[thedoc (OP)]

jc mahne asked the Naked Scientists:
   
Are nerve pulses arriving at muscles  different to ones leaving  them?

I am building an EMG machine for a friend who has had a stroke.
What I'm trying to do is keep track of therapy. We cannot get any time with EMG machines or neurologists due to the National Health system.
I'm trying to find out if any pulses are arriving at his muscles from his brain.I'm not sure if these small pulses will be swamped by the ones leaving his muscles (which are in a spasm) to his brain, or if the waveform is different some how and could be recognized. Thanks in advance. If you don't know the answer could you please help me find someone who does?

What do you think?

[evan_au]

The terminology you are looking for is the difference between afferent nerve impulses and efferent nerve impulses.

[chris]

The information being transmitted to muscles arrives along motor neurones, which exit the spinal cord directly and pass directly to the muscles they supply. Motor neurones terminate at a "motor end plate", which is a specialised junctioned between the nerve and muscle tissue. Activity within the nerve leads to the discharge of the transmitter chemical acetyl choline onto the end plate. Engagement with acetyl choline receptors on the muscle leads to the entry of sodium and calcium into the muscle tissue, which in turn causes the muscle to contract.

As the muscle changes length, stretch-sensitive receptors inside it and within the tendons transmit impulses back to the spinal cord to inform the central nervous system of the rate of change of the length of the muscle and the force being generated. These impulses pass via dorsal root ganglia back into the spinal cord and also send branches up to the brainstem. Unlike the efferent motor neurones, these sensory afferent connections use the excitatory nerve transmitter chemical glutamate.

The mechanics of the action potentials (nerve impulses) generated by both are, however, the same.

[evan_au]

Are nerve pulses arriving at muscles  different to ones leaving  them?

Bear in mind that the muscles themselves produce an electrical potential as they contract, somewhat similar to nerve impulses.

I suspect that the electrical signal from the muscles will overwhelm the electrical signals from the nerves, if you try to measure these signals by surface electrodes anywhere near the muscles.

[chris]

Good point; although it did say "nerve impulses" in the question.