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Introduction to the Nervous System
However, back pain is often accompanied by many other symptoms – ranging from organ dysfunction to referred pain – all of which are caused by damage to the nervous system. Hence, to understand these symptoms, we first need to understand the nervous system in more depth.
The human nervous system is made up of the following components:
The central nervous system (CNS) comprises the brain and the spinal cord, and controls the vast majority of bodily functions. The peripheral nervous system (PNS) is connected to the CNS, but lies beyond it – it provides a nerve supply to the rest of the body, and relays messages to and from the CNS.
The cranial nerves, labelled CN I (1) - CN XII (12), are so called because they exit the brain through holes in the skull (or cranium).
They provide the nerve supply (for example) to the nose via the olfactory nerve (CN I), and to the eyes via the optic nerve (CN II).
Technically speaking, the spinal cord does not run the entire length of the spinal column (that is, from the brain to the base of the spine) – it ends at the junction between the twelfth thoracic vertebra, and the first lumbar vertebra (T12-L1) – the so called thoracolumbar junction.After this, the cord splits into multiple, separate nerves that continue down into the vertebral column – the anatomical name for this feature is the cauda equina, which is Latin for ‘horse’s tail’.
The spinal nerves branch off the spinal cord, exiting through holes in the vertebral column (the intervertebral foramina). A diagram of the spinal nerve pairs is shown opposite.The nerves that exit the spinal column are labelled according to the level of the hole from which they emerge.
This can get slightly confusing, however, because there are eight cervical nerves (see table below) – as a result, the first seven nerves (C1-C7) exit from the holes above the first seven vertebrae (C1-C7); however, the eighth nerve (C8) emerges from the hole below C7. All of the remaining nerves exit from the hole below their corresponding vertebra.
Each of the 43 nerves can be compared to a tree – it has a large trunk, or root, that splits into successively smaller branches, each of which eventually innervates (or provides a nerve supply to) a particular part of the body.
The Peripheral Nervous System
The peripheral nervous system comprises the following sub-components (each of the 43 nerves of the PNS belongs to one, or more, of them):
Autonomic Nervous System
Enteric Nervous System
The somatic nervous system (SNS) is responsible for all of our voluntary movements – movements that require conscious thought before they happen e.g. running (somatic means of, or relating to, the body).
The autonomic nervous system (ANS) is responsible, as its name suggests, for involuntary, or subconscious, nervous activity (autonomous means self-governing). The ANS, for example, controls heartbeat and the function of most bodily organs – it comprises the following, sub-components:
Parasympathetic Nervous System
The enteric nervous system (ENS) is associated with the gastrointestinal (GI) tract (or alimentary canal) that runs from the mouth to the anus (enteric means ‘of the intestines’). It is linked to the ANS, but, unlike the rest of the human body, it is largely (though not completely) independent of the brain.
Together, these systems account for the 31 nerve-pairs that exit the spinal column (and the 12 that exit the head). Each spinal nerve consists of both motor and sensory units and, for this reason, they are referred to as mixed nerves. The motor units relay information away from the spinal cord, passing instructions from the brain to the muscle or organ in question; the sensory units relay information (from the organ, or muscle) to the brain about various sensations, including temperature, pain and pressure.
As a result, nerve root compression (which, in the spine, is caused by compression of the facet joints) can lead to a wide variety of effects, depending on:
So, we have 31 nerves that exit the spinal column, each of which can belong to one or more of the three peripheral systems (and each of which contains both sensory and motor components). Hence, if we can determine the exit points of the three peripheral systems (somatic, autonomic, enteric), and we know which muscle, or region of the body, each individual nerve supplies, then we can determine the exact effect of nerve root compression.
In the following sections, we discuss each of the peripheral systems in more detail. We then provide a map of the relevant, spinal exit points, and discuss the effects of facet joint compression, as they apply to each system.
Next >>> The Somatic Nervous System
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