Question

How nerve cells transfer messages from different body parts to brain ?
And Explain reflex action?

Answer 1

The process starts with a neuron in the periphery. An example might be a sensory neuron in the hand which responds to pressure by changing voltage across the membrane. The nerve cells have long projections called axons. (What we term nerves are bundles of axons with other protective cells)These axons carry impulses as changes in voltage across the membrane along the length of the axon from the cell body to the synapse. A synapse in where two neurons meet and communicate. At the synapse special chemicals are released which alter the voltage in the next cell, so impulses can be transferred onwards. Have a look at this site for more information:

http://en.wikipedia.org/wiki/Sensory_neurons

A reflex action is where a sensory neuron is activated and it affects a motor neuron at the level of the spinal cord. An example is the firing of a stretch receptor in the patellar tendon of the knee, which causes a motor neuron to fire making the leg move. There's a nice web page here: http://bio.rutgers.edu/~gb102/lab_5/103ar.html

I hope this answers your question - I find this sort of physiology / neuroscience fascinating