nerve message transmission. Help please.
bbjorn at mdb.ku.dk
Wed Oct 15 23:32:07 EST 1997
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?
No, not under physiological conditions.
Venlig hilsen (that's in Danish !)
'We all agree that your theory is crazy. The question which divides us is
whether it is crazy enough.' - Niels Bohr
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