceptors found?

A

throughout epidermis

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22
Q

cold receptors

A

excited by fall in temp

myelinated fibres

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23
Q

warm receptors

A

excited by rise in temp
unmyelinated fibres
fire constantly and indefinitely

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24
Q

what determines size of receptive field?

A

2 point discrimination

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25
Q

explain receptive fields

A

sensitive regions - primary neurons synapse on distinct secondary neurons

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26
Q

nociceptors

A

all skin layers, small receptive fields, myelinated A delta or unmyelinated c fibres

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27
Q

Cranial nerves for gustation

A

7, 9, 10

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28
Q

5 tastes

A

umami, sweet, salt, bitter, sour

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29
Q

T1R

A

sweet

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30
Q

T2R

A

bitter

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31
Q

t-mGluR4

A

umami receptor, glutamate

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32
Q

receptor for salt

A

ENac

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33
Q

what are T1R, T2R and mGluR-4?

A

7 pass transmembrane receptors

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34
Q

diversity of receptor family

A

amino acid sequence and heterodimers

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35
Q

3 types of papillae

A

circumvalate, follate and fungiform

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36
Q

taste receptor distribution

A

taste buds found on 3 different types of papillae

taste receptor cells within taste buds differentially express taste receptors - taste fields

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37
Q

taste transduction

A

ultimately leads to neurotransmitter release due to the increase in cAmp and calcium

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38
Q

what do cranial nerves innervate - taste

A

pontine parabrachial nucleus and nucleus of solitary tract in brainstem

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39
Q

further projections from brainstem - taste

A

thalamus, cortex - orbitofrontal and gustatory - amygdala and hypothalamus
input from somatosensory and visceral systems

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40
Q

where do odorant molecules dissolve?

A

mucous lining olfactory epithelium

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41
Q

what receptors do odorant molecules activate?

A

cilia of ORN

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42
Q

What does activation of an ORN lead to?

A

depolarisation propagated to glomeruli within olfactory bulb

postsynaptic mitral cells relay signal to olfactory cortex

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43
Q

Odorant signal transduction

A

bind receptors, G protein activation of adenylate cyclase, cAMP, calcium, sodium influx. Let chloride channels out

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44
Q

feedback system of odorant signalling

A

calcium binds calmodulin reducing affinity for calcium channel for cAMP
activate CAM kinase phosphorylate adenylate cyclase
reduce cAMP
sodium/calcium exchanger
chloride return to normal

45
Q

Where do like ORNs converge?

A

on same glomerulus

46
Q

how can lateral inhibiton of smell occur?

A

neighbour mitral cells and glomeruli through periglomerular and granule cells

47
Q

what allows directional sensitivity of smell?

A

bidirectional input from olfactory epithelium to olfactory cortex

48
Q

sharpening odor code

A

most strongly activated glomeruli, activate mitral cells, activate postsynaptic neurons in olfactory cortex - fire preferrentially

49
Q

the competition model - smell

A

plasticity - activated odorant circuits compete out inactive ones

50
Q

example of competition model

A

mice deficient of calcium channel in some ORNs
still project to glomeruli
stimulate with odorant, only normal neurons function
60 days - inactive eliminated if odorant present

51
Q

ossicles

A

malleus, incus and stapes

52
Q

noise conduction

A

tympanic membrane
vibrate ossicles
stapes on oval window
fluid of cochlea

53
Q

round window

A

vibration of membrane cushions and dampens fluid movement within cochlea

54
Q

3 canals of cochlea

A

vestibular, middle and tympanic canal

55
Q

membrane between vestibular and tympanic canal

A

basilar

56
Q

basilar membrane - ends and pitches

A

thick apical end - low pitch

thin basal end - high pitch

57
Q

what happens due to movement of basilar membrane?

A

displacement of organ or corti

58
Q

what is organ of corti comprised of?

A

sensory hair cells and supporting cells

auditory nerve endings of hair cells

59
Q

what part of organ of corti is in contact with tectorial membrane?

A

stereocilia of hair cells

60
Q

how many rows of stereocilia on hair cells in organ of corti?

A

3 of progressively increasing length

61
Q

firing of auditory nerve endings due to what?

A

movement of stereocilia relative to tectorial membrane, firing increased or decreased depending on direction of movement of stereocilia

62
Q

What cells support hair cells in organ of corti?

A

deiter cells at apical and basal ends

perilymph

63
Q

what part of hair cells in endolymph?

