Lecture 21. Pain Receptors & Pain Pathways

What is nociception?

The unconscious activity induced by a harmful stimulus applied to sensory receptors.

Define algesia.

Sensitivity to pain.

What is allodynia?

Sensation of pain in response to innocuous stimuli.

What characterizes hyperalgesia?

An exaggerated response to noxious stimuli.

What does analgesia refer to?

Absence of pain in response to stimulation which would normally be painful.

What are nociceptors?

Unspecialized (free) nerve cell endings involved in pain perception.

What types of stimuli do nociceptors respond to?

Mechanical, thermal, and chemical stimuli.

What are the two types of pain described?

First (Fast) Pain and Second (Slow) Pain.

What neurotransmitter is primarily associated with Aδ fibers?

Glutamate.

Which neurotransmitter is primarily associated with C fibers?

Substance P.

What is the function of NMDA receptors in pain management?

They play a role in the treatment of chronic pain.

What is peripheral sensitization?

Increased excitability of nociceptors in damaged or inflamed tissues leading to lower thresholds for activation.

Describe central sensitization.

An immediate increase in excitability of neurons in the dorsal horn of the spinal cord after high levels of activity in peripheral nociceptive afferents.

What is the role of endogenous opioid peptides in pain modulation?

They modulate nociceptive input and can cause analgesia.

Explain the gate control theory of pain modulation.

Non-painful input can 'close the gates' to painful input, preventing the pain sensation from traveling to the CNS.

What is referred pain?

Pain that is perceived in a location other than where the noxious stimulus originates.

What is phantom limb syndrome?

Maladaptive plasticity that occurs after the loss of a body part, causing pain to be perceived in the area of the missing limb.

What is visceral pain?

Pain that originates from internal organs, often difficult to localize.

What defines first (fast) pain?

Short-lived, tingling to sharp pain sensation transmitted by Aδ fibers.

What defines second (slow) pain?

Dull, long-lasting pain sensation transmitted by C fibers.

How are viscerosensory neurons different from mechanosensory neurons in terms of density?

Viscerosensory neurons are far fewer per unit area compared to mechanosensory neurons supplying skin.

What can cause referred pain, according to the lecture?

Noxious stimuli originating from a visceral structure perceived as pain in a remote somatic region.

What is the role of the descending pathways in pain modulation?

They involve interactions between local circuits and brain areas that can suppress pain signals.

What neurotransmitter is associated with serotonin release in pain modulation?

Serotonin is released from fibers originating in the raphe magnus nucleus.

What is the implication of unilateral lesions in the anterolateral system?

Symptoms of pain and temperature deficits occur contralaterally to the side of the lesion.