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The
brain and the spinal cord is called the central nervous system.
The
collective name for all other nerves outside of the central nervous system is
called the peripheral nervous system.
It
is by evaluating information sent to it from the peripheral nervous system that
the brain reacts with a course of action.
The
brain is a highly complex organ. It is the controlling organ for all of the body's
functions, the powerhouse which all living creatures have.
This
powerhouse regulates internal functions and controls behaviour. Movement,
motivation, learning, memory and emotions are regulated and controlled by the
brain.
It
has a rich blood supply, the brain of the dog is less than half of 1% of his
body weight and yet over 20% of the blood from the heart is pumped to it. Even
while the body sleeps the brain is still very active.
The
brain tissue is made up of billions of cells arranged to form grey matter and
white matter. Localised grey matter cells are called nuclei and the grey matter
covering the cerebrum
and cerebellum is called cortex.
The
brain is housed in the skull and can be divided into three main areas, the
cerebrum, cerebellum, and the brain stem.
The
cerebrum is the largest part of the brain and it controls learning, behaviour
and emotions. It stores past memories and associations. Within the cerebrum is
housed the limbic system, a network of structures which includes the hypothalamus,
hippocampus and amygdala. This system is involved with emotional
behaviour.
Emotional drive is necessary to ensure that a dog will use sufficient energy to
preserve itself and its species. Emotion is associated with courtship, mating
and the protection of offspring. Emotion is also associated with food and
hunting, escape and self defence and the protection of territory.
The
hypothalamus controls the endocrine system. It regulates temperature and
appetite. It controls the autonomic nervous system;- heart function, breathing
system, gastrointestinal
and urinary functions. It plays a major role in behaviours like rage, pleasure
and escape. It regulates the reproductive system and is involved in the
sleep-wakeful cycle.
The
hippocampus is concerned with processing recent memory.
The
amygdala controls the emotions, fear, anger, pleasure. It
is responsible for defensive actions, fight, flight or freeze.
It receives information directly from the thalamus, and is then able to
activate defence responses. This information is also fed to the amygdala
by the cortex, but the short cut via the thalamus may make the difference
between survival and death or serious injury.
Through
the working of his Limbic system the dog understands his own relationship to the
world around him. This is his value system and this is where he decides to obey
or not based
past experience. He is motivated by different things to us and the argument
between what he instinctively wants to do and what we want him to do is played
out in the limbic system of his brain. If we can influence this system then we
can control his behaviour.
The
cerebellum is involved with movement. It is influenced by the cerebrum which
gives it information of intended muscular activity and it then organises control
of the muscles, balance and co-ordination.
The
brain stem connects the brain to the spinal column. It is responsible for basic
functions of life, heartbeat, breathing, and swallowing - involuntary reflexes.
The
Brain receives its information via neurons, tiny nerve cells, there are billions
of these cells in the dogs body, each one is made up of a cell body with tiny
hairline
structures on it called dendrites, it also has a thread-like tube called an
axon, at the end of the axon there are reception sites or terminal buttons
that make contact with other
neurons via its dendrites. Putting it simply the axon sends, the dendrite
receives the
point of contact or receptor site is called a synapse.
The synapse is the
junction between the axon of the sending cell and the dendrite of the receiving
cell. The communication can only go one way, the cell which sends the
information is called the presynaptic cell and the cell
which receives the information is called the postsynaptic cell.
Neurons have several
thousand synapses, some can have over 10,000, that means that one neuron can
send different messages to thousands or tens of thousands of different cells
simultaneously. This contact causes an electrical impulse which
connects with
the next synapse by the release of a chemical, the chain reaction from cell to
cell continues until the information reaches the brain.
These chemicals are called
neurotransmitters, they transmit information, the brain then evaluates the
information and acts accordingly. The transmitting time of these
neurotransmitters is only a brief pulse, it is always the same size and always
lasts for
the same amount of time. Any unused chemical must be cleared away so that the
synapse is free to accept the next lot of information.
There
are two ways that this is done, much
of the chemical is taken away by a clearing system in the presynaptic cell
taking it back to be re-used, this is called re-uptake..
The
other way is that the chemical is broken down and de-activated by enzymes.
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