Neurons 101: How Your Brain Sends Messages

What Is a Neuron?

Neurons, also known as nerve cells, are the basic units of our nervous system – living cells that specialise in receiving, transmitting, and processing information. Our brain contains billions of these neurons, forming a highly complex and incredibly powerful network—or rather, multiple interconnected networks. These neuronal networks, with the help of our senses, create a picture of our surroundings, store knowledge, make decisions, and control our bodies.

How thoughts, feelings, opinions, plans, memories, self-awareness, and consciousness emerge from these huge networks of neurons is still one of the world’s great unsolved mysteries. But we do know quite a lot about how individual neurons work, and how they interact with each other.

How Does a Neuron Work?

The structure of a neuron includes the central cell body (soma) and several extensions called dendrites and an axon. The soma is where the cell’s energy metabolism and protein synthesis occur. The extensions allow the neuron to transmit nerve impulses and connect with other neurons, muscle cells, or sensory cells.

Dendrites and Axons—A Neuron’s Inbox and Outbox

Dendrites are the typically short, finely branched extensions through which a neuron receives information from other neurons or sensory cells – basically the cell’s inbox.

Axons, on the other hand, are often thicker extensions that carry information to other neurons or muscle cells. Axons don’t have to be long, but they can cover significant distances in the body. For example, long axons are found in the sciatic nerve, stretching from the spine all the way to the big toe!

Information is transmitted along dendrites and axons as electrical impulses—not all that different from how computers work. To speed things up, axons are wrapped in a myelin sheath, an insulating layer with small gaps that allow the impulses to "jump" along the axon more quickly.

Synapses: Connecting Points Between Neurons

The points where the axons of one neuron meet the dendrites of another are called synapses. These synapses link all the neurons in our body.

At most synapses, there’s a tiny gap between the axon and the dendrite, which interrupts the direct transmission of electrical signals. That’s where electrical signals are converted into chemical ones: the axon terminal releases chemicals called neurotransmitters. These neurotransmitters cross the synaptic gap, bind to receptors on the next neuron’s dendrite, and trigger a new electrical signal.

How Are Electrical Signals Generated?

The functioning of neurons is based on their ability to generate and transmit electrical signals. These signals are created by ion channels in the neuron’s cell membrane. When these channels open, electrically charged ions like sodium, potassium, and chloride pass through, altering the voltage between the inside and outside of the cell. At synapses, neurotransmitters cause ion channels to open. Further along the dendrites, and within the soma and axon, there are voltage-sensitive ion channels that open in response to changes in the membrane’s voltage, allowing the signal to continue.

How Neurons Control Our Brain

Our brain doesn’t exist in isolation—it’s constantly connected to the "outside world" of our body, thanks to two types of neurons: sensory neurons and motor neurons.

Sensory Neurons: A Network of Informants

Sensory neurons continuously gather information about the world around us and the state of our body. These special neurons are directly linked to receptor cells, which detect light, sound, temperature, taste, smell, touch, pressure, or chemical stimuli, convert these into electrical impulses, and transmit them to sensory neurons.

Sensory neurons are found wherever our body interacts with the outside world – in our skin, eyes, ears, nose, and mouth. But they also gather information from within the body, relaying details such as blood pressure, blood sugar levels, or how full the bladder is.

Motor Neurons: Getting Things Moving

Motor neurons are essentially the “right-hand man” of our brain. They carry out its commands by connecting to muscle and gland cells. Following orders from the brain, motor neurons activate both voluntary and involuntary muscles, and trigger glands to produce substances like digestive enzymes, sweat, or hormones.

However, most neurons in our body are neither sensory nor motor neurons.

Interneurons: Where the Magic Happens

Interneurons make up about 90% of the cells in our nervous system. They form the complex neural networks that connect sensory and motor neurons.

Interneurons are intensively connected with each other—on average, a single neuron in the brain receives input from around 1,000 synapses. Some synapses are more important than others, with different levels of influence, and some even have an inhibitory effect rather than an excitatory one. These synaptic properties can change over time, playing a crucial role in learning processes.

Interneurons are organised into specialised centres with specific functions. For example, the visual cortex processes the signals received by the sensory neurons in the retina of our eyes into spatial visual impressions. The visual cortex then sends information to the hippocampus, where it’s combined with other sensory data and stored as short-term memories. If an action needs to be taken based on what’s seen, the motor cortex— the control centre for muscle movements—gets involved, and motor neurons are activated.