Pain & Painkillers

1. Pain & Painkillers

2. What is Pain? • Pain (according to the International Association for the Study of Pain)is an unpleasant sensation, which may be associated with actual or potential tissue damage and which may have physical and emotional components.

3. What is Pain? Continued… • Pain is also a more vague term in the English language. The term that refers to damage to a physical component of the body is known as Nociception. Nociception is a neurophysiological term and refers to specific activity in nerve pathways. It is the Transmission Mechanism for Physiological Pain (physical pain).

4. What is Pain? Cont. • Even though pain can be very unpleasant, it is the body’s most profound component of the body’s defence system. Without pain and discomfort, how would we know if something were wrong with our bodies.

5. How Do We Feel Pain? • Nociceptors are the nerve endings or receptors in the bouton that are responsible for detecting and communicating pain. When the nociceptors are stimulated, they transmit signals to the brain through sensory neurons in the spinal cord.

6. How Do We Feel Pain? Cont. • There are two types of nociceptors, A (A-delta) fibres and C fibres. The A fibres are responsible for communicating fast pain. The C fibres are responsible for communicating slow pain. A fibres have a thin myelin sheath or covering, and transmit signals to the brain between 6 and 30 meters per second. So if you cut your finger, which causes fast pain, you know within less than a second. C fibres don’t have a myelin sheath, like bare wire, and send signals between 0.5 and 2 meters per second. So if you have a slow throbbing pain in your foot, and you were 6 ft tall, it would take you one to two seconds to find out.

7. How Do We Feel Pain? Cont… • When a nociceptor is stimulated, it releases several peptide neurotransmitters, but mainly SubstanceP, an 11 amino acid peptide. The A and C fibres have their cell bodies in the dorsal root ganglia, which is a cluster of neuron cells outside the spinal cord. Central extensions of these nerve cells come out of the dorsal root and go into the dorsal horn of the spinal cord. In the dorsal horn, the neurons transmit signals to secondary neurons, by releasing Substance P, which latches onto receptors on the secondary neurons. The signal then travels to the thalamus where pain perception occurs – where you realize that you are experiencing pain. Then the signals are transmitted to tertiary (third) neurons, and travel to the somatosensory cortex in the cerebrum, where the brain determines where the injury is located.

8. Types of Pain? • There are many different types of pain that the body can experience. In a general sense pain can be grouped into two different types: acute and chronic. • Acute Pain: Acute pain is classified as short-term pain that can (for the most part) be identified easily. It is the body’s standard warning of damage to tissue or disease. In many cases acute pain is fast and sharp and decreases during healing.

9. Types of Pain Cont. • Chronic Pain: Chronic pain was originally classified as pain that persisted past 6 months. It is now a little more loosely defined according to different sources. Some classify chronic pain as pain that lasts three months or longer. Others classify chronic pain as pain that lasts longer then the normal associated time with the particular type of injury. It is often more difficult to treat chronic pain then to treat.

10. Types of Pain Cont. • There is also a type of pain that is classified as acute pain but can last the individual’s entire life span. This pain is known as Episodic Pain. This is pain that is classified by the standards of acute pain but can reoccur at different points in time, sometimes without warning. The most common type of Episodic pain is migraine headaches.

11. Types of Pain Cont. • Along with the two basic types of pain, there are also different groups of physiological pain. These groups are determined according to the source and related nociceptors (pain detection neurons).

12. Types of Physiological Pain • Cutaneous Pain: is caused by injury to the skin or superficial tissues. This pain is caused by the termination of the nociceptors just below the skin, and due to the large amount of nerve endings in that area a well defined localised pain of short duration is produced. The most common examples of this are paper cuts and minor burns.

13. Types of Physiological Pain Cont. • Somatic Pain: results from damage to ligaments, tendons, bones, blood vessels and sometimes the nerves themselves. It is detected by the somatic nociceptors. There is a scarcity of these types of receptors in the body, and because of this the pain that is produced is a dull, poorly localised pain of longer duration. The most common examples of somatic pain are sprains and broken bones.

14. Another Type of Physiological Pain. • Visceral Pain: is located within body organs and internal cavities. The visceral nociceptors are the most rare of all the nociceptors. Because of the rarity of the nociceptors the pain that can be produced within the body organs are the hardest to localise and the pain has more of an aching affect on the body. Many instances of visceral pain exhibit “referred” pain, where the pain is localised to an area completely unrelated to the area of injury. This is why it is hard to determine which organs might actually hurt if you have a stomach-ache.

15. Another Type of Physiological Pain • Phantom Pain: is the feeling of pain from a limb or area that is no longer exists or where the area no longer receives physical signals. This pain usually occurs from the memory of that limb or area when it used to be in function.

16. The last type of Physiological Pain • Neuropathic Pain or “Neuralgia”: is pain that results from injury or disease to the nerve tissue itself. Usually disrupts the ability of the sensory nerves to transmit correct information to the thalamus. The pain is usually a result of the brain interpreting stimuli incorrectly, which results in non-existent pain.

