* To detect changes
- * Process sensory information
- * Provide a response.
There are two types of nerve cells. Neurones which transmit electrical signals, and Glial cells which provide nutrients and other material. The synapse is the point at which one nerve impulses passes from one axon to another. Neurotransmitters facilitate this process. Schwann cells, produce myelin sheaths around the neurones. They are mainly required for insulation and also supplying nutrients to individual nerve fibres (axons). The gap between the Schwann cells is known as the Node of Ranvier, which facilitates the rapid conduction of nerve impulses.
There are three types of nerves
- Autonomic nerves, control the involuntary or partially voluntary activities of the body, including heart rate, blood pressure, digestion (Enteric Nervous System), and temperature regulation.
- Motor nerves, control movement through passing information from the brain and spinal cord to the muscles.
- Sensory nerves, relay information from the skin and muscles back to the spinal cord and brain. The information is then processed as pain and other sensations.
Prior to the body responding cells are at rest. The charge outside of the membrane of the nerve cell is positive and inside negative, The inside of the cell is 70 millivolts more negative than the outside. Sodium NA+ is the main extracellular ion, Potassium K+ the main intercellular ion. The cytoplasm also contains many other negatively charged proteins. The cell membrane is impermeable to these charged ions, thereby maintaining the difference between the outside and inside of the cell. When stimulated the permeability of membrane changes. Initially sodium floods into the neurone changing the electrical potential. Initially depolarising, that is, when the electrical stimuli moves towards Zero. When it reaches-55 millivolts it is at threshold and results in the action potential being stimulated. It takes longer for the potassium channels to open and when they do potassium rushes out reversing the process. The sodium channels closes and sodium/potassium pumps help restore the cell to its original resting state.
The body is constantly monitoring the levels of Sodium, Potassium, and Calcium within the blood. Excess or deficiency will impair the proper functioning of the muscles and other systems of the body. Other important minerals are; Chloride, which is a major contributor to the osmotic pressure gradient between the Intercellular fluid ICF and extracellular fluid ECF, and plays an important role in maintaining proper hydration of the cell. Magnesium contributes to the production of energy and cardiovascular function.
For an action potential to be initiated a signal is required. This is achieved through the involvement of Neurotransmitters.
The nervous system works alongside the endocrine system to maintain homeostasis. One aspect of the workings of the nervous system is communication through the involvement of neurotransmitters. These have to be continually recycled and maintained. For nerve impulses to be effectively transmitted there is a need for the neurones to be insulated within a myelin sheath, made up of a high concentration of lipids. Due to its high energy requirements and its high concentration of lipids, the system is susceptible to cellular damage through the activity of free radicals.
Some areas of the brain have high concentrations of iron, which also makes it more susceptible to the risk of lipid peroxidation. The nervous system has a limited ability to replace damaged cells, therefore it is important that the body has the essential nutrients for protecting against free radical damage. These include: zinc, copper, manganese, selenium, and Iron for the production of the enzymes involved in protecting from free radical damage. Also required are antioxidants, such as; Vitamin C and E, coenzyme Q10, carnitine and lipoic acid.
The Neurotransmitter initiates a response. A particular neurotransmitter can have the opposite effects dependent upon the receptor it stimulates. For example, Acetylcholine causes opposite effects in skeletal and heart muscle, due to these cell types producing different kinds of acetylcholine receptors, which trigger different pathways. Once the neurotransmitter has been used it needs to be removed from the synaptic cleft, either through diffusion out of the cleft, degradation through the use of an enzyme, or by re-uptake.
The system has unique energy requirements and needs a constant supply of oxygen and glucose. High demand neurotransmitters require continual recycling and also the production of the enzymes required to synthesise the neurotransmitters.
The major neurotransmitter in the parasympathetic nervous system. It is generally an excitatory neurotransmitter causing muscle contraction. It also plays a role in learning, arousal, memory, attention, cognitive functions, and autonomic functioning. Low levels can lead to uncontrollable tremors and memory loss. It is removed by degradation.
The Amino acids Glutamate and Aspartate
Excitatory neurotransmitters, Glutamate is released by nerve cells in the brain and plays an important role in learning and memory. It is the most common neurotransmitter in the brain. It is removed by re-uptake.
