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Type Ia neurons fibers coil around the central region of both the nuclear bag and the nuclear chain fibers, and relay information about how far and how fast the muscle is being stretched.
MUSCLE SPINDLE SERIES
On the other hand, nuclear chain fibers, are half as long as the nuclear bag fibers, and have their nuclei arranged in series like peas in a pod through the central region.Ĭoiled around the central region are two kinds of sensory neurons that depolarize when the intrafusal fiber is stretched.
MUSCLE SPINDLE FULL
Nuclear bag fibers are ones that have their nuclei concentrated in a wide, central portion of the fiber, like a sack full of oranges. The central portion of the intrafusal muscle fiber contains the muscle fiber’s nuclei, and the arrangement of the nuclei, determines whether the intrafusal muscle fibers are considered nuclear bag fibers or nuclear chain fibers. Therefore, the central region of a intrafusal muscle doesn’t contract, even though the ends do. However these contractile proteins don’t extend through the entire length of intrafusal muscle instead they’re only present at each end of a intrafusal muscle fiber. Just like extrafusal muscle fibers, intrafusal muscle fibers have contractile proteins like actin and myosin. Now, if we pull apart the extrafusal fibers, there’s another proprioceptor called the muscle spindle that lies within the extrafusal fibers.Įach muscle spindle contains multiple intrafusal muscle fibers.
![muscle spindle muscle spindle](http://sweatisfree.com/wp-content/uploads/2018/01/spindle.jpg)
These tendons have proprioceptors called golgi tendon organs which lie at the ends of these extrafusal fibers. Now a muscle looks like it’s made of a bundle of muscle fibers with extrafusal muscle fibers on the outside and intrafusal muscle fibers on the inside.Įxtrafusal muscle fibers provide most of the force during a muscle contraction, and are innervated by lower motor neurons which are also called alpha motor neurons.Įxtrafusal muscle fibers attach to bones with tendons which are a specific type of connective tissue. These proprioceptors are scattered throughout your skeletal muscles, and operate on a subconscious level so you never even notice them. Now, when you stretch or flex your muscles, proprioceptors that detect the position and movement of the muscles initiate reflexes that prevent you from damaging the muscles from overstretching or over contracting.
![muscle spindle muscle spindle](https://ai2-s2-public.s3.amazonaws.com/figures/2017-08-08/88b061e83319374c1c5f06f34a07df0ccd3ca198/3-Figure1-1.png)
![muscle spindle muscle spindle](https://www.bandhayoga.com/images/Free_Images/muscle_spindle.jpg)
This lower motor neuron is also called an alpha motor neuron, and it relays an action potential through an axon that goes to muscles in your legs, which enable you to extend them.
MUSCLE SPINDLE SERIAL
These results suggest that the early discharge of the spindle receptor may be due to contractions of the intrafusal muscle fibers (a serial force with the receptor) in relation to those of the extrafusal muscle fibers (a parallel force).In order to do the forward bend position during your yoga class, your nervous system has to do a number of things.įirst, an upper motor neuron from your brain - specifically your cerebral cortex - has to send a signal down to a lower motor neuron that’s in the anterior horn of the spinal cord. During shortening of the extrafusal muscle fibers against loads, the spindle discharges were facilitated only at the second upward deflection of the muscle tension.The shortening with participation of the intrafusal muscle fibers resulted often in a few additional discharges at the first upward deflection.Ĥ. The effects exerted on muscle spindles in the frog sartorius during contraction of the extrafusal muscle fibers were studied in comparison with those during contraction with participation of the intrafusal fibers.Ģ, The discharges were suppressed without appreciable early discharges during the isometric twitch and tetanic contractions of the extrafusal muscle fibers, whilst some early discharges appeared during the contractions with participation of the intrafusal muscle fibers.ģ.
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