DESCRIBE THE ROLE OF THE NERVOUS SYSTEM IN GENERATING BREATHING RHYTHM

The majority of time that we breathe, this is an involuntary action. We do not have to tell our bodies to breathe, it just will.
However breathing unlike other involuntary working systems such as the heart, can also be voluntary. We can consciously control our breathing if we need to. We can speed up our breathing and hyperventilate (rapid breathing) slow it down, or stop completely (hold our breath). It is important to note, that although we have the ability to do this, our bodies desperately require us to breathe so that we intake oxygen. If there becomes a major need for our bodies to have oxygen i.e. not enough available oxygen already in our body systems then involuntary breathing will over-ride voluntary breathing. This is why we cannot hold our breath indefinitely. We can do it for a short while, but we must breathe again to allow oxygen into our bodies for respiration.
At rest most people have a breathing rate of 15-25 breathes per minute. This breathing rate allows us to take sufficient oxygen into our bodies so that all our body systems get the specific amount of energy they require to work appropriately.
Occasionally, this breathing rate needs to increase; our bodies need more oxygen than at rest, such as during times of exercise.
The amount we breathe is controlled by the CNS (central nervous system) and the peripheral nervous system. This unconscious control is delivered by the ANS (autonomic nervous system). This is controlled by the CNS which works in conjunction with the peripheral nervous system. Autonomic means that this is involuntary; all body systems that are involuntary are controlled by the ANS.
Abrahams (2002 pg 242) states “The autonomic nervous system is divided into two parts; the sympathetic and the parasympathetic system. Both systems generally supply the same organs but with opposing effects”
The Sympathetic Nervous System
This is referred to as the ‘fight or flight’ response. This nervous system usually becomes active when there is usually a need to increase activity of specific body systems. For example during exercise, the body requires a greater amount of oxygen to allow for increased muscle contraction. To increase the amount of available oxygen the body has, the breathing rate needs to increase and also the heart beat as this will allow for the increased amount of oxygen in the blood readily reach where it is needed i.e. the muscles.
The Parasympathetic Nervous System
This is referred to as the ‘rest and digest’ response. This part of the nervous system is regulating our body systems the majority of the time. It keeps a constant pace for the body at rest. After exercise, it has the ability to override the sympathetic nervous system, when the majority of waste products e.g. lactic acid has been removed from the body. It will lower the activity of the heart and respiratory system to return the body to a normal resting state.

So as you can see these two nervous systems work in harmony together, if there was only one present then we could breathe too rapidly all the time which would have a devastating effect on our health. Also we would never be able to increase our normal activity level because we would not be able to cope with the demands of the activity for very long without feeling completely exhausted.
So we know that breathing is usually controlled by the autonomic nervous system, and can be variable i.e. our breathing rate can change. I will now discuss how the nervous system is actually controlled and how it copes with the variations of breathing.

The CNS is controlled by the brain. It is specific areas of the brain that signal what is needed to be done and transmits this information to appropriate areas. For breathing these specific areas are called the respiratory centres of the brain.
Medulla oblongata is part of the brain that is responsible for vital life functions. This includes breathing. Here lies a respiratory centre
There is also an area of the brain called the pons. Very little is known about the pons , the only known parts of the pons are the pneutaxic and the apneustic. However what is known about the pons is that is also contains a respiratory centre. This respiratory centre holds the standard rate of breathing. This standard rate of breathing is variable so that we can breathe faster depending on our situation.



Our respiratory centres in our brains need to know when to increase breathing rate, and when to decrease breathing rate. For all our body systems, there are sensors inside our bodies to detect changes and transmit this information to the specific part of the brain such as the medulla oblongata, which in turn will process this information and allow our body systems to adapt to the changes so they work efficiently.
During breathing, the sensor associated with this is found in aortic arch. The aortic arch is close to the left lung and the heart. When this specific sensor detects low or high oxygen levels or low or high carbon dioxide levels, it will send a signal to the respiratory centres in the brain to act appropriately. This would be to speed up the breathing rate, controlled by the sympathetic nervous system or slow down the breathing rate, controlled by the parasympathetic nervous system. It also transmits information to the brain ,approxiamately 20 times a minute regardless whether or not there is change in oxygen levels of the blood. this helps maintain the typical at rest breathing rate.

To transmit this information from the brain to the respiratory system, special cells are used. These are called neurons. These neurons pass information from the brain, down the spinal cord and back again or from the sensors to the brain for the information to be processed. Then, down the spinal cord following nerve paths to stimulate specific activity. The brain and the spinal cord is the CNS. The nerve pathways branch out all through the body; this is the peripheral nervous system. Neurons in the brain reach the medulla oblongata and from here pass information to the pons. Information passes back to the medulla oblongata, back down the spinal cord and to the peripheral nervous system to carry out the required response.

When we breathe, the diaphragm is supplied with spinal nerves from the C3 C4 and C5 and the intercostal muscles are supplied spinal nerves T1-T12. Our CNS sends signals through this pathway, making our respiratory muscles contract at specific intervals, controlling our breathing rate. When the sensor in the aortic arch detects changes in oxygen levels or carbon dioxide levels in our blood. This information is sent to the brain via neurons. The respiratory centres in the brain process this information and via neurons send information to the respiratory muscles to either contract at a rapid rate or lower the contraction rate i.e. increasing the breathing rate or decreasing the breathing rate or keep the breathing rate at a constant
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It is important to note, that during conscious breathing, the respiratory systems in the brain are over ridden by the cerebella cortex (another area of the brain). According to Gogoi (2010) “. The portion of the brain aiding the thinking process (cerebral cortex) has a major role to play. It sends signals to the rib muscles and the diaphragm for temporarily overriding the respiratory center signals"