Pain Pain: is a subjective sensation that accompanies the activation of nociceptors which signals actual or potential tissue damage. Pain is stimulated by many factors:  Mechanical  Thermal  Electrical  Chemical

Cognitive Influences that affect the feeling of pain:  Duration of pain  Type of personality  Age  Gender  Cultural background  Expectation and previous experiences

Types of pain:  Acute pain  Chronic pain  Somatogenic pain  Neurogenic pain  Referred pain  Psychogenic pain  Phantom pain

Acute Pain (1 day  1 week):  Pain that is sharp (Like a hit with a knife)  Functions to limit movement and prevent further injury (withdrawal reflex)  After 1 week it is called subacute until 3 months. Examples:  Appendicitis  Heart attack

Chronic Pain (Exceeds 6 months): Results from injury Could have a cause and could have no cause! It's latent (comes after a while) Slow, aching, dull Could set a pathway in the nervous system for its own and sends signals with no ongoing tissue damage and the brain misfires and creates pain Examples:  Back pain  Osteoarthritis

Somatogenic pain:  A pain coming from viscera or sclerotome  Not well localized  Could be referred Neurogenic Pain:  It has a neural origin (compression, cut, etc…)  Can be from the nerve itself or from the root  Pain will be felt either at the site in earlier stages  In later stages it is felt along the pathway of the nerve Example:  Sciatica Description of pain: Burning, lighting, tingling

Referred Pain: Originating in one site radiating to another side, Why??? Because, the dorsal root of the spinal cord receives input from both skin and viscera, so the connection between signals from skin and viscera results in that the brain can not tell which is which. Examples:  Heart  pain is felt in the left shoulder  Kidney  pain is felt in the groin  Gall bladder  pain is felt in the right upper quadrant of the abdomen

Psychogenic Pain:  Most of the time there is no pathology!  Try talking to them  Patient with this kind of pain are better sent to the social worker. Phantom Pain:  Sensation of limb that is felt while the limb is amputated nerves are destroyed  Physiologically there is no signals going to the brain  Abnormal discharge in the peripheral nerve fibers are conceived by the brain as pain  Signals from the stump are going to the brain Description of pain: Burning, electric, cramping.

Pathways of Pain: Stimulus  Nciceptors  A-Delta & C fibers  Dorsal horn  Higher centers. Types of neurons:  First order  Second order  Third order Types of receptors:  Nciceptors  Thermoreceptors  Mechanoreceptors  Proprioceptors

Neural Transmission: 1. Afferent: Form the periphery to the brain. 2. Efferent: From the brain to the periphery.  1st order neurons start at the periphery and end at the dorsal horn  2nd order neurons start at the dorsal horn and end at the thalamus and brainstem  3rd order neurons start the thalamus and brainstem and end in the sensory cortex

 Signal move from one neuron to another or from a neuron to a muscle.  We need a neurotransmitter in the presynaptic membrane  synaptic cleft  postsynaptic cleft  Examples of neurotransmitters: ACTH, Substance P, Serotonin, norepinephrine, B-endorphins, enkephalin. Pathway of pain: Injury in periphery  prostaglandin and bradykinin are produced  a primary hyper algesia  secondary hyper algesia  receptors are stimulated  substance P is produced  C fibers and A-Delta fibers send signals to the spinal cord  higher centers

A-Delta Fibers: 1. Myelinated 2. Faster (5  30 m/s) 3. Sharp pain 4. Localized pain 5. Last for a short while 6. Withdrawal reflex C Fibers 1. Unmyelinated 2. Slower (0.5  2 m/s) 3. Thropping, Burning, Dull pain 4. Poorly localized 5. Difused

Controlling pain: 1. Ascending way: Stimulation of A-Alfa and A-Beta fibers stimulates substantia gelatinosa in the spinal cord  enkephalin is produced  inhibition of A-Delta and C fibers  transmission of A-Delta and C fibers is cut off  no pain! 2. Descending pathway (1): By training the patient that the pain is not important Training the patient's cognitive thinking and changing their behavior 3. Descending pathway (2): Using TENS  stimulate higher centers  chemicals are produced  stimulates the spinal cord  cut transmission between 2nd order neurons and 1st order neurons  no pain!

Pain Assessment: Pain is assessed by:  Visual Analog Scale: the scale consists of a line usually 10cm long, the extremes represents the limits of pain experience, one is defined as "NO PAIN" and the other as "SEVER PAIN", the distance between them represents the pain severity.  Pain Charts: can be used to establish spatial properties of pain.  McGill Pain Questionnaire: is a tool with 78 words that describes pain.  Numeric Pain Scale: the patient is asked to rate their pain on a scale from 1 to 10.

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