Nociception and Pain Pathways
Introduction
Pain is a complex physiological and psychological phenomenon that serves as a warning
signal for potential or actual tissue damage. It's not solely determined by physical stimuli,
but also influenced by individual experiences, emotions, and beliefs.
Nociceptors: The Body's Alarm System
Nociceptors are specialized sensory receptors located throughout the body (skin,
organs, muscles, joints) that detect noxious stimuli. They are the free nerve endings
of primary afferent Aδ and C fibers.
These receptors are activated by mechanical, thermal, or chemical stimuli,
essentially acting as the body's alarm system.
Inflammatory mediators released from injured tissues can directly activate
nociceptors or make them more sensitive (primary sensitization).
Types of Pain Fibers: Aδ and C Fibers
The signals from nociceptors are transmitted to the spinal cord via two primary types of
nerve fibers: Aδ and C fibers.
Aδ Fibers
Aδ fibers are lightly myelinated, meaning they have a thin layer of insulation
allowing for relatively fast conduction of nerve impulses.
They respond to both mechanical and thermal stimuli and are responsible for the
initial sharp, localized pain felt after an injury. This is the "ouch" feeling that makes
you quickly withdraw from a painful stimulus.
C Fibers
C fibers are unmyelinated and have a smaller diameter, resulting in slower
conduction speeds compared to Aδ fibers.
They are polymodal, meaning they respond to a wider range of stimuli, including
chemical, mechanical, and thermal.
C fibers transmit the dull, aching, and longer-lasting pain that follows the initial sharp
pain.
Introduction
Pain is a complex physiological and psychological phenomenon that serves as a warning
signal for potential or actual tissue damage. It's not solely determined by physical stimuli,
but also influenced by individual experiences, emotions, and beliefs.
Nociceptors: The Body's Alarm System
Nociceptors are specialized sensory receptors located throughout the body (skin,
organs, muscles, joints) that detect noxious stimuli. They are the free nerve endings
of primary afferent Aδ and C fibers.
These receptors are activated by mechanical, thermal, or chemical stimuli,
essentially acting as the body's alarm system.
Inflammatory mediators released from injured tissues can directly activate
nociceptors or make them more sensitive (primary sensitization).
Types of Pain Fibers: Aδ and C Fibers
The signals from nociceptors are transmitted to the spinal cord via two primary types of
nerve fibers: Aδ and C fibers.
Aδ Fibers
Aδ fibers are lightly myelinated, meaning they have a thin layer of insulation
allowing for relatively fast conduction of nerve impulses.
They respond to both mechanical and thermal stimuli and are responsible for the
initial sharp, localized pain felt after an injury. This is the "ouch" feeling that makes
you quickly withdraw from a painful stimulus.
C Fibers
C fibers are unmyelinated and have a smaller diameter, resulting in slower
conduction speeds compared to Aδ fibers.
They are polymodal, meaning they respond to a wider range of stimuli, including
chemical, mechanical, and thermal.
C fibers transmit the dull, aching, and longer-lasting pain that follows the initial sharp
pain.
