Updated: Apr 8, 2020
First, a brief introduction to the brain:
The brain is divided into multiple subcomponents based off of function. Each section is in charge of a specific process, such as the hippocampus, which is directly related to the ability to learn and remember.
The brain is composed of billions of neurons, or nerve cells, of which there are thousands of different types. Of the different types, however, they can be broken down into three basic categories of neurons (motor, sensory, and interneurons), and they function essentially the same way.
A neuron is composed of a cell body, processes, and axon terminals. The cell body contains the conventional organelles of cells: a mitochondria, nucleus, Endoplasmic reticulum, etc. The processes are the “arms” of the neuron as shown on the picture to the right.
The processes includes the axon and dendritic branches, both of which are crucial for communicating between cells. Finally, the axon terminals contain neurotransmitters, which are the chemicals sent between processes.
The process of communicating between cells is called neurotransmission. It operates through synapses attached to the ends of each axon, the long, extended branch of the neuron, which is received through the dendrites, the “shorter” arms of each neuron. (It is important to note that each neuron contains only one axon but can have multiple dendrites). The presynapses, or axon terminals, are the synapses that are connected to each axon, while the postsynapses, which are the synapses attached to the end of each dendrite, receive the signal.
There are two types of signals: electrical and chemical. Electrical signalling is the transmission of ions across neurons which are connected together by a gap junction. The flow of ions (or other substances) changes the membrane charge of the postsynapse and can either prompt it to signal its own action potential, or make it less susceptible to signalling an action potential.
Similarly, chemical signals occur in a gap between the presynapse and postsynapse, called the synaptic cleft. Within each presynapse are synapse vesicles, which deliver the neurotransmitters to the postsynapse. At the signal of an action potential, which is a nerve impulse sent through the presynapse, the membrane of the presynapse depolarizes, opens up channels, and allows ions to flow in. The neurotransmitter is then released and binds to receptors on the postsynapse, which can then either prohibit the receiving cell from signalling its own action potential, or cause the signalling of an action potential, and the cycle of communication continues.
The brain is a fascinating organ. Just think, all of our emotions and movements are caused by billions of cells signalling back and forth repeatedly, over and over again, hundreds of times a day!