Nucleus gracilis and cuneatus to internal arcuate fibres (sensory decussation, caudal medulla)
Decussation · caudal medulla crosses here
The first synapse of the dorsal column pathway is in the nucleus gracilis and nucleus cuneatus of the closed (caudal) medulla. Second-order axons sweep ventromedially as the internal arcuate fibres and cross the midline just rostral to the pyramidal decussation, forming the medial lemniscus of the opposite side.
Traced from the start
- Cutaneous mechanoreceptors (Meissner, Pacinian, Merkel, Ruffini)Proprioceptors (muscle spindle, Golgi tendon organ, joint receptors)
- Fasciculus gracilis (medial dorsal column)Fasciculus cuneatus (lateral dorsal column)
- Nucleus gracilis and cuneatus to internal arcuate fibres (sensory decussation, caudal medulla)
Detail
- Second-order cell bodies
- Nucleus gracilis and nucleus cuneatus
- Level
- Caudal medulla, just rostral to the pyramidal decussation
- Result
- Medial lemniscus is contralateral to the receptor
When it goes wrong
Any dorsal column lesion below the medulla (spinal cord)
Vibration and joint position sense are lost on the same side as the lesion, because the fibres have not yet crossed
Any lesion above the decussation (medial lemniscus, thalamus, cortex)
Vibration and joint position sense are lost on the opposite side
Practise this structure
1 question in the bank tagged Brainstem.