What is Neuroanatomy?
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 nervous system, at its most fundamental level consists of the single nerve cell, or neuron which is made up of a cell body, dendrites and a long, singlular extension called an axon. Nerve cells are specialized in the detection of stimuli, including production and actual conduction of nervous system signals. Cells of the nerve tissue are unique in that they do not reproduce or repair themselves like other types of cells.
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 encompasses the CNS, consisting of sensory receptors and motor nerves, the PNS serves as an open line of conveyance. Select areas of the body communicate with the brain via cranial nerves, and the spinal cord is connected in the same way but via the spinal nerves. Nerves which communicate a change to the CNS are referred to as afferent nerve fibers and those that conduct CNS responses to the changing conditions out to relevant organs are called efferent nerve fibers. Responses from the CNS are aimed at maintaining internal equilibrium. This arrangement is common to all mammals.
Peripheral Nervous System (PNS)
The PNS is divided into two types of efferent nerve routes: somatic and autonomic. The somatic nerves are involved with functions chiefly related to detecting and responding to external changes, 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) which lubricates and absorbs 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.
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 Development
cerebral hemispheres, limbic system
lateral and 3rd ventricles
tectum, cerebral peduncle
cerebellum, medulla oblongata, pons
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.
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?
If you are interested in neuroanatomy and would like to learn more, please see the following articles:
Video: MIT Introduction to Neuroanatomy Series
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