The Proprioceptive System

Proprioception is the process by which the body can vary muscle contraction in immediate response to incoming information regarding external forces, by utilizing stretch receptors in the muscles to keep track of the joint position in the body.

Proprioception and kinesthesia, the sensation of joint motion and acceleration, are the sensory feedback mechanisms for motor control and posture. These mechanisms along with the vestibular system, a fluid filled network within the inner ear that can feel the pull of gravity and helps the body keep oriented and balanced, are unconsciously utilized by the brain to provide a constant influx of sensory information. The brain can then send out immediate and unconscious adjustments to the muscles and joints in order to achieve movement and balance.

Proprioception, also often referred to as the sixth sense, was developed by the nervous system as a means to keep track of and control the different parts of the body. An example that enables one to best understand this sensory system is one showing what happens if this sensory system is no longer there. A normal person is able to move a finger, knowing where and what the finger is doing, with little effort. The normal person could just volunteer the finger to move back and forth and proprioception would make this an easy task. Without proprioception, the brain cannot feel what the finger is doing, and the process must be carried out in more conscious and calculated steps. The person must use vision to compensate for the lost feedback on the progress of the finger.

The proprioception sensory system is carried out utilizing proprioceptors in the muscles that monitor length, tension, pressure, and noxious stimuli. The muscle spindles, the most complex and studied of the proprioceptors, informs other neurons of the length of the muscle and the velocity of the stretch. The density of muscle spindles within a muscle increases for muscles involved in fine movements, as opposed to those involved in larger course movements. The brain needs input from many of these spindles in order to register changes in angle and position that the muscle has accomplished. There is also more spindles found in the arms and legs, muscles that must maintain posture against gravity.
Another proprioceptor, the golgi tendon organ, is found where the tendons meet the muscle. They send detailed information about the tension occurring in specific parts of the muscle. There are also proprioceptors sending information to the nervous system from joints and ligaments. Depending on the amount, where in the body, and from what proprioceptors the different input is coming from, determines if the information will be made conscious or processed unconsciously. All the input coming into the nervous system is processed, and then depending on the state of the muscle, there are commands sent back to the muscle.

The initiation of proprioception is the activation of a proprioreceptor in the periphery. The proprioceptive sense is believed to be composed of information from sensory neurons located in the inner ear (motion and orientation) and in the stretch receptors located in the muscles and the joint-supporting ligaments (stance). There are specific nerve receptors for this form of perception termed “proprioreceptors”, just as there are specific receptors for pressure, light, temperature, sound, and other sensory experiences. Proprioreceptors are sometimes known as adequate stimuli receptors.

Although it was known that finger kinesthesia relies on skin sensation, recent research has found that kinesthesia-based haptic perception strongly relies on the forces experienced during touch. This research allows the creation of “virtual”, illusory haptic shapes with different perceived qualities.

SIGNS OF PROPRIOCEPTIVE DYSFUNCTION:

1. SENSORY SEEKING BEHAVIORS:

__ seeks out jumping, bumping, and crashing activities

__ stomps feet when walking

__ kicks his/her feet on floor or chair while sitting at desk/table

__ bites or sucks on fingers and/or frequently cracks his/her knuckles

__ loves to be tightly wrapped in many or weighted blankets, especially at bedtime

__ prefers clothes (and belts, hoods, shoelaces) to be as tight as possible

__ loves/seeks out “squishing” activities

__ enjoys bear hugs

__ excessive banging on/with toys and objects

2. DIFFICULTY WITH “GRADING OF MOVEMENT”

__ misjudges how much to flex and extend muscles during tasks/activities (i.e., putting arms into sleeves or climbing)

__ difficulty regulating pressure when writing/drawing; may be too light to see or so hard the tip of writing utensil breaks

__ written work is messy and he/she often rips the paper when erasing

__ always seems to be breaking objects and toys

__ misjudges the weight of an object, such as a glass of juice, picking it up with too much force sending it flying or spilling, or with too little force and complaining about objects being too heavy

__ may not understand the idea of “heavy” or “light”; would not be able to hold two objects and tell you which weighs more

__ seems to do everything with too much force; i.e., walking, slamming doors, pressing things too hard, slamming objects down

__ plays with animals with too much force, often hurting them

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