Long Sensory Pathways (Somatic Sensation)

David A. Morton, Ph.D.Thursday January 31st, 2013

- Anterolateral System (Pain and Temperature Pathway)

- DCML (Vibration and Proprioception)

Objectives• Somatic (general) sensation• ALS and DCML pathways• Identify pathways on sections

Somatic Sensation Pathway OverviewHow many neurons are involved in somatic sensation?

Somatic Sensation Pathway OverviewWhat structures are involved in these pathways?

Somatic Sensation Pathway OverviewWill decussation occur? If so, where?

Somatic Sensation Pathway OverviewDescribe the neurons involved:

Somatic Sensation

General sensation.

Somatic Sensation

General sensation.

Crude (non-discriminative) touch. Cannot localize sensation.

Temperature

Pain

Proprioception

Vibration

Fine (discriminative) touch. Can localize sensation.

Anterior lateral system(ALS)

Dorsal column-Medial Lemniscus(DCML)

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

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)

VPL

Internal capsulePost-ce

ntral g

yrus

Thalamus

3° Order neuron• Location of cell body.• Course of axons.• Location of synapse.

Anterior Lateral System (ALS)

Primary Somatosensory Cortex• 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?

* *

Medial viewLateral 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 SensationPart II: DCML

Proprioception, vibration, fine touch

Dorsal column

1° Order neuron• Location of cell body.• Location of synapse.

Dorsal Column-Medial Lemniscus (DCML)

Grac

ile tr

act

Cune

ate t

ract

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)

Medulla oblongata (caudal)

ALS

Med

ial

lem

nisc

us

Gracile nucleus

Cuneatenucleus

2° Order neuron• Location of cell body.• Location of synapse.

Dorsal Column-Medial Lemniscus (DCML)

Sensory dissociation

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.

Dorsal Column-Medial Lemniscus (DCML)

Locate the ALS and DCML on the following sections:

ALS

Spinal Cord

DCML

Olivary nucleus

Pyramid

4th ventricle

XIIX

IX, XALS

Med

lem

Medulla

ALSMed lem

V

CN V

Pons

What happened in the Pons?

Cerebral peduncle

AQ

III

Red nucleusSubstantia nigra

ALS

ML

Midbrain

Diencephalon

Midbrain

IC

Cereb ped

RN

Mamillary bodies

3rd ventricle

The yellow represents area of a lesion. What sensory loss would you expect?

RL

RL

The yellow represents area of a lesion. What sensory loss would you expect?

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?