The human body has a variety of responses to external and internal stimuli in our environment. It is an evolutionary gift that allows us to sense our surroundings and know if something is wrong outside or inside our bodies. Pain is the initial response of the body, and its causes range from purely psychological to acute life-threatening conditions.
How do we feel pain?
The mechanism of pain is complex, and new advances in understanding how we sense pain are made every day. The basic concept is: we have pain receptors in various parts of our body that transmit signals through nerve endings and up to the spinal cord. This is called the primary afferent nociceptors. Then, the signals go up the spinal cord and into various parts of the brain, namely the reticular activating system -which is responsible for our consciousness-, the thalamus -which has many functions including also skin sensation, vision, and hearing-, and the cortex, which is responsible for localizing our pain site. This part is well known as it can be easily reproduced in tests and labs using cutaneous stimulation. However, this isn’t the whole story, and much of the pain pathways is still unknown. The previous path can explain our skin’s pain sensation, which occurs acutely, burning your finger or needle sticks. Still, it cannot explain the deep pain felt on muscles and tendons nor the chronic pain that occurs in many conditions; psychological pain is a whole different story.
We recognize where it hurts through our brain cortex, which is the most advanced neural network on earth. Our body is represented in the cortex of our parietal lobe. When a part of the body is subjected to a painful stimulus, the impulse will go up the pathway till reaching the same site on the brain every time this part is stimulated. This allows us to localize pain and various other sensations as temperature, vibration, pressure, and light touch.
To understand the topic of left arm pain in detail, another small note is essential in our understanding of localization: even though our brain is so good at localizing our pain, it sometimes mistakes it for somewhere else. Many organs of our bodies are insensitive to pain; our very brains are utterly insensitive to pain. The headaches or any pain in our heads comes from other structures like blood vessels, meninges, muscles, bones, or skin. In the same way, some organs share common pathways with skin sites that are relatively remote. There are various explanations for this phenomenon, but the most gullible one is that when we were embryos, our bodies were very different to what they are today, our hearts were close to our heads, and our testes were inside our abdomens. In the same way, organs nearby and were fed by the same artery or the same nerve are distanced in the adult body, but their neural connection is still intact.
Causes of left arm pain:
Causes of left arm pain are various, some of which are trivial, while others need immediate medical help. One of the best ways to understand the causes is to mention them anatomically and then discuss how each cause can cause pain and how does its pain feels like.
Our skin is the most sensitive part of our body, and the number of pain receptors on its surface is unmatched since it is the first line of defense against the environment and our interface to the world. Superficial injury to the skin, whether physical or chemical, can cause significant arm pain. Here, pain is well localized, and the patient can easily detect the site of affection.