Joint and Muscle Proprioceptors: Types and Movements
Anatomical Classification of Joints
Based on the tissue that is located between joint surfaces. Types:
- Syndesmosis: A union made of fibrous connective tissue or dense fibrous elastic tissue. Examples of dense fibrous tissue are the interosseous membranes that unite the diaphyses of the two bones of the forearm and leg. An example of binding elastic tissue are the yellow ligaments that join the vertebral arches to each other.
- Synchondrosis: Here the tissue is hyaline cartilage. As an example, we have the union with the costal cartilages of the sternum.
- Synostosis: The tissue is bony, so these joints are rigid and have no mobility. For example, the sutures of the bones of the cranium.
- Symphysis: The tissue is similar to the binding of two ligaments (fibrocartilage and connective tissue). As an example, we have the pubic symphysis.
- Diarthrosis or Synovium: In these joints, between the articular surfaces, there is synovial fluid inside the bursa. These joints are equipped with great mobility, therefore they are called true joints.
Functional Classification of Joints
Based on the mobility of the joints. Types:
- Enarthrosis: Articular surfaces are spherical.
- Condyloarthrosis (Condyle): The articular surfaces are elliptical, one of them is convex and the other is concave. It permits movement on two planes.
- Saddle Joint: The articular surfaces are concave in one bone and convex in another, fitting into each other. It is biaxial.
- Trochoid or Rotating Pivot: One of the bones has a cylindrical surface that is related using an articular facet, with another bone that exhibits a concavity. Movement is permitted on only one plane.
- Trochlearthrosis or Hinge: Consists of a perfect congruence between one bone with great concavity and another pulley-shaped that fits into the first. It allows movement only.
- Arthrodia: Synovial joints that are flat surfaces. Sliding movements are possible in any direction, of one bone on another.
- Amphiarthrosis: It is a special joint, since it has no synovial capsule. We find it in the vertebrae, allowing independent movements in all planes.
- Synarthrosis: These are continuous joints where practically no movement exists. The tissue that serves as a nexus varies from the different types of synarthrotic articulation.
Muscle and Tendon Proprioceptors
Proprioception is the perception that gives us the position and movement of our body. This perception arises from the excitation of peripheral receptors (sensory organs) and proprioceptors located in the muscles, joints, and skin.
To receive and control movement or posture, the central nervous system (CNS) needs accurate and permanent information from the peripheral proprioceptors. All these receptors rapidly transmit the received stimuli to the conscious and unconscious parts of the CNS where this information is processed.
This continuous monitoring of movement and body positions will allow us to change motor patterns, learn new ones, optimize motor economy, and prevent injuries.
The proprioceptive receptors are:
- Muscle Spindles: Located inside the muscle, parallel to the muscle fibers. They detect the stretch of the muscle. The CNS responds by provoking muscle contraction.
- Golgi Tendon Organs: These receptors are located in the muscle-tendon junction where they capture the tension produced in that area. The CNS will respond to this stimulation by causing a reflex action of the antagonistic muscles (excitatory) and inhibitory of the agonist muscles, which will decrease muscle tension.
- Pacinian Corpuscles: Receptors located in the periarticular tissues where they respond to rapid variations of movement and deep pressure.
Types of Movement
- Reflex Movement: In the control of this movement, only the spinal cord is involved. The control mechanism is called the reflex arc and this is constituted by an afferent neuron, which carries the peripheral stimuli picked up by the receptors to the spinal cord, where the efferent neuron transmits a motor signal to the muscle.
- Voluntary Movement: The performance of a voluntary movement can have two phases. The first is a learning stage in which the conscious level of control is put up, represented by the cerebral cortex. Once the movement is learned, we move on to a phase of automatic execution in which unconscious levels of control intervene, as represented by the subcortical areas, the cerebellum, and the basal ganglia.