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A muscle spindle, with γ motor and Ia sensory fibers. A type Ia sensory fiber, or a primary afferent fiber, is a type of afferent nerve fiber. [1] It is the sensory fiber of a stretch receptor called the muscle spindle found in muscles, which constantly monitors the rate at which a muscle stretch changes.
When a muscle is stretched, primary type Ia sensory fibers of the muscle spindle respond to both changes in muscle length and velocity and transmit this activity to the spinal cord in the form of changes in the rate of action potentials. Likewise, secondary type II sensory fibers respond to muscle length changes (but with a smaller velocity ...
In each muscle, we have 10-100 tiny muscle-like pockets called muscle spindles. The type II fibers (aka secondary fibers) connect to nuclear chain fibers and static nuclear bag fibers in muscle spindles, but not to dynamic nuclear bag fibers. The typical innervation to muscle spindles consists of one type Ia fiber and 2 type II fibers. [6]
Sensory fiber types Type Erlanger-Gasser Classification Diameter Myelin Conduction velocity Associated sensory receptors; Ia: Aα: 13–20 μm: Yes: 80–120 m/s [5] Muscle spindle fibres Ib Aα: 13–20 μm: Yes: 80–120 m/s: Golgi tendon organ: II: Aβ: 6–12 μm: Yes: 33–75 m/s: All cutaneous mechanoreceptors including pacinian ...
Intrafusal muscle fibers are skeletal muscle fibers that serve as specialized sensory organs (proprioceptors). [ 1 ] [ 2 ] They detect the amount and rate of change in length of a muscle . [ 1 ] They constitute the muscle spindle , [ 2 ] and are innervated by both sensory (afferent) and motor (efferent) fibers.
The Golgi tendon organ (GTO) (also called Golgi organ, tendon organ, neurotendinous organ or neurotendinous spindle) is a proprioceptor – a type of sensory receptor that senses changes in muscle tension. It lies at the interface between a muscle and its tendon known as the musculotendinous junction also known as the myotendinous junction. [1]
Within the sensory nervous system, Secondary sensory endings of the muscle spindle are composed of type II sensory fibers that terminate on nuclear chain fibers and static nuclear bag fibers, but not dynamic nuclear bag fibers. Whereas primary endings respond mostly to rate of change, secondary endings respond mostly to amount of stretch.
The sartorius muscle can move the hip joint and the knee joint, but all of its actions are weak, making it a synergist muscle. [4] At the hip, it can flex, weakly abduct, and laterally rotate the femur. [4] At the knee, it can flex the leg; when the knee is flexed, sartorius medially rotates the leg.