Summary Sensory systems: Nociception, mechanosensation and hearing

SOMATIC SENSORY SYSTEM
General features
•
sensory input → integration → motor output
•
two ways a
signal can be transmitted

specialised sensory neuron stimulus , receptor depolarisation of afferent neuron
-
-


,



-


specialised epithelial receptor
-
stimulus , receptor depolarisation
,
of ES cat
,
Nts

released t detected by receptor of afferent neuron

•
Examples of sensory systems include
-




hearing . touch , vision , smell ,
taste
,
balance
.




thermo reception nociceptive ( pain)
,
+
proprioception 1 perception of position in space )

First order neurons .
Dorsal root
ganglion neurons
What are first order neurons?
0 Pseudo unipolar -
two axon branches -dorsal root ganglion neurons
-pseudounipolar
-involved in mechanosensory and pain/temperature
pathways
• 2
pathways -

mech anos en s ony t paint temperature libres
Transduction
when stimulus
•
energy of a is converted into an electrical signal
transduction cascade
' '



sensory
o




signal transduction → current generator potential action potential
- →




0
stimulus must be strong enough to surpass threshold

Encoding
strength is encoded by
the stimulus the
amplitude of the
•
generator potential t


the
frequency of action potentials
o
affects rate of neurotransmitter release

Adaptation
o
tonic receptor slowly adapt to stimulus -




eg .

muscle stretch / pain receptors ,
static

aphasic receptor rapidly adapt t then produce an off response dynamic
,



Tonic phasic




How do mechanosensory neurons enter the spinal
mechano
sensory I touch
-

enters dorsal root t joins dorsal column cord?
two at on branches
-2 axon branches- one enters SC (CNS) and one
depart from the Soma one runs to
periphery IPNS) t
-




runs to periphery (PNS)
-




One runs to spinal cord ICNS)
-enter via dorsal root
cell bodies are all located in the DRG
-join dorsal column
-




for from the face , so mas trigeminal ganglion
signals are in
-




-

neurons aremyelinated t have large diameters very fast conduction ,



-
A- beta fibres Touch uses A-beta fibres
How do pain and temperature neurons enter the
paint temperature tbreslnocicep.to It thermo captors)
spinal cord?
de cuss atest makes a connection in dorsal horn of SC to an
ascending -decussate
-




neuron
-connect to ascending neuron in dorsal horn of SC
free nerve endings are the main receptors these can either be
-




-




have a small diameter
myelinated or un
myelinated t
very -




relatively
slow conduction (slowest it on
myelinated I Pain/temperature use C fibres and A-delta fibres
-

C fibres t AS fibres

, diftoentreceptorso
follicles detect
Hair a light brush
• encapsulated receptors , low thehold 1 high sensitivity innervated by large myelinated aeons
,
,




rapid central transmission

Meissner corpuscle dynamic deformation ( slipping objects)
-
-




→
connective tissue capsule

→ several lamellae of Schwann cells What’s the function of each of the types of receptor?
40% Of sensory receptor in the hand -meissner corpuscle- dynamic deformation (slipping
-




Pacini an corpuscle
-


vibration objects)
→ subcutaneous tissue
-pacinian corpuscle- vibration
-merkel cell neurite complex- indentation depth
→ Onion like capsule , lamella separated by fluid-filled space
-ruffini corpuscle- stretch
-




-1540 Of cutaneous in the hand
→ 10
receptor
-

mend on neurite complete -

indentation depth
25% Of me than one in the hand
captor
-


Ruffini corpuscle stretch .




→ 20% of methane receptor in the hand
→ also in ligaments t tendons
wee nerve
endings
-
C- fibre LTM -


touch

forces ( pain)
-




nociceptor -
injurious What are receptive fields?
Receptive fields 2 stimuli as distinct, spatial acuity -distinguish 2 simultaneously applied stimuli as
• the ability to
distinguish 2 simultaneously applied stimuli as distinct = 2- distinct
-measure of spatial acuity
point discrimination
-more nerve endings increases spatial acuity
o measure of
spatial acuity
o more nerve endings =
higher spatial acuity
Ascending pathways for so mate sensation What’s the ascending pathway for unconscious
0
Unconscious .




proprioception →
spin o cerebellar tract somatosensation?
°
Conscious -


mechanosensa.li on -spinocerebellar tract (proprioception)
→
body t
posterior portion of head Dorsal column medial
-
-




tennis contract What are the 4 ascending pathways for conscious
somatosensation?
→ face t anterior portion of head -



Trigeminal somatic
sensory
-dorsal column-medial lemniscal tract-
system
mechanosensation, body and posterior head
paint temp
-trigeminal somatic sensory system-
-




→ body t
posterior portion of head spin 0thalamic tract
mechanosensation, face and anterior head
-




→ facet anterior portion of head -




through spinal nucleolus -spinothalamatic tract- pain/temp, body and
of trigeminal complex posterior head
-spinal nucleolus of trigeminal complex- pain/temp,
Dermatome innervation
arising from a
single dorsal root
face and anterior head
-




ganglion t its spinal nerve ( some overlap) -



helps determine
how certain conditions affect specific regions of the
body
input is in
layer IV of Cottee ,
cortex Dermatome- determines how certain conditions affect
sends projections in turn to limbic
+ also
descending signals
structures
specific regions of the body
contains a
[relay station of
complete representation
somatic sensory periphery

i

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1st order neurons

2nd Order neurons
3rd order neuron