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%

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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...

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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...

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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%

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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