Automatic and rhythmic discharge of neurons in the medullary respiratory centre produce inspiration. Impulses travel via the phrenic nerve to the diaphragm.
Other neurons in the brainstem, known as expiratory neurons, are active when ventilation is increased over resting rates. Inspiratory and expiratory neurons also have inhibitory connections to one another. In the pons, the pneumotaxic centre acts as an integrator of inspiratory and expiratory outputs to coordinate and make the process of breathing smooth (E- breathing. 2002 p3).
Although the basic rhythm of respiration is set and coordinated by the inspiratory area, the rhythm can be modified in response to inputs from other brain regions, receptors in the peripheral nervous system and other factors (Tortora & Grabowski, 2000 p383).
According to Waugh & Grant (2002 p256), chemoreceptors are receptors that respond to changes in the partial pressures of oxygen and carbon dioxide in the blood and cerebrospinal fluid. The PH of this fluid is determined by the PH of blood. Atmospheric pressure is the total pressure extended by a mixture of all gases in the air, or it is the sum total of pressures exerted independently, therefore the pressure exerted by each of these separately is called partial pressure (class notes A.C 2002).
Peripheral receptors are located in the aortic bodies; clusters of chemoreceptor are located in the wall of the arch of the aorta, and the carotid bodies, which are oval nodules in the wall of the left and right carotid arteries (Tortora & Grabowski, 2000 p838).
Waugh & Grant (2000 p257) states that nerve impulses generated in the peripheral chemoreceptors are conveyed by the glossophayngeal and vagus nerves to the medulla to stimulate the respiratory centre. The rate and depth of breathing are then increased. An increase in blood acidity stimulates the peripheral chemoreceptor, resulting in increased ventilation, increased carbon dioxide excretion and increased blood PH. When hydrogen increases this stimulates the chemoreceptors which in turn signal the respiratory centre to increase ventilation to get rid of any carbon dioxide (class notes A.C. 2002).
There are other factors that contribute to the regulation of respiration. Because the cerebral cortex has connections with the respiratory centre, we can voluntary alter our pattern of breathing. We can even refuse to breathe at all for a short time. The ability to not breathe, however, is limited by the build up of carbon dioxide and hydrogen in the body. When pressure of carbon dioxide and hydrogen concentration increase to a certain level, the inspiratory area is strongly stimulated, nerve impulses are sent along the phrenic and intercostals nerves to inspiratory muscles, and breathing resumes, whether the person wants it or not.
Nerve impulses from the hypothalamus and limbic system also stimulate the respiratory centre, allowing emotional stimuli to alter respiration as for example in things such as speech, singing, emotional displays such as crying, laughing and fear. Drugs and alcohol affect breathing and so does sleep.
Temperature increases the rate of respiration. A decrease in body temperature decreases respiratory rate. A sudden cold stimulus causes apnea which is a temporary absence in breathing. A sudden severe pain brings about apnea, but prolonged pain increases respiratory rate. Physical or chemical irritation of the pharynx or larynx brings about immediate cessation of breathing followed by coughing or sneezing (Tortora & Grabowski, 2000 p840).
In conclusion, respiration is controlled by nerve cells in the medulla. These cells send impulses down the spinal cord and then via the phrenic nerve to the diaphragm and via the intercostals muscles. The reticular formation has an inbuilt rhythmical pattern of activity which maintains the rhythmical activity of these muscles. The rhythm is supplemented by the Hering-Breur reflex.
Stretch receptors in the lung tissue send impulses via the vagus nerve to the brain stem. The impulses inhibit inspiration when the lungs are distended, and stimulate inspiration when dilated In addition, pain and nerve pulses from exercising limbs, cause an increase in the rate and depth of breathing, by their action on the reticular formation.
WORD COUNT 988
BIBLIOGRAPHY
Jenkins M. Examining GCSE Human Biology. Century Hutchinson Ltd.
Jones M. (1999) Transport, regulation and control. University Press
Tortora G & Grabowski S (2000) Principles of Anatomy & Physiology. Tenth edition. Wiley.
Waugh A & Grant A (2002) Anatomy & Physiology in Health and Illness. Ninth edition. Churchill Livingstone.
‘Control of respiration’ (2002) http:hscvirginiaedu/med
‘Information about the lungs, respiration and diseases of the lungs’ (2002). www.e-breathing.com
‘The respiratory system’ (2002) www.fitnesscomplete.co.uk/chapters/ap/resp.htm
REFERENCES
Tortora G & Grabowski S (2001) ‘Principles of Anatomy and Physiology’ pp 835-848
Waugh A & Grant A (2002) ‘Anantomy and Physiology in Health and Illness’ pp 252-257.
http:hscvirginiaedu/med ‘control of respiration (2002) p1
www.e-breathing .com’introduction about the lungs, respiration and diseases of the lungs’ (2002) p3
www.fitnesscomplete.co.uk/chapters/ap/resp.htm ‘the respiratory system’ (2002) p3
KELLY DETERVILLE
PHYSIOLOGY ESSAY
CONTROL OF RESPIRATION