SENSATIONS

The central nervous system requires a continual flow of information to maintain homeostasis and initiate appropriate responses to change in the internal and external environments. At any given time, our brains receive and respond to many variety of information. However, we are aware only of the information that we CONSCOUSLY focus upon. The central nervous system selects only those bits of information that are important for the moment, and it is only those bits of information that are brought to our conscious level. There is no question that we would collapse into nervous wrecks if our consciousness was forced to deal with all the information arriving at once. The conscious mind is turned off to protect itself from OVERSTIMULATION.

Our ability to sense stimuli is vital to our survival. If pain could not be sensed, burns would be common. An inflamed facet joint or "slipped" disc would progress unnoticed. In short, if we could not "sense" our environment and make the necessary homeostatic adjustments, we could not survive very well on our own.

Sensation refers to a state of awareness of external and internal conditions of the body. Perception refers to the conscious registration of a sensory stimulus.

An awareness of the activities of muscles, tendons, and joints and of equilibrium is provided by the proprioceptive or kinaesthetic sense. It informs us of the degree to which muscles are contracted, the amount of tension created in the tendons, the change of position of a joint, an the orientaiton of the head relative to the ground and in response to movements (equilibrium). The proprioceptive sense enables us to recognize the location and rate of movement of one body part in relation to others. It also allows us to estimate weight and determine the muscular work necessary to perform a task. With the proprioceptive sense, we can judge the position and movements of our limbs without using our eyes when we walk, type, or dress in the dark.

MUSCLE SPINDLES: are the delicate proprioceptive receptors interspersed among skeletal muscle fibres (cells) and oriented parallel to the fibbers. Muscle spindles are stimulated in response to both sudden and prolonged stretch. The muscle spindles monitor changes in the length of a skeletal muscle by responding to the rate and degree of change in length. This information is relayed to the central nervous system to assist in the coordination and efficiency of muscle contraction and prevent muscle strain (tearing).

TENDON ORGANS: are proprioceptive receptors found at the junction of a tendon with a muscle. They help protect tendons and their associated muscles from damage resulting form excessive tension and also function as contraction receptors. They monitor the force of contraction of each muscle. When tension is applied to a tendon, tendon organs are stimulated, and the information is relayed to the central nervous system.

JOINT KINESTHETIC RECEPTORS: are within and around the articular capsules of synovial joints and respond to pressure. Others respond to acceleration and deceleration. Articular ligaments contain receptors similar to tendon organs and mediate reflex inhibitions or adjacent muscles when and excessive strain is placed on the joint.

The nervous system is one of the body's principal control and integrating centers. Through sensation, integration, and response, the nervous system represents the body's most rapid means of maintaining homeostasis. It's slit second reactions, carried out by nerve impulses, can normally make the adjustments necessary to keep the body functioning efficiently.