Final answer:
Referred pain is the conscious perception of visceral sensation projected to a different region of the body, such as pain in the left shoulder and arm as a sign of a heart attack.
Step-by-step explanation:
Referred pain is the conscious perception of visceral sensation projected to a different region of the body. When there are particularly strong visceral sensations, they are often felt in unexpected places. For example, strong visceral sensations of the heart can be felt as pain in the left shoulder and left arm.
The location of referred pain is not random, but a definitive explanation of the mechanism has not been established. The most broadly accepted theory is that the visceral sensory fibers enter into the same level of the spinal cord as the somatosensory fibers of the referred pain location. By this explanation, the brain misinterprets the sensations from the mediastinal region (where the heart is located) as being from the axillary and brachial regions.
Projections from the medial and inferior divisions of the cervical ganglia enter the spinal cord at the middle to lower cervical levels, which is where the somatosensory fibers enter.