The somatosensory system is the components of the central and peripheral nervous system that sense and process touch, pressure, pain, temperature, and body position or proprioception. The detection and processing of this sensory information take place at three main levels—the receptor, circuit, and perceptual levels. Starting at the receptor level, an incoming stimulus excites a sensory receptor. The receptor then converts the stimulus into an electrical signal, generating a graded potential. When this graded potential reaches a certain threshold, a nerve impulse is generated. Next, at the circuit level, this impulse reaches the central nervous system or the CNS through several ascending pathways. The majority of sensory impulses reach the primary somatosensory area of the cerebral cortex, while some proprioceptive impulses are processed in the cerebellum. Finally, the sensory information is interpreted by the CNS at the perceptual level. Only the impulses processed in the cerebral cortex are consciously perceived.