Nervous System Functioning
The nervous system is the communication center of the body. In most cases, including this article, it is spoken in the context of humans, however, other living organisms also have nervous systems.
The role of nervous system functioning is to connect organs to each other via electro-chemical signaling through neurons. Neurons are a type of cell. They are specific to the nervous system and are not found anywhere else in the body.
Figure 1: 
This is a diagram of a neuron. The large mass of the cell is known as the cell body. Within the cell body is the nucleus containing the DNA of the cell. The smaller protrusions from the cell body are known as the dendrites. The axon is the tube-like structure running from the cell body to the right. The protrusions at the end of the axon are known as axon terminals. Electro-chemical signals travel from the dendrites, through the cell body and axon, and out of the axon terminals where they connect to the axons of another neuron’s dendrites.
The brain mediates all of the signals that it receives from organs and sensory systems and acts as the administrator of the body. The brain in return communicates with the body via the same electro-chemical signaling or via neuroendocrine responses by stimulating the release of hormones or other chemicals into the bloodstream.
Nervous System Structure
The nervous system is comprised of two primary parts. The first is the Central Nervous System (CNS). This is where mechanisms such as thought, processing, and maintenance of homeostasis including vital indicators such as heart rate, blood pressure, and others occur. Anatomically, the CNS includes the cerebral cortex, cerebellum, brainstem, and spinal cord.
The cerebral cortex is composed of four lobes: the frontal, temporal, parietal, and occipital lobes.
- The frontal lobe is where processes of higher-level thinking and decision-making take place, usually expressed via language and voluntary movement.
- The temporal lobe is associated with memory encoding and auditory processing.
- The parietal lobe receives and interprets other sensory information that include taste, touch, and temperature.
- The occipital lobe is the visual processing center of the brain where perception, shapes of objects, and color are interpreted.
The cerebellum is the mediator of balance, walking, and coordination. The brainstem regulates heart rate, digestions, swallowing, and breathing. Finally, the spinal cord is a bundle of nerves that runs along the spinal column and is used to mediate signaling that comes from the cerebral cortex, cerebellum, and brainstem to the rest of the body.
The second is the Peripheral Nervous System (PNS). This includes all of the nerves that are located in the head and throughout the body. All nerves connect to the CNS. The PNS is used to send messages from the CNS to muscles and organs for voluntary and involuntary actions. The somatic nervous system summarizes the functions that we do by choice including walking, eating, or playing a sport. The autonomic nervous system then describes the functions that happen involuntarily such as breathing, digestions, or even sweating.
Figure 2:
This is a visual diagram of both the CNS and the PNS in the body. As illustrated by the image, all nerves extend out through the entire body allowing for ‘global’ communication.
The following is a 3-D interactive model of the nervous system functioning.
Organs
Nervous system organs can be separated by CNS and PNS. Within the CNS the brain (cerebral cortex and cerebellum), brainstem, and spinal cord constitute as organs.
The PNS organs consist of the nerve bundles and the ganglia. Nerve bundles are as they sound, bundles of neurons that travel throughout the body until they split up to their terminal destinations. Ganglia are clusters of neuron cell bodies that are commonly found at the spinal cord on the posterior side. Ganglia create and intermediate connection between the PNS and the CNS. These structures are a constitute of the reflex arc of the spinal cord that allow the for a more immediate muscular response than if a signal was to travel all the way to the brain. For example, if you touch a hot pan with the edge of your finger, you will pull away your hand faster than you will have realized that you have burned yourself. This happens because the sensory response of pain is processed at the dorsal root ganglia of the spinal cord to stimulate a response (pull your hand away) while the cognitive realization of what happened is still traveling up your spinal cord to your brain.
Although the PNS connects all organs including the lungs, stomach, liver, etc. they are not considered as part of the nervous system.
Author: Daria Kotov
References (Advanced Reading):
Kandel E.R., & Schwartz J.H., & Jessell T.M., & Siegelbaum S.A., & Hudspeth A.J., & Mack S(Eds.), (2014).
Principles of Neural Science, Fifth Edition. McGraw Hill.