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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. The information carried by type Ia ...
They increase the stretch-sensitivity of the Ia afferents by stiffening the bag 1 intrafusal fibers. Efferent nerve fibers of gamma motor neurons also terminate in muscle spindles; they make synapses at either or both of the ends of the intrafusal muscle fibers and regulate the sensitivity of the sensory afferents, which are located in the non ...
Somatosensory receptors include senses such as pain, touch, temperature, itch, and stretch. For example, a specific muscle fiber called an intrafusal muscle fiber is a type of afferent neuron that lies parallel to the extrafusal muscle fibers thus functions as a stretch receptor by detecting muscle length. [2]
Usually, in this case, motor function of the lower leg will not be impaired. This is a key distinction between saphenous nerve neuropathy and lower back radiculopathy. Saphenous nerve neuropathy only demonstrates sensory alterations, while lumbar radiculopathy will affect the motor, sensory, and deep tendon reflexes of the lower leg. [6]
Signal propagation continues down the anterior rami (Lumbar 4-5 and Sacral 1-5) of the sacral plexus. The sciatic nerve branches off of the sacral plexus in which the tibial and common fibular nerves are wrapped in one sheath. The tibial nerve eventually separates from the sciatic nerve and innervates the gastrocnemius muscle.
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]
A sensory nerve, or afferent nerve, is an anatomic term for a nerve that contains exclusively afferent nerve fibers. [1] Nerves containing also motor fibers are called mixed. Afferent nerve fibers in a sensory nerve carry sensory information toward the central nervous system (CNS) from different sensory receptors of sensory neurons in the ...
The other two classes are the group B nerve fibers, and the group C nerve fibers. Group A are heavily myelinated, group B are moderately myelinated, and group C are unmyelinated. [1] [2] The other classification is a sensory grouping that uses the terms type Ia and type Ib, type II, type III, and type IV, sensory fibers. [1]