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Aunice Reed, M.A. in Marriage and Family Therapy from Touro University, M.S. in Addiction Counseling and B.A. in Psychology, Clinical Track.



Organisms are able to live and keep a stable internal state of equilibrium due to in large part, its efficiency in handling and responding to changes such as temperature and blood gas concentration, as well as the presence of danger in the external world. Changes taking place inside the body or in the external environment which are recognizable by an organism are collectively referred to as stimuli. Actions occurring as a result of incoming stimuli are made possible through the interconnected network of specialized cells called neurons, which ultimately work to conduct neuronal impulses and chemical messages.

To thoroughly understand how the human nervous system functions, you'll need to also know something about its structure, which is referred to as neuroanatomy. Relating strictly to neurological functioning, neurophysiology frequently overlaps, as it is difficult to discuss one without mention of the other.

The Neuron

The nervous system, at its most fundamental level consists of the single nerve cell, referred to as a neuron which is made up of a cell body, dendrites and a long, singular extension called an axon. Nerve cells are specialized in the detection of stimuli, including production and actual conduction of nervous system signals from one neuron to the next. Axons extend over long distances within the human body, even up to more than a meter in length. Impulses moving away from the nerve cell rapidly travel via these long, wire-like extensions, while the dendrites are necessary for receiving information in the form of electrical impulses into the neuron. Cells of nerve tissue are unique in that they do not reproduce or repair themselves like other types of cells.

A Single Nerve Cell


The Nervous System Consists of Two Divisions

The nervous system of a human being consists of two divisions: the central nervous system (CNS) and the peripheral nervous system (PNS). As the brain and spinal cord encompass the CNS, consisting of sensory receptors and motor nerves, the PNS serves as an open line of conveyance for impulses traveling to and from the brain. Nerves communicating stimuli to the CNS are referred to as afferent nerve fibers or axons. Nerves that conduct CNS responses (in response to changing conditions within the body) away from the brain out to relevant organs are called efferent nerve fibers. Responses from the CNS are primarily aimed at maintaining internal equilibrium. This arrangement is common to all mammals.

Cranial Nerves

Select areas of the body communicate with the brain via 12 cranial nerves originating from the brain stem. Each cranial nerve is identified by a number and a name. Some are considered to be part of the PNS, while others are considered to be part of the CNS.

Peripheral Nervous System (PNS)

The PNS is divided into two types of efferent nerve routes: somatic and autonomic, or viseral. The somatic nerves (nerves arising from the spine and running through joints, muscles and skin) are involved with voluntary functions chiefly related to detecting and responding to external changes in the environment, while the autonomic nerve pathways are concerned with changes occurring within the body that are typically vegetative like breathing and the heart rate. Beyond our conscious control or effort, autonomic nervous system functions are further categorized as either sympathetic or parasympathetic, meaning that one increases action (sympathetic) and the other does the opposite, thereby conserving energy (parasympathetic).

Anatomy of the Human Brain

Embryonic Brain Development

The brain and spinal cord develop in the embryo from a tubular structure referred to as the neural tube. Both are protected by an encasing of bone, connective tissue called the meninges and cerebrospinal fluid (CSP) necessary for lubrication and absorbing shock. Extending from the brain's base down to the lumbar region of the vertebral column lies the spinal cord, which is the conductor of neural impulses both to and from the brain (CNS).

Weighing about 3lbs. on average, the human brain is divided down the center longitudinally into right and left hemispheres. Hemispheres of the brain are further encompassed by 4 principle lobes for purposes of locating function and certain structures. The four lobes of the brain are the frontal, temporal, parietal and occipital lobes.

Neural Tube

The entire human CNS is formed from walls   of a tube filled with fluid (the neural tube). The tube itself then becomes the brain's ventricular system.

The entire human CNS is formed from walls of a tube filled with fluid (the neural tube). The tube itself then becomes the brain's ventricular system.

Neural Tube Development Chart

Prosencephalon becomes the diencephalon and the telencephalon. The rhombencephalon further divides into the metencephalon and myelencephalon

VesicalsBecomes The...Ventricular System

Prosencephalon (forebrain)

cerebral hemispheres, limbic system

lateral and 3rd ventricles

Mesencephalon (mid-brain)

tectum, cerebral peduncle

cerebral aqueduct

Rhombencephalon (hindbrain)

cerebellum, medulla oblongata, pons

4th ventricle

spinal cord

spinal cord

spinal canal

The Ventricular System of the Brain

If we were to cut open a human brain, we would discover that it is primarily hollow inside consisting of canals called ventricles, the fluid-filled areas in the brain. These areas make up the ventricular system and the clear, salty fluid within it is cerebrospinal fluid, or CSF. Situated within each of the brain's four ventricles is a group of cells infused with capillaries; this is the choroid plexus. It is responsible for the production of CSF.

