Receptors are energy transducers, or changers. When a stimulus (light, tough, chemicals, sound, etc.) is received by a receptor, the receptor changes it into an electro-chemical form that can be taken up to the brain by neurons.
Receptors are like reporters who snoop around, investigate, and inform us about breaking news. We’ll be concerned with the receptors that have to do with the somatosensory system.
Golgi Tendon Organs (Aα) are receptors that detect muscle tension (force).
Muscle Spindles (Aα, Aβ) are receptors that detect muscle length and velocity.
Meisner’s Corpuscles (Aβ) are receptors that detect touch and movement.
Merkel Cells (Aβ) are receptors that detect fine touch.
Pacianian Corpuscles (Aβ) are receptors that detect vibration.
Ruffini Endings (Aβ) are receptors that detect skin stretch
Hair Follicles (Aβ) are receptors that detect touch movement
Free Nerve Endings (Aβ, Aδ, and C) are free nerve endings (don’t end in a receptor) that detect nociception (high threshold chemoception, mechanoception, and thermoception), temperature, and itch.
The complication: receptors seem to be noisy and information from them can be confusing.¹
For instance, muscle spindles produce signals related to muscle length and velocity, but these exact same signals can be generated at many different positions and velocities.
Similarly, while golgi tendon organs are accurate force sensors, movements are rotations. The exact same muscle force can correspond with varying torques because moment arms change with joint position.