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Afferent nociceptive fibers (those that send information to, rather than from the brain) travel back to the spinal cord where they form synapses in its dorsal horn. This nociceptive fiber (located in the periphery) is a first order neuron.
Nociceptors are categorized according to the axons which travel from the receptors to the spinal cord or brain. After nerve injury it is possible for touch fibres that normally carry non-noxious stimuli to be perceived as noxious. [5] Nociceptive pain consists of an adaptive alarm system. [6]
After a nerve lesion of either C fibers or Aδ fibers, they become abnormally sensitive and cause pathological spontaneous activity. [5] This alteration of normal activity is explained by molecular and cellular changes of the primary afferent nociceptors in response to the nerve damage. [5]
Nociceptors respond to potentially damaging stimuli by sending signals to the spinal cord and brain. This process, called nociception , usually causes the perception of pain . [ 23 ] [ 24 ] They are found in internal organs as well as on the surface of the body to "detect and protect". [ 24 ]
Primary injury occurs at the moment of trauma and includes contusion, damage to blood vessels, and axonal shearing, in which the axons of neurons are stretched and torn. [1] The blood brain barrier and meninges may be damaged in the primary injury, and neurons may die. [7] Cells are killed in a nonspecific manner in primary injury. [8]
Types of afferent fibers include the general somatic, the general visceral, the special somatic and the special visceral afferent fibers. Alternatively, in the sensory system , afferent fibers can be classified by sizes with category specifications depending on if they innervate the skins or muscles.
Finally, as this impulse reaches other sweat glands, it causes an indirect axon-reflex sweat response. Sudomotor axon reflexes can be peripherally amplified in the transmission of the action potential magnitude by acetylcholine. [10] Acetylcholine also activates sudomotor fibers and primary afferent nociceptors, triggering axon reflexes in both.
A noxious stimulus is a stimulus strong enough to threaten the body's integrity (i.e. cause damage to tissue).Noxious stimulation induces peripheral afferents responsible for transducing pain (including A-delta and C-nerve fibers, as well as free nerve endings) throughout the nervous system of an organism.