Neurones normally communicate by using electrical and chemical signals or messages that cause ‘depolarisation’. But sometimes neurones might send out an ‘abnormal’ message. For example, a neurone could send out an excitatory message that causes a larger-than-normal depolarisation. This in turn could make other neurones send out abnormal messages.
If just a single neurone behaves like this and sends out an unusual message, it is unlikely to cause a seizure. But if lots of neurones, from the same part of the brain, send out unusual messages together, then this could cause a seizure to happen. For the messages to cause a seizure:
- each neurone must be excited
- they must be connected to many other neurones within just a few synapses, and
- the message must be large enough to cause the other neurones to act in the same way.
Under these conditions, the message could spread very quickly. If the unusual message causes disrupted activity, this may affect just part of the brain (and cause a partial seizure) or the disrupted activity could spread to affect the whole of the brain (and become a generalised seizure). The part of the brain where the disruption starts is called the ‘epileptic focus’.
The brain and epileptic seizures
The brain has millions of nerve cells (or neurones) which control the way we think, move and feel. The nerve cells do this by passing electrical signals to each other. If these signals are disrupted, or too many signals are sent at once, this causes a seizure (sometimes called a ‘fit’ or ‘attack’).
The brain has many different functions. Our moods, memory, movement, consciousness and our senses are all controlled by the brain, and any of these can be affected if someone has a seizure. They may feel strange or confused, behave in an unusual way, or lose some or all awareness during the seizure.
What might cause neurones to behave differently from normal?
It could be that:
- if neurones are damaged, this might change how they normally work and affect how they send signals
- if there are too many or not enough neurotransmitters, this affects how the neurones can communicate, and could cause seizures
- some neurones have ion channels which are slower than normal, that is the messages are not ‘turned off’ as quickly as they would normally
- some neurones may have different synaptic receptors that receive the neurotransmitters, and this could make it harder for the neurone to stop or ‘switch off’ the message, so the neurone continues to send the message even after it is not needed anymore.