nociception Flashcards
What is nociception?
Nociception is the process by which the sensory nervous system encodes potentially harmful stimuli. It involves signals sent from nociceptors to the central nervous system.
What are the main functions of sensory neurons in nociception?
Sensory neurons detect stimuli through nociceptors, which involves four key processes:
Transduction -conversion of harmful stimuli (mechanical, thermal, or chemical) into electrical signals by nociceptors.
Transmission - The propagation of these electrical signals through primary afferent nociceptors to the spinal cord and then to the brain.
Modulation - The alteration of nociceptive signals within the spinal cord, which can amplify or dampen the pain experience.
Perception - The conscious awareness of pain, where the brain interprets the signals and assigns meaning to them, often leading to a behavioural response.
What is the primary afferent nociceptor?
The primary afferent nociceptor is responsible for transmitting nociceptive signals to the spinal cord, where modulation occurs in the dorsal root ganglia. The spinothalamic tract connects the spinal cord to the thalamus.
What are the types of nociceptive fibers and their characteristics?
AB fibers:
Detect non-noxious mechanical stimuli (e.g., feathers)
Myelinated, large diameter
Propagation speed: 30-70 m/s
Functions: Proprioception, light touch
Ad fibers:
Detect noxious mechanical stimuli (e.g., hammer)
Lightly myelinated, medium diameter
Propagation speed: 2-10 m/s
Functions: Nociception (mechanical, thermal, chemical)
C fibers:
Detect noxious heat and chemical stimuli (e.g., chili pepper, fire)
Unmyelinated, small diameter
Propagation speed: 1 m/s
Functions: Nociception (mechanical, thermal, chemical), innocuous temperature, itch
How are nociceptive signals transmitted to the brain?
Nociceptive signals are consolidated in the dorsal root ganglia and transmitted to the spinal cord, then to the brain (thalamus and cortex), resulting in a pain response.
What role do ion channels play in nociception?
Ion channels are essential for nociception, facilitating the transmission of pain signals. Once in the spinal cord, neurotransmitters are released at synapses to propagate the signal to the brain.
What are transient receptor potential channels (TRP)?
TRP channels are important nociceptors that are not selective for calcium or sodium. They consist of four subunits forming a central pore and include subfamilies like TRPV1 (responsive to heat, pH changes, and chemicals) and TRPM8.
What are the two main types of nociceptive pain?
Somatic Pain:
Arises from the peripheral nervous system (skin, muscles, joints)
Localized, responsive to pain relief (e.g., muscle cramps, sprains)
Visceral Pain:
Arises from internal organs (e.g., uterus, intestine)
Diffuse and difficult to pinpoint, often poorly responsive to pain relief (e.g., appendicitis, dysmenorrhea)
What are inflammatory mediators of pain?
Inflammatory cytokines can promote pain signals recognized by nociceptors, contributing to the sensation of pain. Treatment options may include COX-2 inhibitors and opioids.
What is neuropathic pain?
Neuropathic pain arises from damage to neurons (e.g., spinal cord injury, carpal tunnel syndrome) and can cause pain without stimuli. Neurons cannot be easily repaired, leading to persistent pain.
What are potential treatment options for neuropathic pain?
Treatment options include:
Tricyclic antidepressants - Modulate pain signaling pathways and enhance the effects of neurotransmitters.
Anticonvulsants - Stabilize neuronal membranes and reduce excitability (e.g., gabapentin, pregabalin).
Sodium channel blockers - Target voltage-gated sodium channels to reduce excitability.
Opioids - Provide pain relief but have potential for dependence and side effects.
What are potential therapeutic targets in nociception?
Voltage-Gated Sodium Channels (VGSCs): Key targets in pain management due to their role in action potential generation in nociceptive neurons. Specific α-subunits are enriched in dorsal root ganglia, which signal pain.
Lidocaine: A VGSC blocker that reversibly binds to the inner pore of VGSCs in open and inactivated states, effectively reducing pain signal transmission. It has a higher affinity for inactivated channels, enhancing its effectiveness in treating acute pain.
How does lidocaine function as a pain treatment?
Lidocaine binds reversibly to the inner pore of VGSCs in open and inactivated states, blocking sodium influx and thus reducing pain signaling. It has a higher affinity for inactivated channels than resting ones.
