The Central Nervous System is arguably the most important part of the body because of the way it controls the biological processes of our body and all conscious thought. Due to their importance, they are safely encased within bones, namely the cranium protecting the brain and the spine protecting the spinal cord
Brain Divisions

There are three main components of the brain, namely the brainstem, cerebellum and the forebrain. These are elaborated upon below

• The Brainstem - The brainstem is the connection between the rest of the brain and the rest of the central nervous system. This part of the brain was the first to be found in the evolutionary chain, though has developed over time and via evolution to develop into the two other components. It is primarily concerned with life support and basic functions such as movement, thus meaning that more advanced processes are left to the more evolved areas of the brain, as explained below.
• The Cerebellum - Consisting of two hemispheres, the cerebellum is primarily concerned with movement and works in partnership with the brainstem area of the brain and focuses on the well being and functionality of muscles. The structure can be found below the occipital lobe and adjacent to the brainstem
• The Forebrain - The forebrain lies above the brainstem and cerebellum and is the most advanced in evolutionary terms. Due to its complexity, more info is divulged about this part of the brain below

The Forebrain

The forebrain has many activities that it is responsible for and is divided into many component parts. The below list elaborates on the localised areas of the forebrain and their functions.

• The Hypothalamus - A section of the brain found next to the thalamus that is involved in many regulatory functions such as osmoregulation and thermoregulation. The hypothalamus has a degree of control over the pituitary gland, another part of the brain situated next to it, and also controls sleeping patterns, eating and drinking and speech. The hypothalamus is also responsible for the secretion of ADH (Anti-Diuretic Hormone) via its neurosecretory cells
• The Cerebrum - The cerebrum is the largest part of the human brain, and the part responsible for intelligence and creativity, and also involved in memory. The 'grey matter' of the cerebrum is the cerebral cortex, the centre that receives information from the thalamus and all the other lower centres in the brain.
• The Cerebral Cortex - Part of the cerebrum, this part of the brain deals with almost all of the higher functions of an intelligent being. It is this part of brain that deals with the masses of information incoming from the periphery nervous system, furiously instructing the brain of what is going on inside its body and the external environment. It is this part that translates our nervous impulses into understandable quantifiable feelings and thoughts. So important is the cerebral cortex that it is sub-divided into 4 parts, explained below

1. Frontal Lobe - Found at the front of the head, near the temples and forehead, the frontal lobe is essential to many of the advanced functions of an evolved brain. It deals with voluntary muscle movements and deals with more intricate matters such as thought and speech
2. Parietal Lobe - Situated behind the frontal lobe, this section deals with spatial awareness in the external environment and acts as a receptor area to deal with signals associated with tough.
3. Temporal Lobe - The temporal lobes are situated in parallel with the ears, they serve the ears by interpreting audio signals received from the auditory canal
4. Occipital Lobe - This is the smallest of the four lobe components of the cerebrum, and is responsible in interpreting nerve signals from the eye at the back of the brain

The above components of the brain work in tandem in a healthy brain. However, in some cases the brain can be injured in some way, causing brain damage. The next page looks at how brain damage can affect the way we operate.

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THE NERVOUS SYSTEM

The system of cells, tissues, and organs that regulates the body's responses to internal and external stimuli. In vertebrates it consists of the brain, spinal cord, nerves, ganglia, and parts of the receptor and effector organs.





Cerebrospinal Fluid Circulation
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THE NORMAL CSF The cerebrospinal fluid (CSF) is produced from arterial blood by the choroid plexuses of the lateral and fourth ventricles by a combined process of diffusion, pinocytosis and active transfer. A small amount is also produced by ependymal cells. The choroid plexus consists of tufts of capillaries with thin fenestrated endothelial cells. These are covered by modified ependymal cells with bulbous microvilli. The total volume of CSF in the adult ranges from140 to 270 ml. The volume of the ventricles is about 25 ml. CSF is produced at a rate of 0.2 - 0.7 ml per minute or 600-700 ml per day. The circulation of CSF is aided by the pulsations of the choroid plexus and by the motion of the cilia of ependymal cells. CSF is absorbed across the arachnoid villi into the venous circulation and a significant amount probably also drains into lymphatic vessels around the cranial cavity and spinal canal. The arachnoid villi act as one-way valves between the subarachnoid space and the dural sinuses. The rate of absorption correlates with the CSF pressure. CSF acts as a cushion that protects the brain from shocks and supports the venous sinuses (primarily the superior sagittal sinus, opening when CSF pressure exceeds venous pressure). It also plays an important role in the homeostasis and metabolism of the central nervous system.CSF from the lumbar region contains 15 to 45 mg/dl protein (lower in childen) and 50-80 mg/dl glucose (two-thirds of blood glucose). Protein concentration in cisternal and ventricular CSF is lower. Normal CSF contains 0-5 mononuclear cells. The CSF pressure, measured at lumbar puncture (LP), is 100-180 mm of H2O (8-15 mm Hg) with the patient lying on the side and 200-300 mm with the patient sitting up.

