The brain is a complex and fascinating organ made up of millions of cells, some of which are called neurons. Despite their small size, neurons work together to allow us to do all the essential and fun things we do each day. That is, when we bite into ice cream and experience the sweet creamy taste, or when we hunker down to concentrate, that’s the brain’s neurons at work.
The brain is an electro-chemical organ where the neurons, within the brain, have electrical and chemical properties. Neurons use these electrical and chemical properties to “communicate” with each other. It is this communication between neurons that allows us to function, both with basic tasks and beyond.
Neurons are naturally charged cells with positive, negative, and neutral charges. The charge of a neuron determines whether it will be active and communicate with other neurons, or be inactive. Neurons have a more negative charge on the inside, and a more positive charge on the outside (Figure A). This balance of charge is dynamic as it can be readily changed by other neurons. We know that positive charges repel each other, but positive and negative charges attract each other, hence the expression, “opposites attract.” Within neurons, the “opposites attract” phenomenon comes into play, as positive charges on the outside are attracted to the negative charges on the inside. This influx of positive charges to the inside of the neuron causes an imbalance that results in a charged neuron, ready to communicate with other neurons.
Figure A: Charges inside/outside of a neuron
Neuronal Communication Process
Step 1: Neuron Receives Information
Neurons contain branch-like structures called dendrites (Figure B) that receive input from other neurons, and it is this input that changes the balance of the charges. If the inputs from other neurons are excitatory, then they send more positive charge into the neuron. If the inputs are inhibitory, then they send more negative charge into the neuron.
Figure B: Structure of a neuron
Step 2: Neuron Transmits Information
The electrochemical charges from all other neurons are summed together at a region called the axon hillock, which is the area just before the start of the axon. Dendrites receive information, and axons transmit information. If the sum of the charges reaches a certain “threshold” then an electrical impulse is generated. This impulse is the electrical signal (much like an electrical current) of communication that travels down the axon.
Step 3: Neuron Releases Neurotransmitters
At the end of the axon are structures called axon terminals, or terminal buttons. Once the electrical signal reaches the end of the axon, it causes a chemical release of neurotransmitters. Neurotransmitters are chemical messengers that can bind to and communicate with other neurons as well as muscles and glands.
Step 4: Electrochemical Communication
The neurotransmitters are released into a small space, known as a synapse between the neurons (Figure C). After release, the neurotransmitters float across the synapse and attach, or bind to small proteins called receptors on the dendrites of the next neuron (Figure D). This binding is the final step of the communication cycle, and this final step may give an excitatory or inhibitory message to the receiving neuron. Excitatory messages increase communications and release of neurotransmitters, while inhibitory messages do the opposite.
Figure C: Synapse Figure D: Release of transmitters at synapse
Therapy, Medication, and Neurons
The electrical and chemical properties of neurons allow for therapies such as medications and neurostimulation (also called neuromodulation) techniques to work effectively on the brain.
Medications target the chemical properties of neurons in order to improve well-being.. Other therapies such as brain stimulation target the electrical properties of neurons.
For example, transcranial magnetic stimulation (TMS) is a non-invasive form of therapy that can influence the electrical aspect of neurons. With TMS (Figure E), a magnetic coil is placed against the scalp and magnetic impulses are delivered. These impulses create a small electrical current that provides either excitatory or inhibitory input to the underlying neurons. Hence, TMS therapy generates impulses within neurons in order to improve function. For example, stimulating, or increasing the activity neurons with electrical impulses may help improve certain symptoms such as depression. But, also inhibiting, or reducing the activity of neurons may help reduce other tasks such as feelings of worry or anxiety. In this way, TMS can stimulate or inhibit brain activity depending on which tasks or brain functions are of therapeutic need.
Figure E: TMS administration to a patient