The human nervous system is a marvelously complex construct. Through the ages, we have discovered much about the natural world and how to manipulate it, but the human brain and its subsidiaries have not been thoroughly understood despite great efforts. In a previous post, I presented the layers of the brain’s protective coverings—the dura, arachnoid, and pia—and now I would like to take a look at the brain itself. The brain is divided into four lobes: frontal, parietal, temporal, and occipital.
Origin: Latin, frons (brow/front)
Belonging at the front, i.e., the brow/forehead
Origin: Latin, paries (wall)
Belonging to the walls; in this case, the wall is the top of the skull
Origin: Latin, tempora (temple of the head)
Belonging to the temples, i.e., the part of the head between the forehead and the ear
Origin: Latin, oc– (variant of ob, for towards/against/back of) + caput (head)
Belonging to the back of the head
There are two main branches of the nervous system:
- Central nervous system, which consists of the brain and the spinal cord
- Peripheral nervous system, which consists of everything else
The building blocks of both nervous systems are neurons, which are colloquially known as brain cells. There are two general classes of neurons: sensory and motor. A sensory neuron—quite logically—allows for the recognition of one of the five senses, e.g., the neurons in the optic nerve receive optical sensory input. A motor neuron delivers the impulse to a muscle spindle to allow for movement, e.g., flexing the biceps. Where does the word neuron come from?
Origin: Greek, neuron (sinew/nerve)
So named because nerves have the appearance of sinew
And it turns out that nerve also means sinew, but comes from Latin. This is likely from the observation that a nerve (upon exposure through dissection) looks like sinew! What about the parts of a neuron? A neuron consists of its dendrites, which receive information from other neurons. As for the neuron cell body itself, it is called the soma or the perikaryon. Let’s run through these guys.
Origin: Greek, dendron (tree)
So named because the dendritic processes collectively resemble a tree (see below image)
Origin: Greek, soma (body)
Refers to the cell body
Perikaryon (plural perikarya)
Origin: Greek, peri– (around) + karyon (kernel, taken to mean nucleus)
Around the kernel/nucleus, i.e., the cell body
I’m deliberately leaving out the axon, myelin, nodes of Ranvier, and Schwann cells because there is more to the story, so stick around!