Chapter 8

The Neurological System

Introduction

The nervous system coordinates an animal’s involuntary and voluntary actions. It is also responsible for transmitting signals to the different parts of the body. Nervous systems are found in almost all multicellular animals, but can vary in complexity. Of the multicellular animals, only sponges, mesozoans, and placozoans have no nervous system. Most animals have a nervous system containing a central cord, brain, and nerves which radiate from the cord and brain. The simplest worms have nervous systems of only a few hundred cells while human nervous systems have approximately 100 billion cells.

At a basic level, the nervous system sends signals from one cell to another. Though this can also occur through hormone signaling, hormone signaling is much less specific. Nerve cells are able to send a message on a point-to-point system, allowing for extreme specification. Neural signaling is also able to enact a quicker response than hormone signaling, as nerve signals travel at more than 100 meters per second.

Approaching the nervous system from a more integrative perspective, the nervous system functions to control the entire body. It is able to extract information from the environment and send signals to encode this information to the central nervous system. Then the system processes the information and sends signals to activate a response. Over time the nervous system has evolved to be more complex, allowing for several species to have advanced perception, socialization, coordination, and concurrent processing. For humans, this complexity has allowed us to have language, abstract representation, culture, and more.

Nerve Cells

At a cellular level, the nervous system is composed of specialized cells called neurons or nerve cells. The general neuron has a soma, or cell body, synapses, and a dendrite and axon, the specialized structures which allow them to send and receive signals. The nervous system sends signals as an electrochemical wave. This wave travels along the axon to the synapse, causing chemical neurotransmitters to be released. The receiving cell may be modulated in a number of ways, including becoming excited or inhibited.

The nervous system also contains glial cells which provide metabolic and structural support. Glial cells are not neurons. These cells maintain homeostasis, provide support, nourish, form myelin, and help with signal transmission for neurons. It is estimated that the human brain contains an equal number of neurons and glial cells, though their distribution throughout the brain is by no means equal. One of the most important functions that glial cells perform is support for neurons. Glial cells hold neurons in place and supply the necessary nutrition so that a neuron can send its signal. Glial cells also are able to insulate the neurons electrically and destroy pathogens. These cells also act as waste removal and remove dead neurons from the nervous system.

One type of glial cell is Schwann cells, or oligodendrocytes. These cells generate myelin, which wraps around axons and provides insulation so that an electric pulse can be transmitted more rapidly and efficiently. These cells are referred to as Schwann cells when in the peripheral nervous system and oligodendrocytes when in the central nervous system.

There is also a classification of nerve cells known as identified neurons. A neuron is identified when it has properties which make it distinct from every other neuron in the same animal and if every organism of that species has the same neuron with the same characteristics. These characteristics include gene expression pattern, connectivity, neurotransmitter, and location. Though mollusks, insects, and roundworms have all been found to have several identified neurons, few vertebrates have any identified neurons. The best known identified neuron in vertebrates is the Mauthner cell. This identified neuron is found, in pairs, in fish. Mauthner cells allow fish to curve into a C-shape before propelling forward, a mechanism often used to escape a threat.

Mauthner cells have also been called command neurons. Command neurons are nerve cells which are able to drive a specific behavior. Command neurons are most often present and prevalent in the fast escape systems of a variety of species. The idea of command neurons has, however, become controversial. This is due to the fact that some neurons, previously classified as command neurons, were shown to evoke a response in a very limited set of circumstances. These cells, therefore, did not meet the threshold necessary to be command neurons. Humans have no identified neurons, nor command neurons, at the present time. However, it has been postulated that magical humans may be able to perform their feats due to one or more, as of yet, unidentified identified neurons.

Brain Composition

The human brain is generally structured like other mammals. However, the human brain has a more developed cerebral cortex than any other mammal. When measured using the encephalization quotient, which compensates for body size, the human brain is almost twice that of the bottlenose dolphin and three times that of a chimpanzee. Most of this is due to the cerebral cortex, primarily the frontal lobes. The frontal lobes are associated with abstract thought, planning, reasoning, and self-control. The visual cortex of the cerebral cortex is also enlarged in humans.

In humans, the cerebral cortex is a thick layer of neural tissue. This cortex covers most of the brain. The cortex has many folds which optimize the surface area while minimizing volume. The pattern of folding is similar across humans, though minor differences are seen. The cerebral cortex can be divided into four lobes. These are the frontal, parietal, temporal, and occipital lobes, found beneath the bones of the skull with the same names. Each lobe has numerous cortical areas which perform a particular function, including language, motor control, and vision. Generally, the left and right sides of the cortex are similar in shape and most cortical areas are found on both sides. Some cortical areas do have strong lateralization, especially areas involved in language. Most humans will be left hemisphere dominant for language. The right hemisphere is usually dominant for spatiotemporal reasoning.

Generally, the cerebral cortex is seen as the area of the nervous system where higher thinking is carried out. Certain functions also occur in the brainstem, an area beneath and posterior to the majority of the cerebral cortex. This area, however, normally functions for baser feelings and instincts. Therefore, the brainstem is responsible for baser human thought and emotion which is necessary for survival.

