Sensory Systems and Pathways

Vocabulary flashcards covering somatic, visceral, and visual sensory physiology and pathways based on the lecture material.

Dorsal Column-Medial Lemniscal Pathway

A somatic sensory pathway that conveys high-localization touch, fine gradations of intensity, vibration, movement against skin, joint position sense, and precise pressure judgment to the primary somatosensory cortex.

Fasciculus Gracilis

An ascending tract in the dorsal column that carries proprioception, fine touch, and vibration signals from the lower limbs and legs to the nucleus gracilis in the medulla.

Fasciculus Cuneatus

An ascending tract in the dorsal column that carries proprioception, fine touch, and vibration signals from the upper body and arms to the nucleus cuneatus in the medulla.

Ventrobasal Complex (VBC)

A thalamic region containing the ventral posterolateral (VPL) nucleus, which receives body sensory signals, and the ventral posteromedial (VPM) nucleus, which receives head and face sensory signals.

Astereognosis

The inability to judge or recognize the shapes, forms, or three-dimensional structures of objects by touch, resulting from damage to somatosensory area I.

Amorphosynthesis

A neurological condition caused by unilateral removal of the somatosensory association area, resulting in loss of recognition of complex object forms on the opposite side and oblivion to that half of the body.

Anterolateral Pathway

A sensory system comprising the spinothalamic, spinoreticular, and spinomesencephalic tracts that transmits pain, temperature, tickle, itch, crude touch, and sexual sensations at velocities of $8\text{ to }40\text{ m/s}$.

Syringomyelia

A condition in which a cyst or syrinx expands in the central canal of the spinal cord, preferentially interrupting crossing medial pain and temperature fibers to produce a cape-like distribution of sensory loss.

Neospinothalamic Pathway

A fast pain pathway mediated by thinly myelinated $A\thinspace\text{delta}$ fibers that project to the VPL nucleus of the thalamus and primary somatosensory cortex to convey sharp, acute, well-localized pain.

Paleospinothalamic Pathway

A slow pain pathway mediated by unmyelinated C fibers that project to the reticular formation, tectal area, and periaqueductal gray region to convey diffuse, aching, poorly localized chronic pain.

Brown-Séquard Syndrome

A condition caused by hemisection of the spinal cord, resulting in ipsilateral loss of motor function and DCML sensations (vibration, position, fine touch) alongside contralateral loss of spinothalamic sensations (pain and temperature).

Spinocerebellar Tracts

Sensory pathways that deliver unconscious proprioceptive information regarding limb position, muscle tension, and movement to the cerebellum for automatic coordination.

Labeled Line

A discrete neural pathway defined by specific receptors, peripheral nerves, spinal tracts, thalamic nuclei, and cortical regions that conveys information about a single sensory modality.

Lateral Inhibition

A neural mechanism that sharpens stimulus localization and spatial contrast by suppressing the signal output of neighbouring surrounding neurons.

Mach Band Effect

An optical illusion caused by lateral inhibition in retinal cells, where borders between shaded gray bands appear brighter on the lighter side and darker on the darker side to enhance edge contrast.

Meissner Corpuscle

A rapidly adapting, encapsulated mechanoreceptor innervated by myelinated $A\thinspace\text{beta}$ fibers that detects light touch, texture, and low-frequency pressure.

Merkel Disc

A slowly adapting mechanoreceptor located in the basal epidermis, innervated by myelinated $A\thinspace\text{beta}$ fibers, responsible for detecting continuous touch and pressure.

Pacinian Corpuscle

A rapidly adapting, encapsulated mechanoreceptor in the dermis and subcutaneous layer that opens mechanically-gated cation channels upon deformation to transduce high-frequency vibration and deep pressure.

Ruffini Corpuscle

A slowly adapting mechanoreceptor located in the dermis, innervated by myelinated $A\thinspace\text{beta}$ fibers, that responds to continuous skin stretch.

Pruriceptors

Superficial free nerve ending itch receptors with unmyelinated C fibers that trigger scratching behavior, which in turn activates spinal inhibitory interneurons releasing GABA and glycine to suppress itch transmission.

TRPM8 Channel

A cold-sensitive cation channel found on free nerve endings that opens in response to cool temperatures ($10\text{ to }35\text{ }^\text{o}\text{C}$) or chemical agents like menthol.

TRPV3 Channel

A warmth-sensitive ion channel on free nerve endings activated by warm temperatures ($30\text{ to }45\text{ }^\text{o}\text{C}$) or chemical compounds such as camphor.

Glaucoma

An eye disorder characterized by pathologically elevated intraocular pressure due to aqueous humor accumulation, which compresses retinal neurons and optic nerve fibers, potentially leading to irreversible blindness.

Fovea

The region of highest visual acuity in the center of the macula lutea, characterized exclusively by high-density cones, displaced inner retinal layers, and a 1:1 synaptic ratio with bipolar and ganglion cells.

Myopia

Nearsightedness resulting from an elongated eyeball or overly curved lens, causing light rays from distant objects to focus in front of the retina.

Hyperopia

Farsightedness resulting from a shortened eyeball or overly thin lens, causing light rays to focus behind the retina.

Presbyopia

An age-related loss of lens elasticity that impairs accommodation, making it difficult for individuals over age 40 to focus on near objects.

Accommodation

The process by which parasympathetic fibers of the oculomotor nerve (CN III) contract the ciliary muscle, slackening zonular fibers to allow the lens to become more rounded and increase its refractive power for near vision.

Protanope

A form of X-linked red-green color blindness caused by the complete absence of functional red cones.

Deuteranope

A form of X-linked red-green color blindness caused by the complete absence of functional green cones.

Tritanopia

A rare form of color blindness caused by a lack of blue cones, inherited on a non-sex chromosome.

Nyctalopia

Night blindness caused by a deficiency in Vitamin $A_1$ (all-trans retinal), which reduces retinal levels and decreases rhodopsin synthesis in rods.

Referred Pain

Pain perceived at a location distant from its actual source, occurring when visceral and somatic primary afferent neurons converge on the same second-order projection neuron in the spinal cord.

Primary Hyperalgesia

An excessive sensitivity and overreaction to painful stimuli occurring directly within damaged or inflamed tissue due to peripheral sensitization.

Allodynia

A condition where a normally non-painful stimulus, such as light touch, evokes a painful sensation due to lowered receptor thresholds.

Meyer's Loop

The inferior pathway of the geniculocalcarine optic radiation that loops through the temporal lobe, carrying visual information from the superior visual field to the lower bank of the calcarine fissure.

Pupillary Light Reflex

An autonomic reflex where light on the retina triggers afferent signals via CN II to pretectal nuclei, activating Edinger-Westphal nuclei to send parasympathetic efferents via CN III to constrict the sphincter pupillae muscle.

Dermatome

An area of skin whose sensory innervation comes from a single spinal nerve root.

Herpes Zoster

A painful viral infection of a dorsal root ganglion that causes severe dermatomal pain and skin eruptions as the virus travels outward along peripheral sensory axons.

Phototransduction

The biochemical process of converting light into electrical signals, where light activation of photopigments activates transducin and cGMP phosphodiesterase to lower cGMP levels, closing cGMP-gated $\text{Na}^+$ channels and hyperpolarizing the photoreceptor cell.