The Conscious & Unconscious Nervous System
- Human Neurology

The Central Nervous System is arguably the most important part of the body because of the way it controls the biological processes of our body and all conscious thought. Due to their importance, they are safely encased within bones, namely the cranium protecting the brain and the spine protecting the spinal cord
Brain Divisions

There are three main components of the brain, namely the brainstem, cerebellum and the forebrain. These are elaborated upon below

• The Brainstem - The brainstem is the connection between the rest of the brain and the rest of the central nervous system. This part of the brain was the first to be found in the evolutionary chain, though has developed over time and via evolution to develop into the two other components. It is primarily concerned with life support and basic functions such as movement, thus meaning that more advanced processes are left to the more evolved areas of the brain, as explained below.
• The Cerebellum - Consisting of two hemispheres, the cerebellum is primarily concerned with movement and works in partnership with the brainstem area of the brain and focuses on the well being and functionality of muscles. The structure can be found below the occipital lobe and adjacent to the brainstem
• The Forebrain - The forebrain lies above the brainstem and cerebellum and is the most advanced in evolutionary terms. Due to its complexity, more info is divulged about this part of the brain below

The Forebrain

The forebrain has many activities that it is responsible for and is divided into many component parts. The below list elaborates on the localised areas of the forebrain and their functions.

• The Hypothalamus - A section of the brain found next to the thalamus that is involved in many regulatory functions such as osmoregulation and thermoregulation. The hypothalamus has a degree of control over the pituitary gland, another part of the brain situated next to it, and also controls sleeping patterns, eating and drinking and speech. The hypothalamus is also responsible for the secretion of ADH (Anti-Diuretic Hormone) via its neurosecretory cells
• The Cerebrum - The cerebrum is the largest part of the human brain, and the part responsible for intelligence and creativity, and also involved in memory. The 'grey matter' of the cerebrum is the cerebral cortex, the centre that receives information from the thalamus and all the other lower centres in the brain.
• The Cerebral Cortex - Part of the cerebrum, this part of the brain deals with almost all of the higher functions of an intelligent being. It is this part of brain that deals with the masses of information incoming from the periphery nervous system, furiously instructing the brain of what is going on inside its body and the external environment. It is this part that translates our nervous impulses into understandable quantifiable feelings and thoughts. So important is the cerebral cortex that it is sub-divided into 4 parts, explained below

1. Frontal Lobe - Found at the front of the head, near the temples and forehead, the frontal lobe is essential to many of the advanced functions of an evolved brain. It deals with voluntary muscle movements and deals with more intricate matters such as thought and speech
2. Parietal Lobe - Situated behind the frontal lobe, this section deals with spatial awareness in the external environment and acts as a receptor area to deal with signals associated with tough.
3. Temporal Lobe - The temporal lobes are situated in parallel with the ears, they serve the ears by interpreting audio signals received from the auditory canal
4. Occipital Lobe - This is the smallest of the four lobe components of the cerebrum, and is responsible in interpreting nerve signals from the eye at the back of the brain

The above components of the brain work in tandem in a healthy brain. However, in some cases the brain can be injured in some way, causing brain damage. The next page looks at how brain damage can affect the way we operate .





