SOMATOSENSORY SYSTEMS
q inform about objects around us through touch
q inform about position and movements of our body parts
     (proprioception)
q monitor the temperature
q inform about painful, itchy and tickling stimuli

The cell bodies of the first-order somatosensory afferent neurons
 are located in posterior root or cranial root ganglia
All the peripheral terminal branches of a 1° axon form only one
type of somatosensory receptor.




Meissner corpuscle
Pacinian corpuscle
Ruffini corpuscle
Merkel complex

Muscle spindle
Golgi tendon organ
http://www.nature.com/nrneurol/journal/v10/n7/images/nrneurol.2014.99-f1.jpg
Free nerve endings

Peripheral Somatosensory Axons



The 1° afferent is a pseudounipolar neuron that has its cell
body located in a peripheral (spinal or cranial) ganglion.


Spinal cord gray matter



lamina (Rexed 1952)
nuclei
I
ncl. apicalis (ncl. posteromarginalis)
II + III
substantia gelatinosa Rollandi
IV + V
ncl. proprius
VI
ncl. thoracicus (Stilling – Clark‘s ncl.) C8-L3
VII
substantia intermedia
VIII
medial group of motoneurons
IX
lateral group of motoneurons
X
zona centralis, the grey substance around the central canal

Spinal cord grey matter



Lemniscal system



Anterolateral system



http://www.frca.co.uk/images/pain_spinal_cord2.gif
Anterolateral system
q Anterior spinothalamic tract
q Lateral spinothalamic tract

Somatosensory pathways
Lemniscal system
§younger
§perception with high
    discrimination ability
§discriminative touch,
    proprioception
Anterolateral system
(neospinothalamic pathway)
§older
§perception with low
    discrimination ability
§crude touch, pain and
    temperature

Spinoreticular tract
(paleospinothalamic pathway)
§the oldest
§not somatotopically arranged
§arouses the cerebral cortex (ARAS)
§report to the limbic cortex about the nature
    of a stimulus
§

Proprioception
q static component of proprioception
§information from UL and LL mediates one pathway
q dynamic (kinesthetic) component of proprioception
§information from UL and LL mediate separate pathways
      Spinal cord – reflexes
      Cerebellum – coordination of movements
      Cerebral cortex – consious proprioception

fasciculus gracilis
et cuneatus
fasciculus gracilis
ncl. Stilling-Clark
fasciculus cuneatus
ncl. gracilis et cuneatus
ncl. cuneatus lateralis
tr. bulbocerebellaris
tr. spinocerebellaris ant.
tr. spinocerebellaris post.
tr. cuneocerebellaris
Non-conscious proprioception
static
dynamic

Conscious proprioception
q static proprioception
§     DRG – fasciculus gracilis et cuneatus – gracile and
         cuneate (bulbar) nuclei – tr. bulbo-thalamo-corticalis –
         SI
q dynamic proprioception
§     LL + caudal part of trunk
         tr. spinocerebellaris post – ncl. Z (rostral to gracile ncl.) –
         medial lemniscus – ncl. VPL thalami – SI
§     UL + cranial part of trunk
         lateral cuneate ncl. – contralateral medial lemniscus –
         ncl. VPL thalami – SI

fasciculus gracilis
et cuneatus
fasciculus gracilis
ncl. Stilling-Clark
fasciculus cuneatus
tr. spinocerebell. post.
ncl. gracilis et cuneatus
tr. bulbothalamicus (lemn. med.)
tr. thalamocorticalis
gyrus postcentralis (SI)
gyrus postcentralis (SI)
lemniscus medialis
ncl. cuneatus lateralis
static
dynamic




CN V



Maxillary nerve
Mandibular nerve


CN V - pathways
qtouch, pain and temperature
qtouch (discriminative touch)
qproprioception (muscles,
    temporomandibular joint,
    teeth)

CN V - spinal nucleus









Somatosensory cortex – a. 3,1,2






Somatotopic organization
VPM
VPL

VISCEROSENSORY PATHWAYS
q carry information from the thoracic, abdominal and
     pelvic cavities, and from the cardiovascular system
q utilize autonomic pathways to reach the CNS
q
q participate in important reflexes
q
q most of them end in the hypothalamus

VS fibres in the parasympathetic nerves
q pseudounipolar neurons in the inferior ganglion of CN IX
§   mucosa of oropharynx → ncl. commissuralis
         (reflex contractions of pharyngeal muscles during swallowing)
§ carotid sinus (baroreceptor)
§ carotid body (chemoreceptor) → dorsal respiratory ncl.
qpseudounipolar neurons in the inferior ganglion of CN X
§heart, respiratory organs and GIT → ncl. commissuralis
§information about acidity of gastric juice → lateral
     hypothalamus (apestat)
§ aortic arch (baroreceptor)
q

Solitary nucleus (ncl. of solitary tract)









VS fibres in the sympathetic system
q information about pressure, vibrations, temperature
     and pain from visceral organs
q dorsal root ganglion
q ncl. proprius
q tr. spinothalamicus → ncl. ventralis posterolateralis thalami
     → somesthetic cortex
q tr. spinoreticularis

http://clinicalgate.com/wp-content/uploads/2015/06/f19-02-9781437702941.jpg



Illustrations were copied from:
Neuroscience Online, the Open-Access Neuroscience
Electronic Textbook
Department of Neurobiology and Anatomy
University of Texas Medical School at Houston