A

stereocilia within tectorial membrane

64
Q

how each is each cilium connected?

A

tip link - filamentous link bounded by myosin at each end

65
Q

Displacement of stereocilia - what happens next?

A

create force through myosin heads at ends of tip link
opns mechano-electrical transduction channel
transient, calcium
change in cell length occurs - flexion of membrane/force in lateral membrane

66
Q

Prestin

A

maintain cell length

67
Q

example of prestin - mice

A

Deficient - gene has 2 alleles so got intermediate length of cells

68
Q

what shape do sterocilia make?

A

V

69
Q

Do hair cells depolarise?

A

no

70
Q

what does influx of calcium lead to? hearing

A

NT release from vesicles at presynpatic membrane

ion channels postsynpatic open and depolarise cell - action potential

71
Q

what are NT vesicles in hair cell attached to?

A

electron dense body called synaptic ribbon

72
Q

3 semicircular canals and motions they detect

A

anterior - nodding
lateral - sideways shake
posterior - head tilt

73
Q

where are hair cells found in vestibular apparatus?

A

swellings called maculae

ampulla

74
Q

name of ampullar organs contain hair cells

A

cristae

75
Q

what do hairs in cristae detect?

A

rotation of head

76
Q

what do hairs in maculla detect?

A

linear movement and head position

77
Q

what are hair cells of crista engulfed by?

A

gelatinous cupula

78
Q

fluid - crista and macula

A

cristae - perilymph

macula - endolymph

79
Q

crista - displacement of cells and firing

A

hairs moved by perilymph - firing of hair cells in one direction, opposite direction decreased firing

80
Q

layer of crystals in maculae

A

otoliths on surface of endolymph

81
Q

movement of otoliths

A

crystals move under gravity

82
Q

Conductive deafness causes

A

ear wax, blocked eustachian tube, otitis, otosclerosis

83
Q

treating otosclerosis

A

stapedectomy or fenestration

84
Q

sensironeural deafness - root cause

A

hair cell damage in organ of corti

85
Q

causes of sensironeural deafness

A

menieres disease - increased endolymph

ageing, infection, trauma

86
Q

do hair cells regenerate in mammals - hearing?

A

no, but do in birds

87
Q

regenerating hair cells in birds

A

hair cells excluded onto apical surface

surrounding cells resume stem cell like behaviour

88
Q

nerve deafness

A

damage to auditory nerve

atherosclerosis, lesion

89
Q

tinnitus

A

ringing in ears caused by degeneration of organ of corti

90
Q

hereditary deafness

A

congenital, slowly progressing, adult onset

100 mutant genes known

91
Q

genes responsible for more than 50% severe AR nonsyndromic deafness

A

GJB2 GJB6

92
Q

near vision lens

A

ciliary muscles contract and lens round up

93
Q

point of greatest visual acuity - high concentration of?

A

fovea - cones

94
Q

lens to correct short and long sighted

A

short sighted - concave

long sighted - convex

95
Q

photoreceptor cells

A

rods and cones

96
Q

what lines the rods and cones?

A

pigmented epithelium

97
Q

role of RPE

A

absorb excess light

98
Q

activation of photoreceptors…

A

release of pigment

depolarisation of bipolar cells

99
Q

what do bipolar cells activate?

A

RGC

100
Q

where do RGC axons converge?

A

ONH

101
Q

rods pigment

A

rhodopsin

102
Q

cones pigments

A

red, blue or green

103
Q

converge of signal - sight

A

many receptors synapsing onto bipolar cells

lateral inhibition by horizontal cells

104
Q

rhodopsin in darkness

A

inactive, cGMP is high and ion channels open
membrane potenital -40
tonic release of NT

105
Q

rhodopsin in light

A

bleaching - activated retinal
opsin decreases cGMP, closes sodium channels, hyperpolarisation -70
NT release

106
Q

patterning of retina - on/off

A

on/off pattern middle/outside to determine if light excites or inhibits

107
Q

retina-tectum mapping

A

Ephrin A and EphA receptors
temporal RGC anterior
nasal posterior as nasal has less ephA receptors

108
Q

scotoma

A

defect of central field - blind spot is a natural scotoma
lesion of fovea - greatest lack of acuity
occlusion blood vessel, vit B12 deficiency

109
Q

colour blindness

A 
x-linked, males 
trichromats are normal 
dichromats miss one pigments 
commonly red-green blindness 
monochromats v rare

Brain Function and Malfunction (7 decks)

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