GABA (gamma-aminobutyric acid) and Glycine
Act as inhibitory neurotransmitters. They are located in CNS (1/3 in the brain). They are removed by re-uptake. Valium enhances GABA activity. It is dependent upon vitamin B6 for its synthesis. GABA deficiency has been associated with anxiety, insomnia, panic attacks, palpitations, trembling, seizures and cold clammy hands. While in excess it has been implicated in schizophrenia, Alzheimer's, migraine, multiple sclerosis, epilepsy and bipolar disorders. Supplementation of GABA is difficult as it does not pass the blood brain barrier, so a more effective approach may be in boosting levels through foods that aid it its synthesis.
Function as neurotransmitters and hormones. Catecholamines are produced by the adrenal glands, which are found on top of the kidneys. They are released into the blood during times of physical or emotional stress. The major catecholamines are dopamine, norepinephrine, and epinephrine. Dopamine also acts as a hormone and is involved in the control of motor function. It has a role in cognition and also pleasure and motivation. Its deficiency results in rigidity, tremors, and brandykinesia.
Excitatory and causes an increase in heart rate, muscle strength, blood pressure, and sugar metabolism. Norepinephrine increases heart rate and blood pressure, triggers the release of glucose from energy stores, increases blood flow to skeletal muscle, reduces blood flow to the gastrointestinal system, and inhibits voiding of the bladder and gastrointestinal motility. It increases alertness and arousal, speeds up reaction time, and has been shown to play a role in a person's mood and ability to concentrate. In response to low blood pressure and stress Norepinephrine promotes vasoconstriction, which is a narrowing of the blood vessels thereby increasing blood pressure. It is removed by re-uptake or degradation.
Excitatory. It is primarily located in the Substantia nigra of the brain. It is involved in movement and coordination, emotional responses, addictive behaviours, pleasurable experiences, and muscle tone. It is removed by re-uptake or by the activity of the enzymes MAO, and COMT.
Synthesised in the Central nervous system and also in enterochromaffin cells of the gastrointestinal tract, which produces around 90% of the body's serotonin levels. It is derived from tryptophan. Serotonin is an excitatory neurotransmitter. It has various functions within the body, including that of the regulation of mood, sensory perception, temperature regulation, appetite, and sleep induction. Stress may have an effect of lowering Serotonin levels. Low levels of serotonin have been associated with depression, greater impulsivity, insomnia and eating disorders. While excess leading to restlessness, agitation, muscle cramps and confusion. Activities that can naturally raise serotonin levels are; positive thinking, exposure to light, and exercise.It is removed by re-uptake.
Formed from Arginine on demand and acts immediately. Plays a role in memory and learning. It is also a potent vasodilator.
Small proteins produced by neurones which are responsible for slow onset and longer lasting effects. Enkephalins, endorphins, and dynorphins help with analgesia, mood stabilisation, pleasure, memory and learning.
A peptide that is triggered by intense afferent painful stimuli. It modulates the neural response to pain and mood.
As is evident from the above brief descriptions, the neurotransmitters work very much in harmony alongside hormones, Dopamine acts as both. That is one reason why mental and cognitive conditions are harder to treat. Cause and effect is another complicating factor, as seen with Serotonin. Low levels lead to depressive symptoms, while having a positive frame of mind causes serotonin levels to rise. For most higher level cognitive functioning there is an interaction between a number of neurotransmitters. Disruption within the endocrine system can also exhibit similar manifestations, for example hyperthyroidism increasing feelings of anxiety.
Dysfunctions can occur at a structural level. Damage to the nerves themselves due to some trauma. The Myelin sheath surrounding the axons, which is important for the electrical stimuli to travel throughout the axion, may become eroded, thereby reducing the functional capability of the axon.
Neurotransmitters may be affected as a result of a lack of nutrients to produce the neurotransmitter. Or a lack of enzymes to metabolise and synthesise the precursors required. For example phenylalanine is required to produce Dopamine, Epinephrine and Norepinephrine. Missing the enzyme phenylalanine hydroxylase will result in a buildup of phenylalanine within the body. Brain cells are particularly sensitive to phenylalanine levels resulting in brain damage.
