Northwestern University Feinberg School of Medicine
Somatosensory
Pathways
NUPTHMS
NeuroSIPE Lecture 1 continued
September 28, 2010
Ascending
Pathways
Dorsal column
• Discriminative touch, vibratory sense &
Proprioception
Anterolateral system
• Pain, Temperature, & Crude Touch
2
Lemniscal
Pathways
Lemniscal pathways conduct high resolution
(spatial and temporal) sensation
Dorsal column-medial lemniscal system
• Conducts high resolution touch & proprioception
- Spatial- discriminative aspects such as location and intensity
- Temporal- conducted to sensory cortex in two synapses
• Sensory neuron cell bodies in the dorsal root ganglia
• Ascend through fasciculus gracilis or cuneatus
• Synapse in the caudal medulla in nucleus gracilis or
cuneatus
• Cross through internal arcuate fibers and ascend
through medial lemniscus
• Synapse with VPL nucleus of thalamus
• Ascend through posterior limb of internal capsule to
sensory cortex
3
Anterolateral
System
One Lemniscal Pathway
• Spinothalamic Tract
• High spatial and temporal resolution pain
and temperature
• Low spatial resolution (crude) touch
Two Extralemniscal pathways
• Spinoreticular Tract
• Spinomesencephalic Tract
• Extralemniscal pathways are
phylogenetically older and conduct low
resolution sensation
4
Anterolateral
System
Spinothalamic tract
• Conducts high resolution (spatial and temporal) pain
& temperature
- Spatial resolution; discriminative aspects such as localization and intensity
(sharp pain)
- Temporal resolution; conducted to sensory cortex in two synapses (fast pain)
• Conducts low spatial resolution (crude) touch
• Sensory neuron cell bodies in the dorsal root ganglia
• Synapse immediately in dorsal horn & cross over
through anterior commissure
• Takes two to three segments for decussating fibers to
reach other side
• Ascend through anterolateral white matter
• Synapse in VPL of thalamus
• Ascend through posterior limb of internal capsule to
sensory cortex
5
Anterolateral
System
Extralemniscal- Spinoreticular &
Spinomesencephalic Tracts
Spinoreticular Tract
• Low spatial and temporal resolution
- Indirect pathway to sensory cortex (slow/chronic aching pain)
• Conveys emotional and arousal aspects of pain
• Sensory neuron cell bodies in the dorsal root ganglia
• Synapse immediately in dorsal horn & cross over
through anterior commissure
• Terminates and synapses in medullary-pontine reticular
formation
• Ascend to and synapse in intralaminar thalamic nuclei
• Ascends in widely diffuse fashion to cerebral cortex
6
Anterolateral
System
Extralemniscal continued
Spinomesencephalic Tract
• Also indirect pathway to cortex
• Sensory neuron cell bodies in the dorsal root
ganglia
• Synapse immediately in dorsal horn &
cross over through anterior commissure
• Terminates and synapses in superior colliculi,
reticular formation, and periaqueductal gray
matter
• Participates in central modulation of pain
(next lecture by Jules Dewald)
7
Spinocerebellar tracts
Sensory input and “interneuron
activity/state” input to cerebellum for
control of movement.
Each of 4 tracts never reach
conscious perception.
1. Dorsal spinocerebellar tract
• Large myelinated axons carrying proprioceptive,
touch and pressure sensation from leg/trunk
• Rapid feedback to cerebellum about ongoing
movements
• Sensory neurons synapse with Clarke’s
nucleus.
2. Cuneocerebellar tract
• Arm/Neck equivalent to dorsal spinocerebellar,
sensory neurons synapse with cuneate nucleus
8
Spinocerebellar tracts
3. Ventral spinocerebellar tract
• Arise from leg interneurons in central gray
matter NOT SENSORY NEURONS
• Information about activity/state of spinal cord
interneurons (thought to reflect activity of
descending motor pathways)
• “double-crosses” (anterior commissure and
superior cerebellar peduncle) and terminates
ipsilaterally in cerebellum
4. Rostral spinocerebellar tract
• Arm equivalent to ventral spinocerebellar tract
9
4. Rostral
spinocerebellar tract
• Arm equivalent to ventral
spinocerebellar tract
10
Sensory Loss Patterns
11
Sensory Loss Patterns
12
Spinal Cord Lesions
Transverse cord lesion at the
lumbar level
13
Spinal Cord Lesions
Hemicord lesion at the
lumbar level, right side
• Brown-Sequard Syndrome
14
Spinal Cord Lesions
Small central cord lesion at
the cervical level
• Central Cord Syndrome
15
Spinal Cord Lesions
Large central cord lesion at
the cervical level
• Central Cord Syndrome
16
Spinal Cord Lesions
Posterior cord lesion at the
cervical level
• Posterior Cord Syndrome
17
Spinal Cord Lesions
Anterior cord lesion at the
cervical level
• What are the key findings that
would make this presentation more
likely an SCI versus a CVA?
18