FoundationalConceptsNeuroscience

along the axon into the central nervous system. A DRG dendrite func-
tions just like an axon, except that action potentials propagate toward
the cell body instead of away from it.
Somatosensory neurons have spatial receptive fields—the region of
skin where a physical stimulus elicits activity in the specified neuron.
Axons of somatosensory neurons in the DRG synapse with cells in the
spinal cord and with cells in the medulla of the brainstem. From there,
the somatosensory circuitry continues into the thalamus. Somatosen-
sory neurons in the thalamus then project to the anterior parietal
lobes in the cerebral cortex (Fig. 16.3.). Spatial receptive field informa-
tion is maintained along this pathway such that a somatosensory map
of the body is constructed in the parietal lobes. The various locations
in the body are represented along the postcentral gyrus, immediately
posterior to the central sulcus.
Just as the primary visual cortex (V1) in the occipital lobe contains
a topographic representation (map) of visual space, the primary
somatosensory cortex (S1) contains a topographic representation
of somatosensory space—the surface of one’s own body. Like other
sensory areas of the cortex, the somatosensory cortex receives signals
from the contralateral side of the body. A lesion in $1 produces a loss
of sensation in a particular region of the body related to where the
lesion is on the body map in S1. Such a lesion is the somatosensory
analogue of a visual scotoma.