| When a person experiences an injury, such as a stubbed toe, specialized cells called nociceptors sense potential tissue damage (1) and send an electric signal, called an impulse, to the spinal cord via a sensory nerve (2). A specialized region of the spinal cord known as the dorsal horn (3) processes the pain signal, immediately sending another impulse back down the leg via a motor nerve (4). This causes the muscles in the leg to contract and pull the toe away from the source of injury (6). At the same time, the dorsal horn sends another impulse up the spinal cord to the brain. During this trip, the impulse travels between nerve cells. When the impulse reaches a nerve ending (7), the nerve releases chemical messengers, called neurotransmitters, which carry the message to the adjacent nerve. When the impulse reaches the brain (8), it is analyzed and processed as an unpleasant physical and emotional sensation. |
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