Primary somatosensory cortex (postcentral gyrus, Brodmann areas 3, 1 and 2)
Cortex or muscle · contralateral homunculus
Third-order axons end in the postcentral gyrus, arranged as a sensory homunculus with the leg on the medial surface and the face and hand on the lateral convexity, with the lips and fingers over-represented. The cortex resolves the discriminative aspects of touch, such as localisation, texture and shape, rather than detecting the stimulus itself.
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)
- Nociceptors and thermoreceptors (free nerve endings)
- Dorsolateral tract of Lissauer and dorsal horn synapse (Rexed laminae I, II and V)
- Anterior (ventral) white commissure
- Medial lemniscusLateral spinothalamic tract (anterolateral system)Anterior spinothalamic tract (crude touch and pressure)
- Ventral posterolateral nucleus of the thalamus (third-order neurone) and thalamocortical radiation
- Primary somatosensory cortex (postcentral gyrus, Brodmann areas 3, 1 and 2)
Detail
- Homunculus
- Leg medial (anterior cerebral artery); face and hand lateral (middle cerebral artery)
- Function
- Localisation, two-point discrimination, stereognosis, graphaesthesia
When it goes wrong
Parietal cortical lesion (middle cerebral artery stroke, tumour)
Cortical sensory loss: astereognosis, agraphaesthesia, impaired two-point discrimination and sensory extinction on double simultaneous stimulation, with pinprick, temperature and vibration relatively preserved
Anterior cerebral artery infarct
Contralateral leg sensory loss with leg-predominant weakness
Practise this structure
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