A very brief introduction to neuroscience
This is a sub-topic from Bernardo Kastrup's amazing book- Why Materialism Is Baloney - How true skeptics know there is no death and fathom answers to life, the universe, and everything. Following is my annotation of his surprisingly brief yet clear introduction to neuroscience.
The brain is composed of two main types of cells: neurons and glial cells. Neurons do the actual work of processing information, while glial cells perform support functions like insulation, structural and metabolic support, etc. We'll be focusing solely on neurons.
Each neuron is composed of three main parts: the neuron's body, the dendrites, and the axon. The neuron's body is the main part of the cell, responsible for coordinating all of neuron's activities. The dendrites are extensions of the neuron's body that contains many branches. The axon is a long, thin, cablelike projection that extends far from the neuron's body so to connect it to other neurons. The tip of the axon typically branches out into several terminals.
The brain is basically a giant network of interconnected neurons. Roughly speaking, the axon of a given neuron connects, through its multiple branching terminals, to dendrites of many other neurons. The point where an axon terminal meets a dendrite is called a synapse. The terminal and the dendrite don't actually touch: a tiny gap remains in between them, which is called a synaptic cleft.
Here is how the whole thing operates: the body of a neuron generates an electric charge. The axon of the neuron carries this electric charge all the way to its terminals. If and when the electric charge grows strong enough to cross a certain threshold, it triggers the release of certain chemicals at the terminals, which are called neurotransmitters. When this happens, the neuron is said to have fired. The neurotransmitters release, then drift across the synaptic cleft by fitting into chemical receptors. The corresponding stimulus can be an excitatory one - causing the other neuron to increase its own electric charge - or an inhibitory one - causing the other neuron to reduce its electric charge - depending on the neurotransmitter released. Whether a given neuron fires or not - that is, whether it releases neurotransmitters or not - is thus determined by how many other neurons connected to its dendrites are firing or not, and by what type of neurotransmitters - inhibitory or excitatory - they release when they do fire. A neuron only fires when it has been stimulated with enough excitatory neurotransmitters released by other neurons and provided that it has not been too inhibited by inhibitory neurotransmitters.
The entire process has electric aspects - namely, the buildup of electric charge - and chemical aspects - namely, the release of neurotransmitters. We thus say that the brain operates on the basis of electrochemical processes.
A neural network is basically a set of neurons connected together, through synapses, according to some network topology. There can be huge chains of interconnected neurons in the brain: neurons connected to other neurons, which in turn are connected to other neurons, and so on. These networks can also contain closed cycles, whereby a neuron at the end of a chain connects back to a neuron at the beginning of the chain. The brain can be seen as a superset of many neural networks.
Brain activity is associated with the firings of neurons in a natural network. Though there are many neurons in a network, typically only a subset of them is actually firing when observed. Neuroscientists can scan a living brain and see which subset of a neural network is actually active. We call each one of these active subsets a neural process.
Conscious experience correlates with certain neural processes in the brain, which are then called the neural correlates of consciousness. Naturally, neural processes can be excitatory or inhibitory, depending on whether the neurotransmitters they release respectively increase or decrease the electric charge of connected neurons.