Cerebrospinal Fluid (CSF)

The purpose of the CSF is to serve as a lubricant and absorbs shock against the skull. It is also responsible for circulation of nutrients, and elimination of the brain's waste products. CSF resides in the ventricles, subarachnoid space of the skull, and within the spine. An adult CNS contains approximately 150ml of CSF, most of it in the subarachnoid space. Total CSF production over a 24-hour time period is 400ml-600ml. It is constantly being replaced, about 5 times each day.

The Choroid Plexus is the Blood-CSF Barrier

"The choroid plexus is a complex network of capillaries lined by specialized cells and has various functions"(Jarvis et al., 2020).

"The choroid plexus is a complex network of capillaries lined by specialized cells and has various functions"(Jarvis et al., 2020).

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Animation: CNS Development in Utero

Important Directional Terms

When neuroanatomy is studied, some understanding of certain directional, anatomical terms is warranted. This helps with comprehending the specific location of structures and are also used in the study of anatomy in general.

coronal plane - refers to a plane dividing the brain into front and back portions.

sagittal plane - refers to a plane dividing the brain into left and right halves.

traverse plane - refers to a horizontal plane dividing the brain into top and bottom portions.

lateral or medial - suggests that a structure is towards the side (lateral) or towards the middle (median).

superior or inferior - towards the "top of" is superior, towards the "bottom of" or underneath refers to inferior.

anterior or posterior - anterior means towards the front end or head. Posterior suggests towards the back, tail or hind end

ventral - towards the front, or towards the belly

rostral - towards the nose, or towards the front end

caudal - towards the tail (or hind end of)

dorsal - towards the back, which is interchangeable with "posterior" as well. In the brain, this would be like looking down from above onto it. So the orientation for the brain refers to the top of it.

Video: MIT Introduction to Neuroanatomy Series

Of Special Interest: Brain Imaging

Brain imaging is a revolutionary and innovative concept, as it is used to examine a live brain. Before discovery of this technique, study of the brain largely consisted of removing and dissecting a dead brain which made it difficult to diagnose and treat neurological conditions in living people. Today, there are several methods that permit production of pictures of the living brain:

Computed Tomography (CT Scan)

The CT Scan was invented by Godfry Hounsfields and Allan Cormack, who both received the Nobel Prize in 1979. The purpose of the CT Scan is to view slices of the brain in a living individual. For the first time, the ventricles and as well as organization of gray matter and white matter were seen without an invasive procedure. This imaging test uses X-Rays to produce images.

Magnetic Resonance Imaging (MRI)

The CT Scan is still being frequently prescribed; however another procedure on the horizon is now replacing it. Technology developed by Dr. Raymond Damadian, Magnetic Resonance Imaging (MRI) refers to a technique utilized for purposes of viewing living organs without use of X-Rays. This particular form of imaging uses an electromagnetic energy field (radio waves), which passes through the brain of an individual at a certain frequency while the head is positioned between magnetic poles. An MRI takes the information about how the brain's hydrogen atoms react to the magnetic field produced. The collected information is then put into a computer program that creates a map of the brain and an image showing how the hydrogen atoms in the brain are distributed.

Functional Brain Imaging (FMRI)

Both of the above techniques are very helpful for diagnosing structural damage and changes within the brain, namely tumors and swelling, but many of the problems experienced by individuals are not observable simply by looking at the anatomical structure of the brain. Many problems are functional, that is chemical and/or electrical in nature. This is where Positron Emission Tomography (PET) and Functional Magnetic Resonance Imaging (fMRI) scans become useful. PET and fMRI scans detect fluctuations in metabolism and the flow of blood through the tissues within particular brain regions, revealing the most active parts of the brain during certain activities or situations.

Want to Learn More About Neuroscience?

If you are interested in reading more about neuroanatomy, or neuroscience in general, see the following article from this author:


Bear, M.F., Connors, B.W., & Paradiso, M.A. (2007). Neuroscience Exploring the Brain (3rd Ed.). Baltimore, M.D.: Lippincott Williams and Wilkins.

Javed K, Reddy V, Lui F. (2020). Neuroanatomy, Choroid Plexus. Treasure Island, F.L.: StatPearls Publishing. Retrieved from:

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2012 Aunice Yvonne Reed


medbelcher on May 07, 2012:

Good Stuff!

Aunice Yvonne Reed (author) from Southern California on May 05, 2012:

Hello ksinll! It's refreshing to see that there are actually people interested in such topics! Will be writing more:)

ksinll on May 02, 2012:

I love this type of stuff, would definitely be interested in seeing more.

Aunice Yvonne Reed (author) from Southern California on May 02, 2012:

Thanks for stopping by to read Everlearn! Glad it is helpful to you. I enjoy learning about the brain, immensely!

everlearn from Greater New York Region on May 02, 2012:

Thanks! I am trying to learn more about language acquisition and this helps with some of my readings.

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