Third-Order Neurons : conduct impulses from the thalamus to the primary somatosensory area of the cortex on the same side.
Somatic sensory impulses ascend to the cerebral cortex via 3 general pathways:
1. Dorsal Column-Medial Lemniscus Pathway to the Cortex
Conscious proprioception from limbs, trunk and neck.
1. First-order neurons extend from sensory receptors in limbs, trunk & neck into the spinal cord and ascend to the medulla oblongata on the same side. 2. In the spinal column, the axons make up the dorsal columns which consist of Gracile Fasciculus (pelvic limbs) and Cuneate Fasciculus (thoracic limbs). These axon terminals synapse with second-order neurons in the Gracile Nucleus or the Cuneate Nucleus of the medulla. 3. Axons from second-order neurons cross to the opposite side of the medulla and enter the Medial Lemniscus (a tract that extends from the medulla to the Ventral Posterior Nucleus of the Thalamus). 4. Once in the thalamus, axons from second-order neurons synapse with third-order neurons which project their axons to the primary somatosensory area of the cerebral cortex.
179
Made with FlippingBook Publishing Software