The Neuron | What Are the Brain's Core Communication Wires?

Dendrites are branched, tree-like extensions protruding from the neuron's cell body. Their primary function is to act as the main receivers of signals from other nerve cells. The term 'dendrite' comes from the Greek word 'dendron,' meaning 'tree,' which accurately describes their appearance. This extensive branching dramatically increases the surface area available for receiving incoming information. When a signal arrives from a neighboring neuron, typically in the form of chemical messengers called neurotransmitters, it binds to receptors on the dendritic surface. This interaction is then converted into a small electrical current that travels down the dendrite toward the soma, or cell body. In essence, dendrites are the sophisticated antenna system of the neuron, collecting information from thousands of other cells to determine whether the neuron itself will fire an impulse.

The soma, also known as the cell body, is the central processing unit and metabolic core of the neuron. It houses the nucleus, which contains the cell's genetic blueprint (DNA), and is surrounded by cytoplasm filled with essential organelles like mitochondria, which generate energy. The soma's primary role is to integrate the multitude of electrical signals channeled to it from its dendrites. It continuously sums up these incoming excitatory and inhibitory signals. If the cumulative electrical charge reaches a specific threshold, the soma initiates a powerful, all-or-nothing electrical impulse called an action potential. Beyond signal integration, the soma is responsible for the overall health and maintenance of the neuron, synthesizing proteins and other molecules necessary for the function and survival of the entire cell, including its axon and dendrites.

The axon is a single, long, cable-like projection that transmits the integrated electrical signal (the action potential) away from the soma to other neurons, muscles, or glands. It functions as the primary output cable of the neuron. Many axons are covered in a fatty substance called the myelin sheath, which is periodically interrupted by gaps known as nodes of Ranvier. This myelin acts as an insulator, allowing the electrical signal to jump from node to node, a process called saltatory conduction. This dramatically increases the speed and efficiency of signal transmission, enabling rapid communication across the nervous system.

These three parts work in a precise sequence to ensure unidirectional information flow. First, dendrites receive chemical signals from other neurons at a junction called the synapse. They convert these into weak electrical signals and pass them to the soma. The soma then acts as an integrator, summing up all the signals. If the combined signal is strong enough to cross a critical threshold, the soma generates an action potential at a specialized region called the axon hillock. This strong electrical pulse then travels down the length of the axon to its terminals, where it triggers the release of neurotransmitters, passing the message to the dendrites of the next neuron in the chain.

Damage to any part of a neuron severely compromises its function and can disrupt neural circuits. If dendrites are damaged, a neuron loses its ability to receive information effectively, which is a factor in the cognitive decline seen in neurodegenerative diseases like Alzheimer's. Damage to the soma is often catastrophic, leading to the death of the entire neuron, as it cannot be repaired. Axonal damage, which occurs in spinal cord injuries or diseases like multiple sclerosis (where the myelin sheath is destroyed), severs the communication line. This can result in a loss of motor control, sensation, or cognitive function, depending on the pathway that is interrupted. The central nervous system has a very limited capacity for neuronal repair and regeneration, making such damage largely permanent.