The human sensory system is designed to give us the information we need to manage the challenges of the world. We take in vast amounts of information every minute of the day, much of it not relevant, the brain deciding what is important and what is not. We are familiar with vision, hearing and touch and consciously and unconsciously use the incoming information to guide our actions and responses in daily life. However, there are two more sensory input systems, related to the others, which are vital to normal functioning. These are the sensory feedback we get from our bodies and the joint position sense.
Profound loss of sensory input is more common than we think as it happens every time we get a numb, dead feeling arm when we wake up. When I woke up with my arm completely numb I moved if off my chest grumpily twice until I began to understand, by feeling the arm gradually from the elbow up, that it was my own arm I was trying to get rid of. The loss of sensibility was so great that as far as I was concerned the arm did not exist and therefore must have belonged to someone else. Without our sensory input we are limited in our abilities.
In my work as a physiotherapist I have treated all kinds of conditions and some of these interactions were very instructive. A patient who had had a stroke got hold of my hand and moved it back and forth, bending and straightening the fingers and stretching the wrist. Suddenly I realised that he thought it was his arm! He could feel nothing from his own arm when he did the same movements to it, so moving my arm seemed entirely natural until he looked more closely at it and realised it wasn't his. The next time you get a dead arm in bed, try and move it. Apart from feeling unpleasant, the limb is extraordinarily difficult to move, it feels right out of control and just lies there despite you willing it to move.
Sensory input, the constant incoming signals to the brain from the various parts of the body, informs us what is going on and where we are in space. This is much more important than we realise. Losing muscle power is difficult but people adapt and manage well but losing sensory information from a body part makes it extremely difficult or impossible to use the part. Losing sensibility is more troublesome than losing muscle power, although both are important.
In stroke we see the lack of movement easily, what we don't see is the underlying sensory abnormality which may be partly or wholly responsible for the disability. Joint position sense (JPS), also called proprioception, is the body sense which indicates to our brain where our joints are at all times. The sense also tells us what state our joints are in such as what angle they are at, what muscular effort is being exerted and in which direction the effort is being expended.
The positions of our joints are constantly being monitored by the integrative centre of our brain, fed by the sensory input of our JPS. Without this stream of input we can't understand the position of our joints and limbs and so are unable to plan what action to take next. Planning the next movement we want to depend on the ability to have accurate information coming in from the JPS.
Losing the sense of feeling our body parts accurately is fundamentally important to our ability to manage independent movement in our daily lives. Paraplegia, stroke and direct nerve trauma can cause loss of proprioception but lesser injuries can reduce this sense also. Anterior cruciate ligament rupture or even an ankle sprain can reduce the precision of the JPS and make treatment advisable. Physiotherapy rehabilitation skills are used to develop increased proprioception in many conditions and both stroke and sports therapists must be equally aware of its importance.
About the Author:
Jonathan Blood Smyth is a Superintendent Physiotherapist at an NHS hospital in the South-West of the UK. He specialises in orthopaedic conditions and looking after joint replacements as well as managing chronic pain. Visit the website he edits if you are looking for physiotherapists in Leeds.