Neuron Function- How Nerve Cells Conduct Electrical Signals

What Neurons Actually Are

Neurons are specialized cells in your nervous system that transmit information through electrical and chemical signals. Unlike other cells in your body, neurons are built for communication. They don't store energy, build tissue, or fight infections. Their sole job is receiving, processing, and passing along signals.

You have approximately 86 billion neurons in your brain alone. Each one can connect to thousands of others, creating a network that controls everything you think, feel, and do.

The Anatomy of a Neuron

Understanding how neurons work starts with knowing their structure. Each part serves a specific function in signal transmission.

Key Components

• Dendrites – Branch-like extensions that receive signals from other neurons. The more dendrites a neuron has, the more connections it can make.
• Cell Body (Soma) – Contains the nucleus and most of the cell's organelles. This is where incoming signals are integrated.
• Axon Hillock – The junction between the cell body and axon. This is where the decision to fire happens.
• Axon – A long, slender projection that carries the electrical signal away from the cell body. Some axons are covered with a fatty sheath called myelin.
• Axon Terminals (Terminal Buttons) – End points where the neuron communicates with the next cell. These release neurotransmitters into the synapse.

How Neurons Generate Electrical Signals

Neurons maintain an electrical gradient across their membrane, called the membrane potential. This is the foundation of everything they do.

Resting Membrane Potential

At rest, a neuron maintains a voltage of about -70 millivolts relative to the outside. This negative charge exists because:

• Potassium ions (K+) are more concentrated inside the cell
• Sodium ions (Na+) are more concentrated outside the cell
• The cell membrane is more permeable to potassium than sodium
• The sodium-potassium pump actively moves 3 Na+ out and 2 K+ in using ATP

This imbalance creates potential energy stored in the electrochemical gradient. The neuron is essentially a biological battery waiting to be discharged.

The Action Potential

When a neuron receives enough stimulation from neighboring cells, the membrane potential shifts toward a threshold (usually around -55 millivolts). If this threshold is reached, an action potential is triggered.

The action potential follows an all-or-nothing principle. The neuron either fires completely or doesn't fire at all. There's no partial firing, no "almost" firing.

The process happens in phases:

1. Depolarization – Sodium channels open. Na+ rushes into the cell, making the inside positive (up to +40mV).
2. Repolarization – Sodium channels close, potassium channels open. K+ exits the cell, bringing voltage back down.
3. Hyperpolarization – Potassium channels stay open a bit too long. The cell briefly becomes more negative than resting state.
4. Recovery – Sodium-potassium pump restores the original ion distribution.

Signal Propagation Down the Axon

An action potential at the axon hillock triggers identical action potentials in adjacent sections of the axon. The signal propagates like a wave along the membrane.

In unmyelinated axons, this wave travels continuously along the entire length. It's slower because every section of membrane must undergo the full depolarization-repolarization cycle.

In myelinated axons, the process is different. Myelin is an insulating layer that wraps around the axon, created by glial cells called oligodendrocytes in the CNS and Schwann cells in the PNS.

Saltatory Conduction

Myelin prevents current from leaking through the membrane. The signal essentially jumps between nodes of Ranvier (gaps in the myelin sheath). These nodes contain a high concentration of voltage-gated sodium channels.

This jumping process is called saltatory conduction (from the Latin word for "leaping"). It's dramatically faster—up to 150 meters per second compared to 1-2 meters per second in unmyelinated fibers.

This is why diseases that damage myelin (like multiple sclerosis) cause such severe neurological problems. Signals can't jump between nodes, so communication slows to a crawl.

How Neurons Communicate With Each Other

Neurons don't actually touch. They communicate across tiny gaps called synapses. When an action potential reaches the axon terminals, it triggers a cascade that releases chemical messengers.

Synaptic Transmission

• Action potential arrives at axon terminal
• Voltage-gated calcium channels open, Ca2+ rushes in
• Calcium causes vesicles containing neurotransmitters to fuse with the membrane
• Neurotransmitters are released into the synaptic cleft
• Neurotransmitters bind to receptors on the postsynaptic neuron
• This can excite, inhibit, or modulate the postsynaptic neuron

After release, neurotransmitters are quickly cleared from the synapse. Some are reabsorbed by the presynaptic neuron, some are broken down by enzymes, and some diffuse away. This clearing process is why drug timing matters—SSRIs work by blocking reuptake of serotonin, prolonging its effect in the synapse.

Types of Neurons

Not all neurons are built the same. Their structure relates directly to their function.

Factors That Affect Signal Speed

Several variables determine how quickly signals travel through your nervous system:

• Axon diameter – Larger diameter means less resistance to current flow. Giant squid axons (used in classic neuroscience experiments) are large enough to poke with electrodes.
• Myelination – Myelinated axons conduct 5-50 times faster than unmyelinated ones of the same diameter.
• Temperature – Warmer temperatures increase conduction velocity. This is why hypothermia slows reflexes.
• Node spacing – Optimal spacing between nodes of Ranvier balances speed and metabolic cost.

Getting Started: Understanding Neuron Function

If you want to study how neurons work, here's a practical starting point:

Basic Study Approach

1. Start with the ion channels. Without voltage-gated sodium and potassium channels, there's no action potential.
2. Learn the ion distributions. Inside negative, outside positive—that's the foundation.
3. Follow the sequence: stimulus → graded potential → threshold → action potential → synaptic release.
4. Understand why myelin matters. Speed and metabolic efficiency.
5. Trace one complete circuit. Sensory input → integration → motor output.

Key Terms to Memorize

• Membrane potential
• Resting potential (-70mV)
• Threshold potential (-55mV)
• Depolarization
• Repolarization
• Action potential
• Saltatory conduction
• Synaptic transmission
• Neurotransmitter

Why This Matters

Every thought you have, every movement you make, every sensation you experience depends on this electrical signaling. When it goes wrong—through disease, injury, or toxins—the consequences are immediate and often severe.

Local anesthetics block sodium channels, preventing pain signals from reaching the brain. Spider toxins that target ion channels can cause paralysis or uncontrolled neuron firing. Psychiatric medications work by modifying neurotransmitter levels at synapses.

The biology is elegant, but the purpose is simple: rapid communication across your body, controlled by electrochemical gradients maintained at enormous metabolic cost. Your neurons use electricity to think, move, and perceive. That's the whole system, explained in plain terms. 🧠