nerve message transmission. Help please.

[Brian Bjørn]

Paul Attard wrote:

> Please excuse my intrusion, but I am in need of some basic information
> on the way nerves transmit and receive information.

Well, it is okay to intrude, but maybe you should have taken just a quick
look at a basic textbook in neurophysiology before posting here...

> What is the method by which messages are sent to muscles via the nerves?
> (electro chemical)?

Electrical and chemical. Nerve impulses (action potentials) arriving at the
neuromuscular junction are 'translated' into a chemical signal. The chemical
signal is the release of a transmitter substance, acetylcholine (ACh), that
diffuses across the space separating the nerve terminal and the muscle
fiber. Anchored in a specialised region of the muscle fiber receptors (AChR)
for ACh are found. AChR is a transmembrane protein. It is a socalled
ligand-gated ion channel, i.e. an ion channel that is controlled by the
binding and unbinding of other molecules. When ACh gets bound to AChR the
channel opens causing a depolarization of the muscle membrane. This membrane
depolarization is 'translated' into muscle contraction in a series of events
known as the excitation-contraction coupling.

> If it is electro/chemical what sort of levels.  I assume the greater the
> level the greater the reaction?

No, not really. Action potentials are all-or-none responses: If a certain
treshold level is reached an action potential with a distinct shape
(amplitude and duration) is fired. The transmitter release from one single
nerve terminal is therefore also an all-or-none response. The motor system
is organized in a way where one motor neuron innervates a certain number
(from a few till a few thousands) of muscle fibers. A motor neuron and its
innervated muscle fibers is known as a motor unit. The strength of
contraction is controlled by the number of motor units recruited.

> Can these levels be measured?

Yes, there are different electrophysiological ways of assessing nerve and
muscle function. The techniques are quite sofisticated and requires a lot
more explanation and understanding of the basic principles underlying the
function of the motor system.

> Are the same nerves used to transmit as well as to receive?
> (simplex/duplex)?

 No, not under physiological conditions.
--
Venlig hilsen (that's in Danish !)


Brian Bjørn
http://www.mdb.ku.dk/bbjorn/
'We all agree that your theory is crazy. The question which divides us is
whether it is crazy enough.' - Niels Bohr