Somatosensory pathway

Medical neuroscience

1. Somatosensory pathway
Domina Petric, MD

2. Introduction
Planets
Dwarf
Planets
Sensory pathwaysconsist of the chain of neurons,
from receptor organ to cerebral cortex,
that are responsible for the perception of sensations.

3. pseudounipolar neuron spinal cordthalamus
decussation
parietal lobe of somatosensory cortex
Anatomical features

4. Anatomical features
•The firstafferentneuronis a
pseudounipolarneuron.
•Itscell bodyislocated in a
peripheral (spinal or cranial)
ganglion.

5. Pseudounipolar neuron
It has:
•peripheral axon that forms or
innervates somatosensory receptors
•central process that synapses with
secondafferent neuron(s) in a spinal
cord or brain stem nucleus.

6. https://figures.boundless-
cdn.com/19525/large/figure-35-01-04.jpeg

7. Second and third afferent
neuron
•The secondafferentneuronmay synapse
with thirdafferent neurons in the spinal
cord.
OR
•They may ascend the neuraxisto synapse
with thirdafferent neurons in the
thalamus.

8. Decussation
•There is a decussationin each
somatosensory pathway below the
level of the thalamus.
•Decussation means that axons are
crossing the midline to the opposite
side of the spinal cord or brain stem.

9. Thalamic nucleus
•All somatosensory pathways include a
thalamic nucleus.
•The thalamic neurons send their axons in
the posterior limb of the internal capsule
to end in the cerebral cortex.
•Most somatosensory pathways terminate
in the parietal lobe of the cerebral cortex.

10. Peripheral somatosensory
axons (first afferent neurons)
•form the
muscle and
tendon
receptors
•carry body
proprioceptive
information
•the largest
diameter and
the thickest
myelin
•form free
nerve
endings
•carry dull
pain, deep
pain, crude
touch or
warm/hot
information
•the smallest
1°afferent
axons
•unmyelinated
•form free
nerve
endings
•carry sharp
pain or
cool/cold
information
•thinly
myelinated
and larger
than the
Type C
•form
encapsulated
endings in
skin and
joints,hair
follicle
endings or
Merkel disks
in skin
•myelinated
•diameter
between
group I and
A delta
•The
morphology
of the
peripheral
somatosensory
axon is also
related to the
conduction
velocity of
the action
potentials
generated by
the axon.
Type CGroup I Type AδType AβVelocity

11. Conduction velocity
•It is determined by electrically stimulating the
axon and recording the time (latency) it takes
the electrically elicited action potential to reach
a recording electrode.

12. Somatotopic organisation
•Somatosensory
neurons are
topographically
(spatially)
organized so that
adjacent neurons
represent
neighboring regions
of the body or face.

13. Somatotopic organisation
•Itis preserved by a precise point-to-point
somatotopicpattern of connections from the
spinal cord and brain stem to the thalamus and
cortex.
•Withineach somatosensory pathway there is a
complete map (spatial representation) of the
body or face in each of the somatosensory
nuclei, tracts and cortex.

14. The sensory information
processed by the somatosensory
systems travels along different
anatomical pathways
depending on the information
carried.

15. Medial lemniscalpathway(body
discriminativetouch and proprioception)
•The posterior (dorsal) column ormedial
lemniscalpathwaycarries and processes
discriminative touch and proprioceptive
information from the body.
•The afferents carrying discriminative touch
informationare kept separatefrom those
carrying proprioceptive information up to the
level of the cerebral cortex.

16. https://www.studyblue.com/notes/note/n/nervous-system/deck/14558031

17. Main sensorytrigeminalpathway(face
discriminativetouch and proprioception)
•Themain sensory trigeminal
pathwaycarries and processes
discriminative touch and
proprioceptive information from the
face.
•It is the cranial homologue of the
medial lemniscalpathway.

18. http://what-when-how.com/neuroscience/the-cranial-
nerves-organization-of-the-central-nervous-system-part-3

19. Neospinothalamicpathway(body
sharp, pricking,painand cool, cold)
•Theneospinothalamicpathwaycarries
and processes sharp, pricking pain and
dropping temperature (cool, cold)
information from the body.
•The pain informationis well localized.
•The sensations are short lasting:˝fast˝or
˝first˝pain elicited by tissue-damaging
cutaneous stimuli.

20. Neospinothalamicpathway
•Characterised by somatotopic
representation.
•Most of the ascending afferents of the
spinal pain pathways travel with the
neospinothalamicafferents in a fiber
tract:the spinothalamictract or
anterolateral spinothalamictract.

21. https://www.pinterest.com/pin/515943701040737204

22. Spinal trigeminalpathway(pain,
temperatureand crude touchfrom face)
•Thespinal trigeminal
pathwaycarries and processes crude
touch, pain and temperature
information from the face.
•It is the cranial homologue of the
spinothalamicpathways.

23. https://openi.nlm.nih.gov/detailedresult.php?img
=PMC3205483_SNI-2-128-g002&req=4
Nucleus caudalis lesioning: Case report of chronic traumatic headache relief.
Sandwell SE, El-Naggar AO -Surg Neurol Int (2011)

24. Literature
•http://nba.uth.tmc.ed
u/neuroscience/s2/ch
apter04.html
(Neuroscience
electronic book,
Patrick Dougherty,
Ph.D.,Department of
Anesthesiology and
Pain Medicine,MD
Anderson Cancer
Center)
•openi.nlm.nih.gov
•www.studyblue.com
•what-when-how.com