Sensory systems Flashcards
1
Q
What are sensory systems for?
A
awareness of environment
protection of harm
conscious control
2
Q
What are exteroreceptors used for?
A
receptors for external stimuli
3
Q
examples of exteroreceptors
A
photoreceptors, hair cells, olfactory receptors, skin receptors eg mechanoreceptors
taste receptors
4
Q
proprioceptors
A
muscle reflexes and body position
5
Q
central organisation of senses
A
project to cerebellum with branch to cortex via thalamus
6
Q
what projection does not pass through thalamus before cortical area?
A
olfactory
7
Q
perceptual threshold
A
brain decides what is necessary to fully perceive eg selective hearing
8
Q
meissners corpuscles
A
sensitive touch/tapping
9
Q
ruffinis corpuscles
A
touch and pressure
10
Q
merkels discs
A
touch
11
Q
pacinian corpuscle - where are they found?
A
subcut tissue in palms of hands and soles of feet, genitals, GIT
12
Q
pascinian corpuscles respond to?
A
vibration or tickle
rapidly acting mechanoreceptors
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
14
Q
tonic receptors
A
slowly adapting receptors respond for duration of stimulus
15
Q
phasic receptors
A
rapidly act to a constant stimulus and turn off
16
Q
meissners corpuscles are found where?
A
subepidermal location in hands, feet, forearm, tip of tongue
17
Q
where are merkel cells found?
A
basal layer of the skin
18
Q
what are merkel cells?
A
free nerve endings that terminate in discs
19
Q
what are merkel cells associated with in most mammals?
A
whiskers
20
Q
hair root nerve endings
A
rapidly adapting a delta fibres
21
Q
where are thermoreceptors found?
A
throughout epidermis
22
Q
cold receptors
A
excited by fall in temp
myelinated fibres
23
Q
warm receptors
A
excited by rise in temp
unmyelinated fibres
fire constantly and indefinitely
24
Q
what determines size of receptive field?
A
2 point discrimination
25
explain receptive fields
sensitive regions - primary neurons synapse on distinct secondary neurons
26
nociceptors
all skin layers, small receptive fields, myelinated A delta or unmyelinated c fibres
27
Cranial nerves for gustation
7, 9, 10
28
5 tastes
umami, sweet, salt, bitter, sour
29
T1R
sweet
30
T2R
bitter
31
t-mGluR4
umami receptor, glutamate
32
receptor for salt
ENac
33
what are T1R, T2R and mGluR-4?
7 pass transmembrane receptors
34
diversity of receptor family
amino acid sequence and heterodimers
35
3 types of papillae
circumvalate, follate and fungiform
36
taste receptor distribution
taste buds found on 3 different types of papillae
| taste receptor cells within taste buds differentially express taste receptors - taste fields
37
taste transduction
ultimately leads to neurotransmitter release due to the increase in cAmp and calcium
38
what do cranial nerves innervate - taste
pontine parabrachial nucleus and nucleus of solitary tract in brainstem
39
further projections from brainstem - taste
thalamus, cortex - orbitofrontal and gustatory - amygdala and hypothalamus
input from somatosensory and visceral systems
40
where do odorant molecules dissolve?
mucous lining olfactory epithelium
41
what receptors do odorant molecules activate?
cilia of ORN
42
What does activation of an ORN lead to?
depolarisation propagated to glomeruli within olfactory bulb
| postsynaptic mitral cells relay signal to olfactory cortex
43
Odorant signal transduction
bind receptors, G protein activation of adenylate cyclase, cAMP, calcium, sodium influx. Let chloride channels out
44
feedback system of odorant signalling
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
Where do like ORNs converge?
on same glomerulus
46
how can lateral inhibiton of smell occur?
neighbour mitral cells and glomeruli through periglomerular and granule cells
47
what allows directional sensitivity of smell?
bidirectional input from olfactory epithelium to olfactory cortex
48
sharpening odor code
most strongly activated glomeruli, activate mitral cells, activate postsynaptic neurons in olfactory cortex - fire preferrentially
49
the competition model - smell
plasticity - activated odorant circuits compete out inactive ones
50
example of competition model
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
ossicles
malleus, incus and stapes
52
noise conduction
tympanic membrane
vibrate ossicles
stapes on oval window
fluid of cochlea
53
round window
vibration of membrane cushions and dampens fluid movement within cochlea
54
3 canals of cochlea
vestibular, middle and tympanic canal
55
membrane between vestibular and tympanic canal
basilar
56
basilar membrane - ends and pitches
thick apical end - low pitch
| thin basal end - high pitch
57
what happens due to movement of basilar membrane?
displacement of organ or corti
58
what is organ of corti comprised of?
sensory hair cells and supporting cells
| auditory nerve endings of hair cells
59
what part of organ of corti is in contact with tectorial membrane?
stereocilia of hair cells
60
how many rows of stereocilia on hair cells in organ of corti?
