Neural Integration in Sensory Systems - Processing at Perceptual Levels

2. Processing of the sensory information • Levels of neural integration in sensory systems: • Receptor level — the sensor receptors • Circuit level — ascending pathways in the CNS • Perceptual level — neuronal circuits in the cerebral cortex

3. Processing at the Perceptual Level Motor cortex Somatosensory cortex Thalamus Reticular formation Cerebellum Pons Medulla Circuit level (processing in ascending pathways) 2 Spinal cord Free nerve endings (pain, cold, warmth) Muscle spindle Receptor level (sensory reception and transmission to CNS) 1 Joint kinesthetic receptor Figure 13.2

6. Rexed’s Lamina • Some important nuclei • Substantia gelatinosa (II) • Nucleus proprius (IV) • Dorsal nucleus of Clark • Intermediolateral cell column • Motor neuron pools

8. SUMMARY: PATHWAYS IN THE SPINAL CORD Ascending (afferent) pathways (sensation) Descending (efferent) pathways (motor commands) * *

9. Spinal Tracts

10. Dorsal Column Ascending Pathway • Deep touch, visceral pain, vibration, and proprioception • Fasciculus gracilis and cuneatus carry signals from arm and leg • Decussation of 2nd order neuron in medulla • 3rd order neuron in thalamus carries signal to cerebral cortex

11. Spinothalamic Pathway • Pain, pressure, temperature, touch, • Decussation of the second order neuron occurs in spinal cord • Third order neurons arise in thalamus and continue to cerebral cortex

12. Spinoreticular Tract • Pain signals from tissue injury • Decussate in spinal cord and ascend with spinothalamic fibers • End in reticular formation (medulla and pons) • 3rd and 4th order neurons continue to thalamus and cerebral cortex

13. Corticospinal Tract • Precise, coordinated limb movements • Two neuron pathway • upper motor neuron in cerebral cortex • lower motor neuron in spinal cord • Decussation in medulla

14. Nucleus reticularisparagigantocellularis Pain inhibitory complex p_reisi@med.mui.ac.ir