If a body part is damaged or injured, action potentials are carried to the regions of the brain that detect pain. Explain how the arrangement of a sensory neurone can allow the action potentials to reach the brain very quickly.
Osteoarthritis pain can be eased by transcutaneous electrical nerve stimulation (TENS). Electrical impulses are used to stimulate the nerve endings at, or close to, the site of the pain. Self-adhesive electrodes are placed on the skin and connected to a small, portable power unit. Fig. 9.1 shows a TENS machine in use. It is believed that TENS stimulates the release of natural painkillers called endorphins, which are similar in shape to painkilling drugs such as morphine.
Suggest the way in which endorphins may reduce pain.
Suggest advantages of using TENS to relieve pain rather than more conventional treatment.