6.6. Applying Anatomy
Thoracic Nerves in Context
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It is well known that some patients who are having a myocardial infarction report pain in the left and/or right arms, jaw and back. This is sometimes due to referred pain. Referred pain comes about when there is a convergence of neural signals in the spinal cord. For example, visceral pain neurons from the heart synapse with the same spinal cord neuron as somatic pain neurons from the skin. The brain is, under normal circumstances, more likely to receive pain signals from the skin, and so it interprets this mixed signal as being from the skin). Another common example of referred pain is seen with gall bladder and liver problems, which result in shoulder pain.
Shingles occurs when the varicella-zoster virus infects the sensory neurons in spinal or cranial nerves. The varicella-zoster virus is acquired during chicken pox and lies dormant in the body. When the virus is reactivated shingles develops. The infection of the sensory neuron (and sometimes motor neuron) results in inflammation in the neuron itself and in the dermatome of the affected nerve. This is commonly on the thorax. A rash that presents as painful blisters spreads across one area on one side of the body (only one side is affected because only one spinal nerve is affected). Shingles most commonly occurs in people aged 50+.
Phrenic nerve and the thoracotomy
A thoracotomy is a procedure where the thoracic cavity is opened by making an incision in an intercostal space and using rib spreaders to access the lungs and/or heart. During this procedure, one can visualise the phrenic nerve running on the lateral aspect of the pericardium, and care is taken not to damage it.