explain
pain
section
2
page
30
A closer look at alarm signals
Sniffing little reporters can set off alarm bells
T
hroughout your entire nervous system, there are
millions of sensors. They are like reporters that are
constantly sniffing around and surveying their area for
activity. These sensors sit in the walls and at the end of
individual nerve cells (neurones), and they give the
neurones the ability to convey information. See page 60 for
more on neurones.
Sensors can be quite specialised. Some will respond to
mechanical forces (M) such as pinch or pressure. Some
respond to temperature changes (T), both hot and cold.
Others respond to the presence of chemical changes (C),
either from outside your body (eg. nettles, allergens) or
from inside your body (chemicals released by cells, or
carried in body fluids eg. lactic acid). When sensors
respond to a stimulus, such as acid or a pinch, they open
so that positively charged particles from outside the
neurone rush into the neurone. This sets up an electrical
impulse in the neurone.
These sensors, alongwith the sensors in your eyes (specialised
to respond to light), ears (specialised to respond to sound
waves) and nose (specialised to respond to chemicals in the
air) are your first protection against potential harm. Your
brainwill be warned about themost dangerous stimuli and
if one type of sensor fails anothermay take over.
As well as the sensors being specialised, the neurones in
which they sit can be specialised. For example, the
electrical impulses in some neurones travel 150 kilometres
per hour and in others, only one kilometre per hour. The
information that the neurones give the central nervous
system is quite limited. For example, the spinal cord is told
‘increased temperature inmy area’, or ‘increased acid level
inmy area’, or ‘DANGER! inmy area’. The complex
sensations that we are aware of, like ‘tearing’, ‘stretching’,
‘ripping’, ‘painful’ and ‘agonising’, are produced by the
brain’s construction of events, which is based on its
evaluation of
all
the information available to it, not only
the dangermessages.
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meet some sensors responding to inputs