Tutorials » Human Neurology » The Conscious & Unconscious Nervous System
The Conscious & Unconscious Nervous System - Human Neurology



The Central Nervous System is arguably the most important part of the body because of the way it controls the biological processes of our body and all conscious thought. Due to their importance, they are safely encased within bones, namely the cranium protecting the brain and the spine protecting the spinal cord
Brain Divisions

There are three main components of the brain, namely the brainstem, cerebellum and the forebrain. These are elaborated upon below

• The Brainstem - The brainstem is the connection between the rest of the brain and the rest of the central nervous system. This part of the brain was the first to be found in the evolutionary chain, though has developed over time and via evolution to develop into the two other components. It is primarily concerned with life support and basic functions such as movement, thus meaning that more advanced processes are left to the more evolved areas of the brain, as explained below.
• The Cerebellum - Consisting of two hemispheres, the cerebellum is primarily concerned with movement and works in partnership with the brainstem area of the brain and focuses on the well being and functionality of muscles. The structure can be found below the occipital lobe and adjacent to the brainstem
• The Forebrain - The forebrain lies above the brainstem and cerebellum and is the most advanced in evolutionary terms. Due to its complexity, more info is divulged about this part of the brain below

The Forebrain

The forebrain has many activities that it is responsible for and is divided into many component parts. The below list elaborates on the localised areas of the forebrain and their functions.

• The Hypothalamus - A section of the brain found next to the thalamus that is involved in many regulatory functions such as osmoregulation and thermoregulation. The hypothalamus has a degree of control over the pituitary gland, another part of the brain situated next to it, and also controls sleeping patterns, eating and drinking and speech. The hypothalamus is also responsible for the secretion of ADH (Anti-Diuretic Hormone) via its neurosecretory cells
• The Cerebrum - The cerebrum is the largest part of the human brain, and the part responsible for intelligence and creativity, and also involved in memory. The 'grey matter' of the cerebrum is the cerebral cortex, the centre that receives information from the thalamus and all the other lower centres in the brain.
• The Cerebral Cortex - Part of the cerebrum, this part of the brain deals with almost all of the higher functions of an intelligent being. It is this part of brain that deals with the masses of information incoming from the periphery nervous system, furiously instructing the brain of what is going on inside its body and the external environment. It is this part that translates our nervous impulses into understandable quantifiable feelings and thoughts. So important is the cerebral cortex that it is sub-divided into 4 parts, explained below

1. Frontal Lobe - Found at the front of the head, near the temples and forehead, the frontal lobe is essential to many of the advanced functions of an evolved brain. It deals with voluntary muscle movements and deals with more intricate matters such as thought and speech
2. Parietal Lobe - Situated behind the frontal lobe, this section deals with spatial awareness in the external environment and acts as a receptor area to deal with signals associated with tough.
3. Temporal Lobe - The temporal lobes are situated in parallel with the ears, they serve the ears by interpreting audio signals received from the auditory canal
4. Occipital Lobe - This is the smallest of the four lobe components of the cerebrum, and is responsible in interpreting nerve signals from the eye at the back of the brain

The above components of the brain work in tandem in a healthy brain. However, in some cases the brain can be injured in some way, causing brain damage. The next page looks at how brain damage can affect the way we operate.





Tutorials » Human Neurology » The Conscious & Unconscious Nervous System
The Conscious & Unconscious Nervous System - Human Neurology



The Central Nervous System is arguably the most important part of the body because of the way it controls the biological processes of our body and all conscious thought. Due to their importance, they are safely encased within bones, namely the cranium protecting the brain and the spine protecting the spinal cord
Brain Divisions

There are three main components of the brain, namely the brainstem, cerebellum and the forebrain. These are elaborated upon below

• The Brainstem - The brainstem is the connection between the rest of the brain and the rest of the central nervous system. This part of the brain was the first to be found in the evolutionary chain, though has developed over time and via evolution to develop into the two other components. It is primarily concerned with life support and basic functions such as movement, thus meaning that more advanced processes are left to the more evolved areas of the brain, as explained below.
• The Cerebellum - Consisting of two hemispheres, the cerebellum is primarily concerned with movement and works in partnership with the brainstem area of the brain and focuses on the well being and functionality of muscles. The structure can be found below the occipital lobe and adjacent to the brainstem
• The Forebrain - The forebrain lies above the brainstem and cerebellum and is the most advanced in evolutionary terms. Due to its complexity, more info is divulged about this part of the brain below

The Forebrain

The forebrain has many activities that it is responsible for and is divided into many component parts. The below list elaborates on the localised areas of the forebrain and their functions.

