Dr. Ravish Patwardhan comments… Movement, Sensation, & Pain in the Brain

Dr.Ravish Patwardhan has encountered numerous patients with problems related to movement and sensation of pain.  Yet, the pathways of how movement or sensation travel, either from or to the brain from the body, are important to consider in every instance.

Movement of the left side of the body is located in the right half of the brain, along the motor cortex.  If someone wanted to move her left arm, for example, her motor cortex would fire, sending a message through the area called the internal capsule, then via the brainstem where they cross over to the other side, and go down the left spinal cord to the level of the arm, where peripheral nerves would then be relayed this message, which relays the message to the muscle that contracts.

 Sensation is divided into broad categories of “fine touch” and separately, “pain.”  For fine touch, sensation that is felt in the fingertips then travels through peripheral nerves to the spinal cord (on the same side), up the brainstem, and then crossing in the upper brainstem to the opposite side of the brain’s parietal lobe.  Vibration sensation, position sensation, and fine touch are mediated in this way.

Pain is more complicated, in the sense that if the left hand touches a hot stove, then the peripheral nerve again mediates this from skin receptors to the opposite spinal cord (crossing immediately).  Then, travelling up the spinal cord, these fibers travel up the brainstem to an area of the brain called the thalamus.

What is important to realize is that this simplistic model, though accurate in many ways, is mediated by other nerves not already mentioned here.  For example, nerves in the spinal cord and brain mediate the signal, modifying it or inhibiting it.  So, if pain is felt in some nerves, en route to the brain this signal may be modified by an inhibitory neuron, so that the brain may not feel the same magnitude of pain it would otherwise have felt.  This important discovery, notes Dr.Ravish Patwardhan, that a neurosurgeon can intervene by placing an electrode wire next to the spinal cord (outside the dura, or lining of the spinal cord, called an “epidural” approach) and run a low current which will help patients who suffer from severe pain syndromes.

There are also reports in the literature about intervening for pain control by placing a stimulator electrode series within the brain.  Obviously, many of these techniques are used only as last resorts.  In addition, techniques where a small portion of the spinal cord is sectioned have also been employed, and these have varying success rates.

Peripheral nerves which are cut (i.e. nerves after they have left the spinal cord) have an ability to regenerate at about 1 mm per day (about an inch a month); though this rate is slow, it is present, and if a nerve is cut from a knife stab wound, it may be sewn together to allow regeneration of some function over time.  Nerves cut in the spinal cord or brain, however, don’t have such capacity.

Much more can be said about movement and sensation, and new research always seems to be ongoing for pain control, notes Dr. Ravish Patwardhan.