![muscle spindle muscle spindle](https://www.purposegames.com/images/games/background/31/31394.jpg)
decreased firing of spindle afferent ( negative feedback).muscle contraction (both extra- and intra-fusal fibres).activation of alpha and gamma motor neurons.depolarization and generation of action potentials in the spindle afferent.the sequence is ( click here for an animation):.
![muscle spindle muscle spindle](https://media.sciencephoto.com/image/c0040777/800wm/C0040777-Muscle_spindle.jpg)
the patellar reflex is an example of a stretch reflex (muscle spindles in the quadriceps muscle are activated).this idea of a fusi, fusiform shape describes the shape of this muscle spindle or rather the capsule that surrounds these. And so, the boundary of these specialized muscle fibers by this capsule allows the anatomists to call these intrafusal muscle fibers. The discussion stresses the possible role of muscle spindles in the conditioning process. STRETCH REFLEX: increased activity in the spindle afferents causes depolarization of alpha motor neurons ( monosynaptic reflex), contracting the extrafusal muscle fibres So, the muscle spindle is a collection of muscle fibers that are found within a capsule. secondary endings are static (they signal the amplitude of the change).primary endings are dynamic (they respond to the velocity of the change).muscle stretch deforms the nerve endings, causing depolarization ( mechanoreception).this tonic activity maintains a basal level of tension in the muscle, due to the same mechanism described below for the stretch reflex.when the muscle is at rest, the spindle has a low level of tonic activity.muscle spindles are mechanoreceptors that signal MUSCLE STRETCH.It has been established that this is not the case by direct visual observation of intrafusal contraction in isolated living spindles, by intracellular recording from intrafusal fibres, and by light and electron microscopy of cat muscle spindles. Complete resolution of the problem was delayed until 1980 because the glycogen depletion technique suggested that static γ axons frequently innervated the bag₁ fibre (Fig. Examples include the stomach, intestines, womb, bladder and blood vessels, and it also controls the opening and closing of the pupils of the eye. The other one, the 'bag₁ fibre', is separately controlled by dynamic axons (Fig. : a sensory end organ in a muscle that is sensitive to stretch in the muscle, consists of small striated muscle fibers richly supplied with nerve fibers, and is enclosed in a connective tissue sheath. Smooth muscle is found in walls of hollow organs and structures of the body that need to be able to contract without conscious input from the brain. Primary and secondary sensory fibers spiral around and terminate on the central portions of intrafusal fibers, providing the sensory component of the structure via stretch-sensitive ion-channels of the axons. One of them, the 'bag₂ fibre', is controlled by static γ axons which sometimes share this innervation with the nuclear chain fibres. The muscle spindle has both sensory and motor components. The controversy was to a large extent resolved by the discovery in the early 1970s that there were two types of nuclear bag fibres which are structurally and mechanically quite different. Barker and colleagues maintained that the same motor axon frequently terminated on both types of intrafusal fibre. Boyd maintained that two types of intrafusal muscle fibre, nuclear bag fibres and nuclear chain fibres, were separately innervated by different types of small γ motor axons. However, within the body of skeletal muscles, there are also specialized encapsulated muscle fibres that form part of muscle spindles. The controversy in the 1960s about the motor innervation of mammalian muscle spindles is described.