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Somatosensory PathwaysLectures 11-13
Organization of the Course
Spinal Cord
Brainstem/ Cerebellum
Sensory Pathways
Cerebrum
Motor Pathways
Cranial Nerves
Other Pieces of the puzzle
Overview and Development
Last FridayTask 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 ObjectivesDescribe 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 PathwaysDorsal Column / Medial Lemniscus
◦Light touch, proprioception, vibration of bodyAnterolateral System
◦Pain, temperature of bodyPost-synaptic Dorsal ColumnTrigeminal
◦Light touch, proprioception, vibration of face◦Pain, temperature of face
Solitary◦Visceral sensations of body and head
Dorsal Column / Medial Lemniscus PathwayLight touch, vibration,
proprioceptionConscious 3 neuron pathwayDecussates 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?
A. 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. Th
e grac
ile fa
scicu
lus contai
..
The s
oma for t
he 1st ord
er ...
The 3
rd ord
er neu
ron decu
s...
This
pathway c
arries l
ight t
o...
25% 25%25%25%
:30
Anterolateral System
SpinothalamicSpinoreticularSpinotectal (aka Spinomesencephalic)Pain, temperature, pressureConscious and subconscious2-3 neuron pathwayDecussates at level of Spinal CordGlutamate, 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?
A. 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. Th
e 2nd ord
er neuro
n decus..
.
The s
oma of t
he 3rd
order
n...
The c
omponents ca
rried by t
h..
The A
LS is
not converg
ent,
d...
25% 25%25%25%
:30
Post-synaptic Dorsal Column Pathway
Convergent, divergent, oscillating pathways/circuits
Convergent pathways◦ Many neurons synapse onto fewer
neurons
◦ More typical within cerebral cortex
Oscillating circuits◦ Cerebellar cortex -> deep nuclei ->
cerebellar cortex
Divergent pathways
◦ One neuron synapses onto more neurons
◦ Transmits one signal to multiple places
◦ Post-synaptic dorsal column is an example
◦ Spinoreticular and spinotectal are examples
Analyzing Case StudiesYour 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 SyndromeYour 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.
Your patient has impingement to the lateral funiculus at C7 on the right side. Which of the following is most likely?
A. Your patient suffers pain in the C7 dermatome on the right.
B. Your patient suffers pain C7 and below on the right.
C. Your patient suffers pain in the C7 dermatome on the left.
D. Your patient suffers pain C7 and below on the left. Your p
atient s
uffers p
ain in
...
Your pati
ent suffer
s pain
C7...
Your pati
ent suffer
s pain
in t.
.
Your pati
ent suffer
s pain
C7...
25% 25%25%25%
:30
Your patient has no sensation at all on the left side of the body. Which of the following sites of damage is most likely?
A. C1 spinal cord on the right.
B. C1 spinal cord on the left.
C. Upper medulla on the right.
D. Upper medulla on the left. C1 sp
inal co
rd on th
e right.
C1 spinal
cord
on the le
ft.
Upper medulla
on the rig
ht.
Upper medulla
on the le
ft.
25% 25%25%25%
:30
Research topicsSmall groupsTake turns to discuss updates and thoughts
about topicsIf 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.
ConclusionL-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 NerveOpthalmic (V1)
◦Sensation◦Sup. Orbital fissure
Maxillary (V2)◦Sensation◦Rotundum
Mandibular (V3)◦TM joint sensation◦TM joint musculature◦Ovale
Trigeminal NucleiChief 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 NeurotransmittersSubstance P (+) - painCCK (+)Glutamate (+)Enkephalin (-) - pain
Solitary PathwaySensory 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 nucleusInformation 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 KNOWBaroreflexes – Heart, vessels
(ex. Carotid sinus)Chemoreflexes – Carotid &
aortic bodies
Solitary Pathway NeurotransmittersGABASubstance PEnkephalinsSomatostatinCCK
Your patient has no sense of taste but all other functions seem to be fine. Which of the following structures may be damaged?
A. Caudal Solitary Nucleus
B. Rostral Solitary Nucleus
C. Facial NerveD. Glossopharynge
al NerveCau
dal Solit
ary N
ucleus
Rostral
Solitary
Nucleus
Facia
l Nerv
e
Glossophary
ngeal N
erve
0% 3%0%
97%
Your patient cannot feel anything on the right side of the face. Which of the following is most likely damaged?
A. Left Chief sensory nucleus
B. Right Chief sensory nucleus
C. Left Trigeminal lemniscus
D. Right Trigeminal lemniscus Le
ft Chief se
nsory
nucleus
Right C
hief se
nsory
nucleus
Left Trig
eminal le
mniscus
Right T
rigeminal
lemniscus
9% 9%
55%
27%
Your patient’s breathing rate is abnormal when under stress. Which structure would carry information about oxygen saturation in the blood to the medulla?
A. Glossopharyngeal nerve
B. Vagus nerveC. Caudal portion of
solitary nucleusD. Baroreceptors in
the carotid artery Glossophary
ngeal n
erve
Vagus n
erve
Caudal p
ortion of s
olitary
n...
Barore
cepto
rs in th
e caro
tid ...
0% 0%0%
100%
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