Somatosensory system: general overview. Mechanoreceptors. Thermoreceptors. Nociceptors.
The somatosensory system is responsible for detecting and processing various sensations from the body, including:
- Touch
- Pressure
- Vibration
- Proprioception (limb position and movement)
- Temperature
- Pain
This system relies on a network of specialized sensory receptors, neural pathways, and processing centers in the brain.
The system relies on a 3-neuron relay system. Impulses are carried from receptors via afferent neurons to the dorsal root ganglia where the bodies of the 1st order neurons are located. The 1st order neurons travel through the spinal cord, synapsing to the 2nd order neurons. The 2nd order neurons then convey information to the 3rd order neurons of the thalamus, or the cerebellum. From here, the 3rd order neurons project to the postcentral gyrus (primary somatosensory cortex) of the cortex.
The somatosensory receptors are located in:
- Skin and mucous membranes. (exteroception)
- Muscles, tendons and joints. (proprioception)
- Visceral organs. (interoception)
The 1st order neurons are enveloped in connective tissue together with muscle, tendon, cutaneous cells or hair follicles. The tissue capsule + afferent terminal form a “somatosensory receptor”.