PHYSIOLOGY - Somatosensory system and ascending tracts Flashcards
(199 cards)
1
Q
what senses does the DCML pathway transmit
A
fine touch
proprioception
vibration
2
Q
what are the 1st order neurones of the DCML
A
peripheral nerves to medulla oblongata
3
Q
sensory information enters the spinal cord where
A
dorsal root ganglion
4
Q
signals from where travel in the fasciculus cuneatus to the cuneate nucleus in the DCML
A
upper limb - T6 and above
5
Q
signals from where travel in the fasciculus gracilis to the gracile nucleus in the DCML
A
lower limb - below T6
6
Q
is the fasciculus gracilis or cuneatus more lateral
A
fasciculus gracilis is medial
fasciculus cuneatus is lateral
7
Q
where do all fibres in the DCML decussate
A
medulla
8
Q
what are the second order neurones in the DCML and where do they travel through
A
medulla (cuneate or gracile nucleus)
to the thalamus
contralateral medial lemniscus in brainstem
9
Q
what are the 3rd order neurones in the DCML and what do they travel through
A
VP nucleus of thalamus to the primary sensory cortex of the brain through internal capsule
10
Q
what does the spinothalamic tract transmit
A
pain
temperature
pressure
11
Q
describe the path of the 1st order neurones of the spinothalamic tract
A
peripheral nerves, enter spinal cord, ascend 1-2 levels and synapse at tip of dorsal horn (substantia gelatinosa)
12
Q
describe the path of second order neurones of the spinothalamic tract
A
substantia gelatinosa to the thalamus
13
Q
where do fibres of the spinothalamic tract decussate
A
spinal cord
14
Q
after decussating the spinothalamic splits to form how many pathways
A
anterior and lateral
15
Q
which pathway transmits crude touch and pressure
A
anterior spinothalamic
16
Q
what does the lateral spinothalamic tract transmit
A
pain and temperature
17
Q
describe 3rd order neurones of the spinothalamic tract
A
VP nucleus of the thalamus through internal capsule to the primary sensory cortex
18
Q
what does the spinocerebellar tract control
A
unconscious info from muscles to ipsilateral cerebellum
19
Q
what are the 4 tracts of the spinocerebellar tract
A
posterior
anterior
cuneocerebellar
rostral tract
20
Q
which tracts transmit info from muscles of upper limb to cerebellum
A
rostral and cuneocerebellar
21
Q
which tracts transmit info from muscles of lower limbs to cerebellum
A
anterior and posterior
22
Q
which tract decussates twice meaning the signals go to the ipsilateral cerebellum
A
anterior spinocerebellar
23
Q
what are the 3 categories of the somatosensory system
A
exteroceptive - cutaneous
proprioceptive
enteroceptive - internal
24
Q
what is the cell body location of 1st order sensory neurones
A
dorsal root ganglia
25
what has its 1st order neurone cell body in the cranial ganglia
CN V - sensory innervation of the anterior head
26
sensory 3rd order neurone cell bodys are all located where
thalamus
27
stimulus opens a anion/cation selective ion channel in peripheral terminal or primary sensory afferent eliciting a depolarising receptor potential
cation
28
the amplitude of the receptor potential is inversely proportional/proportional to the stimulus intensity
proportional
29
a supra-threshold receptor potential triggers an all or none action potential conducted by the axon, at a ____ proportional to its amplitude
frequency
30
what is the relationship between stimulus strength and amplitude of observed and why
non-linear
| greater sensitivity to change at low stimulus strength
31
what is the term for the type of energy that a sensory cell is tuned to respond to
modality - the adequate stimulus
32
what detects mechanical forces on the skin (touch, pressure, vibration)
skin mechanoreceptors
33
what detects proprioception / mechanical forces acting on joints and muscles
joint and muscle mechanoreceptors
34
what detects temperature
cold and warm thermoreceptors
35
what detects pain
mechanical, thermal and polymodal nociceptors
36
what detects itch - irritant e.g. chemical on skin or mucous membranes
itch receptors
37
what mediates fine discriminatory touch
low threshold mechanoreceptors
38
what mediates cold through to hot temperatures but not extremes
low threshold thermoreceptors
39
if there is increasing stimulus strength resulting in an increased rate of firing of LRMs and perception of increased intensity, will the qualitative character of the perception e.g. pressure change e.g. to pain
not if only LTMs are activated
40
what is another name for high threshold units
nociceptors
41
mechanical nociceptors (HTMs) respond to what
high intensity mechanical stimuli
| e.g. distension (stretch) and pressure in inflammation
42
thermal nociceptors respond to what
extreme degrees of heat - over 45 or under 10-15
43
chemical nociceptors respond to what
exogenous and endogenous chemical substances in the tissue e.g. in inflammation
44
give 4 chemicals that chemical nociceptors will respond to
```
prostaglandins
bradykinin
serotonin (5-HT)
histamine
(also K+, H+ and ATP and others)