There may be a failure of removal of the neurotransmitter from the synaptic cleft, as a result of a failure of re-uptake or degradation. Thereby the receptor will be in continuous state of excitation which can be harmful.
While researchers are still debating the full function of sleep, it is known that sleep deprivation affects the brain’s ability to function. Another aspect of sleep is the role of cortisol which follows the sleeping pattern, in that it is at is lowest in the evening and gradually increases during the night, until it reaches its peak at around 6 - 8am.
This rise in cortisol level helps us to get going in the morning. Coffee also has the effect of raising cortisol levels. Stress also raises cortisol levels which is why unresolved stress can often lead to insomnia. It would be interesting to know how cortisol patterns are with people who adopt a different sleep cycle.
Should one worry if one gets less than the often quoted 7 to 8 hours, probably not, unless it is connected to high levels of stress. Long term stress is very damaging to the body, resulting in weight gain, particularly abdominal fat, impairs cognitive and emotional functioning, and results in a state of exhaustion. Dealing with stress levels are important to getting not just the right quantity of sleep, but the right amount of quality sleep.
In the early 1990s it was noticed in an experiment that when subjects were plunged into darkness for 14 hours they reverted to two phases of sleep. The first one of 4 hours followed by a waking period of 1 to 2 hours, followed by another session of 4 hours. This was seen by many as a natural rhythm. Evidence from a variety of sources throughout history has also mentioned the idea of there being two sleeping patterns, the first sleep followed by the second, with an ‘intermission’ between. Some have interpreted this as being an example of polyphasic sleep, and have experimented with other sleeping patterns throughout the day. But is the previous illustration an example of polyphasic sleep? Two things are noticeable in the original experiment. First the subjects developed a pattern of 8 hours sleep, and secondly the interval between lasted 1 to 2 hours and not a full days work. Polyphasic sleep seems to be superior only under specific short term conditions, that is, during periods of sleep deprivation. If you are only able to achieve 3 hours of sleep it is better to get 3 hours through taking short naps throughout the day rather than one long 3 hours of sleep. But this pattern is only sustainable for a short period.
In the above experiment there was a wakeful period of 1 to 2 hours. I wonder what difference it would make to someone who often awakens during the night to be told that this may be a natural rhythm rather than an example of insomnia. Nothing prevents sleep more than the worry about not getting enough. Often when someone awakes they stay in bed worrying about getting off to sleep again, thus preventing the very thing that they desire the most. Getting up for a short period may be more beneficial. But getting up to do what? Possible using the time to write a journal may be beneficial as there would be no expectation as regards the amount achieved, the writing may turn out to be valuable reflections.
A new term has entered the sleep vocabulary, that of, ‘sleep hygiene’. If you find yourself getting up and then unable to return to sleep it is worth considering whether the activity one has just engaged is has been beneficial or has been counterproductive. An obvious example would be drinking coffee. Coffee raises cortisol levels which are associated with levels of alertness. Cortisol levels during the night are naturally at their lowest. Stress also raises cortisol levels, so attempting to catch up on work would probably result in keeping one awake rather than aiding one to return to that second sleep.
During the day cortisol levels slowly fall, with there being a particular dip around midday, and early afternoon. Eating around this time helps to raise energy levels. In many countries this has been associated with a time of partaking in a siesta. The siesta however is not an example of polyphasic sleep. If one finds that this is a period of extreme fatigue then it is more of a reflection of lack of sleep during the night.
There is much talk about the idea of what is important is not the quantity of sleep but the quality, with too much sleep being as detrimental as too little. While this seems obvious, what is also apparent is that one does not go from wakefulness to deep sleep instantaneously, and the quantity needed reflects this. Sleep deprivation affects levels of alertness and quality of performance, as well as decreasing levels of positive mood.
Sleeping patterns that follow the natural circadian rhythms of the body, which will have individual variations, would seem to be more beneficial for long term health.
[ i ] Parallax section below. Click on the section below to upload image. Don't worry if it looks weird in the Weebly editor. It'll look normal on your published site.
To edit or delete your image, press the "toggle" button below. Then, hover over your image until a popup appears with the "edit" and "delete" options. Since these are parallax sections, you may need to scroll a bit up or down to be able to click on the "edit image" popup.