• The Hypothalamus - A section of the brain found next to the thalamus that is involved in many regulatory functions such as osmoregulation and thermoregulation. The hypothalamus has a degree of control over the pituitary gland, another part of the brain situated next to it, and also controls sleeping patterns, eating and drinking and speech. The hypothalamus is also responsible for the secretion of ADH (Anti-Diuretic Hormone) via its neurosecretory cells
• The Cerebrum - The cerebrum is the largest part of the human brain, and the part responsible for intelligence and creativity, and also involved in memory. The 'grey matter' of the cerebrum is the cerebral cortex, the centre that receives information from the thalamus and all the other lower centres in the brain.
• The Cerebral Cortex - Part of the cerebrum, this part of the brain deals with almost all of the higher functions of an intelligent being. It is this part of brain that deals with the masses of information incoming from the periphery nervous system, furiously instructing the brain of what is going on inside its body and the external environment. It is this part that translates our nervous impulses into understandable quantifiable feelings and thoughts. So important is the cerebral cortex that it is sub-divided into 4 parts, explained below

1. Frontal Lobe - Found at the front of the head, near the temples and forehead, the frontal lobe is essential to many of the advanced functions of an evolved brain. It deals with voluntary muscle movements and deals with more intricate matters such as thought and speech
2. Parietal Lobe - Situated behind the frontal lobe, this section deals with spatial awareness in the external environment and acts as a receptor area to deal with signals associated with tough.
3. Temporal Lobe - The temporal lobes are situated in parallel with the ears, they serve the ears by interpreting audio signals received from the auditory canal
4. Occipital Lobe - This is the smallest of the four lobe components of the cerebrum, and is responsible in interpreting nerve signals from the eye at the back of the brain

The above components of the brain work in tandem in a healthy brain. However, in some cases the brain can be injured in some way, causing brain damage. The next page looks at how brain damage can affect the way we operate.





Tutorials » Human Neurology » The Conscious & Unconscious Nervous System
The Conscious & Unconscious Nervous System - Human Neurology



The Central Nervous System is arguably the most important part of the body because of the way it controls the biological processes of our body and all conscious thought. Due to their importance, they are safely encased within bones, namely the cranium protecting the brain and the spine protecting the spinal cord
Brain Divisions

There are three main components of the brain, namely the brainstem, cerebellum and the forebrain. These are elaborated upon below

• The Brainstem - The brainstem is the connection between the rest of the brain and the rest of the central nervous system. This part of the brain was the first to be found in the evolutionary chain, though has developed over time and via evolution to develop into the two other components. It is primarily concerned with life support and basic functions such as movement, thus meaning that more advanced processes are left to the more evolved areas of the brain, as explained below.
• The Cerebellum - Consisting of two hemispheres, the cerebellum is primarily concerned with movement and works in partnership with the brainstem area of the brain and focuses on the well being and functionality of muscles. The structure can be found below the occipital lobe and adjacent to the brainstem
• The Forebrain - The forebrain lies above the brainstem and cerebellum and is the most advanced in evolutionary terms. Due to its complexity, more info is divulged about this part of the brain below

The Forebrain

The forebrain has many activities that it is responsible for and is divided into many component parts. The below list elaborates on the localised areas of the forebrain and their functions.

• The Hypothalamus - A section of the brain found next to the thalamus that is involved in many regulatory functions such as osmoregulation and thermoregulation. The hypothalamus has a degree of control over the pituitary gland, another part of the brain situated next to it, and also controls sleeping patterns, eating and drinking and speech. The hypothalamus is also responsible for the secretion of ADH (Anti-Diuretic Hormone) via its neurosecretory cells
• The Cerebrum - The cerebrum is the largest part of the human brain, and the part responsible for intelligence and creativity, and also involved in memory. The 'grey matter' of the cerebrum is the cerebral cortex, the centre that receives information from the thalamus and all the other lower centres in the brain.
• The Cerebral Cortex - Part of the cerebrum, this part of the brain deals with almost all of the higher functions of an intelligent being. It is this part of brain that deals with the masses of information incoming from the periphery nervous system, furiously instructing the brain of what is going on inside its body and the external environment. It is this part that translates our nervous impulses into understandable quantifiable feelings and thoughts. So important is the cerebral cortex that it is sub-divided into 4 parts, explained below

