Lecture 14 Ascending Sensory Pathways

review of thalamus

• collection of nuclei located within the brain

Internal Capsule

• Posterior limb (PLIC): positioned b/w the globus pallidus and the thalamus. Contains ascending fibers running from the thalamus to the cortex.

• damage to the IC means very likely damage to the thalamus

Ascending Somatosensory Pathways (corticopetal)

• in most cases, somatosensory pathways are:

  • modality specific: diverge when the neurons enter the spinal cord

  • majority of them consist of 3 neurons

    • Primary, secondary, tertiary

    • first order (sensory receptor), second order (crossing midline), third order (ends up in brain)

  • Crosses midline at level of 2nd order neuron (spinal cord or brainstem)

  • are organized somatotopically to bring in sensation from the body and head

Primary Ascending Pathways

• dorsal column system (medial lemniscus pathway DCML)

• anterolateral column system (neospinothalamic pathway NST)

• trigeminal system: face, head, upper neck sensation

secondary ascending pathways

• spinothalamicreticular tract

• paleospinothalamic pathway

DCML: Dorsal column (medial lemniscus)

• posterior funiculus (white matter)

• Function: proprioception, fine touch, vibration

• Cutaneous mechanoceptors and proprioceptors

• thick myelinated receptors (Aa, AB)

• 1st order: ascend the spinal cord medially in the dorsal column

• 2nd order: cross midline at the medulla

DCML Picture

• picture

Anterolateral column (neospinothalamic)

• function: deep pressure, crude touch, sharp pain, tickle, temp (cold)

• nociceptors and thermoreceptors

• thin myelinated receptors (A?)

• 1st order: terminate laterally in the SC

• 2nd order: cross midline in SC (ascend in the anterolateral column)

NST picture

• Picture

Anterolateral column (paleospinothalamic and spinothalamic reticular)

• function: dull pain, temp (warm), pain awareness

• nociceptors and thermoceptors

• thick unmylinated receptors (C)

• 1st order: synapse laterally in the SC

• 2nd order: cross midline in SC (ascend in the anterolateral column)

PST and STR picture

• picture

Trigeminal system

• principal nucleus:

  • receives and transmits fine touch, proprioception

  • second-order neuron pons to thalamus

• spinal nucleus:

  • receives and transmits pain, temp

  • second-order neuron medulla to thalamus

Trigeminal picture

• picture