Muscle Spindles and Sensory Nerve Fibers

Vocabulary terms and definitions covering muscle spindle structure, Lloyd-Hunt sensory nerve classifications, and reflex responses.

Nuclear bag fibers (NBF)

Intrafusal muscle fibers within muscle spindles that have static or dynamic functions.

Nuclear chain fibers (NCF)

Intrafusal muscle fibers within muscle spindles that have static functions.

Group Ia fiber (primary afferent)

A sensory nerve classified as an A\α fiber with annulo-spiral endings across all intrafusal fibers; activation causes agonist contraction and antagonist relaxation.

Group Ib fiber

A sensory nerve fiber classified as an A\α fiber arising from the Golgi tendon organ; activation causes agonist relaxation.

Group II fiber (secondary afferent)

A sensory nerve fiber classified as an A\β fiber with flower-spray endings on static bag and chain fibers of muscle spindles.

Dynamic $\gamma$ fiber (efferent)

An efferent motor fiber supplying intrafusal muscle fibers via plate endings.

Static $\gamma$ fiber (efferent)

An efferent motor fiber supplying intrafusal muscle fibers via trail endings.

Type III sensory nerve

A Lloyd-Hunt sensory nerve corresponding to $Aδ$ fibers that innervates pain and cold receptors.

Type IV sensory nerve

A Lloyd-Hunt sensory nerve corresponding to $C$ fibers that innervates pain and temperature receptors.

Annulo-spiral ending

Receptor ending formed by primary afferent Group Ia fibers on muscle spindle intrafusal fibers.

Flower-spray ending

Receptor ending formed by Group II secondary afferent fibers primarily on static bag and chain intrafusal fibers.

$Aδ / C$ afferent reflex response

A reflex pattern in which the affected side undergoes flexor contraction while the unaffected side undergoes extensor contraction.