1. Frontal Lobe - Found at the front of the head, near the temples and forehead, the frontal lobe is essential to many of the advanced functions of an evolved brain. It deals with voluntary muscle movements and deals with more intricate matters such as thought and speech
2. Parietal Lobe - Situated behind the frontal lobe, this section deals with spatial awareness in the external environment and acts as a receptor area to deal with signals associated with tough.
3. Temporal Lobe - The temporal lobes are situated in parallel with the ears, they serve the ears by interpreting audio signals received from the auditory canal
4. Occipital Lobe - This is the smallest of the four lobe components of the cerebrum, and is responsible in interpreting nerve signals from the eye at the back of the brain

The above components of the brain work in tandem in a healthy brain. However, in some cases the brain can be injured in some way, causing brain damage. The next page looks at how brain damage can affect the way we operate.



Myelin Sheath

Myelin is a substance that forms the myelin sheath associated with nerve cells. This sheath is a layer of phospholipids that increases the conductivity of the electrical messages that are sent through the cell. Diseases such as multiple sclerosis are a result in a lack of this myelin sheath, with the resultant effect being that the conductivity of signals is much slower severely decreasing the effectiveness of the nervous system in sufferers.
In total, there are 43 main nerves that branch of the CNS to the peripheral nervous system (the peripheral system is the nervous system outside the CNS. These are the efferent neurones that carry signals away from the CNS to the peripheral system.
Somatic Nervous System

These efferent fibres are divided into the somatic nervous system and the autonomic nervous system. The somatic fibres are responsible for the voluntary movement of our body, i.e. movement that you consciously thought about doing.
The Autonomic Nervous System

The autonomic nervous system incorporates all the impulses that are done involuntarily, and are usually associated with essential functions such as breathing, heartbeat etc. However this type of system can further be broken down into the sympathetic and parasympathetic systems which keep one another in check in a form of negative feedback such as the release of insulin and glucagon in sugar control of the blood.

Causes of Brain Damage

The brain is a highly specialised tissue, far more complex than today's 21st century supercomputers. Due to this magnificent complexity, even the slightest damage can have extreme consequences
The brain can be damaged in a variety of ways, and depending on the areas damaged and the severity of the damage, it can prove relatively harmless to fatal. Some causes of brain damage are below

• Genetics - A dysfunctional hereditary gene could have been passed on to the offspring which prevented the full development of a healthy brain
• Blow - A sufficient blow to the head can supercede the skulls defences (particularly at the temple) and can therefore allow structural damage to occur.
• Lack of Blood - Lack of blood to the brain can cause severe problems for the cells associated with the brain. A human can survive for four minutes without oxygen before the brain damage becomes so severe there is no realistic chance of survival. A stroke is an event where there is a blood shortage to the brain, which is caused by a blood clot
• Tumours - Cancer has been a major non-infectious disease more recognised over the last decade, and more cases of brain tumours are detected nowadays due to more sophisticated techniques. The continued growth of these cancerous cells puts pressure on the brain, which can cause a blood clot or directly cause brain damage due to the pressure of the tumour pressing against it.

Types of Brain Damage

• Aphasia - A type of brain damage affecting communication capabilities in the organism. This can range from the inability to construct a sentence either in voice or on paper, to the inability to recognise speech itself. This sort of damage focuses on the frontal lobe area of the brain
• Visual Neglect - This is where the information collated on one half of the brain is rejected and therefore the sufferer can only operate with one eye, because the part of the brain receiving visual information from the other eye is not functioning properly. In some cases, sufferers may only be able to paint half a painting or eat one half of a plate of food as they are unaware of the information about the other half of the environment.
• Amnesia - Or retrograde amnesia, this sort of damage affects the memory, caused by degeneration / damage in the frontal lobe. Sufferers have memory blanks when relating to past experiences in their life
• Agnosia - This unusual sort of brain damage is where sufferers still have the complete ability to see around them (unlike visual neglect), though cannot relate their surroundings in a quantifiable way, i.e. they fail to recognise a familiar surrounding, person or object, due to a malfunction in recalling past events involving the surrounding, person or object .

