1. Basic Plan for Somatosensory Info to Consciousness
Quaternary (4 ) o
Action Potential
Initiation Site
Outside the CNS! 1 2 3 4

2. Dorsal Column System – Symptoms Associated with Lesions
What is the symptom associated with the lesion?

3. Lateral Spinothalamic Tract – Symptoms Associated with Lesions

4. Trigeminal System: Complete Touch (and Pain) pathways

5. Trigeminal System: Complete Touch (and Pain) pathways

6. Trigeminal System – Symptoms Associated with Lesions
This is a diagram or cartoon of the brain stem, a little bit of the spinal cord down here and not shown are the thalamus and cortex, up here.

7. Cerebellar Tracts: Non-Conscious Proprioception
Flocculonodular Lobe
Receptor
DRG
Spinal Cord:
Dorsal Nucleus of Clarke
Restiform Body s y n a p e
Primary 1 o
Secondary 2
Dorsal Spinocerebellar Tract
Anterior Lobe
Posterior Lobe
Paramedian Lobule
Cerebellar
Nuclei
Dorsal
Spino-
Cerebellar Tract
T1 to L2
Inferior Cerebellar Peduncle
Cuneo-
Cerebellar Tract
Cuneocerebellar Tract
C2 to T4
Dorsal root fibers in spinal segments C2 to T4 carry muscle spindle and exteroceptive information in the ipsilateral cuneate fasciculus to the main cuneate nucleus
Medulla

8. Lesions and Clinical Deficits – Tabes Dorsalis
Degeneration of myelinated afferent fibers in the dorsal columns, (destroys large diameter axons), is a late stage of syphilis.
Symptoms:
Severe deficits in touch and position sense but often little loss of temperature perception and of nociception. Bilateral lesion = bilateral effects.
Area of Lesion

9. Lesions and Clinical Deficits - Syringomyelia
Gliosis and cavitation in midline of the spinal cord – CSF enters the cord. The larger the cavitation, the more tracts affected. One possible cause is a Chiari Malformation. Other causes include trauma, infection. (anything that compresses the CSF)
Symptoms:
Bilateral loss of pain and temperature at the level of the lesion (segments involved).
Area of lesion
Now you can have interruption of the lateral spinothalamic tract fibers as they cross the midline. This occurs commonly in
Syringomyelia – gliosis and cavitation of the cervical segments of spinal cord and brainstem (occasionally occurs at other levels of the spinal cord. Interrupts the lateral and anterior spinothalamic tracts as they cross the spinal cord in anterior gray and white commissures. Patient has segmental losses of pain and thermal sensibility often bilateral and some impairment of touch sensation. As cavitation expands, other tracts and cells become involved.
Here on this MRI is an example. It is often associated with maldevelopment and a particular kind of brain malformation. But overall this condition is fairly rare. Difficult to estimate the numbers, somewhere between 1/1800 and 1/18,000
Can be tumors and other causes – but essentially obstruction of the CSF flow forces it into the spinal cord, creating the Syrinx [searinks]
It is often bilateral because the fibers from both sides are crossing in the middle. Typically occus in cervical segments, but can occur at other levels. Again because the fibers have ascending, sensitivity loss may start a few dermatome segments down from the level of the lesion.
[[[ Tabes Dorsalis due to syphilis induces a selective destruction of nerve fibers at the point of entrance of the dorsal root into the spinal cord, especially in lower thoracic and lumbosacral regions. Results in Stabbing pains in lower limbs – may be severe, paresthesia (prickling, tingling or creeping sensation in skin) with numbness in the lower limbs. 3. Hypersensitivity of skin to touch, heat, and cold; 4. Loss of sensation in the skin of parts of the trunk and lower limbs; loss of awareness that the urinary bladder is full; 5. Loss of appreciation of posture or passive movements of the limbs, especially the legs; 6 loss of deep pain sensation such as when the muscles are compressed 7. Loss of pain sensation in skin in side of nose, medial border of forearm, lateral border of leg 8. Ataxia of lower limbs as result of loss of proprioceptive sensibility 9. Hypotonia 10. Loss of tendon reflexes – degeneration of afferent fiber. ]]]]

10. Lesions and Clinical Deficits - Wallenberg’s
Lateral Medullary (Wallenberg’s) Syndrome – Symptoms include loss of pain and temperature on the ipsilateral head/face, contralateral loss of pain and temperature in the body, and ataxia.
ALS (lateral spinothalamic tract)
Trigeminal Nucleus
Spinal Trigeminal Tract
Dorsal
Spinocerebellar Tract
Ventral
Lateral Medullary (Wallenberg’s) Syndrome- lesion of the dorsolateral medulla (occlusion of posterior inferior cerebellar artery); produces ipsilateral loss of pain and temperature in the head/face (spinal tract & nucleus of V) and contralateral loss of pain and temperature in the body due to interruption of spinal lemniscus.
Now this commonly occurs with occlusion of the posterior inferior cerebellar artery, which as you can see here essentially wraps around the medulla.

11. LESIONS and Clinical Deficits – Brown-Sequard Syndrome
Hemisection of the spinal cord, often in the cervical spinal cord – (it is rare for the entire hemisection to be affected, but this does occur, more often incomplete hemisection is found).
Symptoms:
a) Loss of fine discrimination touch, vibration, and position sense ipsilaterally for body regions from affected dermatome and down
b) Loss of pain and temperature contralaterally for body regions from affected dermatome and down (small region of bilateral loss of pain and temp at level of lesion and 2 segments below)
c) Motor Effects: – Ipsilateral Spasticity and Weakness
Click for Slide Animation DC
Arch Neurol (2001) 58: 1470.

12. Approach to starting from symptoms
Body
Head
Trigeminal System/Pathway
What modalities?
Pain & temp only
Fine Discrimination Touch
only
Spinal Trigeminal tract
(ipsi) or
Spinal Trigeminal nucleus
VTT (Ventral Trigeminothalamic Tract
(contra)
Main Trigeminal Nucleus
(ipsi)
all modalities focal = Trigeminal ganglion
(ipsi)
all modalities entire face – VPM (ventral posterior medial nucleus of the thalamus)
(contra)

13. Approach to starting from symptoms
Body
Head
Which modality?
pain & temp only
nonconscious proprioception
ataxia, cluminess
Fine discrimination touch only
ALS
dorsal column - medial lemniscus
pathway
spinocerebellar tracts/pathways
widespread or focal?
widespread (entire body) –
but without other modalities
lateral spinothalamic tract
(contra)
widespread (entire body) medial lemniscus
(contra)
focal or relatively focal – without other modalities – spinal cord – dorsal horn (2o cell bodies)
(ipsi)
focal – spinal cord – dorsal funiculus
(ipsi)
Combination of modalities: If all symptoms are on the same side of the body then it has to be AFTER both pathways have crossed the midline (THUS CONTRA) – so above the medulla. Could be in tracts as they sit next to each other just before they reach the thalamus, or in VPL or in cortex.
If it is a loss of touch on one side of the body and a loss of pain & temperature mostly on the other side but with a small region of bilateral pain & temp loss – this is key for spinal cord lesion.