Understanding Neurons, Glial Cells, Axons, Dendrites, and Synapses

Neurons: The Building Blocks of the Nervous System

Neurons are fundamental cells of the nervous system, representing the anatomical and functional unit of the human brain. They are specialized cells designed to receive, carry, and transmit electrochemical signals called nerve impulses.

Neurons are irreplaceable. Once they age, are injured, or die, they cannot be replaced. This is because these cells are primarily formed during the prenatal period of gestation. A child is born with the largest number of neurons, approximately 100 billion, which immediately begin to decrease in number.

Glial Cells: Supporting the Neurons

The name 'glial' comes from the Greek root 'glia,' meaning concrete. These cells lack axons and are not essential for directly processing information in the nervous system. However, their functions are vital to the nervous tissue:

• Serve as support to neurons, providing the scaffolding on which they are held.
• Regulate the chemical microenvironment in the immediate vicinity of neurons, which is essential for their normal operation.
• Some produce myelin, which functions as an insulating substance around the axons, determining their conduction velocity.
• Others are part of the defense system and are mobilized to areas of injured or infected nerve tissue.

Axons: Transmitting Nerve Impulses

An axon is a long, thin nerve fiber that extends from a region called the axon hillock of the soma. The role of the axon is to conduct nerve impulses from the neuronal soma to other neurons, muscles, or glands. The length of the axon depends on the neuron within the body.

The axon is covered by a layer of myelin and nodes of Ranvier (open spaces in the myelin sheath) that increase the speed of nerve impulse conduction.

Dendrites: Receiving Nerve Impulses

Dendrites are branched protoplasmic extensions, typically short, that specialize in the reception and conduction of nerve impulses to the soma. Most synapses a neuron receives are located on the dendrites, but they can also be found on the cell surface.

They branch deeply from one or more main trunks, splitting at sharp angles, in a tree-like fashion, ending bluntly at no great distance from the cell body.

Synapses: Connecting Neurons

A synapse is the functional union between two neurons that allows the passage of nerve impulses from one nerve cell to another. In a synapse, we distinguish between two neurons: the presynaptic neuron, located before the synapse, and the postsynaptic neuron, located after the synapse.

The presynaptic neuron leads the nerve impulse to the synapse, and the postsynaptic neuron transmits the nerve impulse from the synapse to another neuron.