The Human Body: Nervous System


The Human Nervous System
- Human Neurology

The nervous system is essentially a biological information highway, and is responsible for controlling all the biological processes and movement in the body, and can also receive information and interpret it via electrical signals which are used in this nervous system
It consists of the Central Nervous System (CNS), essentially the processing area and the Peripheral Nervous System which detects and sends electrical impulses that are used in the nervous system
The Central Nervous System (CNS)

The Central Nervous System is effectively the centre of the nervous system, the part of it that processes the information received from the peripheral nervous system. The CNS consists of the brain and spinal cord. It is responsible for receiving and interpreting signals from the peripheral nervous system and also sends out signals to it, either consciously or unconsciously. This information highway called the nervous system consists of many nerve cells, also known as neurones, as seen below.
The Nerve Cell


Each neurone consists of a nucleus situated in the cell body, where outgrowths called processes originate from. The main one of these processes is the axon, which is responsible for carrying outgoing messages from the cell. This axon can originate from the CNS and extend all the way to the body's extremities, effectively providing a highway for messages to go to and from the CNS to these body extremities.
Dendrites are smaller secondary processes that grow from the cell body and axon. On the end of these dendrites lie the axon terminals, which 'plug' into a cell where the electrical signal from a nerve cell to the target cell can be made. This 'plug' (the axon terminal) connects into a receptor on the target cell and can transmit information between cells.




neuron
also known as a neurone or nerve cell) is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous system, which includes the brain, spinal cord, and peripheral ganglia. A number of specialized types of neurons exist: sensory neurons respond to touch, sound, light and numerous other stimuli affecting cells of the sensory organs that then send signals to the spinal cord and brain. Motor neurons receive signals from the brain and spinal cord, cause muscle contractions, and affect glands. Interneurons connect neurons to other neurons within the same region of the brain or spinal cord.
A typical neuron possesses a cell body (often called the soma), dendrites, and an axon. Dendrites are thin structures that arise from the cell body, often extending for hundreds of micrometres and branching multiple times, giving rise to a complex "dendritic tree". An axon is a special cellular extension that arises from the cell body at a site called the axon hillock and travels for a distance, as far as 1 m in humans or even more in other species. The cell body of a neuron frequently gives rise to multiple dendrites, but never to more than one axon, although the axon may branch hundreds of times before it terminates. At the majority of synapses, signals are sent from the axon of one neuron to a dendrite of another. There are, however, many exceptions to these rules: neurons that lack dendrites, neurons that have no axon, synapses that connect an axon to another axon or a dendrite to another dendrite, etc.
All neurons are electrically excitable, maintaining voltage gradients across their membranes by means of metabolically driven ion pumps, which combine with ion channels embedded in the membrane to generate intracellular-versus-extracellular concentration differences of ions such as sodium, potassium, chloride, and calcium. Changes in the cross-membrane voltage can alter the function of voltage-dependent ion channels. If the voltage changes by a large enough amount, an all-or-none electrochemical pulse called an action potential is generated, which travels rapidly along the cell's axon, and activates synaptic connections with other cells when it arrives.

How the Body Works : The Regions of the Brain

The Reflex Arc[back to top]

The three types of neurones are arranged in circuits and networks, the simplest of which is the reflex arc.
In a simple reflex arc, such as the knee jerk, a stimulus is detected by a receptor cell, which synapses with a sensory neurone. The sensory neurone carries the impulse from site of the stimulus to the central nervous system (the brain or spinal cord), where it synapses with an interneurone. The interneurone synapses with a motor neurone, which carries the nerve impulse out to an effector, such as a muscle, which responds by contracting.
Reflex arc can also be represented by a simple flow diagram:
Organisation Of The Human Nervous System
[back to top]

The human nervous system is far more complex than a simple reflex arc, although the same stages still apply. The organisation of the human nervous system is shown in this diagram:
It is easy to forget that much of the human nervous system is concerned with routine, involuntary jobs, such as homeostasis, digestion, posture, breathing, etc. This is the job of the autonomic nervous system, and its motor functions are split into two divisions, with anatomically distinct neurones. Most body organs are innervated by two separate sets of motor neurones; one from the sympathetic system and one from the parasympathetic system. These neurones have opposite (or antagonistic) effects. In general the sympathetic system stimulates the “fight or flight” responses to threatening situations, while the parasympathetic system relaxes the body. The details are listed in this table:

The human spinal cord consists of nerves that connect the brain to nerves in the body. It is a superhighway for messages between the brain and the rest of the body. The spinal cord is surrounded for most of its length by the bones (vertebrae) that form the spine.
* * *
The human spinal cord, part of the central nervous system, is generally around 17 inches long, and extends from the brain to the lower back.
Your spine is protected by the vertebral column (also known as the spinal column or backbone).
The human spinal column is made up of 33 bones - 7 vertebrae in the cervical region, 12 in the thoracic region, 5 in the lumbar region, 5 in the sacral region and 4 in the coccygeal region.The outer layer of the human spinal cord consists of white matter, i.e., myelin-sheathed nerve fibers.

