Nociception and Pain Pathways Overview

The detection of noxious stimuli (tissue-damaging stimuli).

Specialized receptors detecting tissue-damaging stimuli.

Fast-conducting, myelinated nerve fibers, leading to sharp, pricking pain.

Slow-conducting, unmyelinated nerve fibers, leading to dull, aching, throbbing pain.

A stimulus that could damage tissue and is detected by nociceptors.

General Visceral Afferent fibers carry pain signals from internal organs.

Pain from GVA fibers is poorly localized due to large, overlapping receptor fields. It often feels like a dull ache or cramping.

GVA pathways primarily use slow-conducting 'C' fibers, contributing to the dull, persistent nature of visceral pain.

General Somatic Afferent fibers carry pain signals from skin, muscles, and joints.

Pain from GSA fibers is more precise due to smaller receptive fields and involvement of faster 'A delta' fibers.

The pathway carrying pain signals from the skin and superficial tissues. Uses both fast (A-delta) and slow (C) fibers.

The pathway carrying pain signals from muscles, joints, and internal organs. Primarily uses slower (C) fibers.

Superficial and deep pain pathways differ in their fiber types and conduction speed, resulting in distinct qualities of pain sensation.

Both superficial and deep pain pathways are vulnerable to nerve damage, affecting the transmission of pain signals.

Neurological exams can test the integrity of both superficial and deep pain pathways, aiding in diagnosis and prognosis of nerve damage.

Both superficial and deep pain pathways are susceptible to injury. Damage to these pathways can disrupt the transmission of pain signals.

The route pain signals travel from injury site to the brain for processing and reaction.

An intact pain pathway requires a functioning nociceptive afferent fiber, spinal cord segment, afferent neuron, and brain regions involved in pain perception and response (Parietal & Frontal lobes).

A lesion along the pain pathway can disrupt the transmission of pain signals, resulting in a reduced or absent pain response.

Observing an animal's reaction (e.g., withdrawal, vocalization) to a stimulus helps assess their pain perception.

Apply increasing pressure to assess pain response, starting gently and increasing gradually to avoid tissue damage.

A pathway in the spinal cord that transmits superficial pain signals (pain from the skin) to the brain. The tract is called spinothalamic in primates.

Pain that originates from the skin or superficial tissues. This pain is well-localized and sharp. It is mediated by the spinocervicothalamic tract.

The principle that different areas of the body are represented by specific regions of the brain. This allows for precise localization of sensory information.

A common neurological test to assess superficial pain sensation by lightly and briefly pinching the skin.

Deep pain originates from muscles, joints, or internal organs and is often dull and poorly localized. Superficial pain is sharp, well-localized, and originates from the skin. Different pathways and types of nerve fibers are involved in transmitting each type.

A pathway carrying deep pain and visceral sensation signals to the brain. It's less precise than the spinothalamic tract, meaning the animal feels pain but can't pinpoint where it's coming from.

Pain originating from muscles, joints, or internal organs, often described as dull or aching. Transmitted via the spinoreticular tract.

The spinoreticular tract is multi-synaptic and diffuse, meaning the signals travel through many different neurons before reaching the brain. This lack of direct connection makes it difficult to pinpoint the source of deep pain.

Apply pressure to the base of the toenail using hemostats, avoiding the skin. This stimulates nociceptors in the periosteum of the third phalanx, which helps assess deep pain.

If an animal has lost its deep pain sensation, this indicates large and widespread damage to the spinoreticular tract.

The trigeminal system (CN V - cranial nerve 5) receives sensation of touch and pain from the head and projects these signals to the trigeminal ganglion.