```
45
what do polymodal nociceptors respond to
more than one stimuli
46
what are the 3 types of adaptation of sensory nerve cells
tonic/static response - slow adapting (SA)
phasic/dynamic response - fast adapting (FA)
very phasic/dynamic response - very fast adapting
47
what kind of AP will tonic (SA) receptors produce
continuous information to CNS - greater the stimulation intensity the greater the firing rate
48
what kind of AP will phasic (FA) receptors produce
respond quickly to stimuli but stop responding upon continual stimulation
49
with FA receptors the number of impulses is proportional to the rate of ____
change of stimulus
50
VFA receptors respond only to
very fast movement
51
give an example of an SA receptor
stretch receptors
52
give an example of a FA receptor
some muscle spindle afferents
53
give an example of a VFA receptor
pacinian corpuscle
54
what are the 4 groups of primary sensory afferent fibres
Aa
Ab
Ad
C
55
which of the 4 groups of primary sensory afferent fibres has the biggest diameter
Aa
56
which of the 4 groups of primary sensory afferent fibres has the thickest myelination
Aa
57
which of the 4 groups of primary sensory afferent fibres has the fastest conduction velocity
Aa
58
which of the 4 groups of primary sensory afferent fibres is unmyelinated
C
59
nociceptors are tonic/phasic
phasic (FA)
60
what are the 2 types of pain fibre
Ad
| C
61
how would you describe the receptors found on the ends of the type Ad and C pain fibres
free dendritic nerve endings
62
thermoreceptors are tonic/phasic
phasic
63
what kind of fibres respond to warm temperatures
C fibres
64
what kind of fibres respond to cold temperature
Ad fibres
65
are cold or warm thermoreceptors more common
cold
66
what allows adaptation to warm temperature if it remains constant
switch from initial phasic response which changes very quickly based on minute temperature changes
to tonic if it remains constant
67
what is the term for increased sensitivity to pain
hyperalgesia
68
primary hyperalgesia is thought to be due to what
nociceptor sensitisation
69
secondary hyperalgesia is thought to be due to what
central sensitisation
70
what drugs can induce hyperalgesia
opioids
71
what is a receptive field
target territory from which a single sensory unit can be excited - area on skin corresponding to the territory of one sensory neurone
72
how is RF related to innervation density and therefore sensory acuity
inversely related - bigger the RF the less densely innervated and therefore the less sensory acuity of that area
73
can skin contain overlapping RFs?
yes
74
name an area with a very small RF and therefore high density of innervation and high acuity
finger tip (2mm)
75
what is 2 point discrimination
the minimum distance required between two simultaneous stimulations applied to be registered
76
how is 2 point discrimination clinically tested
applying 2 sharp point stimuli separated by a variable distance at different sites on the body surface
77
how are cutaneous receptors subdivided - 4 types
small field - type 1 unit
wide field - type 2 unit
SA or FA
SA1 SA2 FA1 FA2
78
what is the fibre type of free nerve endings
Ad or C
79
what is the fibre type of follicular nerve endings
Ab or Ad
80
what is the receptor and parent fibre type of merkel cell neurite complex
Ab
| SA1
81
what is the receptor and parent fibre type of meissner corpuscles
Ab
| FA1
82
what is the receptor and parent fibre type of Ruffini endings
Ab
| SA2
83
what is the receptor and parent fibre type of Pacinian corpuscles
Ab
| FA2
84
what nerve endings are encapsulated
pacinian corpuscles
ruffini endings
meissner corpuscles
85
which of the following has the smallest RF
pacinian corpuscles
ruffini endings
meissner corpuscles
meissner corpuscles
86
where are free nerve endings found in the skin
everywhere
87
merkels discs are tonic/phasic
tonic (SA)
88
where are merkel discs found in the skin and in what distribution
near border of dermis and epidermis
| abundant in skin locations where 2 point discrimination is highest, also in moderate numbers in hairy skin
89
what do merkel discs detect
pressure
| differentiate texture and shape of objects
90
what can merkel cells develop
high mortality cancer
91
meissner's corpuscles are tonic/phasic
phasic (FA)
92
where are meissner's corpuscles found in the skin and in what distribution
in dermis, mainly on palms of hands, soles of feet, lips and tongue
93
are meissner's corpuscles present in hairy skin
no
94
what do meissner's corpuscles detect
fine touch - allow 2PD
95
what do pacinian corpuscles detect
pressure
96
pacinian corpuscles are tonic/phasic
phasic (FA)
97
pacinian corpuscles are the smallest/largest category of mechanoreceptors
largest
98
where are pacinian corpuscles found
dermis, hypodermis, ligaments, external genitalia
| fascia
99
what is a group of merkel cells called
Iggo dome
100
An iggo dome is innervated by a single/many myelinated fibre(s)
