Nervous System Structure

Our nervous system coordinates our whole body it helps us move, tells our endocrine system when to release certain hormones, and leads to intricate and complex psychological phenomena. In order to do this, it needs to be able to send and receive signals in a coordinated fashion. In order to understand how this happens let’s look at the structures and explore how they lead to the function we see.

Divisions of The Nervous System

Our nervous system is divided into two major parts the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is composed of our brain and spinal cord and functions as the controller and coordinator. While our peripheral nervous system feeds information to our CNS and carries orders out to our various muscles, glands, and organs. From there the PNS is further subdivided into the somatic and autonomic nervous systems based on function which we will look at in more detail later.

Nervous System Cells

Before we get ahead of ourselves let’s look at the cells that comprise the nervous system. The major functional unit of the nervous system is the neuron. It is a specialized cell that transmits signals via electrical impulses called action potentials.

The Neuron

While neurons come in a wide array of different shapes they all have the same general features in common. Like most other cells they contain a nucleus and organelles However these aren’t equally distributed within the cell. Instead, all of the organelles exist in a centralized cell body or soma.

Radiating outwards from the cell body are small appendages called dendrites. These “branches” receive incoming information from other cells and send it into the soma.

Branching off of the soma at what is called the axon hillock is a larger appendage called an axon. Axons allow for the propagation of action potentials and initiate signals to other cells.

A myelin sheath wraps around each axon like the rubber coating of a copper wire. This sheath helps speed up conduction of action potentials by insulating the axon from its environment.

At intervals small gaps called Nodes of Ranvier allow fresh ions to flow in and maintain the action potential as it speeds along the axon.

If we followed this axon down to its end we would find small knobs at the end called boutons. These boutons house and release neurotransmitters that “tell” other cells what to do.

These neurotransmitters will diffuse away from the neuron into the synaptic cleft formed between one nerve terminal and its target. This target could be another neuron, a muscle or a wide array of glands and organs throughout our body.

Central Nervous System

For now, let’s dive into the CNS and explore its structure big and small. If we took a slice out of our brain or spinal cord and looked at it we would notice a color difference between different parts. The color difference is formed by different parts of the functional unit of our nervous system, the neuron.

The darker portion called grey matter lies on the outer surface of our brain and is comprised of neuron cell bodies. While the lighter portion called white matter lies inside the grey matter and consists of axons covered in myelin.