Sensory receptors of the body can be classified according to three different classification schemes. They can be grouped based on stimulus type, location, or by receptor structure. We will be classifying the receptors of the general senses by receptor structure. The two primary structure types are found below along with all of the receptors falling into these two categories.
Simple Receptors of the General Senses
Nonencapsulated nerve endings:
This is an incredibly widespread receptor type. Receptors found in this category are primarily responsible for detecting temperature change and pain. To a lesser extent some receptors in this category are responsible for detecting pressure changes and even itch. The three types of non encapsulated nerve endings are found below.
Free Nerve Endings: simply modified dendrites of 1st order sensory neurons. detect pain and temp change.
Tactile (merkel) discs: Light touch receptors
Hair follicle receptors: free nerve endings wrapped around hair follicles that detect bend in hairs
Encapsulated Nerve Endings:
Tactile Corpuscles: Discriminative touch receptors. Highly abundant in finger tips.
Lamellar Corpuscles: Often visible to the naked eye when removed from skin, these incredibly large receptors are stimulated by deep pressure. However, they respond only when pressure is first applied, and therefore are more accurately described as vibration receptors.
Bulbous corpuscles: Also called ruffini endings, these receptors are similar to golgi tendon organs but are found in other types of connective tissue. They detect deep and continuous pressure.
Muscle spindles: found in skeletal muscle, these complex receptors measure muscle length and are involved in the stretch reflex.
Tendon organs: Found in muscle tendons, these receptors respond to and measure tension. Involved in the tendon reflex.
Joint kinesthetic receptors: Made up of several previously mention receptor types, receptors in this group measure joint capsule stretch.