Somatosensation refers to senses of the body, including touch, position, vibration, pain, and temperature sensation. These are called the primary modalities (types) of somatosensation. There are different somatosensory receptors in the skin and deep tissues for different somatosensory stimuli. Mechanoreceptors detect touch and vibration, thermoreceptors detect temperature, and nociceptors detect noxious stimuli that cause pain. Other mechanoreceptors in skeletal muscles, tendons, and joint tissues detect the position of body parts relative to each other.
Somatosensory information travels along nerves in the axons of pseudounipolar neurons. For most of the body, the somas of these neurons are in posterior spinal nerve root ganglia, but for the face, and a few other parts of the head, they are in the ganglia of the trigeminal nerves. The peripheral axons of these neurons connect to somatosensory receptors in skin and deep tissues, and their central axons enter the spinal cord, via posterior spinal nerve roots, or the brainstem, via the trigeminal nerves.
Some somatosensory information from around the ears, mouth, and throat travels into the brainstem in a few other cranial nerves.