the first neuron in a chain is a primary neuron. the dendrites of this neuron are part of the receptor that detects a specific stimulus. the cell bodies of these neurons reside in the of spinal nerves. the axon projects to a secondary neuron within the cns. the secondary neuron is . the cell body of this neuron resides within either the posterior horn of the spinal cord or a . the axon of a secondary neuron projects either to the thalamus for sensations or to the cerebellum for proprioception. the secondary neuron to the thalamus synapses with the tertiary neuron, the third neuron in the chain. the tertiary neuron is also an interneuron, and its cell body resides within the . the axon of the tertiary neuron projects to the primary somatosensory cortex of the parietal lobe.