Mechanisms and Classification of the Human Nervous System

Classification of Nerves

Classification of Nerves by Origin

Nerves can be classified based on their origin (where they exit the central nervous system):

• Cranial Nerves: Nerves exiting the brain. They are responsible for transmitting information regarding sight, hearing, smell, chewing, speech, and other vital functions.
• Spinal Nerves: Nerves exiting the spinal cord. They manage the transmission of information to control internal organs such as the heart, lungs, liver, kidneys, and so on.

Functional Classification of Nerves

According to their function, nerves can be classified as:

• Sensory (Afferent) Nerves: Receive the sensations perceived by receptor organs and transmit them to the Central Nervous System (CNS).
• Motor (Efferent) Nerves: Transmit impulses from the central system to the effector organs (muscles and glands).
• Mixed Nerves: They contain both sensory and motor fibers, allowing them to perform both functions.

Nervous System Operation

The Nerve Impulse

Neurons transmit information at high speed via nerve impulses. Nerve impulses are electrical changes in the membrane of the neuron.

When the neuron is at rest, the outside of its plasma membrane is positively charged and the interior is negatively charged. When the neuron receives a stimulus, a local increase in permeability occurs, favoring the passage of positive charges inside the neuron until the inside becomes positive and the outside negative. This change, the nerve impulse, is then transmitted from the dendrites to the cell body and from there to the axon.

Synaptic Communication

Neurons communicate through special contacts called synapses, through which the nerve impulse passes from one neuron to another.

The synapse is the communication junction between two neurons and is established through chemical messengers called neurotransmitters.

At the ends of the axons, there are specialized structures called synaptic knobs (or terminals), which contain numerous vesicles filled with neurotransmitters. When the nerve impulse reaches the end of the axon, the contents of the synaptic vesicles are released, and the neurotransmitters leave the space between the two neurons, called the synaptic cleft.

The neurotransmitters bind to the membrane of the next neuron and cause a new nerve impulse.

Functional Division of the Nervous System

The nervous system can be functionally divided into the somatic and autonomic systems, depending on whether the response produced is voluntary or involuntary.

The Somatic Nervous System (SNS)

The Somatic Nervous System (SNS) consists of the nerve centers and nerves responsible for voluntary movements.

The Autonomic Nervous System (ANS)

The control of the internal organs is regulated by the Autonomic Nervous System (ANS), consisting of nerves that connect the different organs to the spinal cord, medulla, or hypothalamus.

The ANS is a crucial part of the nervous system, encompassing components of both the Central Nervous System and the Peripheral Nervous System. Its operation is independent of conscious will; it is unconscious and automatic. Its importance is vital because it controls essential functions such as digestion, respiration, blood circulation, and excretion.