Generation Muscle and nerve impulse generation is initiated by neurotransmitters.

Noradrenaline [Ne] One of the main transmitters of the nervous system.

Effect The effect of [Ne] is mainly sympathetic.

Target [Ne] is released at a target organ. Its actions at the target organ are dictated by
the receptor at that target organ.

Alpha In general [Ne] stimulates alpha receptors to a greater degree than beta receptors.

Na+ [Ne] stimulation of alpha receptors increase the permeability for the inward
movement of sodium.

Exciting This inward movement of sodium causes depolarisation and the net effect
is excitatory.

Lungs Alpha receptors are sited in the lungs and cause broncho-constriction
Blood and those in the blood vessels cause vasoconstriction.

Beta In general, stimulation of beta receptors cause an increase in the
Receptors permeability for the outward movement of potassium, resulting in
hyperpolarisation, and is therefor inhibitory.

Heart Beta receptors in the heart act as excitatory receptors, therefor increasing
the heart rate and contractility.

Lungs In the lungs Beta receptors cause bronchdilation.

Blood Beta receptors in the blood vessels cause vasodilation.



  Chemical Control of Respiration


During tissue metabolism, Carbon Dioxide[c02] and Water [h2o] are produced


In the presence of a substance called Carbonic Anhydrase, they are converted to Carbonic acid [h2co3]=co2 + h2o = h2co3


Carbonic acid quickly breaks down into Hydrogen ions and Bicarbonate ions


co2 + h2o = h2co3 which breaks down to [h+]+[hc0-3


Any increase in co2= an increase in h


Homeostasis- = The respiratory system tries to maintain proper levels of Carbon Dioxide and oxygen and are also extremely sensative any changes.


The normal Partial pressure of oxygen in arterial blood is105 mmhg


Receptors= There are receptors located within the Medulla which is the central Chemosensative area and they monitor any changes in the Hydrogen ion concentrations in the blood


Within the Carotid and Aortic bodies are the Peripheral Chemoreceptors and they are sensative to any changes in Hydrogen ions, Carbon Dioxide and oxygen levels in the blood


An increase in the Carbon Dioxide level [called Hypercapnia] stimulates the Central Chemosensative area and the Peripheral Chemoreceptors which send impulses to the Inspiratory area to increase the rate and depth of breathing. This is called Hyperventilation, and will normaly eliminate Carbon Dioxide and return the Partial pressure of Carbon Dioxide and Hydrogen ions to their normal levels


A fall in the Partial pressure of Carbon Dioxide will not affect the breathing and does not stimulate the receptors. The breathing remains the same until normal levels are attained.


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