Long Sensory Pathways (Somatic Sensation)
- Anterolateral System (Pain and Temperature Pathway)
- DCML (Vibration and Proprioception)
David A. Morton, Ph.D.
Thursday January 31st, 2013
Objectives
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•
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Somatic (general) sensation
ALS and DCML pathways
Identify pathways on sections
Somatic Sensation Pathway Overview
How many neurons are involved in somatic sensation?
Somatic Sensation Pathway Overview
What structures are involved in these pathways?
Somatic Sensation Pathway Overview
Will decussation occur? If so, where?
Somatic Sensation Pathway Overview
Describe the neurons involved:
Somatic Sensation
General sensation.
Somatic Sensation
General sensation.
Crude (non-discriminative) touch. Cannot localize sensation.
Temperature
Anterior lateral system
(ALS)
Pain
Proprioception
Vibration
Dorsal column-Medial Lemniscus
(DCML)
Fine (discriminative) touch. Can localize sensation.
Receptor distribution is NOT uniform over the body surface; receptor density varies, as
does receptive field size.
Results in distorted cortical maps representing different parts of the body.
Anterior Lateral System (ALS)
General sensation.
• Crude (non-discriminative) touch. Cannot localize sensation.
• Temperature
• Pain
Anterior Lateral System (ALS)
1° Order neuron
• Location of cell body.
• Location of synapse.
• Collaterals.
• Reflex connections.
Anterior Lateral System (ALS)
1° Order neuron
• Location of cell body.
• Location of synapse.
• Collaterals.
• Reflex connections.
Anterior Lateral System (ALS)
2° Order neuron
• Location of cell body.
• Decussation.
• Course of axons.
• Location of synapse.
Anterior Lateral System (ALS)
2° Order neuron
• Location of cell body.
• Decussation.
• Course of axons.
• Location of synapse.
Anterior Lateral System (ALS)
3° Order neuron
• Location of cell body.
• Course of axons.
• Location of synapse.
Internal capsule
VPL
Thalamus
Primary Somatosensory Cortex
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•
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Brodmann’s areas.
Somatotopic organization.
Homunculus.
Contrast cortex area for hand to elbow.
A vascular lesion of which cerebral artery would result in loss of somatic sensation from the hand? From the foot?
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Medial view
Lateral view
Anterior view
• Ascending visceral afferent input travels in the
anterolateral system (dashed) and through
multisynaptic circuits via the reticular formation of
the brain stem (spino-reticulo-thalamic pathway)
(solid).
• These fibers influence both specific and diverse
areas of the cerebral cortex.
• Thalamic relays include intralaminar and midline
nuclei and cortical areas include orbitofrontal
cortex, insula and anterior cingulate gyrus.
Explain the sensory loss with a pathological enlargement of the central canal at the
level of C 5,6,7. Why might there be atrophy of the hand muscles?
Define a dermatome and explain why they are
useful. Know the dermatomes represented at
the level of the back of the head, shoulder,
thumb, middle finger, small finger, nipple,
umbilicus, inguinal ligament, big toe, small toe
and anus.
Somatic Sensation
Part II: DCML
Dorsal Column-Medial Lemniscus (DCML)
1° Order neuron
• Location of cell body.
• Location of synapse.
Proprioception,
vibration, fine touch
Dorsal Column-Medial Lemniscus (DCML)
1° Order neuron
• Location of cell body.
• Location of synapse.
Dorsal Column-Medial Lemniscus (DCML)
2° Order neuron
• Location of cell body.
• Location of synapse.
Dorsal Column-Medial Lemniscus (DCML)
2° Order neuron
• Location of cell body.
• Location of synapse.
Gracile
nucleus
ALS
Medial
lemniscus
Cuneate
nucleus
Sensory dissociation
Medulla oblongata (caudal)
Dorsal Column-Medial Lemniscus (DCML)
The somatotopic organization of the Medial Lemniscus (ML):
• "Feet down" in medulla.
• "Feet lateral" in pons.
• "Feet up" in midbrain
Dorsal Column-Medial Lemniscus (DCML)
3° Order neuron
• Location of cell body.
• Course of axons.
• Location of synapse.
Dorsal Column-Medial Lemniscus (DCML)
Trace.
Locate the ALS and DCML on the following sections:
Spinal Cord
DCML
ALS
Medulla
4th ventricle
X
ALS
IX, X
XII
Pons
V
What happened in the Pons?
Midbrain
AQ
III
Red
nucleus
Diencephalon
3rd ventricle
IC
RN
Midbrain
Mamillary bodies
The yellow represents area of a lesion. What sensory loss would you expect?
R
L
The yellow represents area of a lesion. What sensory loss would you expect?
L
R
Below the lesion:
• Loss of pain and temp from left side
• Loss of proprioception/vibration
from right side
The right side of the pons is lesioned. What sensory loss would you expect?