3 of progressively increasing length
61
firing of auditory nerve endings due to what?
movement of stereocilia relative to tectorial membrane, firing increased or decreased depending on direction of movement of stereocilia
62
What cells support hair cells in organ of corti?
deiter cells at apical and basal ends
| perilymph
63
what part of hair cells in endolymph?
stereocilia within tectorial membrane
64
how each is each cilium connected?
tip link - filamentous link bounded by myosin at each end
65
Displacement of stereocilia - what happens next?
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
Prestin
maintain cell length
67
example of prestin - mice
Deficient - gene has 2 alleles so got intermediate length of cells
68
what shape do sterocilia make?
V
69
Do hair cells depolarise?
no
70
what does influx of calcium lead to? hearing
NT release from vesicles at presynpatic membrane
| ion channels postsynpatic open and depolarise cell - action potential
71
what are NT vesicles in hair cell attached to?
electron dense body called synaptic ribbon
72
3 semicircular canals and motions they detect
anterior - nodding
lateral - sideways shake
posterior - head tilt
73
where are hair cells found in vestibular apparatus?
swellings called maculae
| ampulla
74
name of ampullar organs contain hair cells
cristae
75
what do hairs in cristae detect?
rotation of head
76
what do hairs in maculla detect?
linear movement and head position
77
what are hair cells of crista engulfed by?
gelatinous cupula
78
fluid - crista and macula
cristae - perilymph
| macula - endolymph
79
crista - displacement of cells and firing
hairs moved by perilymph - firing of hair cells in one direction, opposite direction decreased firing
80
layer of crystals in maculae
otoliths on surface of endolymph
81
movement of otoliths
crystals move under gravity
82
Conductive deafness causes
ear wax, blocked eustachian tube, otitis, otosclerosis
83
treating otosclerosis
stapedectomy or fenestration
84
sensironeural deafness - root cause
hair cell damage in organ of corti
85
causes of sensironeural deafness
menieres disease - increased endolymph
| ageing, infection, trauma
86
do hair cells regenerate in mammals - hearing?
no, but do in birds
87
regenerating hair cells in birds
hair cells excluded onto apical surface
| surrounding cells resume stem cell like behaviour
88
nerve deafness
damage to auditory nerve
| atherosclerosis, lesion
89
tinnitus
ringing in ears caused by degeneration of organ of corti
90
hereditary deafness
congenital, slowly progressing, adult onset
| 100 mutant genes known
91
genes responsible for more than 50% severe AR nonsyndromic deafness
GJB2 GJB6
92
near vision lens
ciliary muscles contract and lens round up
93
point of greatest visual acuity - high concentration of?
fovea - cones
94
lens to correct short and long sighted
short sighted - concave
| long sighted - convex
95
photoreceptor cells
rods and cones
96
what lines the rods and cones?
pigmented epithelium
97
role of RPE
absorb excess light
98
activation of photoreceptors...
release of pigment
| depolarisation of bipolar cells
99
what do bipolar cells activate?
RGC
100
where do RGC axons converge?
ONH
101
rods pigment
rhodopsin
102
cones pigments
red, blue or green
103
converge of signal - sight
many receptors synapsing onto bipolar cells
| lateral inhibition by horizontal cells
104
rhodopsin in darkness
inactive, cGMP is high and ion channels open
membrane potenital -40
tonic release of NT
105
rhodopsin in light
bleaching - activated retinal
opsin decreases cGMP, closes sodium channels, hyperpolarisation -70
NT release
106
patterning of retina - on/off
on/off pattern middle/outside to determine if light excites or inhibits
107
retina-tectum mapping
Ephrin A and EphA receptors
temporal RGC anterior
nasal posterior as nasal has less ephA receptors
108
scotoma
defect of central field - blind spot is a natural scotoma
lesion of fovea - greatest lack of acuity
occlusion blood vessel, vit B12 deficiency
109
colour blindness
```
x-linked, males
trichromats are normal
dichromats miss one pigments
commonly red-green blindness
monochromats v rare
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