a single myelinated fibre innervates the merkel cells in an Iggo dome
101
what do merkel cells express that makes them mechanosensitive
Piezo2 - mechanosensitive cation channel
102
where are Krause end bulbs found
border of the skin and mucous membranes
103
Ruffini end-organs are tonic/phasic
tonic (SA)
104
Ruffini end-organs respond to what
stretch and shearing forces
105
where are Ruffini end-organs found
dermis and joint capsules
106
where are muscle spindles and golgi tendon organs
skeletal muscle
107
what do muscle spindles and golgi tendon organs detect
stretch
108
how many spinal nerves are there for each section
```
C1-8
T1-12
L1-5
S1-5
coccygeal
```
109
what is a dermatome
area of skin innervated by the left and right dorsal root of a single segment
110
what nerve innervates the anterior head
CN V
111
shingles is an infection of what
dorsal root ganglion
112
what virus causes shingles
reactivation of varicella zoster
113
what does varicella zoster cause in children
chicken pox
114
does shingles usually occur in 1 or more ganglions
typically a single ganglion
115
what does shingles look like
extremely painful, inflamed and blistered skin in the dermatome innervated by that ganglion
116
what is found in the grey matter of the spinal cord
cell bodies and sensory afferent terminals
117
what is found in the white matter of the spinal cord
fibre tracts
118
how many laminae of rexed are there in the grey matter of the spinal cord
10
119
nociceptors (Ad and C) terminate in which laminae of rexed
I and II (also V for Ad fibres)
| visceral nociceptors terminate on laminae I and V but not II
120
LTMs (AB) terminate in which laminae of rexed
III to VI
121
proprioceptors (Aa) terminate in which laminae of rexed
VII to IX
122
give and example of a sensory receptor that uses Aa fibres
proprioceptors of skeletal muscle
123
give and example of a sensory receptor that uses Ab fibres
mechanoreceptors of skin
124
give and example of a sensory receptor that uses Ad fibres
pain
| temperature
125
give and example of a sensory receptor that uses C fibres
temperature
pain
itch
126
what 2 tracts make up the DCML pathway
cuneate (lateral) and gracile tract (medial)
127
the dorsal columns are further divided into what from lateral to medial
cervical - thoracic - lumbar - sacral
128
where do 1st order neurones of the DCML synapse for spinal reflexes
deep in the dorsal horn upon 2nd order neurones
129
what is stereognosis
ability to recognise an object by feeling it
130
how do you test fine touch
2PD
131
how do you test conscious proprioception
ask patient to close eyes - can they recognise when body part moved up / down
132
how can you test vibration sensation
128Hz tuning fork with onset offset reporting from bony prominence
133
what is lateral inhibition
when one neurone is active it inhibits the activity of its neighbours via inhibitory interneurones to sharpen stimulus
134
what does lateral inhibition lead to
contrast enhancement
135
the trigeminal system conveys general somatic information from the anterior head including the ...
```
oral and nasal cavities
paranasal sinuses
teeth
intracranial dura
cerebral arteries
```
136
where do impulses originate in the trigeminal system
terminals of the 2 trigeminal nerves each of which has 3 divisions
137
what are the 3 divisions of CN v
v1 - ophthalmic
v2 - maxillary
v3 - mandibular
138
where are the soma of the sensory neurones of the trigeminal system located
trigeminal sensory ganglion
139
central terminals of the trigeminal nerve synapse upon second order neurones in the _______ or the _____
chief sensory nucleus or the spinal nucleus
140
what stimuli go to the chief sensory nucleus
general tactile stimuli
141
what stimuli go to the spinal nucleus
pain and temperature
142
second order neurones decussate and project via _____ to the _____ of the _____
the trigeminal lemniscus to the VPM nucleus of the thalamus
143
3rd order neurones relay information to the cortex via ___
thalamocortical neurones
144
where is the somatosensory cortex (SI) located
post central gyrus of the parietal cortex immediately posterior to the central culcus
145
what is the somatosensory cortex adjacent to
posterior parietal cortex (SII)
146
SI is divided into _____ areas which are
```
Broadmann areas
BA 3a
BA 3b
BA 1
BA 2
```
147
where does the somatosensory cortex receive input from
VP thalamus
148
which broadman areas recieve most input from VP thalamus
70% - 3a and 3b - initial processing
| 30% - 1 and 2 - more complex processing
149
BA 3a receives information from
proprioceptors
150
BA 3b receives information from
cutaneous mechanoreceptors e.g. merkel cells and meissners corpuscles
3a
151
BA 1 receives information from
cutaneous mechanoreceptors and 3b
152
BA 2 receives information from
joint afferents, golgi tendon organs, deep tissues
| 3a and 3b
153
how many cell layers does the somatosensory cortex have
6
154
thalamic inputs to SI terminate mainly on neurones within layer ___ which projects cells ___
4 (IV)
