SOMATOSENSORY SYSTEMS
 inform about objects around us through touch
 inform about position and movements of our body parts
(proprioception)
 monitor the temperature
 inform about painful, itchy and tickling stimuli
The somatosensory receptor and its central connections
determine the modality specificity of the neurons forming a
somatosensory pathway.
The cell bodies of the first-order somatosensory afferent neurons
are located in dorsal root or cranial root ganglia
All the peripheral terminal branches of a 1° axon form only one
type of somatosensory receptor.
The adequate stimulus: mechanical force, temperature change,
tissue damage, chemical action.
Meissner corpuscle
Pacinian corpuscle
Ruffini corpuscle Merkel complex
Muscle spindle Golgi tendon organ
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
Anterolateral system
 Anterior spinothalamic tract
 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
 static component of proprioception
 information from UL and LL mediated by one pathway
 dynamic (kinesthetic) component of proprioception
 information from UL and LL mediated by 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
 static proprioception
 DRG – fasciculus gracilis et cuneatus – gracile and
cuneate (bulbar) nuclei – tr. bulbo-thalamo-corticalis –
SI
 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
 touch, pain and temperature
 touch (discriminative touch)
 proprioception (muscles,
temporomandibular joint,
teeth)
CN V - spinal nucleus
Somatosensory cortex – a. 3,1,2
Somatotopic organization
VPM VPL
VISCEROSENSORY PATHWAYS
 carry information from the thoracic, abdominal and
pelvic cavities, and from the cardiovascular system
 utilize autonomic pathways to reach the CNS
 participate in important reflexes
 most of them end in the hypothalamus
VS fibres in the parasympathetic nerves
 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.
 pseudounipolar 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)
Solitary nucleus (ncl. of solitary tract)
VS fibres in the sympathetic system
 information about pressure, vibrations, temperature
and pain from visceral organs
 dorsal root ganglion
 ncl. proprius
 tr. spinothalamicus → ncl. ventralis posterolateralis thalami
→ somesthetic cortex
 tr. spinoreticularis
Illustrations were copied from:
Neuroscience Online, the Open-Access Neuroscience
Electronic Textbook
Department of Neurobiology and Anatomy
University of Texas Medical School at Houston