Somatic Sensation: Touch-Pressure, Temperature, and Pain Receptors & Pathways

Vocabulary practice flashcards covering touch-pressure receptors, ascending somatic sensory pathways, pain types, referred pain, TRP channels, central sensitization, and pain modulation mechanisms based on the lecture notes.

Somatic Receptors

Receptors that carry sensory information from the framework or outer parts of the body, including skin, skeletal muscles, tendons, and joints.

Meissner's Corpuscle

A rapidly adapting mechanoreceptor located in the skin that senses touch and pressure, associated with myelinated $A\beta$ fibers.

Merkel's Corpuscle

A slowly adapting mechanoreceptor that detects continuous touch and pressure, associated with myelinated $A\beta$ fibers.

Free Neuron Ending

Slowly adapting, unencapsulated nerve endings in tissues that function as nociceptors, thermoreceptors, or mechanoreceptors.

Pacinian Corpuscle

A rapidly adapting mechanoreceptor formed by concentric connective tissue layers surrounding a nerve ending, specialized for sensing vibration and deep pressure.

Ruffini Corpuscle

A slowly adapting mechanoreceptor located in the skin that responds to skin stretch, associated with myelinated $A\beta$ fibers.

Dorsal Column System

An ascending sensory pathway that transmits body movement, limb position, fine touch discrimination, and pressure, synapsing first in brainstem nuclei before crossing to the contralateral thalamus and somatosensory cortex.

Anterolateral Pathway

An ascending sensory pathway for pain and temperature in which central processes of first-order neurons synapse in the dorsal horn, and axons of second-order neurons cross the spinal cord to ascend in anterolateral white matter to the thalamus.

Brown-Séquard Syndrome

A condition caused by hemisection of the spinal cord, resulting in ipsilateral spastic paralysis and loss of vibration, proprioception, and fine touch, along with contralateral loss of pain and temperature sensation below the lesion level.

Cortical Homunculus

A somatotopic map of the body in the primary somatosensory cortex in the postcentral gyrus, where the size of represented body regions is proportional to the density of sensory innervation rather than anatomical size.

TRP Channels (Transient Receptor Potential Proteins)

A family of nonspecific ion channel proteins in sensory receptor endings that open in response to specific temperature ranges or chemical stimuli, primarily allowing $Na^+$ entry to produce receptor potentials.

TRPV1

A transient receptor potential channel activated by temperatures greater than $42^\circ\text{C}$, as well as capsaicin and ethanol.

TRPM8

A transient receptor potential channel activated by cold temperatures below $25^\circ\text{C}$ and by menthol.

Nociceptors

High-threshold pain receptors on free nerve endings associated with small-diameter $A\delta$ or $C$ fibers that detect stimuli causing or threatening tissue damage.

Pain

An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.

Acute Physiological Nociceptive Pain

Pain that occurs when a noxious stimulus is applied to normal, uninjured tissue.

Pathophysiological Nociceptive Pain

Pain that occurs when tissue is damaged or inflamed, which may be spontaneous or manifest as hyperalgesia and allodynia.

Hyperalgesia

An increased pain intensity experienced in response to a stimulus that normally produces pain.

Allodynia

Pain elicited by stimuli that are normally below the threshold required to produce pain.

Neuropathic Pain

Pain resulting from injury or disease of peripheral or central neurons, causing damaged neurons to discharge spontaneously and produce burning or electrical pain qualities.

Central Pain

A form of neuropathic pain caused by damage to central pain-processing neurons in the thalamus.

Referred Pain

Pain localized to a site other than its actual origin, occurring when visceral and somatic primary afferents converge onto the same ascending central neurons in the spinal cord.

Central Sensitization

An increased excitability of pain pathway neurons in the spinal cord caused by prolonged nociceptor activity, leading to increased firing rates and persistent pain.

Endogenous Analgesia System

A descending neural system involving opioid-releasing neurons and non-opioid components that modulates and reduces the transmission of pain information to consciousness.

The Pain Gate

A physiological mechanism in the dorsal horn of the spinal cord where stimulation of non-painful touch fibers ($A\beta$ fibers) closes the gate to block transmission of pain signals carried by $A\delta$ and $C$ fibers.