Somatosensory System II: Cutaneous Receptors Flashcards

Vocabulary flashcards covering muscle spindle mechanisms, mechanotransduction, receptive fields, and cutaneous mechanoreceptors from Lecture 10.

Muscle Spindle Primary Ending

A sensory receptor unit consisting of a Group Ia primary afferent wrapped in annulospiral endings around intrafusal muscle fibres, most commonly of the nuclear bag type.

Muscle Spindle Secondary Ending

A sensory receptor unit consisting of a Group II secondary afferent making flower spray endings exclusively onto nuclear chain type intrafusal muscle fibres.

Nuclear Bag Intrafusal Fibres

A category of intrafusal muscle fibres characterized by nuclei arranged and concentrated in a central bag region.

Nuclear Chain Intrafusal Fibres

A category of intrafusal muscle fibres characterized by nuclei aligned along a straight chain.

Fusimotor System

The physiological control mechanism where gamma motor neurons ($\gamma\text{MNs}$) stimulate intrafusal muscle fibres to contract simultaneously with extrafusal muscle fibres ($\alpha\text{MNs}$), preventing intrafusal slackness during muscle shortening.

Mechanotransduction

The physiological process where mechanical energy from tissue deformation is converted into a voltage change (receptor potential) in sensory afferent neurons.

Mechanical Threshold

The minimum amount of skin indentation required to evoke action potentials in a cutaneous afferent neuron.

Cutaneous Receptive Field

The specific region of skin capable of evoking action potentials in a given cutaneous afferent neuron when stimulated.

Glabrous Skin

Smooth, non-hairy skin found on regions such as the palms and soles that contains four primary types of cutaneous mechanoreceptors.

Merkel Cell-Neurite Complex

A superficial, slowly adapting Type 1 (SA1) mechanoreceptor consisting of a sensory neuron and the Merkel cells it contacts, responsible for sensing edges, curvature, and texture.

Meissner's Corpuscle

A superficial, fast-adapting Type 1 (FA1) mechanoreceptor in glabrous skin that detects low-frequency vibrations ($30\text{--}50\,\text{Hz}$) and motion across the skin, crucial for slip detection and grip control.

Ruffini Endings

Deep, slowly adapting Type 2 (SA2) mechanoreceptors sensitive to lateral skin stretch, exhibiting regular firing discharge during sustained indentation with a threshold of $300\,\mu\text{m}$.

Pacinian Corpuscle

A deep, fast-adapting Type 2 (FA2) mechanoreceptor enclosed in concentric fluid-filled laminae that senses acceleration and high-frequency vibration ($50\text{--}500\,\text{Hz}$) with a threshold of $0.08\,\mu\text{m}$.

Slowly Adapting Type 1 (SA1) Receptors

Cutaneous afferents located in superficial skin layers that have small receptive fields with sharp borders, display irregular firing during sustained indentation, and have a mechanical threshold of $30\,\mu\text{m}$.

Slowly Adapting Type 2 (SA2) Receptors

Cutaneous afferents located in deep skin layers that have large receptive fields with obscure borders, display regular firing during sustained stimulation, and respond to lateral skin stretch.

Fast Adapting Type 1 (FA1) Receptors

Cutaneous afferents in superficial skin layers with small receptive fields that show no static response to sustained indentation, make up approximately $40\%$ of hand innervation, and have a mechanical threshold of $6\,\mu\text{m}$.

Fast Adapting Type 2 (FA2) Receptors

Cutaneous afferents in deep skin layers with large receptive fields that respond to stimulus acceleration and high-frequency vibrations ($50\text{--}500\,\text{Hz}$), possessing an extremely low mechanical threshold of $0.08\,\mu\text{m}$.