Anatomy and Chemistry Basics
The Sensory System
The somatic (general) senses collect information about cutaneous sensations (tactile sensations on the surface of the skin) and proprioceptive sensations. The following stimuli are detected:
Tactile stimuli are detected by mechanoreceptors and produce sensations of touch and pressure:
Merkel discs are receptors with free nerve endings that detect surface pressure (light touch). They are located deep in the epidermis.
Root hair plexuses are receptors with free nerve endings that surround hair follicles and detect hair movement.
Corpuscles of touch (Meissner's corpuscles) are receptors with encapsulated nerve endings located in the dermal paillae (near the surface) of the skin that detect surface pressure (light touch).
Pacinian corpuscles are encapsulated nerve receptors that detect deep pressure and are located in the subcutaneous layer (below the skin).
Thermal stimuli are detected by free nerve ending thermoreceptors sensitive to heat or cold.
Pain stimuli are detected by free nerve ending nociceptors.
Proprioceptive stimuli are detected by the following receptors:
Muscle spindles are mechanoreceptors located in skeletal muscles. They consist of specialized skeletal muscle fibers enclosed in a spindle-shaped capsule made of connective tissue.
Golgi tendon organs are mechanoreceptors located at the junctions of tendons and muscles.
Joint kinesthetic receptors are mechanoreceptors located in synovial joints.