17. Other Aspects of Injury • Cells at the site of injury also release prostaglandins, bradykinins, histamine and serotonin, which are polypeptides that are involved in causing inflammation and swelling. Prostaglandins are released from cells at the site of injury and cause pain themselves.

18. Pain Control • When your brain discovers that you are in pain, special neurons in the brain and spinal cord release endorphins. The endorphins latch onto opiate receptors on the pain-transmitting neurons and reduce the output of substance P. The brain also releases serotonin that inhibits dorsal horn cells, and it releases adrenalin which blocks spinal nociceptor neurons.

19. Pain Control Cont. • Acupuncture and accupressure physically stimulate the release of endorphins and the reduction of pain. Also, aerobic exercise increases production of endorphins, which is why many people feel so great after exercise.

20. Painkillers • There are two main types of chemical painkillers, the opiates or narcotics, and the non-opiates. The opiates are derived from opium, either naturally, or created synthetically.

21. Opiates or Narcotic Painkillers • Opiates act on the neurons in the dorsal horn and reduce the output of substance P, in the same way as the endorphins. Opiates include heroin, Dilaudid, codeine, hydrocodone, oxymorphone, and oxycodone. Synthetic opiates include Demerol, methodone, Lomotil, Dromoran, Darvon, and many others. In addition to being extremely addictive, the opiates also have many side effects. For example, morphine lowers blood pressure, alter consciousness, cause respiratory depression, addiction and constipation.

22. Non-opiates • Non-opiates include aspirin, acetaminophen and the NSAIDs, or non-steroidal anti-inflammatory drugs, like Ibuprofen, (Advil). The non-opiates inhibit the production of cyclooxygenase, which inhibits the production of prostaglandin. This interferes with the pain signals where they originate at the nerve endings outside the spinal cord and reduces swelling and inflammation, which also reduces pain. The NSAID’s also have side effects and can damage the liver and kidneys. Aspirin has been linked to Reye’s Syndrome in children, and can cause bleeding.

23. Antidepressants • Some antidepressants are used to treat shingles and facial neuralgia, (nerve pain). The antidepressants increase the supply of serotonin. Also, some anticonvulsants (drugs used to treat epilepsy) are sometimes used to treat neuropathic pain, (nerve pain), although the medical community is not sure why this works. Some migraines are effectively treated with anti-histamine.

24. Bibliography • Adams, Raymond D. & Victor, Maurice: Principles of Neurology, 4th Edition, McGraw Hill, NY, 1989, Chap 7, pp 103-117 • Guyton, Arthur C., MD.: Basic Human Physiology: Normal Function and Mechanisms of Disease, Philadelphia, 1971, Chap 33, pp 405-415 • Diamond, M.C., Scheibel, A.B., Elson, L.M.: The Human Brain Coloring Book, Harper & Row Publishers, NY, 1985, Chart 4-5 • Beers, Mark H., M.D. & Berkow, Robert, M.D. Editors: The Merck Manual of Diagnosis and Therapy, 17th Edition, N.J., 1999, Chapter 167, pp 1363-1374 • The Incredible Machine, National Geographic Society, Washington, 1986 • Ritter, Robert J.: Biology, Nelson Canada, 1993 • Dorland’s Illustrated Medical Dictionary 24th Edition, W.B. Saunders Company, Philadelphia, 1965 • Painkillers – Basic Overview, http://us.geocities.com/davidsamelman/pain.html • Painkillers – Analgesics, www.surgerydoor.co.uk/medical_conditions/Indices/P/painkillers.htm • Explaining Medicine – Narcotic Pain Killers, www.narcotic.explainingmedicine.com • Analgesic, http://en.wikipedia.org/wiki/Analgesic • BSC 2085 L/Anatomy and Physiology Lab – Spinal Cord XS, http://faculty.tcc.fl.edu/scma/aplab/Practical%20Three/SpinalcordXS.htm • Dorsal root, (including Image: Gray675.png), http://en.wikipedia.org/wiki/Dorsal_root • A/P Lab – A Website for Human Anatomy & Physiology, Spinal cord c.s. with dorsal root, http://bioweb.uwlax.edu/aplab/Table_of_Contents/Lab_06/Dorsal_Root • Managing Chronic Pain, U.S. Food and Drug Administration, www.fda.gov/fdac/features/2004/204_pain.html • Nociceptor, http://en.wikipedia.org/wiki/Nociceptor • The Management Of Pain, American Society of Anesthesiologists, www.asahq.org/patientEducation/managepain.htm • What are Painkillers?, Cancer Research UK, www,cancerhelp.org.uk/help/default.asp?page=5975 • Chronic Pain: How to Get Relief, familydoctor.org, http://familydoctor.org/551.xml?printxml • Anti-inflammatory Painkillers, www.patient.co.uk/showdoc/27000440 • Pain, http://en.wikipedia.org/wiki/Pain • Explaining Medicine: Educate yourself about pain and prescription pain killers, www.explainingmedicine.com/pain