Which nerves are depolarized second and are responsible for contracting muscles?

Motor fibers are essential for initiating muscle contraction, as they are specifically designed to carry signals from the central nervous system (CNS) directly to muscle tissues. When these fibers become depolarized, they trigger action potentials that lead to the release of neurotransmitters at the neuromuscular junction. This process ultimately results in muscle contraction.

Motor fibers, also known as alpha motor neurons, are highly specialized neurons enabling voluntary movement by connecting with skeletal muscles. Their primary role is to ensure that the correct muscles contract at the right time, enabling coordinated movement. This differentiates them from sensory fibers and autonomic fibers, which have different functions in the body's nervous system.

The other types of fibers mentioned serve different purposes. For example, A-Delta fibers are involved in transmitting sharp pain signals, B fibers typically conduct autonomic functions, and C fibers convey dull, aching pain sensations. These functionalities do not relate directly to muscle contraction, reinforcing the significance of motor fibers in this context.