Pain

The ability to perceive pain involves: Transduction Transmission Perception Modulation Describe Modulation.

All along the pathway, the nervous system can alter which signals are getting transmitted and how signal is transmitted...there are lots of mechanisms to either amplify or suppress signals. This can occur along the entire pathway, including: Periphery (nociceptor) Spinal Cord Thalamus Cerebral Cortex

How do capsaisin creams work to provide analgesic effects?

Capsaisin binds to vanilloid receptors, VR1s, and thermoreceptors on nociceptive axons. This causes Ca2+ to enter to cell and release substance P. Sustained use, however, will cause the depletion of substance P and renders the nociceptor dysfunctional for an extended period of time.

What is fibromyalgia syndrome? Describe the symptoms and etiology.

Fibromyalgia syndrome is characterized by chronic widespread pain affecting all extremities. There are many associated symptoms such as sleep disturbances, insomnia, fatigue, IBS, etc. Etiology is unknown, but risk factors such as trauma, sexual abuse, and stress have been identified.

Describe modulation at the nociceptor, specifically the mechanism by which the periphery can become sensitized to a stimulus. Why would the body sensitize a free nerve ending that has been damaged?

If significant enough damage occurs, a number of signals can be sent out, including: Bradykinin, Prostaglandins, 5-HT, etc. Ultimately, these can cause the release of Substance P. Substance P will bring mast cells to the area, cause histamine release, etc...which will trigger an inflammatory response and enhance blood flow. HOWeVER, it can also lower the threshold for firing action potentials! So, it's easier to get that free nerve ending to respond to a less intense signal. Therefore, the individual is more sensitive to pain, and so they are more likely to protect themselves.

The duration of physiologic pain determines whether any pathologic pain that occurs is acute or chronic. Describe how long 'chronic' pain lasts, its clinical manifestations, and therapy options.

Lasts longer than 6 months, longer than the expected healing time It causes increased peripheral transduction sensitivity and central sensitization. This causes an abnormal state of responsiveness and increases the ability of nociceptors to respond to painful signals. Depression can be a significant factor.

What kinds of pain management can target the spinal cord?

Mild pain is managed with nonopioid analgesics like NSAIDs or acetaminophen. Moderate pain can be controlled with low-potency opioids like codeine. Severe pain requires more potent doses of opioids like morhpine and fentanyl.

What is neuropathic pain?

Neuropathic pain results when there is tissue injury in the nerves themselves. The pain may result from altered central processing of nociceptive input. Symptoms include constant aching w/ sharp, shooting, burning, or shock-like pain Treatments include antidepressants and convulsants.

What is the etiology of migraine headaches? What causes them?

Neurovascular abnormalities Genetic components Overall, not well understood. Pain isn't really coming from the brain, its coming from the meninges and the vasculature.

What is the difference between nociception and pain?

Nociception is the actual detection of some tissue damaging stimulus by sensory receptor cells. Pain is the unpleasant sensory and emotional experience with actual or potential tissue damage. Pain is more broad, it has more context, more emotion associated with it.

Describe modulation at the spinal cord, specifically the mechanism by which suppression of nociceptive input occurs.

Once a signal travels from the periphery to the spinal cord, it has to synapse onto a second neuron. At the synapse, we can get additional input from the periaqueductal gray matter (PAG) and the raphe nuclei (located in the midbrain and brainstem), which can modulate the release of endogenous opioids within the synapse. These opiates will suppress the transmission of the nociceptive input to higher levels.

Describe the pharmacologic methods to target the cortex.

Opioids TCAs SSRIs SNRIs Anti-convulsants

The ability to perceive pain involves: Transduction Transmission Perception Modulation Describe Perception.

Perception refers to one's conscious awareness of the stimulus. The cortex interprets nociceptive input as painful, and it is influences by awareness, emotions, previous experiences, etc. Pain perception involves multiple areas of the cerebral cortex, not just the primary somatosensory cortex.

Pain management can be directed at what three points of modulation?

Periphery Spinal Cord Cortex

There are two major subtypes of pain. Physiologic Pain Pathologic Pain Differentiate the two and describe them.

Physiologic pain occurs when tissue damage occurs. Pathologic pain occurs AFTER tissue damage occurs. It can cause long-term changes along the somatosensory pathways from the periphery to the cortex. Therefore, pain can be significantly enhanced and even non-noxious stimuli can cause pain (allodynia - hypersensitivity).

