Somatosensory Pathways
Lectures 11-13
Organization of the Course
Spinal Cord
Brainstem/
Cerebellum
Sensory Pathways
Overview and
Development
Cerebrum
Other Pieces
of the puzzle
Cranial
Nerves
Motor Pathways
Last Friday
Task due this Friday midnight (so I can
grade them and provide feedback before
exams!)
 Cerebellar histology – my office hours are
this afternoon 2-3 and Wed. 2-3

Sensory Pathways Objectives

Describe the structures, functions, locations,
neurotransmitters, and decussation level for
each sensory pathway
◦ DC/ML
◦ ALS
 Spinothalamic
 Spinotectal
 Spinoreticular
◦ Trigeminal
◦ Solitary

Analyze case studies using knowledge of the
somatosensory pathways.
Overview of Sensory Pathways

Dorsal Column / Medial Lemniscus
◦ Light touch, proprioception, vibration of body

Anterolateral System
◦ Pain, temperature of body

Trigeminal
◦ Light touch, proprioception, vibration of face
◦ Pain, temperature of face

Solitary
◦ Visceral sensations of body and head
Dorsal Column / Medial Lemniscus
Pathway
Light touch, vibration, proprioception
 Conscious
 3 neuron pathway
 Decussates in the lower medulla (arcuate
fibers)
 AcH and Glutamate (excitatory)

DC/ML course
● 1st order - Cell body in DRG
○ Fasciculus Gracilis (FGr) (Posterior - Medial)-anything below T7 level and
below
■ Light touch, vibration, position sense from ipsilateral leg and lower
trunk
■ Periphery → FGr → Gracile Nucleus (NuGr)
○ Fasciculus Cuneatus (FCu) (Posterior - Lateral)- T6 Level and above
■ Same as above, but from ipsilateral arm and upper trunk
■ Periphery → FCu → Cuneate Nucleus (NuCu)
● 2nd order - Cell body in NuGr (LE); NuCu (UE)
○ Cross/decussate at Internal arcuate fibers (IAF) into ML
○ ML ends at Ventral posterolateral nucleus of thalamus nucleus (VPL)
● 3rd order - Cell body in VPL
○ VPL to Somatosensory cortex (Postcentral Gyrus; Brodmann 3,1,2)
Anterolateral System
Spinothalamic
Spinoreticular
Spinotectal (aka Spinomesencephalic)
 Pain, temperature, pressure
 Conscious and subconscious
 2-3 neuron pathway
 Decussates at level of Spinal Cord
 Glutamate, Substance P, enkephalin,
cholecystokinin, serotonin (and others)
ALS course
● 1st order- Cell body in DRG
○ Periphery → DRG → Dorsal Horn (DH)
■ Synapses with 2nd order in DH
● 2nd order - Cell body in Dorsal Horn - Lamina 1&2
○ Cross/decussate from DH through Anterior white commissure to
Anterolateral system (ALS)
○ ALS = Primary route is Spinothalamic tract = conscious perception of
pain
● Branch off → intralaminar nucleus (Thalamus) = alert/arousal
■ Main Branches:
● Reticular formation = Spinoreticular tract = wakefulness
● Midbrain = Spinotectal tract = Pain modulation
● Hypothalamus = Spinohypothalamic Tract = Emotional and
autonomic responses to pain
● 3rd order - Cell Body in VPL
○ VPL to Somatosensory cortex (Postcentral Gyrus/ Posterior Paracentral
Gyrus; Brodmann 3,1,2)
Post-synaptic Dorsal Column
Pathway
Convergent, divergent, oscillating
pathways/circuits


Convergent pathways

Divergent pathways
◦ Many neurons synapse onto fewer neurons
◦ One neuron synapses onto more neurons
◦ More typical within cerebral cortex
◦ Transmits one signal to multiple places
Oscillating circuits
◦ Post-synaptic dorsal column is an example
◦ Cerebellar cortex -> deep nuclei ->
cerebellar cortex
◦ Spinoreticular and spinotectal are examples
Analyzing Case Studies
Your patient has damage to the Right
dorsal column of the spinal cord from the
T11-T12 vertebral disc.
 Which pathways are damaged?
 What functions are lost and where?

Brown-Sequard Syndrome
Your patient has a hemisected spinal cord
at SC level T8 (left side affected).
 What somatosensory pathways are
damaged?
 What functions are lost and where?


