Processes sensations of fine touch pressure twopoint discrimination vibration and proprioception

- consists primarily of group II fibers.

- Course: primary afferent neurons have cell bodies in the dorsal root. Their axons ascend ipsilaterally to the nucleus gracilis and nucleus cuneatus of the medulla. From the medulla, the second-order neurons cross the midline and ascend to the contralateral thalamus, where they synapse on third-order neurons. Third-order neurons ascend to the somatosensory cortex, where they synapse on fourth-order neurons.

b. Anterolateral system

- processes sensations of temperature, pain, and light touch.

- consists primarily of group III and IV fibers, which enter the spinal cord and terminate in the dorsal horn.

- Course: second-order neurons cross the midline to the anterolateral quadrant of the spinal cord and ascend to the contralateral thalamus, where they synapse on third-order neurons. Third-order neurons ascend to the somatosensory cortex, where they synapse on fourth-order neurons.

2. Mechanoreceptors for touch and pressure (Table 2-5)

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