User:JBujko/sandbox

= Motor Nerve =

Structure and Function
A motor nerve is a nerve located in the central nervous system (CNS), usually the spinal cord, that sends motor signals from the CNS to the muscles of the body. Motor nerves act as efferent nerves which carry information out from the CNS. This mode of communication is opposite compared to sensory nerves, which send signals from sensory receptors in the periphery to the CNS. There are also nerves that serve as both sensory and motor nerves called mixed nerves.

Motor nerve fibers transduce signals from the CNS to peripheral neurons and in proximity of muscle tissue. Motor nerve axon terminals innervate skeletal and smooth muscle, as they are heavily involved in muscle control. Motor nerves tend to be rich in ACh vesicles because the motor nerve, a bundle of motor nerve axons that deliver motor signals and signal for movement and motor control. Calcium vesicles reside in the axon terminals of the motor nerve bundles. The high calcium concentration outside of presynaptic motor nerves change the size of EPP s (End-Plate potentials).

Protective tissues

Within motor nerves, each axon is wrapped by the endoneurium, which is a layer of connective tissue that surrounds the myelin sheath. Bundles of axons are called fascicle s, which are wrapped in perineurium. All of the fascicles wrapped in the perineurium are wound together and wrapped by a final layer of connective tissue known as the epineurium.

Spinal Cord Exit
Most motor pathways originate in the motor cortex of the brain. Signals run down the brainstem and spinal cord contralaterally, on the same side, and exit the spinal cord at the ventral horn of the spinal cord on either side. Motor nerves communicate with the muscle cells they innervate through motor neurons once they exit the spinal cord.

== Motor Neuron/Nerve Types == Motor nerves can vary based on the subtype of motor neuron they are associate with.

Alpha

Alpha motor neurons target extrafusal muscle fibers. Motor nerves associated with these neurons innervate extrafusal skeletal muscle fibers and responsible for starting muscle contraction. These nerve fibers have the largest diameter of the motor neurons, and require a higher conduction velocity.

Gamma
Gamma motor neurons, like alpha motor neurons, take part in the process of muscle contraction. The nerves associated with these type of neurons do not send signals that directly adjust the lengthening or shortening of muscles. However, these nerves are important for signalling to keep muscle spindles rigid.

Beta
These lower motor neurons similar to alpha and gamma motor neurons. Beta motor neurons and nerves innervate intrafusal fibers of muscle spindles. These nerves are responsible for signaling slow twitch muscle fibers.

Neuroregeneration
There are problems with neuroregeneration due to many sources, both internal and external. There is a weak regenerative ability of nerves and new nerve cells cannot simply be made. The outside environment can also play a role in nerve regeneration. Neural stem cells (NSCs), however, are able to differentiate into many different types of nerve cells. This is one way that nerves can "repair" themselves. NSC transplant into damaged areas usually leads to the cells differentiating into astrocytes which assists the surrounding neurons. Schwann cells have the ability to regenerate, but the capacity that these cells can repair nerve cells declines as time goes on as well as distance the Schwann cells are from site of damage.