Final answer:
The two types of lower motor neurons are alpha motor neurons, which innervate extrafusal muscle fibers for movement, and gamma motor neurons, which target intrafusal muscle fibers to regulate muscle tone and reflexes.
Step-by-step explanation:
There are two types of lower motor neurons: alpha motor neurons and gamma motor neurons. Alpha motor neurons innervate extrafusal muscle fibers, which are the main force-generating component of a muscle. Gamma motor neurons target the intrafusal muscle fibers of the muscle spindle, playing a crucial role in the regulation of muscle tone and reflexes.
Both types of motor neurons are essential for voluntary and reflexive movements. The alpha motor neurons are responsible for the contraction of skeletal muscle fibers, facilitating movement and generating the necessary force, while gamma motor neurons maintain muscle tone and sensitivity of the stretch reflex.
The number of muscle fibers innervated by a single motor neuron is called a motor unit, and varies depending on the required precision and force of the muscle action. Larger motor units are found in muscles that require strong contractions like the quadriceps, while small motor units, which allow for finer control, are found in muscles like the extraocular muscles responsible for eye movements.