These are bundled into specialized tracts that conduct impulses triggered by pressure, pain, heat, and other sensory stimuli or conduct motor impulses activating muscles and glands. The inner layer, or gray matter, is mainly composed of nerve cell bodies. Within the gray matter, running the length of the cord and extending into the brain, lies the central canal through which the cerebrospinal fluid circulates.A spinal cord injury (SCI) can occur anywhere along the spinal cord. It is the result of damage to cells in the spinal cord and causes a loss of communication between the brain and the parts of the body below the injury.Complete and Incomplete Spinal cord injuries (SCI)

Complete Spinal Cord Injury: Generally persons with a complete spinal cord injury suffer a loss of sensation and motor ability caused by bruising, loss of blood to the spinal cord, or pressure on the spinal cord; cut and severed spinal cords are rare. Generally, complete spinal cord injuries result in total loss of sensation and movement below the site of the injury.
Incomplete Spinal Cord Injury: An incomplete spinal cord injury does not result in complete loss of movement and sensation below the injury site. These injuries are usually classified as:
a) Anterior cord syndrome: Damage to the front of the spinal cord, affecting pain, temperature and touch sensation, but leaving some pressure and joint sensation. Often motor function is unaffected.
b) Central Cord Syndrome: Form of incomplete spinal cord injury in which some of the signals from the brain to the body are not received, characterized by impairment in the arms and hands and, to a lesser extent, in the legs. Sensory loss below the site of the spinal injury and loss of bladder control may also occur. This syndrome, usually the result of trauma, is associated with damage to the large nerve fibers that carry information directly from the cerebral cortex to the spinal cord. These nerves are particularly important for hand and arm function. Symptoms may include paralysis and/or loss of fine control of movements in the arms and hands, with relatively less impairment of leg movements. The brain's ability to send and receive signals to and from parts of the body below the site of trauma is affected but not entirely blocked.
c) Brown-Sequard syndrome: Injury to the lateral half of the spinal cord. The condition is characterized by the following clinical features found below the level of the lesion - contralateral hemisensory anesthesia to pain and temperature, ipsilateral loss of propioception, and ipsilateral motor paralysis. Tactile sensation is generally spared.
d) Spinal contusions: The most common type of spinal cord injury. The spinal cord is bruised but not severed. Inflammation and bleeding occurs near the injury as a result of the injury.
e) Injuries to individual nerve cells: Loss of sensory and motor functions in the area of the body to which the injured nerve root corresponds.

The spine is surrounded by many muscles and ligaments to give it strengthCervical (neck) injuries (C1 - C8)

C1 or atlas: The Atlas is the topmost vertebra, and along with C2, forms the joint connecting the skull and spine. Its chief peculiarity is that it has no body, and this is due to the fact that the body of the atlas has fused with that of the next vertebra.
C2 or axis: Forms the pivot upon which C1 rotates. The most distinctive characteristic of this bone is the strong odontoid process (dens) which rises perpendicularly from the upper surface of the body. The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and front part of the third vertebra.
Injuries to C-1 and C-2 can result in a loss of many involuntary functions including the ability to breathe, necessitating breathing aids such as ventilators or diaphragmatic pacemakers.
C4 (cervical vertebra): The fourth cervical (neck) vertebra from the top. Injuries above the C-4 level may require a ventilator for the person to breathe properly.
C5 5th cervical vertabrae down from the base of the skull, found in the neck. C5 injuries often maintain shoulder and biceps control, but have no control at the wrist or hand.
C6 (cervical vertebra): The sixth cervical (neck) vertebra from the top. The next-to-last of the seven cervical vertebrae. An injury to the spinal cord between C6 and C7 vertebrae is called a C6-7 injury. These injuries generally allow wrist control, but no hand function.
C7 or vertebra prominens: The most distinctive characteristic of this vertebra is the existence of a long and prominent spinous process, hence the name vertebra prominens. In some subjects, the seventh cervical vertebra is associated with an abnormal pair of ribs, known as cervical ribs. These ribs are usually small, but may occasionally compress blood vessels (such as the subclavian artery) or nerves in the brachial plexus, causing unpleasant symptoms. C-7 and T-1 can straighten their arms but still may have dexterity problems with the hand and fingers. Injuries at the thoracic level and below result in paraplegia, with the hands not affected.
C8 Although there are seven cervical vertebrae (C1-C7), there are eight cervical nerves (C1-C8). All nerves except C8 emerge above their corresponding vertebrae, while the C8 nerve emerges below the C7 vertebra. In other words C8 is a nerve root not a vertebrae.
Thoracic Vertebrae (T1- T12)

