Neuron

Tiny cells help your body work.

They send fast signals. These signals move like little sparks. These sparks move through your body.

One part of the cell is the body. Long parts grow out of the body. These parts act like wires. They carry signals to other cells.

Cells talk to each other. They use tiny bits of chemicals. This helps the signal jump across. The signal moves from one cell to the next.

Some cells feel things. They feel light or sound. Other cells help you move. They tell your muscles to work.

These cells are very important. They help you see and move. They make your body work well.

Neurons are special cells in your body.

They send fast electric signals through your nervous system. This system includes your brain and your spinal cord.

Most animals have these cells. However, plants and fungi do not have them.

A neuron has a few main parts. The soma is the cell body. It holds the nucleus. Long parts grow out of the soma. These are called dendrites. They look like branches on a tree.

Another part is the axon. The axon is like a long wire. It carries signals away from the cell body. In humans, an axon can be over one meter long.

Neurons talk to each other using synapses. A synapse is a tiny gap between cells.

To cross this gap, the cell lets out chemicals. These are called neurotransmitters. These chemicals pass the signal to the next cell.

There are three main types of neurons. Sensory neurons feel things like light or sound. Motor neurons tell your muscles to move. Interneurons connect neurons to each other in the brain.

Neurons are special cells that make up the nervous system in almost all animals.

They are very busy cells that send electrical signals to each other. These signals are called action potentials. This process helps your body receive and send information. Most of these cells live in the central nervous system. This includes your brain and your spinal cord.

Without these cells, animals could not react to the world around them. Plants and fungi do not have these types of cells.

A neuron has a few main parts that help it work. The soma is the cell body of the neuron. It holds the nucleus and makes many proteins.

Growing out of the soma are many branches called dendrites. These branches look like a tree, which scientists call a dendritic tree.

Another part is the axon, which is a long, thin part. The axon carries signals away from the soma. It starts at a swelling called the axon hillock. This part is very good at starting electrical signals.

How do these cells talk to one another?

They use tiny gaps called synapses to pass messages. The signal travels down the axon to the axon terminals. At these terminals, the cell releases tiny amounts of chemicals. These are called neurotransmitters.

The chemicals float across the gap to reach the next cell. This next cell might be another neuron. The signal can then move through a neural circuit. This is like a path of connected cells working together.

Scientists have studied these cells for a long time.

An anatomist named Camillo Golgi grouped them into two types. He called them Type I if they had long axons. He called them Type II if they had short axons. We also know that these signals first appeared a long time ago. They likely appeared 700 to 800 million years ago. This was during a time called the Tonian period. This was a very important moment in the history of life.

Neurons do different jobs depending on where they are.

Sensory neurons respond to things like light, sound, or touch. They send these signals to your brain. Motor neurons do the opposite job. They carry signals from the brain to control your muscles. Interneurons stay in the brain or spinal cord to connect neurons together. In humans, some axons are very long. A motor neuron can reach from your spine all the way to your toes. This can be more than one meter long.

A neuron is a specialized, excitable cell that functions within a neural network. These cells are the primary components of nervous tissue in almost all animals. They work by firing electrical signals known as action potentials. These signals allow the nervous system to receive, conduct, and process impulses. The nervous system is divided into the central nervous system, which includes the brain and spinal cord, and the peripheral nervous system.

While neurons are essential for animal life, plants and fungi do not possess them.

The signaling process is a complex mix of electrical and chemical events. Every neuron is enclosed by a plasma membrane, which is a bilayer of lipid molecules. This membrane acts as an electrical insulator. However, it contains embedded protein structures like ion channels and ion pumps. These proteins manage the movement of ions such as sodium, potassium, chloride, and calcium. The interaction between these channels and pumps creates a voltage difference across the membrane.

When the voltage changes enough over a short time, the neuron generates an all-or-nothing electrochemical pulse called an action potential. This pulse travels rapidly down the axon to activate synaptic connections.

Neurons communicate with one another through specialized connections called synapses. Most signals cross from the axon of one neuron to the dendrite of another. However, synapses can also connect an axon to an axon or a dendrite to a dendrite. At the end of the axon, specialized structures called synaptic boutons release minute amounts of chemical neurotransmitters.

These chemicals cross the synaptic gap to reach the target cell. This chemical transmission allows the signal to pass from a presynaptic neuron to the next cell. The resulting signals can be excitatory, which increases voltage, or inhibitory, which reduces it.

The anatomy of a neuron is highly specialized for this transmission. The soma, or cell body, is a compact structure containing the nucleus. Most protein synthesis occurs here, supported by microscopic clumps called Nissl bodies.

Extending from the soma are dendrites, which are branched filaments. These branches often form fractal patterns known as a dendritic tree.

The axon is a long, cable-like projection that carries signals away from the soma. It begins at a swelling called the axon hillock, which serves as the spike initiation zone. The axon ends at axon terminals, where it can transmit signals to other cells.

Neurons are generally classified into three functional types. Sensory neurons respond to external stimuli like light, sound, or touch. They send these signals to the spinal cord and then to the sensorial areas of the brain. Motor neurons carry signals from the brain and spinal cord to control muscle contractions or glandular output. Finally, interneurons act as connectors between other neurons within the brain or spinal cord. When these different neurons connect functionally, they form a neural circuit.

Evolutionary history shows that the ability to generate electrical signals is an ancient innovation. Molecular evidence suggests this capability first appeared roughly 700 to 800 million years ago during the Tonian period. The predecessors of modern neurons were likely peptidergic secretory cells. Over time, these cells gained new gene modules. These modules allowed them to create ion channels and post-synaptic scaffolds. This transition enabled the development of fast electrical signaling in early animals.

The scale of neurons can be truly immense. While a soma might only be 10 to 25 micrometers in diameter, an axon can be much longer. In humans, a single motor neuron axon can exceed 1 meter in length to reach from the spine to the toes. Sensory neurons in adults can have axons running over 1.5 meters long. Even giraffes possess single axons that run several meters along their necks. Scientists have studied these massive structures using the squid giant axon, which can be 0.5 to 1 millimeter thick.