Pain is such a small word but it carries an enormous amount of weight in both our physical and physiological world. It is something that everyone experiences. While trying to better understand some aspects of pain; I started to put together a storyboard. I quickly realized, the story of pain is extremely difficult with its endless twists and turns. Nonetheless, I decided to at least start the story and share some of my illustrations and experiments with different illustration/web techniques.
Thank you for visiting!
- Laura Johnston
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An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
Disproportionate hypersensitivity to stimuli; increase feeling of pain from something that would normally cause pain; increase response
Nociceptive responses to non-noxious stimuli; stimulus creating a sensation of pain which normally would not provoke pain
Pins-and-needles or electric-shock-like sensations; abnormal reaction to stimulus
Pain that persists over a long period of time which started due to an injury or ongoing cause - disease
Pain caused by a lesion or disease of the somatosensory nervous system (sensory system)
There are three types of neurons, all of which play important roles in pain transmission and reaction(s):
Sensory Neurons (Afferent) Nociceptors are sensory neurons that play a key role in pain detection and transmission. Somatic pain results from the activation of nociceptor pain receptors close to the body surface/muscles where as viseral pain orginates from internal organs. The sensory neurons transmit the pain signal to the central nervous system (CNS).
Interneurons: Neurons located solely in the central nervous system. Involved in processing sensory information, sending out commands and other complex actions,
Efferent (motor) Neurons: Transmit information - commands from CNS to effector organs.
Peripheral Nervous System: Allows for reaction to physical environment.
Free nerve ending - innervate skin, muscle, or organs
Cell body (soma) in the DRG
Peripheral terminal; free nerve endings, no myelin sheath
Peripheral axon region
Nociceptors are pseudounipolar nerve cells,both terminals can send and receive signals (neurotransmmiters, pH changes, & etc.)
The external noxious stimuli are transduced-translated by the nociceptor into electrical signals. The activation of the nociceptor depends on adquate external stimuli, location of the nociceptor, and type of stimuli.
Nociceptors can respond to mechanical (pressure or mechanical deformation), thermal and/or chemical noxious stimuli brought on by damage, abnormal cell growth, and/or inflammation. Nociceptors are generally categorized as thermal, mechanical, chemical, polymodal; respond to multiple types of stimuli, and silent/sleeping; normally unresponsive but become responsive after tissue injury/inflammation occurs.
Representative cross section of the neuron
*Involved in pain C and Aδ (A-delta)
In some cases Aβ can be stimulated by high threshold stimuli
Nociceptor Aδ Fibers
A delta fibers are lightly myelinated and are faster in the conduction of pain signal; normally associated with sharp pain
Node of Ranvier - Space in between
Myelinated: a Schwann cell makes up the myelin sheath
Layers of myelin
Schwann cell nucleus; Schwann cell, wraps around the axon
Nociceptor C Fibers
Most nociceptors are unmyelinated, C fibers (slow); normally associated with dull ache, second-order pain sensation.
A Unmyelinated Schwann cells can surround (ensheath) several c-fibers ; bundling them together.
C fibers can be subclassified:
Peptidergic: can release neuropeptides like substance P & calcitonin- gene related peptides CGRP
Non peptiderigic do not have neuropeptides; mainly associated with skin
It is important to note that recent studies would suggest further classifications of nociceptors based on transcriptomic, morphological and funcational characteristics.