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
◦ Post-synaptic Dorsal Column
◦ 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


Post-synaptic Dorsal Column
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)
Which of the following is TRUE
concerning the DC/ML pathway?
ig
ht
sl
ca
rr
ie
Th
is
p
at
hw
ay
rn
or
de
3r
d
to
...
...
on
eu
r
1s
or
th
e
m
af
so
Th
e
de
er
.
to
rd
sc
lu
fa
sc
icu
e
gr
ac
il
Th
e
cu
s
..
on
ta
i..
25% 25% 25% 25%
Th
e
The gracile fasciculus
contains sensory
information for the LE but is
not internally organized.
B. The soma for the 1st order
neuron is in the dorsal root
ganglion.
C. The 3rd order neuron
decussates.
D. This pathway carries light
touch, proprioception, and
deep pressure components.
A.
:30
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)
Which of the following is FALSE
concerning the ALS?
...
ot
co
nv
er
ge
nt
,d
th
..
by
Th
e
AL
Si
sn
nt
sc
ar
r ie
d
or
d
3r
d
co
m
po
ne
so
Th
e
Th
e
2n
d
m
ao
or
de
rn
ft
he
eu
ro
n
de
cu
er
n
s..
...
.
25% 25% 25% 25%
Th
e
The 2nd order neuron
decussates.
B. The soma of the 3rd
order neuron is in the
VPL.
C. The components
carried by this pathway
are pain, temperature,
and deep pressure.
D. The ALS is not
convergent, divergent,
or oscillating.
A.
:30
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.
Yo
ur
..
pa
in
ffe
rs
pa
tie
nt
su
ffe
rs
su
nt
pa
tie
Yo
ur
25%
C7
.
t..
pa
in
pa
in
ffe
rs
su
nt
pa
tie
Yo
ur
in
C7
.
...
in
pa
in
ffe
rs
su
D.
nt
C.
pa
tie
B.
Your patient suffers pain in
the C7 dermatome on the
right.
Your patient suffers pain
C7 and below on the right.
Your patient suffers pain in
the C7 dermatome on the
left.
Your patient suffers pain
C7 and below on the left.
Yo
ur
A.
..
Your patient has impingement to
the lateral funiculus at C7 on the
right side. Which of the following is
25% 25% 25%
most likely?
:30
th
e
le
ft.
25%
on
th
e
ul
la
on
Up
pe
r
m
ed
ul
la
m
ed
Up
pe
r
in
sp
C1
rig
ht
.
le
ft.
th
e
al
co
rd
on
th
e
on
al
co
rd
D.
in
C.
sp
B.
C1 spinal cord on
the right.
C1 spinal cord on
the left.
Upper medulla on
the right.
Upper medulla on
the left.
C1
A.
rig
ht
.
Your patient has no sensation at all
on the left side of the body. Which
of the following sites of damage is
25% 25% 25%
most likely?
:30
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.
Conclusion

L-E ch. 6 for Wednesday
◦ Focus on pathways

Cerebellar histology task due Friday at
midnight
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. and Chief 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

Your patient has no sense of taste
but all other functions seem to be
fine. Which of the following
structures may be damaged?
op
ha
ry
ng
lN
Gl
os
s
Fa
c ia
ea
lN
er
ve
er
ve
s
uc
ry
N
ol
ita
tra
lS
3%
0%
le
u
cle
us
Nu
Ro
s
D.
0%
ar
y
C.
So
lit
B.
Caudal Solitary
Nucleus
Rostral Solitary
Nucleus
Facial Nerve
Glossopharyngeal
Nerve
Ca
ud
al
A.
97%
Your patient cannot feel anything on
the right side of the face. Which of
the following is most likely damaged?
55%
27%
Le
f
tT
sc
us
al
l
em
ni
sc
us
le
m
ni
rig
em
in
al
so
ry
en
ie
fs
Ch
Ri
gh
t
Ri
gh
t
us
nu
cle
en
so
ry
ef
s
hi
tC
Le
f
9%
nu
cle
us
9%
Tr
ige
m
in
Left Chief sensory
nucleus
B. Right Chief sensory
nucleus
C. Left Trigeminal
lemniscus
D. Right Trigeminal
lemniscus
A.
Your patient’s breathing rate is abnormal
when under stress. Which structure would
carry information about oxygen saturation
in the blood to the medulla?
100%
...
th
e
in
to
rs
0%
ca
ro
tid
n.
..
ar
y
ol
it
of
s
Ba
ro
re
ce
p
po
rt
io
n
Va
gu
s
ne
rv
e
0%
Ca
ud
al
er
ve
ea
ln
D.
0%
ar
yn
g
C.
op
h
B.
Glossopharyngeal
nerve
Vagus nerve
Caudal portion of
solitary nucleus
Baroreceptors in
the carotid artery
Gl
os
s
A.
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

Read Bear Ch. 12 for Monday