| which projects cells towards the surface of the cortex and deeper layers
155
what extend across the layers of the sensory cortex
vertical columns
156
each column consists of neurones with similar ____ and ____
inputs and responses
157
if a finger is amputated what happens to the area of SI representing that finger
it will be utilised by other sensory inputs - cortical representation of adjacent fingers will expand into territory
158
if the sensory input from a finger increases e.g. violin player what happens to its contralateral cortical representation
expands
| e.g. use right finger a lot, part on left side of brain will expand as contralateral
159
what does the posterior parietal cortex (SII) do
receives and integrates information from SI and other cortical areas - visual, auditory and sub-cortical areas - thalamus - deciphers the deeper meaning of the information
160
damage to the posterior partial cortex can cause what
bizarre neurological disorders with simple sensory skill intact
e.g. agnosia, astereognosia, hemispatial neglect syndrome
161
damage to the right parietal cortex resulting in neglect syndrome would present how
patient doesnt believe the left side of the world exists, will even discount left side of body
162
what order neurones are nociceptors
first
163
pathological pain is adaptive/maladaptive
maladaptive
164
Ad fibres mediate ___ ___ pain
| C fibres mediate ___ ___ pain
Ad - fast first
| C - slow second
165
Ad fibres respond to what noxious stimuli
thermal and mechanical
166
C fibres respond to what kind of pain
all noxious stimuli - polymodal
167
give 3 receptors that are activated by noxious heat
TRPA1
TRPC3
TRPV1
168
H+ activates what channels
acid sensing ion channels (ASICs)
169
ATP activates what receptors
P2X and P2Y receptors
170
bradykinin activates what receptors
B2 receptors
171
what are peptidergic polymodal nociceptors
subset of C fibres with afferent and efferent functions
172
what does the afferent limb of peptidergic polymodal nociceptors do
transmits nociceptive information to the CNS via release of glutamate and peptides
173
what does the efferent limb of peptidergic polymodal nociceptors do
release of pro-inflammatory mediators contributing to neurogenic inflammation
174
noxious stimulation in the long term increases/decreases spinal excitability
increases - contributes to hyperalgesia and allodynia
175
what is neurogenic inflammation
peptides such as substance P and CGRP (calcitonin gene-related peptide) released from free nerve endings of peptidergic nociceptor due to tissue damage or inflammatory mediators
176
what does substance P do
vasodilation and extravasation of plasma proteins
release of histamine from mast cells
sensitises surrounding nociceptors
177
what does CGRP do
induces vasodilation
178
what follows on from neurogenic inflammation
primary and secondary hyperalgesia and allodynia
179
visceral pain tends to be what in nature
dull aching throbbing
180
visceral afferents from nociceptors follow _____ pathways before reaching the dorsal horn
sympathetic
181
why can the brain interpret pain coming from the viscera as originating from an area of skin distant to the internal organ
some visceral and skin afferents converge upon the same spinothalamic neurones - all cells with a visceral RF will also have a separate cutaneous RF
182
where may heart pain e.g. angina be referred
T1 - T5
183
where may pain from the gall bladder be referred
C4
184
what causes viscerosomatic pain
when inflammatory exudate from a diseased organ contacts a somatic (body wall) structure
185
what is an example of viscerosomatic pain
appendicitis may start as diffuse visceral pain in the umbilical region that moves down to the iliac fossa and progresses to sharp viscerosomatic pain
186
can nociception occur in the absence of pain
yes pain is just awareness of the nociception
187
where can stomach/pancreas pain be referred
epigastric region
188
liver can refer pain to
side of neck
189
diaphragm/lungs can refer pain to
shoulder
190
pain evoked by activity in nociceptors can be reduced by simultaneous activity in ___
LTMRs (AB)
191
what theory explains the reduction in pain when AB fibres are stimulated
gate control theory
192
what are the 2 major pain pathways
spinothalamic
| spinoreticular
193
spinoreticular transmits more ____ pain
| spinothalamic more ___ pain
SRT - slow
| STT - fast
194
spino____ tract makes extensive connections with reticular nuclei in brainstem (e.g. PAG, parabrachial nucleus)
spinoreticular
195
SRT is involved in what
autonomic responses to pain, arousal, emotional responses, fear of pain
196
what temperate change can we perceive
as small as 0.01 degrees
197
what lesion can be seen with vit B12 deficiency and tabes dorsalis (complication of syphilis)
DCML lesion
198
if lesion to DCML is in spinal cord, sensory loss will be contra/ipsilateral
ipsilateral
199
damage to the spinothalamic tract will have contra/ipsilateral sensory loss
contralateral
