Our sensory system conveys the information we need to our brains so we can make the right decisions in daily life. Huge amounts of information flow in to our brain at all times and we must decide the importance or otherwise of this. Hearing, touch and sight are clearly used by use to manage our responses to the challenges of normal life but there are other sensory modalities which are just as important in our mobility. The feelings coming in from all our bodily structures such as our muscles, ligaments, discs and joints are very important for normal movement function. Joint position sense is more specifically related to our joints and is also called proprioception.
Have you ever woken up in the night to find you have a numb and dead arm? I woke up on my back to find an arm laid across my chest so I lifted it off to the side. Very soon it came back. I moved it again, this time with a bit more speed. It came back. Gradually waking up I felt up the arm until I got to my shoulder. It was my own arm! Since I had laid on my arm, cutting off the blood supply to the nerve or compressing it, all sensory input to my brain from the arm had been cut off. My arm did not exist as far as by brain was concerned and when I gripped and moved my arm I had no sense that it was mine. As far as I was concerned the lack of feeling coming in meant that the arm had to be someone else's.
Compression of the nerves in the arm or cutting off their circulation in the same manner can completely interrupt the incoming messages to the brain, making the brain think that the area of the body does not exist at all and therefore has no movement function. The brain is unable to picture the limb and its position so is cannot plan any useful movement for the limb either. Working as a physiotherapist for over twenty years has left me with a clear view of the importance of sensory input in our management of normal movement.
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.
The loss of movement is the most obvious disability we see when we observe a stroke patient, but what we don't see is the loss of accurate sensory input, an impairment which may be more disabling overall. The joint position sense (JPS), also called proprioception, is the ability which allows our system to understand at any point where our joints are, what stresses are acting on them, how fast they are moving and how much muscle effort is being expended.
Monitoring of the positions, stresses and effort being exerted through all our joints is streaming in to our brains all the time from the joint position sense and other sense organs in our muscles and tendons. We need all this incoming information to make sense of where our limbs are so that we are in a position to do the next actions we desire. Accurate JPS information is essential if we are to be able to plan our next movement.
The loss of the ability to feel any part of our body accurately can have profound consequences, reducing our functional independence in many normal daily activities. Typical conditions include stroke, paraplegia and direct nerve damage but more surprising injuries can reduce JPS input. A sprained ankle or ruptured anterior cruciate ligament reduces the accuracy of joint position sense and requires rehabilitation. Physiotherapists are skilled in the rehabilitation of proprioceptive ability in multiple conditions.
Jonathan Blood Smyth is Superintendent of a large team of Physiotherapists at an NHS hospital in Devon. 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 Brighton or elsewhere in the UK.
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