The human brain is not well understood by either magical or non-magical neuroscientists. Brain mapping has been attempted for years and, though some areas, like the language center, are generally mapped out, they are neither understood nor universal for all humans. There are no easy techniques for neurosurgeons who must operate on the brain. Due to the individual connections that each human brain makes, each patient may be slightly different. For instance, though language tends to be dominantly found in the left hemisphere, there are individuals whose language centers are dominant in the right hemisphere. In addition, it is possible to survive and live with only one hemisphere of the cerebral cortex. Though difficult, the brain is able to adapt, form new connections, and eventually function quite successfully with only one lobe. This means that an individual who may have been left hemisphere-dominant for language can lose their left hemisphere and eventually learn to communicate effectively again. This is because the human brain is constantly forming new connections and reshaping itself, so it is possible for a person with only a right hemisphere to form a new language center. Clearly, the human brain is complex and further research is needed so that it can be better understood.

Nervous System Mapping

The nervous system is composed of nerves, cylindrical bundles of axons that emanate from the brain and spinal cord. These nerves branch repeatedly to reach every part of the body. Nerves were first recognized by the Greeks, Romans, and ancient Egyptians, though their internal structure was not known until they were examined under a microscope. Nerves consist primarily of axons and membranes which wrap around and separate the axons into fascicles. The neurons which create nerves do not reside in nerves. Instead, their soma are located either in the brain, spinal cord, or peripheral ganglia.

Every any more advanced than sponges has a nervous system. However, even organisms without a nervous system have cell-to-cell signalling which is a neural precursor. In bilateral animals, such as humans and the majority of extant species, the nervous system has a common structure which originated over 550 million years ago in the Ediacaran period. The nervous system of vertebrates can be divided into the central nervous system and peripheral nervous system.

The central nervous system is the main division of the nervous system, consisting of the brain and spinal cord. The spinal canal houses the spinal cord and the cranium houses the brain. The central nervous system is enclosed and protected by the meninges. The meninges is a three-layered system of membranes. The outer layer is known as the dura matter. The skull also protects the brain while the spinal cord is protected by vertebrae.

The peripheral nervous system refers to all the nervous system structures not found in the central nervous system. Most nerves are considered part of the peripheral nervous system. The peripheral nervous system can be divided into somatic and visceral parts. The somatic part includes nerves which innervate the muscles, skin, and joints. The visceral part is also known as the autonomic nervous system. This system includes the nerves which innervate blood vessels, glands, and the internal organs. The autonomic nervous system can be further divided into the sympathetic nervous system and the parasympathetic nervous system.

The nervous system of vertebrates may also be divided into grey matter and white matter. Grey matter is actually pink or light brown in living tissue and contains a high proportion of soma. It can be found in cortical layers lining the surface of the brain and spinal cord as well as in clusters of neurons which reside within the brain and spinal cord. White matter is mainly myelinated axons and takes its color from the myelin. White matter is composed of all the nerves, as well as a majority of the interior of the brain and spinal cord.

Magical Implications

The nervous system is the system of the human body implicated in magical potential. This means that it is currently believed that magic is able to be performed by humans due to the nervous system. The predominant theory is that, within each soma, there are organelles called magical mitochondria. Identical to normal mitochondria, which produce ATP (a cellular energy source), magical mitochondria take basic supplies gathered from the environment and turn them into magic. This will usually occur faster in a magical environment. When produced in neurons, this magic can then be secreted as a neurotransmitter. In this way magic is able to travel throughout the body. When it reaches an extremity, most commonly the fingers, the magic can be released to perform a variety of tasks, sometimes with the help of foci.

This theory is further substantiated by the fact that there is a high concentration of nerve endings within the fingertips. This allows humans to experience a range of sensation through touch, but may also allow magic to gather and then exit the body. The use of the hands is necessary in almost all spellwork. If magic travels through and is expelled by the nervous system, the hands would be the optimal choice for magical transport.

It is known that magic is carried through the blood, as blood can be removed from a magical being and retain its magical properties. However, though magic may also be produced and transported through blood, blood would not allow for the specialization of spells that we see in our world today. In addition, concentration, focus, and intent would not influence a spell’s outcome to the effect we see in human magic. For these attributes to influence spells the way we observe in the magical world, the nervous system would need to be the main source of magic for humans. Magic also moves through the body faster than cardiovascular transport alone would allow. It is, therefore, the current opinion of the scientific community that the cardiovascular system is a secondary magical system and that the nervous system is the primary magical system of the magical human body.

It is important to make the distinction that the nervous system is the primary magical system for humans and not all magical life forms. After all, it is also known that even species without a nervous system are able to have magic. However, this magic is less focused and shows no true intent. The magic of these species tends to be random or works to protect the organism and insure its survival.

At present, there are several research projects underway considering the origin of magic within the human body, as well as how magic functions within the human body. There are also several promising studies regarding the properties and purpose of magical blood. These studies are long term projects and do not intend to publish any findings for several years yet. Until then, we can only speculate based off of the information we already know regarding the wonders of the human body, particularly, the magical nervous system.

Next Chapter: Magical Reproduction