Nervous system: Structure and function

The nervous system is involved in nearly everything we do from how we see, to how we walk and talk. Now, the main cells of the nervous system are called neurons.

These make up the brain, the spinal cord, and the peripheral nerves that reach the rest of the body. The nervous system is responsible for detecting and reacting to changes happening both in and outside of the body.

To do that, it gathers sensory signals from the internal and external environment, which are then analyzed. Then, motor signals are sent, which results in an action in response to the change.

So, for example, if you sense pain from touching a hot stove, you jerk your hand away; if you sense your stomach is full, your digestive system starts working harder; if you sense your blood pressure is low, your heart pumps faster.

Okay, let’s start by looking at the neurons that make up the nervous system. These are composed of a cell body, which contains all the cell’s organelles, and nerve fibers that extend out from the cell body.

These fibers are either dendrites that receive signals from other neurons or axons that send signals along to other neurons.

The space between where two neurons come together is called a synapse, and that’s where the axon of one neuron releases chemical messengers called neurotransmitters.

These will travel through the synapse and reach the dendrite of the next neuron, causing it to send a signal down its axon. This is how a signal can pass from neuron to neuron.

Now, the nervous system is divided into the central nervous system, including the brain and spinal cord, and the peripheral nervous system, which are the nerves that connect the central nervous system to muscles and other organs in the rest of the body.

The peripheral nervous system is divided into the somatic nervous system, which controls the voluntary movement of our skeletal muscles and the autonomic nervous system, which is further divided into the sympathetic and parasympathetic nervous systems and controls the involuntary movement of smooth muscles and glands in our organs.

Okay, let's start with the central nervous system. The brain and spinal cord are both covered by the meninges, which are three protective layers of membranous tissue.

The inner layer of the meninges is the pia mater; the middle, web-like layer is the arachnoid mater; and the thicker, outer layer is the dura mater.

These first two, the pia mater and arachnoid mater, form the subarachnoid space, which houses the cerebrospinal fluid, or CSF.

CSF is a clear, watery liquid that circulates around the spinal cord and brain, cushioning them from impact and bathing them in nutrients.

Now, zooming in, the brain has a few regions. The largest is the cerebrum, which is divided into two cerebral hemispheres held together by a thick bundle of fibers called corpus callosum.

The right cerebral hemisphere controls the left side of the body, while the left cerebral hemisphere controls the right side of the body. This means any damage to one side of the cerebrum will affect the opposite side of the body.

The cerebral cortex is responsible for initiating and regulating movement and processing sensory information, like hearing, vision, smell, and touch. It also controls important functions, like language, learning, emotion, and making decisions.

Next, there’s the cerebellum, which sits down at the base of the skull. The cerebellum helps with coordinating movement, precision, and balance.

And finally, there’s the brainstem, which is located right in front of the cerebellum. The brainstem is made up of three parts—midbrain, pons, and medulla—and it connects to the spinal cord. It also helps regulate blood pressure, breathing, swallowing, coughing, vomiting, and digestion.

The spinal cord is a long rod of nervous tissue that extends down from the brainstem to the lumbar region, or the lower back, and is surrounded by the vertebral or spinal column.

The spinal column is formed by a series of bones called vertebrae, each of which has an opening that lets the spinal cord pass through.

Now, the peripheral nervous system consists of twelve pairs of cranial nerves pairs that exit from the skull and 31 pairs of spinal nerves that exit various regions of the spinal cord and connect with the rest of the body.