What is referred pain and why/how does it occur?

Referred pain refers to the fact that pain can be perceived in an area of the body that is not the actual site of injury. This happens because some nociceptors distribute not just to dermatomes, but also to viscera. So it's not uncommon for the same neurons that innervate some internal organ to also feed into another neuron that also getting input from some region of the skin. A good example of this is MIs, which are often perceived as pain in the jaw or left arm.

Describe the non-pharmacologic methods to target the cortex.

Remember that the perception of pain is complex. We can use: Distraction - less able to integrate the pain experience when other stimuli is present Imagery - alters the perception of painful stimuli Relaxation - conditioned response, increases blood flow Biofeedback - increase endorphins, conditioned response Hypnosis Neuronal circuits can 'learn' that an area of the body is painful, so they can continue to fire even in the absence of input. This is very difficult pain to manage.

There are two different pathways that can bring info from the body to the brain. What are they?

Spinothalamic tract - info from the body Trigeminothalamic tract - info from the face

What is diabetic neuropathy?

Symptoms are burning pain, numbnes, tingling, etc. Caused by damage to large axons in peripheral nerves, which carry fine touch sensations. This results in unopposed nociceptive input to the spinal cord. Treatment includes patient education, foot care and glucose control.

Switching gears to migraine headaches. Describe the symptoms and the four stages of a migraine. Prodrome Aura Attack Postdrome

Symptoms include: unilateral throbbing w/nausea, vomiting, photophobia, phonophobia, and lacrimation. Can last hours to days. Prodrome - 1 or 2 days preceding (constipation, depression, food cravings, etc.) Aura - immediately preceding or during the headache; this is often a visual disturbance Attack - throbbing, pulsating headache Postdrome - headache gone but feel drained

What kinds of pain management can target the periphery?

The application of heat or cold can alter blood flow and reduce swelling. NSAIDs can decrease prostaglandins, which thereby interrupts peripheral transmission. (less substance P release) Local anesthetic agents can be used and work by blocking or diminishing nociceptive impulses by blocking sodium influx through voltage gated sodium channels (Ex: lidocaine)

What is the mechanism of the pathology of fibromyalgia? What are the treatment options?

The mechanism of pathology involves disordered pain mechanisms within the CNS. Treatment includes restoring sleep patterns, exercise, and alleviating any depression. Pregabalin, an anti-seizure medication that is used to target pain pathwyas can be helpful.

What is trigeminal neuralgia?

This is characterized by sudden, momentary, but excruciating pain. May feelsharp or shooting, like a shock. Patients may be pain free between episodes or may have a dull ache. May result from compression of the trigeminal nerve by other structures, which can cause demyelination and irritation. Treatment includes anticonvulsants, surgical nerve decompression, and gamma radiosurgery

What is somatotropic organization?

This means that certain parts of the body are innervated by different nerves...think of the homunculus.

What do we mean when we say that neural pathways travel from sensory receptors to the CONTRALATERAL primary somatosensory cortex in the parietal lobe?

This means, basically, that stimulus sensed on one side of the body, the left for example, will travel to the somatosensory cortex in the RIGHT cerebral hemisphere. Contralateral side.

The ability to perceive pain involves: Transduction Transmission Perception Modulation Describe Transduction.

Transduction begins in the periphery, and can be defined as the transformation of a tissue damaging stimulus into an electrochemical signal.

The ability to perceive pain involves: Transduction Transmission Perception Modulation Describe Transmission.

Transmission refers to the neural pathways that carry nociceptive information into the central nervous system; it's the firing of signals all the way up to the somatosensory cortex.

What are the triggers and treatment options for migraine headaches?

Triggers are different for everyone, but common ones include: menstruation, stress, food, alcohol consumption. Treatment includes: identifying and avoiding triggers, antiepileptics, ergot alkaloids (vasoconstrictors, 5-HT agonists), NSAIDs, antidepressants, etc.

The duration of physiologic pain determines whether any pathologic pain that occurs is acute or chronic. Describe how long 'acute' pain lasts, its clinical manifestations, and therapy options.

acute pain is < 3 months in duration It manifests clinically with elevated heart rate, respiratory rate, BP; pallor, sweating, and nausea. There is often grimacing, crying, or moaning. Short-term therapy is indicated, and includes nonopioids, opioids, etc.