Anatomy Bones and Muscles · MU Pleven

145. System for temperature and pain.

Walks through the pain and temperature system from nociceptors and their A-delta and C fibres, through the dorsal root ganglia and spinal cord, to the spinothalamic tract and thalamus. It then sets out the anterolateral system with its neospinothalamic and paleospinothalamic routes, and the spinal trigeminal pathway carrying facial pain. A labelled picture and a focus marker on the spinothalamic tract are included.

Inside: 2 sections · 1 labelled picture · 10 flashcards · 2 min

Topic 144 of 236 in the MU Pleven syllabus for Anatomy Bones and Muscles (Medicine, Year 2). The free AceMed note covers it in 2 sections, about 362 words (2 min of reading), with 10 flashcards.

In this note

  1. SYSTEM FOR PAIN & TEMP.
  2. Components :

Components :

  1. 1. Sensory neurons (Nociceptors) :
  • Nociceptors often have free nerve ending.
  • Pain fibers :
  • A -delta : fast, transmit sharp, well -localized pain sensation.
  • C fibers : Slower, transmit dull, diffuse or burning pain sensation.
  1. 2. Peripheral nerves
  2. 3. Dorsal Root Ganglia :

Containing cell bodies of sensory neurons.

  1. 4. Spinal Cord :

Neurons enter the spinal cord & synapse with II, III, III & IV lamina.

  1. 5. Ascending pathways :

The spinothalamic tract is a major ascending pathway for pain & temp.

forming the spinothalamic tract is located in a spinal ganglion (eFig. 9.52). Axons then enter the spinal cord through the posterior root to reach the posterior horn. From here, axons have two courses: some synapse immediately on second-order neurons in the posterior horn gray matter (lamina I and V), and others have axonal collaterals that ascend or descend one to two spinal cord segments in the posterolateral tract of Lissauer before synapsing with the second-order neurons in the gray matter (eFig. 9.51). Axons of the second-order

neurons then cross obliquely over two to three spinal cord segments within the anterior commissure of the spinal cord to join the anterolateral tract on the contralateral side (eFig. 9.52). These second-order axons ascend through the CNS to reach the third-order neuronal cell bodies in the ventral posterior lateral nucleus of the thalamus (eFig. 9.52). Axons from the third-order neurons then project through the posterior limb of the internal capsule to reach the primary somatosensory cortex (eFig. 9.52).

  1. 6. Thalamus
  2. 7. Somatosensory cortex.

✓ focus here

★ Pain & temp. pathways :

  1. 1. The anterolateral system - AL.
  • 1° spinal ganglia → 2° dorsal horn (I, II, & V) → X
  • neospinothalamic (fast pain + temp.) → (lat. spinothalamic column) → 3° ventral posterolateral thalamic nucleus → 1° somatosensory cortex.
  • paleospinothalamic → (Ant. spinothalamic column) → 3° Reticular formation + hypothalamus (midbrain) → 4° interlaminar nuclei of the thalamus → 1° somatosensory cortex.
  1. 2. Spinal trigeminal pathway from the face :
  • 1° trigeminal ganglion → 2° spinal trigeminal nucleus (pons + medulla) → X → trigeminal lemniscus
  • fibers carrying fast pain → the same ↑↑
  • fibers w slow pain → the same ↑↑

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