explain
pain
section
2
page
34
Sendingmessages
A critical number of open sensors will start the response
N
eurones are electrically excitable. Every
time a sensor opens and positively charged
particles rush in, the neurone becomes a little
more excited. Whenmore sensors open and the
excitement inside the neurone reaches a
critical level, a rapidwave of electrical current
travels up the neurone. This electrical current
is themessage, technically called a ‘spike’, or
an ‘action potential’. Action potentials are the
way that nerves carrymessages – an action
potential is a singlemessage.
On the graph on the facing page, the horizontal
axis is time and the vertical axis is level of
excitement (electrical charge or, for the
electricians amongst you, the potential
difference or voltage across themembrane of
the neurone). Note at the start of the graph,
how the level of excitement varies, mainly due
to the number of sensors that are open. Also
note the critical
‘all or none’
threshold at
which an action potential (message) occurs.
When the actual level of excitement gets close
to the critical level of excitement, then even
small events that only open a few sensorsmay
set off themessage. So, if this neurone was
specialised to carry ‘danger’ messages, then
just a small stimulus like a tinymovement or a
change in temperature can be enough tomake
it reach the critical threshold andmaymake it
hurt (depending of course on the conclusions
made by the brain).
Remember, whenwe are talking about danger
reception, themessage that is sent along the
nerve to your spinal cord only says ‘danger’.
It does not say ‘pain’.
Somehow the spinal
cord and brain has to receive and analyse these
inputs and createmeaningful experiences
whichmay ormay not include pain.
