Long Sensory Pathways Somatic Sensation Anterolateral System Pain

Long Sensory Pathways (Somatic Sensation) - Anterolateral System (Pain and Temperature Pathway) - DCML (Vibration and Proprioception) David A. Morton, Ph. D. Thursday January 31 st, 2013

Objectives • • • 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) Po st -c en tra lg yr us 3° Order neuron • Location of cell body. • Course of axons. • Location of synapse. Internal capsule VPL Thalamus

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 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. Do rsa l co lum n Proprioception, vibration, fine touch

Dorsal Column-Medial Lemniscus (DCML) tra ct te ea Cu n Grac ile tr act 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 4 th ventricle X IX, X Olivary n ucleus Pyram Med lem ALS XII id

Pons V ALS CN V What happened in the Pons? Med lem

Midbrain AQ III ALS ML bs Su Red nucleus ia nt ta a gr un ed lp ra ni b re Ce cle

Diencephalon 3 rd ventricle IC RN Ce reb ped 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?