Pain in ischemia and organ lesions
One of the most clinically significant conditions is cardiogenic pain. Its root cause is myocardial ischemia, which inevitably develops due to insufficient coronary blood flow. Under conditions of oxygen deprivation in heart tissues, various biologically active substances begin to actively form. It is these compounds that act as triggers: they chemically irritate sensory nerve endings.
A crucial feature of the pathogenesis of cardiogenic pain is the obligatory involvement of sympathoadrenal mechanisms. The clinical picture in this condition is extremely specific. The patient experiences not only severe physical suffering but also a profound, highly pronounced emotional reaction accompanied by a panic sense of dread and fear of imminent death.
Central and neuropathic pain
This group includes conditions provoked by dysfunction of the nervous system structures themselves, both central and peripheral.
- Hemialgias represent severe, excruciating, and extremely difficult-to-bear pains that are always strictly localized in the left or right half of the head. The primary cause lies within the central nervous system: a pathological irritation of the thalamus neurons occurs. Growing tumors, past strokes, or other severe cerebrovascular diseases can act as etiological factors for such irritation.
- Causalgia, often referred to in clinical practice as "burning pain", has a different nature. It arises exclusively upon partial damage to a peripheral nerve, when its conductivity is incompletely impaired. The specific burning character of these sensations is directly related to the irritation of autonomic nerve fibers running within the damaged trunk.
- Facial pain is traditionally caused by the development of trigeminal neuralgia or manifestations of sympathalgia.
Phenomena of pain projection and referral
Normal physiology distinguishes a whole range of phenomena in which the brain incorrectly localizes the source of tissue damage.
Projected pain occurs in cases where the irritant is localized on the proximal segment of a nerve, yet the painful sensation itself is projected distally, strictly along the course of its trunk. A classic example is neuralgic pain: during continuous mechanical irritation of a nerve or its spinal root, the patient feels severe pain directly in the area innervated by this nerve.
Referred pain has a more complex central mechanism. During damaging stimuli to internal organs, a person feels discomfort not in the affected organ itself, but in completely distant superficial areas of the body — on the skin. This is explained by the functional characteristics of spinothalamic tract neurons. These cells simultaneously receive excitatory inputs from two different sources: the skin and muscles with internal organs. Due to such neuronal convergence, the central nervous system projects visceral pain onto the corresponding skin dermatomes.
Phantom limb pain is a unique physiological condition that develops in patients after a limb amputation. In this case, the pain is clearly felt in the missing part of the body. The pathogenetic basis of this phenomenon lies in local processes: a scar forms at the end of the surgically severed nerve. Upon irritation of this scar, a generator of pathologically enhanced excitation (GPEE) is formed, sending powerful false impulses to the brain.
Itch as a variant of pain
Within the study of sensory system physiology, itch is defined not as an independent feeling, but as a strictly special form of pain sensation. The main mechanism of its formation lies in the functional dissociation of cutaneous afferent influences that normally operate in strict coordination. Disruption of this balance leads to the appearance of a specific itchy sensation.
Briefly: answers to topical questions
What are the classic Head zones for referred pain in myocardial infarction?
The classic Head zones in myocardial infarction and cardiac pathology correspond to the Th3–Th4 spinal segments and the left upper thoracic segment. Referred pain in myocardial ischemia is projected into the following areas:
- Left hemithorax — the zone of somatic afferent input.
- Left arm — the area of pain radiation due to the convergence of visceral and somatic impulses.
- Left scapula — the area to which segmental pain radiates during myocardial infarction.
To remember the mechanism of referred pain, imagine a "General Switchboard": signals from the skin and internal organs arrive at the exact same neurons of the spinothalamic tract. The brain, accustomed to receiving signals from the skin more frequently, mistakenly "projects" the pain from the organ onto the superficial areas of the body.
Class and exam questions
Why does cardiogenic pain cause a fear of death?
This is due to the active involvement of sympathoadrenal mechanisms in the pathogenesis, which trigger a systemic stress response accompanied by pronounced emotions and panic.
What is the main condition for the onset of causalgia?
Causalgia (burning pain) occurs only upon partial nerve injury with preserved residual conductivity and obligatory irritation of autonomic fibers.
How does phantom pain form after amputation?
A scar forms on the stump of the severed nerve. At its slightest irritation, a generator of pathologically enhanced excitation (GPEE) arises, and the brain perceives these signals as pain in the missing limb.
How does projected pain differ from referred pain?
Projected pain is felt along the course of a single damaged nerve (distally from the site of irritation), whereas referred pain occurs on the skin during internal organ pathology due to signal convergence in the spinal cord.
What else to study on this topic
- Mechanisms of formation of the generator of pathologically enhanced excitation (GPEE)
- Topography of dermatomes and pathways of the spinothalamic tract
- The role of biologically active substances in the initiation of cardiogenic pain
- Trigeminal neuralgia and facial sympathalgias
- Dissociation of afferent influences in itch
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