Brain & synapses The average adult human brain weighs around 3 pounds (approximately 1.4kg) and is about the size of a medium cauliflower. It contains around 100 billion nerve cells, called neurones, which are connected by 100 trillion connections, known as synapses. Neurones can be seen as the building blocks of the brain and synapses as the links in the network. Electrical signals, together with chemical reactions that are passed through the synapses allow the brain to carry out its many important functions. The brain can be divided into 4 areas known as ‘lobes’. Although they have strong connections with each other, they can largely be defined by the cognitive processes that they carry out.