Human vertebra pictureThe thoracic vertebrae increase in size from T1 through T12 and represent the 12 thoracic vertebrae. The thoracic vertebrae are situated between the cervical (neck) vertebrae and the lumbar vertebrae. These thoracic vertebrae provide attachment for the ribs and make up part of the back of the thorax or chest.

Damage or SCI's above the T1 vertebra affects the arms and the legs. Injuries below the T1 vertebra affect the legs and trunk below the injury, but usually do not affect the arms and hands. Paralysis of the legs is called paraplegia. Paralysis of the arms and legs is called quadriplegia.
T-1 to T-8 most often control of the hands, but poor trunk control as the result of lack of abdominal muscle control.
T-9 to T-12 allow good trunk control and abdominal muscle control. Lumbar and Sacral injuries yield decreasing control of the hip flexors and legs. Individuals with SCI also experience other changes. For example, they may experience dysfunction of the bowel and bladder.
Lumbar Vertebrae (L1- L5)
The lumbar vertebrae graduate in size from L1 through L5. These vertebrae bear much of the body's weight and related biomechanical stress.
The lumbar vertebrae are the largest segments of the movable part of the vertebral column, and are characterized by the absence of the foramen transversarium within the transverse process, and by the absence of facets on the sides of the body.
Some individuals have four lumbar vertebrae, while others have six. Lumbar disorders that normally affect L5 will affect L4 or L6 in these individuals.
L1 The first lumbar vertebra is at the level as the ninth rib. This level is also called the important transpyloric plane, since the pylorus of the stomach is at this level.
L3 - L5 A lot of motion in the back is divided between these five motion segments with segments L3 - L4 and L4 - L5 taking most of the stress. L3 - L4 and L4 - L5 segments are most likely to breakdown from wear and tear causing such conditions as Osteoarthritis.
L4 - L5 and L5 - S1 are the most likely to herniate (herniated disc, bulging disk, compressed disk, herniated intervertebral disk, herniated nucleus pulposus, prolapsed disk, ruptured disk, slipped disk). The effects of this can cause pain and numbness that can radiate through the leg and extend down to the feet (sciatica).
L5 The fifth lumbar vertebra is the most common site of spondylolysis and spondylolisthesis.
Sacral Spine (s1 - S5)
The Sacrum is located behind the pelvis. Five bones (abbreviated S1 through S5) fused into a triangular shape, form the sacrum. The sacrum fits between the two hipbones connecting the spine to the pelvis located just below the lumbar vertebrae.
It consists of four or five sacral vertebrae in a child, which become fused into a single bone after age 26. The sacrum forms the back wall of the pelvic girdle and moves with it.
The first three vertebrae in the sacral have transverse processes which come together to form wide lateral wings called alae. These alae articulate with the blades of the pelvis (ilium).
As part of the pelvic girdle, the sacrum forms the back wall of the pelvis and also forms joints at the hip bone called the sacroiliac joints. The sacrum contains a series of four openings on each side through which the sacral nerves and blood vessels run. The sacral canal runs down the center of the sacrum and represents the end of the vertebral canal.
Back pain or leg pain (sciatica) can typically arise due to injury where the lumbar spine and sacral region connect (at L5 - S1) because this section of the spine is subjected to a large amount of stress and twisting.
People with rheumatoid arthritis or osteoporosis are inclined to develop stress fractures and fatigue fractures in the sacrum.
The sacrum is shaped diferent in males and females. In females the sacrum is shorter and wider than in males.
The bottom of the spinal column is called the coccyx or tailbone. It consists of 3-5 bones that are fused together in an adult. Many muscles connect to the coccyx.

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