What Is Pain?

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In medicine pain relates to a sensation that hurts. If you feel pain it hurts, you feel discomfort, distress and perhaps agony, depending on the severity of it. Pain can be steady and constant, in which case it may be an ache. It might be a throbbing pain – a pulsating pain. The pain could have a pinching sensation, or a stabbing one.

The English word ‘pain’ probably comes from Old French (peine), Latin (poena – meaning punishment pain), or Ancient Greek (poine – a word more related to penalty), or a combination of all three.

Only the person who is experiencing the pain can describe it properly. Pain is a very individual experience.

The NIH (National Institutes of Health) National Pain Consortium estimates that the public health burden of pain affects one third of America’s population at a cost of between $560 billion and $635 billion each year.

What Is Pain? What Causes Pain?


In medicine pain relates to a sensation that hurts. If you feel pain it hurts, you feel discomfort, distress and perhaps agony, depending on the severity of it. Pain can be steady and constant, in which case it may be an ache. It might be a throbbing pain – a pulsating pain. The pain could have a pinching sensation, or a stabbing one.

The English word ‘pain’ probably comes from Old French (peine), Latin (poena – meaning punishment pain), or Ancient Greek (poine – a word more related to penalty), or a combination of all three.

Only the person who is experiencing the pain can describe it properly. Pain is a very individual experience.

The NIH (National Institutes of Health) National Pain Consortium estimates that the public health burden of pain affects one third of America’s population at a cost of between $560 billion and $635 billion each year.

The British Pain Society quoted England’s Chief Medical Officer, who said that annually more than five million people in the UK develop chronic pain. Unfortunately, one third of them do not recover. 11% of adults and 8% of children in the UK suffer severe pain.

According to Medilexicon’s medical dictionary, Pain is:

1. A variably unpleasant sensation associated with actual or potential tissue damage and mediated by specific nerve fibers to the brain where its conscious appreciation may be modified by various factors.

2. Term used to denote a painful uterine contraction occurring in childbirth.

Types of pain

Acute pain – this can be intense and short-lived, in which case we call it acute pain. Acute pain may be an indication of an injury. When the injury heals the pain usually goes away.

Chronic pain – this sensation lasts much longer than acute pain. Chronic pain can be mild or intense (severe).

How do we classify pain?

Pain can be nociceptive, non-nociveptive, somatic, visceral, neuropathic, or sympathetic:

  • Nociceptive Pain
    – Somatic
    – Visceral
  • Non-Nociceptive
    – Neuropathic
    – Sympathetic

Nociceptive Pain – specific pain receptors are stimulated. These receptors sense temperature (hot/cold), vibration, stretch, and chemicals released from damaged cells.

Somatic Pain – a type of nociceptive pain. Pain felt on the skin, muscle, joints, bones and ligaments is called somatic pain. The term musculo-skeletal pain means somatic pain. The pain receptors are sensitive to temperature (hot/cold), vibration, and stretch (in the muscles). They are also sensitive to inflammation, as would happen if you cut yourself, sprain something that causes tissue damage.

Pain as a result of lack of oxygen, as in ischemic muscle cramps, are a type of nociceptive pain. Somatic pain is generally sharp and well localized – if you touch it or move the affected area the pain will worsen.

Visceral Pain – a type of nociceptive pain. It is felt in the internal organs and main body cavities. The cavities are divided into the thorax (lungs and heart), abdomen (bowels, spleen, liver and kidneys), and the pelvis (ovaries, bladder, and the womb). The pain receptors – nociceptors – sense inflammation, stretch and ischemia (oxygen starvation).

Visceral pain is more difficult to localize than somatic pain. The sensation is more likely to be a vague deep ache. Colicky and cramping sensations are generally types of visceral pain. Visceral pain commonly refers to some type of back pain – pelvic pain generally refers to the lower back, abdominal pain to the mid-back, and thoracic pain to the upper back (see below for the meaning of referred pain).

Nerve Pain or Neuropathic Pain

Nerve pain is also known as neuropathic pain. It is a type of non-nociceptive pain. It comes from within the nervous system itself. People often refer to it as pinched nerve, or trapped nerve. The pain can originate from the nerves between the tissues and the spinal cord (peripheral nervous system) and the nerves between the spinal cord and the brain (central nervous system, or CNS).

Neuropathic pain can be caused by nerve degeneration, as might be the case in a stroke, multiple-sclerosis, or oxygen starvation. It could be due to a trapped nerve, meaning there is pressure on the nerve. A torn or slipped disc will cause nerve inflammation, which will trigger neuropathic pain. Nerve infection, such as shingles, can also cause neuropathic pain.

Pain that comes from the nervous system is called non-nociceptive because there are no specific pain receptors. Nociceptive in this text means responding to pain. When a nerve is injured it becomes unstable and its signaling system becomes muddled and haphazard. The brain interprets these abnormal signals as pain. This randomness can also cause other sensations, such as numbness, pins and needles, tingling, and hypersensitivity to temperature, vibration and touch. The pain can sometimes be unpredictable because of this.

Sympathetic Pain

The sympathetic nervous system controls our blood flow to our skin and muscles, perspiration (sweating) by the skin, and how quickly the peripheral nervous system works.

Sympathetic pain occurs generally after a fracture or a soft tissue injury of the limbs. This pain is non-nociceptive – there are no specific pain receptors. As with neuropathic pain, the nerve is injured, becomes unstable and fires off random, chaotic, abnormal signals to the brain, which interprets them as pain.

Generally with this kind of pain the skin and the area around the injury become extremely sensitive. The pain often becomes so intense that the sufferer daren’t use the affected arm or leg. Lack of limb use after a time can cause other problems, such as muscle wasting, osteoporosis, and stiffness in the joints.

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