- د.محمد علي 2026Book 37:43
- د. ناجي
- د. محمد الشريف
- سبورة د. محمد الشريف
- ملزمة د. محمد الشريف
🟠 General Characteristics of Somatic Sensory Pathways
- 🖇 Any pathway is made of 3 Order Neurons (1st – 2nd – 3rd ON).
- 🖇 All are Ascending Tracts → going upward (opposite of Motor = Descending).
- 🖇 1st ON always originates from Dorsal Root Ganglion (DRG).
- 🖇 Cerebral Cortex = Manager (final perception: type + intensity + location).
- 🖇 Thalamus = Secretary (relay station before reaching cortex).
- 🚨 Decussation: most fibers cross to the opposite side → explains why left cortex lesion affects right body side.
🟣 Crude Touch Pathway (Ventral Spinothalamic Tract)
- 📌 Sensation: Crude Touch (basic awareness without localization/discrimination).
- 📌 1st ON: from DRG → ends in Lamina II, III, IV.
- 📌 2nd ON: starts in those laminae → crosses (Decussation) → goes to VPLN of Thalamus.
- 📌 3rd ON: from VPLN → via Thalamic Radiation → to Cerebral Cortex.
🟣 Pain & Temperature Pathway (Lateral Spinothalamic – Paleospinothalamic)
- 📌 Sensation: Slow Pain + Temperature.
- 📌 Fiber type: Type C fibers (Type 4).
- 📌 1st ON: from DRG → ends in Substantia Gelatinosa (Lamina II, III).
- 📌 2nd ON: starts from Lamina II, III → crosses to opposite side → ascends via Spinal Lemniscus.
- 📌 2nd ON termination: in a Specific Nucleus of Thalamus.
- 📌 3rd ON: from Specific Nucleus → Thalamic Radiation → to Cortex.
- 🚨 Extra relay compared to Crude Touch (Spinal Lemniscus + Specific Nucleus) → because pain requires stronger filtering to protect the body.
🟠 Key Points & Questions
- 🖇 Every sensory pathway = 3 Order Neurons.
- 🖇 1st ON always originates from DRG.
- 🖇 Opposite-side sensation due to Decussation.
- 🖇 Cortex vs. Thalamus: Cortex = Manager, Thalamus = Secretary.
- 🖇 Pathway differences:
- Ventral (Crude Touch): 2nd ON ends in VPLN.
- Lateral (Pain/Temperature): additional relay (Spinal Lemniscus) + ends in Specific Nucleus.
🟠 General Characteristics of Somatic Sensory Pathways
- 🖇 Any pathway is made of 3 Order Neurons (1st – 2nd – 3rd ON).
- 🖇 All are Ascending Tracts → going upward (opposite of Motor = Descending).
- 🖇 1st ON always originates from Dorsal Root Ganglion (DRG).
- 🖇 Cerebral Cortex = Manager (final perception: type + intensity + location).
- 🖇 Thalamus = Secretary (relay station before reaching cortex).
- 🚨 Decussation: most fibers cross to the opposite side → explains why left cortex lesion affects right body side.
🟣 Crude Touch Pathway (Ventral Spinothalamic Tract)
- 📌 Sensation: Crude Touch (basic awareness without localization/discrimination).
- 📌 1st ON: from DRG → ends in Lamina II, III, IV.
- 📌 2nd ON: starts in those laminae → crosses (Decussation) → goes to VPLN of Thalamus.
- 📌 3rd ON: from VPLN → via Thalamic Radiation → to Cerebral Cortex.
🟣 Pain & Temperature Pathway (Lateral Spinothalamic – Paleospinothalamic)
- 📌 Sensation: Slow Pain + Temperature.
- 📌 Fiber type: Type C fibers (Type 4).
- 📌 1st ON: from DRG → ends in Substantia Gelatinosa (Lamina II, III).
- 📌 2nd ON: starts from Lamina II, III → crosses to opposite side → ascends via Spinal Lemniscus.
- 📌 2nd ON termination: in a Specific Nucleus of Thalamus.
- 📌 3rd ON: from Specific Nucleus → Thalamic Radiation → to Cortex.
- 🚨 Extra relay compared to Crude Touch (Spinal Lemniscus + Specific Nucleus) → because pain requires stronger filtering to protect the body.
🟠 Key Points & Questions
- 🖇 Every sensory pathway = 3 Order Neurons.
- 🖇 1st ON always originates from DRG.
- 🖇 Opposite-side sensation due to Decussation.
- 🖇 Cortex vs. Thalamus: Cortex = Manager, Thalamus = Secretary.
- 🖇 Pathway differences:
- Ventral (Crude Touch): 2nd ON ends in VPLN.
- Lateral (Pain/Temperature): additional relay (Spinal Lemniscus) + ends in Specific Nucleus.