Neuroanatomy

Anatomy is the study of an organism's structure and includes several branches of study. Neuroanatomy is the specific study of the organization of the nervous system in both animals and humans. The nervous system is an extremely complex network of electrical impulses that relays messages to and from the brain. The brain then interprets that information and sends out instructions for a response to the rest of the body.

The history of neuroanatomy is lengthy and well documented. Ancient Egyptians, Romans, and Greeks all explored the human body and its organ functions. The oldest document mentioning the brain is a medical papyrus from Egypt. Known as the Edwin Smith Surgical Papyrus, it was written between 3000 and 2500 B.C.E. Scholars including Hippocrates, Plato, Alcmaeon of Croton, Galen, and Leonardo da Vinci were fascinated by and made extensive studies of neuroanatomy. Since that time, medical science and understanding regarding the human brain and nervous system have expanded greatly. With modern technology, neuroanatomical exploration is able to extend to the smallest neuron and map out the functions of the various sections of the brain.

Brief History

Ancient peoples held various beliefs concerning the seat of human thought, emotion, intelligence, and the senses. Many of the ancient Egyptians believed the brain was a useless lump of gooey tissue, and ridded their mummies of it quickly and with no sentiment. The dominant belief among Egyptians and Mesopotamians was that the heart was the organ of greatest importance. The author of the Edwin Smith Surgical Papyrus described two severe head wounds that had exposed brain tissue and how the living brain was fluttering and throbbing under the surgeon's hands. Furthermore, the document describes the effects of brain injury on gross motor functions, such as speech and movement, and includes a physical description of the anterior fontanelle, the meninges, and cerebrospinal fluid.

By the fifth century B.C.E., Hippocrates taught that sensations, emotions, and thoughts originate from the brain. He believed that it was because of the brain that humans suffered ailments such as insomnia or insanity. Ultimately, he declared that the brain was the most powerful organ within the human body. Alcmaeon of Croton traced the main sensory nerves back to the brain and his teachings encouraged the practice of dissection and anatomical study. Two early Greek physicians were the first to make systematic and scientific studies of human remains. Herophilus and Erasistratus offered the first glimpse of the structure of the human brain and nervous system.

Aristotle made the first mention of the cerebellum in the fourth century B.C.E. and Galen wrote about its functions. Erasistratus distinguished the cerebrum at the front of the skull from the cerebellum, which is at the back.

The earliest known illustration of the brain in Western history is included in an eleventh century manuscript. Discoveries in neuroanatomy continued to be made over the centuries, and during the Renaissance period, Leonardo da Vinci made detailed drawings of the brain. After an experiment with ox brains in the early 1500s, he discovered that the ventricles within it contain cerebrospinal fluid. Vesalius published the first drawing of the base of the brain while Archangelo Piccolomini recognized the distinction between the white and grey matter of the brain.

It wasn't until the invention of technology capable of examination on a molecular level that scientists were able to advance understanding of the structure and function of the nervous system. Applying microscopic and electric technology provided insight about the neurological network.

Overview

Neuroanatomy is grouped under the field of cognitive neuroscience, along with neurobiology and neuropsychology. The anatomical aspects of the nervous system include the brain, spinal cord, and their related parts. Although the brain only weighs roughly 3.5 pounds, it contains billions of neurons, trillions of glial (support) cells, and more than one thousand trillion synapses. Visually, the brain is pinkish-gray and mushy; a double handful of fluttering, quivering tissue that is the control center for the nerve network. It is protected by bone, membrane, and fluid and uses 20 percent of the body's oxygen and glucose supply. Without either, the brain often suffers irreversible damage from cellular death.

The brain has four main areas: the brain stem, cerebellum, diencephalon, and cerebrum. It is divided into two hemispheres, which are linked by the corpus callosum. Parts of the brain have ridges (gyri) and grooves (sulci), along with fissures that compartmentalize the regions of the brain. Further into the brain are hollow chambers called ventricles, which are filled with fluid and connect to the spinal cord. It is protected by cerebrospinal fluid, which cushions and buoys the brain, and a special blood barrier that prevents chemicals and some hormones from entering the brain. The brain stem contains the medulla oblongata, which holds the nerves that affect senses and motor skills that run from the spinal cord to the brain. It regulates basic functions such as breathing. Also within the brain stem are the pons, which relays messages from the cortex and the cerebellum, and the midbrain. The midbrain contains the visual and auditory reflex centers.

The two hemispheres known as the cerebellum coordinate movement and balance. The diencephalon holds the thalamus, hypothalamus, subthalamus, and epithalamus. These organs control bodily functions and mental processes such as the automatic nervous system, sensory input, sleeping, and information processing. The left and right hemispheres are divided by fissures and cataloged into lobes: frontal, occipital, temporal, and parietal.

The spinal cord connects the brain with the rest of the body via the brain stem and is a vital link in the nervous system network. It has two rows of nerve roots on each side, forming thirty-one pairs of spinal nerves. It has four different regions: the cervical, thoracic, lumbar, and sacral. The thirty-one segments of the spine are relative to the thirty-one nerve pairs: eight cervical nerves, twelve thoracic nerves, five lumbar nerves, five sacral nerves, and one coccygeal nerve.

Neuroanatomy also includes the structure and study of the nerve network and their purpose. The nervous system is divided into two parts, the central nervous system (CNS) and the peripheral nervous system (PNS). CNS contains the brain and spinal cord while PNS describes the nerve pathways throughout the rest of the body. PNS is further divided into the somatic, or voluntary, system and the automatic system. These refer to the conscious functions of the body as well as the unconscious functions, such as digestion.

A neuron, or nerve cell, conducts electrochemical messages from one part of the body to another. They are composed of a cell body and two types of fibers: dendrites and axons. They work in tandem with glial cells, also called neuroglia, which offer support and protection.

Bibliography

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