Pain is an ancient protective mechanism which generally helps us to avoid injury.
However, tolerance for pain varies from one individual to another.
Page 2 Means of Reducing Pain (Analgesia)
Pain can be reduced by any of the following:
(1) Endorphins ("morphine from within"). Endorphins are chemicals found naturally within the body which tend to block the sensation of pain.
(2) Drugs. Clinically, a number of drugs are used to block or reduce the sensation of pain.
(3) Competing inputs. Competing pain stimuli tend to minimize each other.
The body usually recognizes one pain stimulus at a time. Thus, an individual may "bite
his lip" when he anticipates a painful experience.
Page 3 Characteristics of Pain
The pain receptor is not a specific receptor organ, as with most senses. This receptor is referred to as a free nerve ending.
Excessive stimulation can result in pain. If any of the other senses receives excessive stimulus, for example exposure to excessive light or excessive noise, this can result in pain.
Pain Reflex Arc - Generally, a pain sensory input causes a reflex action long before the information reaches the cerebral cortex and the pain is consciously perceived. For example, you will remove your hand from a hot object before you realize you have been burned.
Page 4 Pathway for the Conscious Sensation of Pain
As usual, the pathway leading to conscious sensation of pain consists of three neurons.
(1) The first neuron is the afferent (sensory) neuron from the free nerve ending. Within the CNS, it synapses with the interneuron.
(2) The axon of the interneuron crosses to the opposite side of the CNS. It then ascends the neuraxis in a fiber tract known as the lateral spinothalamic tract. This tract is found in the lateral funiculus (see Figure 12-6). In the thalamus, the interneuron synapses with the third neuron.
(3) The third neuron projects to the appropriate location of the postcentral gyrus of the cerebral hemisphere. Here, this information is interpreted or recognized as a pain sensation from a particular part of the body.