The peripheral nervous system

The peripheral nervous system (PNS)

The peripheral nervous system consists of all the nerves outside the brain and spinal cord. These nerves serve as communication pathways between the central nervous system (CNS) and the rest of the body. They connect sensory organs (such as the eyes, ears, skin, tongue, and nose) to the brain and spinal cord, allowing the body to respond to external and internal stimuli.

Functions of the peripheral nervous system

1. Transmitting information: The PNS sends information from sensory organs to the CNS. For example, it carries signals when a person feels thirsty, hungry, or experiences pain.
2. Providing responses: The PNS helps the CNS provide timely responses, such as making the body act when a person needs to drink water, eat, or relieve themselves.

These functions help the body to act appropriately and safely, ensuring all systems work together properly.

Structure of nerves

Nerves are made up of nerve cells (neurons), which are specialized cells that transmit information throughout the body. Each neuron has a cell body, a nucleus, and cytoplasm. The cytoplasm contains branches called dendrites that receive information from the environment and send it to the cell body.

At the opposite end of the cell body is a long, thread-like extension called the axon. The axon carries the nerve signal to other neurons or organs. The axons in different nerves vary in length, depending on their location. For example, the sciatic nerve, which is responsible for transmitting information to the limbs, has long axons that run from the waist down to the feet.

Types of nerve cells and their functions

There are three main types of nerve cells:

1. Sensory nerves: These nerves receive information from sensory organs (like eyes, ears, and skin) and send it to the CNS for processing. For example, they send signals when you touch something hot or see something bright.
2. Motor nerves: These nerves carry information from the CNS to the muscles and organs, instructing them to take action. For example, motor nerves send signals that make your muscles move when you decide to walk or lift something.
3. Relay (intermediate) nerves: These nerves act as connectors, passing information between sensory nerves and motor nerves. They help transmit the signals from sensory nerves to motor nerves, allowing the body to respond appropriately.

Differences between the central nervous system and the peripheral nervous system

Central Nervous System (CNS)	Peripheral Nervous System (PNS)
Made up of the brain and spinal cord.	Made up of nerves outside the brain and spinal cord.
Nerves are protected by the skull and the vertebral column.	Nerves are not covered by bones. They extend freely from muscles or tissues.
The main function is to receive stimuli from inside and outside the body and provide interpretations.	The main function is to connect the CNS with other body parts, transmitting stimuli from sensory organs and the body to the CNS, and then sending the body's response back to the sensory organs.