Nervous System: Structure, Function and Neurons

Nervous System: Structure and Function

The nervous system is formed by nervous tissue, which connects the organs of the central nervous system to the rest of our body.

Nerve Classification by Function

• Sensory nerves transmit information from the senses and organs to the central nervous system.
• Motor nerves transmit information from the central nervous system to muscles and organs, which carry out a functional response.

Division of the Nervous System

The nervous system is divided into two main parts:

Somatic nervous system

The somatic nervous system is composed of nerves that connect skeletal muscles to the central nervous system and is responsible for voluntary acts.

Autonomic nervous system

The autonomic nervous system, also called the vegetative nervous system, is composed of nerves that connect internal organs to the central nervous system and regulates involuntary functions. Its organs are regulated through two antagonistic systems:

• Sympathetic nervous system, which stimulates the body for activity.
• Parasympathetic nervous system, which inhibits activity, and vice versa.

The Neuron

The structure of a neuron distinguishes two differentiated parts: the cell body or soma, which is the largest and contains the nucleus and cytoplasm, and its extensions.

There are two types of extensions:

• Dendrites: short and highly branched extensions that connect the neuron with other neurons.
• Axon: a long, unbranched extension ending in a terminal branching.

The axon is protected by a myelin sheath, a fatty substance that gives the white matter its color. Axons are wrapped in myelin sheath and grouped into bundles called nerve fascicles, which are the nerves.

How Neurons Function

Functional neurons transmit nerve impulses, which propagate along the neurons as electrical currents of short duration. The impulse enters through the dendrites, passes through the cell body, and leaves through the axon.

Neurons transmit impulses to other neurons through connections called synapses. A synapse does not exist as a physical contact between neurons; impulse transmission occurs through neurotransmitters, which are chemical messengers.

Neuron Regeneration

Unlike many other cells, the body establishes new synapses as neurons grow, which is necessary for the functioning of the nervous system. However, neurons are generally not replaced once specialized, as they cannot reproduce.