Table of Contents
What do muscle spindles respond to?
Muscle spindles are sensitive to changes in velocity and are innervated by type 1a nerve fibers. These afferent nerve fibers conduct the impulse directly to the spinal cord, where they are immediately conducted via interneurons to alpha motor neurons, which stimulate muscle contraction.
What are nuclear bag fibers?
A nuclear bag fiber is a type of intrafusal muscle fiber that lies in the center of a muscle spindle. Each has many nuclei concentrated in bags and they cause excitation of the primary sensory fibers. Nuclear bag fiber.
What is Neuromuscular spindle?
n. A spindle-shaped end organ in skeletal muscle in which afferent nerve fibers terminate and which is sensitive to passive stretching of the muscle enclosing it.
What neuron directly controls the sensitivity of a muscle spindle?
gamma motor neurons
The central nervous system controls muscle spindle sensitivity via the fusimotor system that consists of muscle spindles along with gamma motor neurons also called fusimotor neurons.
What receptors are found in the nuclear bag area of neuromuscular spindle?
The nuclear bag fibers are classified as static or dynamic. The intrafusal fibers are innervated by motor nerves (the gamma motor neurons) and two different types of sensory fibers: the type Ia stretch receptors and the type II afferent sensory receptors.
Which of the following types of neurons Innervates nuclear bag intrafusal fibers that signal a change in muscle length?
Gamma motor neurons
Motor neurons are divided into two groups. Alpha motor neurons innervate extrafusal fibers, the highly contracting fibers that supply the muscle with its power. Gamma motor neurons innervate intrafusal fibers, which contract only slightly.
What is intrafusal and extrafusal?
Extrafusal muscle fibers comprise the bulk of muscle and form the major force-generating structure. Intrafusal muscle fibers are buried in the muscle, and they contain afferent receptors for stretch, but they also contain contractile elements.
Which neurons innervate the intrafusal muscle fibers?
Innervation. They are innervated by gamma motor neurons and beta motor neurons. Gamma efferents from small multipolar neurons from anterior gray column innervate it. These form a part of neuromuscular spindles.
What do gamma motor neurons innervate?
The gamma motor neurons innervate the muscle spindle at each end. They allow contraction of the intrafusal fibers and increase their sensitivity to stretch. In this way the gamma motor neurons form an important muscle stretch reflex mechanism that acts in conjunction with the alpha motor neurons.
What does the gamma motor neuron do?
Gamma motor neurons regulate the gain of the stretch reflex by adjusting the level of tension in the intrafusal muscle fibers of the muscle spindle. This mechanism sets the baseline level of activity in α motor neurons and helps to regulate muscle length and tone.
Where do gamma motor neurons innervate a muscle spindle?
Gamma motor neurons innervate intrafusal fibers, which do not contribute significantly to muscle force.
What type of efferent neuron Innervates intrafusal muscle fibers?
Motor neurons are divided into two groups. Alpha motor neurons innervate extrafusal fibers, the highly contracting fibers that supply the muscle with its power. Gamma motor neurons innervate intrafusal fibers, which contract only slightly.
What is extrafusal?
Medical Definition of extrafusal : situated outside a striated muscle spindle extrafusal muscle fibers — compare intrafusal.
Which of the following Innervates the ends of intrafusal fibers?
Because they innervate all 3 types of intrafusal fibers, Group Ia afferents provide information about both length and velocity. Group II afferents (also called secondary afferents) innervate the ends of the nuclear chain fibers and the static nuclear bag fibers at specialized junctions termed flower spray endings.
What does gamma motor neuron activation do?
Activation of gamma motor neurons prevents this temporary insensitivity by causing a weak contraction of the intrafusal fibers, in parallel with the contraction of the muscle. This contraction keeps the spindle taut at all times and maintains its sensitivity to changes in the length of the muscle.