The Nervous System Overview

The central nervous system (CNS) is composed of the brain and spinal cord.

The peripheral nervous system (PNS) is made up of all the nerves outside the brain and spinal cord.

Nerve cells, also known as neurons, are responsible for communication and control within the nervous system.

Glial cells, or neuroglia, support nerve cell function.

The cell body of a neuron contains the nucleus and other essential cellular structures.

The axon is a long, thin extension from the cell body that carries electrical impulses.

The axon hillock is the area where the axon leaves the cell body, where the electrical impulse originates.

Telodendria are branches at the end of the axon that split into terminal buttons.

Terminal buttons are tiny, swollen structures at the ends of telodendria that release neurotransmitters.

Dendrites are short, highly branched extensions that receive chemical messages from other neurons.

Myelinated axons are covered by a fatty substance called myelin, which insulates the axon and speeds up signal transmission.

Myelin is made by glial cells like Schwann cells in the peripheral nervous system and oligodendroglial cells in the central nervous system.

The nodes of Ranvier are gaps in the myelin sheath that allow the electrical signal to jump between them, speeding up transmission.

Schwann cells are glial cells found in the peripheral nervous system that produce myelin and guide regenerating axons.

Oligodendroglial cells are glial cells in the central nervous system that produce myelin and can insulate more than one axon.

Astrocytes are glial cells that form part of the blood-brain barrier, a protective structure that regulates what substances can pass into the brain.

Ependymal cells are glial cells that help produce cerebrospinal fluid, which cushions and protects the brain and spinal cord.

Microglial cells are glial cells that act as the immune system of the brain and spinal cord, defending against foreign invaders and damaged cells.

A nerve is a bundle of axons running together outside the CNS.

Bundles of axons within the CNS, like the brain and spinal cord, are called tracts.

Nerve damage can lead to degeneration of axons and myelin, but Schwann cells can guide axon regeneration.

Bell's Palsy is a condition that involves a viral infection of the facial nerve, leading to facial paralysis.

Crocodile tears syndrome is a rare condition that can occur after Bell's Palsy, causing the patient to cry when eating.

In crocodile tears syndrome, axons that normally trigger salivation can become misdirected and stimulate tears instead.