Poliovirus

In poliomyelitis, also called polio, “polio” refers to the poliovirus, which is an enterovirus that invades the intestines, “myel” refers to the spinal cord which is affected in the disease, and -itis refers to inflammation.

So poliomyelitis is an enteroviral disease first enters the body through the intestines, but then spreads and causes nerve injury in the spinal cord.

Former US president Franklin D. Roosevelt contracted polio when he was a baby, and it left him wheelchair-bound.

Broadly speaking, the nervous system consists of two parts.

The central nervous system consists of the brain and the spinal cord.

So the peripheral nervous system includes the nerves that fan out from the central nervous system to reach the skin, muscles, and organs.

Now looking at the cross-section of the brain, there’s gray matter at the periphery of the brain. This is called the cerebral cortex and it consists of nerve cell bodies.

Just inside the gray matter of the brain, is the white matter, and it consists of nerve axons.

In contrast, if you look at the cross-section of the spinal cord, the white matter is on the outside and the gray matter is on the inside, and overall it kinda looks like a butterfly.

If we draw a horizontal line through the spinal cord, the front half is the anterior or ventral half, and the back half is the posterior or dorsal half.

And the butterfly wings are sometimes referred to as horns; so we have two dorsal horns that contain cell bodies for sensory neurons and two ventral horns that contain cell bodies for motor neurons.

So for example, if you step on a lego in your living room, the sensation of discomfort is carried from the nerves in your foot, through the peripheral nervous system to reach the dorsal horn in the spinal cord.

It then travels up the spinal cord to the brain, letting you know that there’s tissue damage.

In response, your brain sends a message through the upper motor neurons, which are part of the cerebral cortex, and down the spinal cord to a lower motor neuron which is located in the anterior horn of the spinal cord.