Biomaterial Database

The avian muscle spindle. 1992

A Maier

Department of Cell Biology, University of Alabama, Birmingham 35294.

The literature on the morphology and physiology of the avian muscle spindle is reviewed, with emphasis placed on the period from 1960 to 1991. Traits similar to or different from mammalian spindles are recognized. Apart from receptors with low intrafusal fiber counts, bird spindles contain two or three types of intrafusal fiber. Unlike that of mammals, the equatorial fiber structure in birds does not lend itself to classification into nuclear bag and nuclear chain types. Avian intrafusal fibers are separable into types based on differences in myosin heavy chain composition and motor innervation, but apportionment of these fiber types to individual spindles is more variable in birds than in mammals. There is morphological evidence in birds for the existence of both gamma and beta innervation; however, confirmation of these systems by physiological experiments is at best sketchy. A general lack of physiological data is currently the greatest drawback to a better understanding of how the avian receptor works, and what role it plays in sensorimotor integration.

UI	MeSH Term	Description	Entries
D008854	Microscopy, Electron	Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.	Electron Microscopy
D009132	Muscles	Contractile tissue that produces movement in animals.	Muscle Tissue,Muscle,Muscle Tissues,Tissue, Muscle,Tissues, Muscle
D009470	Muscle Spindles	Skeletal muscle structures that function as the MECHANORECEPTORS responsible for the stretch or myotactic reflex (REFLEX, STRETCH). They are composed of a bundle of encapsulated SKELETAL MUSCLE FIBERS, i.e., the intrafusal fibers (nuclear bag 1 fibers, nuclear bag 2 fibers, and nuclear chain fibers) innervated by SENSORY NEURONS.	Muscle Stretch Receptors,Neuromuscular Spindles,Receptors, Stretch, Muscle,Stretch Receptors, Muscle,Muscle Spindle,Muscle Stretch Receptor,Neuromuscular Spindle,Receptor, Muscle Stretch,Receptors, Muscle Stretch,Spindle, Muscle,Spindle, Neuromuscular,Spindles, Muscle,Spindles, Neuromuscular,Stretch Receptor, Muscle
D009475	Neurons, Afferent	Neurons which conduct NERVE IMPULSES to the CENTRAL NERVOUS SYSTEM.	Afferent Neurons,Afferent Neuron,Neuron, Afferent
D009476	Neurons, Efferent	Neurons which send impulses peripherally to activate muscles or secretory cells.	Efferent Neurons,Efferent Neuron,Neuron, Efferent
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D001717	Birds	Warm-blooded VERTEBRATES possessing FEATHERS and belonging to the class Aves.	Aves,Bird