Sense of Pain & Temperature

A 35-year-old male presents to the emergency department with a sharp, burning pain in his left lower leg following a traumatic injury a week ago. On examination, there is no visible sign of tissue damage, but the patient reports extreme discomfort even with light touch. You suspect activation of specific pain pathways involving nociceptors.

Which of the following best describes the function of nociceptors in this patient’s pain response?

• They are specialized receptors that detect non-harmful stimuli and suppress pain signals.

• They transmit pain signals exclusively through unmyelinated C fibers, resulting in fast pain transmission.

• They detect harmful or potentially harmful stimuli and relay this information to the central nervous system to initiate a protective response.

• They are mechanoreceptors that only respond to deep pressure, and are unlikely to be involved in this type of injury.

Answer explanation

Explanation: Nociceptors are specialized receptors that detect noxious (harmful or potentially harmful) stimuli, such as injury or extreme temperature. They activate and relay this information to the central nervous system, initiating a pain response to protect the body from further damage. This matches the patient's experience of sharp, burning pain after injury, a typical nociceptive response.

Central sensitization contributes to neuropathic pain by the following mechanisms:

• Reduction in the activity of GABAergic interneurons

• Hyperexcitability of dorsal horn neurons due to increased calcium influx

• Enhanced sensitivity of peripheral nociceptors

• Upregulation of sodium channels in central neurons

A 45-year-old woman presents with severe neuropathic pain three months after a spinal surgery. She describes the pain as electric shocks radiating down her legs. You suspect that changes in neurotransmitter activity in the dorsal horn of the spinal cord may be contributing to her chronic pain.

Which neurotransmitter is most likely involved in the activation of pain transmission in the dorsal horn in this patient’s case?

• Dopamine

• Glutamate

• Serotonin

• Acetylcholine

Answer explanation

Explanation: Glutamate is the primary excitatory neurotransmitter released by nociceptive sensory neurons in the dorsal horn of the spinal cord. It plays a key role in pain transmission and is particularly involved in the sensitization processes underlying chronic pain, such as neuropathic pain. The patient’s description of electric shock-like pain is characteristic of neuropathic pain, which often involves altered glutamate signaling in the central nervous system.

Which of the following are mechanisms that lead to hyperalgesia?

• Sensitization of nociceptors due to the release of inflammatory mediators

• Increased release of GABA from interneurons

• Activation of TRPV1 channels by bradykinin and prostaglandins

• Decreased expression of prostaglandins during tissue injury

Which of the following are types of nociceptors?

• Thermal nociceptors

• Mechanical nociceptors

• Polymodal nociceptors

• Silent nociceptors