Hint: there might be a combination of segmental deficits
and below the lesion deficits.
Research topics
Small groups
Take turns to discuss updates and thoughts about
topics
 If you have a general plan for how to lay out your
paper, explain it and get feedback



GOAL: To work through thoughts, plans,
organization by explaining it to another person.
Producing communication (speaking, writing)
often leads to more complete thoughts than just
absorbing communication (listening, reading).
Being able to articulate your thoughts now will
lead to a better product in the end.
Sensation of face and viscera!

Trigeminal Pathway
◦ Nuclei:
◦ Nerves:

Solitary Pathway
◦ Nuclei:
◦ Nerves:
Trigeminal Nerve

Opthalmic (V1)
◦ Sensation
◦ Sup. Orbital fissure

Maxillary (V2)
◦ Sensation
◦ Rotundum

Mandibular (V3)
◦ TM joint sensation
◦ TM joint musculature
◦ Ovale
Trigeminal Nuclei

Chief Sensory Nucleus
◦ Fine + discriminative touch, vibration sense

Mesencephalic Nucleus
◦ Proprioceptive input
• Trigeminal Motor Nucleus
◦ Motor to TMJ muscles

Spinal Trigeminal Nucleus
◦ Pain + Temperature stimuli, Crude touch
◦ Spinal Trigeminal Tract
◦ From here, information travels to ___________
Motor Pathway (V)



Proprioception from Mesencephalic N.
Pain, temp, touch from Spinal N.
Descending control from cerebral cortex
(corticonuclear pathway, to be discussed)

To Motor Nucleus

Lower Motor Neurons through V3
(mandibular nerve) to muscles of
mastication
Sensory of face

Split into 3 parts:
◦ Proprioception
 To Mesencephalic Nucleus
 Decussates – contralateral
◦ Touch
 To Sensory Nucleus
 Bilateral
◦ Pain and temperature
 To Spinal Nucleus
 Decussates – contralateral

All go to contralateral VPM (through trigeminal lemniscus)
◦ Touch also goes to ipsilateral VPM

All also send info to: RF, Hypoglossal Nuc., Facial Nuc.,V Motor Nuc.

From VPM to sensory cortex (post-central gyrus)
Trigeminal Neurotransmitters
Substance P (+) - pain
 CCK (+)
 Glutamate (+)
 Enkephalin (-) - pain

Solitary Pathway

Sensory pathway for Cranial Nerves:
◦ VII Facial
◦ IX Glossopharyngeal
◦ X Vagus

Solitary Nucleus
◦ Rostral part = taste
◦ Caudal part = throat, mouth sensation
Taste (Rostral part)

Taste sensation from:
◦ ANT 2/3 of tongue
 Facial Nerve (VII)
◦ POST 1/3 of tongue
 Glossopharyngeal Nerve (IX)
◦ Taste buds at root of tongue, epiglottis
 Vagus Nerve (X)

Synapses in rostral part of solitary nucleus
◦ Ascends to ipsilateral VPM, synapses, continues to sensory
cortex
◦ Sends info to hypoglossal nucleus
◦ Sends info to salivatory nucleus
 (salivation reflex)
Visceral Sensations (Caudal part)

IIV Facial Nerve
 Glands (submandibular, sublingual, lacrimal)

IX Glossopharyngeal Nerve






Parotid gland
Mucosa of pharynx
Tonsilar sinus
POST 1/3 of tongue
Carotid body
X Vagus Nerve




Pharynx
Larynx
Aortic bodies
Thoracic & abdominal viscera
 Ex. peristalsis
Visceral Sensations (Caudal part)


Sensory information synapses in caudal
solitary nucleus
Information is relayed to:
◦ Ipsilateral Hypothalamus
 (central regulatory center for autonomic functions)
◦ Ipsilateral Motor Nucleus of Vagus N.
 (descending visceral motor control)
◦ Ipsilateral Nucleus Ambiguus
 (gag reflex)
◦ Ipsilateral Amygdala
 (fear center)
NICE TO KNOW
Baroreflexes – Heart, vessels (ex.
Carotid sinus)
 Chemoreflexes – Carotid & aortic
bodies

Solitary Pathway Neurotransmitters
GABA
 Substance P
 Enkephalins
 Somatostatin
 CCK

Review






General Anatomy
Development
Support Systems
Spinal Cord
Brainstem
Cerebellum & Pathways
◦ Spinocerebellar (4 parts), pontocerebellar, reticulocerebellar,
ceruleocerebellar, raphecerebellar, hypothalamocerebellar,
olivocerebellar
◦ Nucleocortical, corticonuclear, corticovestibular
◦ Efferent fibers

Somatosensory Pathways
◦ DC/ML, ALS, postsynaptic
◦ Trigeminal
◦ Solitary