Muscular Action and Simple Contraction

Innervation, within the context of muscle movement, refers to the process by which nerve fibers supply, stimulate, and regulate the function of muscle tissue. It is the communication link between the nervous system and muscles, enabling the control of muscle contraction, coordination, and movement. The motor neurons, which are specialized nerve cells, transmit electrical impulses from the central nervous system (CNS) to the muscle fibers, generating a response in the form of muscle contraction. Motor neurons can be classified into two types:

1. Upper motor neurons (UMNs): These neurons originate in the motor regions of the brain, specifically the cerebral cortex and brainstem. UMNs form synapses with lower motor neurons within the spinal cord and are responsible for conveying signals that regulate voluntary and involuntary muscle movements.
2. Lower motor neurons (LMNs): These neurons are located in the spinal cord and connect with muscle fibers through specialized structures called neuromuscular junctions. LMNs receive signals from upper motor neurons and transmit them directly to the muscle fibers, initiating muscle contraction.

The strength, precision, and coordination of muscle movement are determined by the degree of innervation, which is influenced by the number of motor neurons and muscle fibers involved, the frequency of nerve impulses, and the synchronization of signals from multiple motor neurons. Proper innervation is essential for maintaining muscle tone, executing complex motor tasks, and enabling rapid response to sensory input.
In summary, innervation is a critical aspect of muscle movement, as it facilitates the transmission of nerve impulses from the central nervous system to muscle tissue, ultimately controlling and regulating muscle contraction, coordination, and function.

The simple innervation^[1] of a muscle results in an activity which may be divided into three parts:

1. latent period,
2. period of contraction,
3. and period of relaxation.

A muscle, scientifically speaking, does not contract simultaneously with the stimulations, but about one hundredth of a second after stimulation. This latent period, however, is negligible and the time involved, even if it were considerably longer, is well below any time-value used in piano playing.

The periods of contraction and relaxation vary greatly with the condition of the muscle and the particular muscle used. A fixed time for all muscles cannot therefore be given, although normally both phases occur in a very small part of a second. Any twitch (reflex action) takes less time than any isolated or repeated movement demanded by piano-technique. Consequently, the contractile speed of a muscle, (or lack of it), cannot account for any difficulties in muscular action as applied to the piano.
A normal muscle can contract and relax with sufficient speed to meet any needs of the pianist. In a simple contraction, generally termed "twitch", a muscle does not shorten more than one-fourth of its total length.

[1] innervate vt. [< IN¹- + NERVE + - ATE¹] Med. 1. to supply (a part of the body) with nerves 2. to stimulate (a nerve, muscle, etc.) to movement or action.