Nervous control system, PAIN (physiology) Flashcards
What is pain?
It is an unpleasant sensory or emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
List three functions of pain
-Protection of tissue.
-Alerts you of any tissue damage.
-Activation of pain escape mechanisms.
Name and differentiate btwn the two types of pain
•Fast pain:
-detected by myelated A fibres.
-perception occurs rapidly.
-stimulus causes a sharp, bright localised pain.
- not felt in deeper tissues.
•Slow pain:
-detected by unmyelated c fibres.
-perception slow and gradual.
-causes dull, intense, diffuse unpleasant feeling.
What is the difference btwn physiologic and pathologic pain?
Physiologic pain has a sudden onset and can be receded during the healing process.
Pathologic pain is caused by nerve injury due to toxins, ischemia or diabetes.
Three classifications of pain according to its location(6)
•Superficial somatic pain-pain on the skin surface such is pricking, burning.
•Deep pain- pain is felt in skeletal muscles, joints, tendons, fascia.
•Visceral pain- pain in the visceral organs.
What is referred pain?
Irritation on a visceral organ but the pain is felt at a distant somatic structure.
What is phantom pain?
When you are feeling pain where the missing body part should be.
What are the components needed for pain perception? (5)
-Nociceptors
-Primary afferent neuronal pathways
-Dorsal horn of the spinal cord
-Ascending tracts of the brain
-Descending pathways
What are nociceptors?
Sensory receptors that respond to potentially damaging stimuli.
Where are nociceptors commonly found? (4)
-In joint capsules
-In the superficial portion of skin
- In the periostea of bones
- Around the walls of blood vessels
What are nociceptors sensitive to? (3)
-Temperature extremes
-Mechanical injury
-Dissolved chemical, such as chemicals released by injured cells.
Four types of nociceptors and what they respond to.
Mechanical- respond to strong pressure.
Chemical- respond to chemicals such as histamine, bradykinin.
Thermal- Responds to very hot or cold temperatures.
Polymodal- respond to combinations of stimuli.
Which substances does the injured tissue release during an injury? (3)
Substance P, bradykinin and potassium.
What do mast cells release during an injury?
Histamine
What are other substances released during an injury?
-Serotonin, Ach, prostaglandins and leukotrienes, ATP.
Name and describe the two types of fibers that transmit pain stimuli from nociceptors
Myelated type a fibers- transmit fast, or prickling pain.
Unmyelated type c fibers- transmit slow, aching, burning pain.
Name three neurons involved in the ascending pain pathway as well as the pathway they transmit stimuli in.
Primary neuron- from nociceptors to dorsal horn.
Secondary neuron-from dorsal horn to thalamus.
Tertiary-from thalamus to cortex.
What is the role of the descending pathway of pain?
Produces analgesia
Explain the gate theory of pain.
Inhibitory interneuron which is stimulated by the descending neuron in the dorsal horn releases opiods.
These opiods will inhibit the release of substance P and the depolarization of the secondary neuron.
Therefore the pain stimulus will not be sent to the thalamus and cortex.
How does the descending pathway reduce pain?
It forms a neuron which synapses with the primary neuron of the ascending pathway.
This neuron will release serotonin and noradrenaline which will inhibit the release of substance P.
Pain stimulus will not be sent to the secondary neuron, to the thalmus and cortex.
