Degrees of Contraction | Moderate Degree versus Strong Contraction

A contraction may be the result of either of two muscular conditions:

1. First, all the muscle fibers may contract to a moderate degree, producing, by their summation, a force effect;
2. Secondly, some of the fibers may contract strongly, and the others remain passive, producing the same force effect.

The former view would demand a nerve impulse to the muscle as a whole; a form of mass action rather at variance with the essentially integrative action of the organism. In support of this view is the evidence produced by experiment upon the excised living muscle of the cold-blooded animals. In these cases the degree of contraction of the muscle depends upon the intensity of the stimulus, an increase in the stimulus producing an increase in contraction up to a point beyond which the muscle does not contract.
Since the electric current used for stimulation may reasonably be supposed to traverse the entire muscle regardless of the intensity of the current, this phenomenon of graded response supports the first view that in any muscular contraction all the fibers are contracted, their degrees of contraction varying with the stimulus.

A second, somewhat more promising view, holds that as the stimulus increases in intensity, new fibers are added to those already functioning, thus changing the total response without changing the response of the original fibers. This view, of course, is in close agreement with the commonly observed "spread" of muscular activity with an increase in the stimulus. It seems probable, therefore, that both reactions actually occur in any movement of sufficient variation. Experimentation upon the excised muscle has shown that a single muscle can give graded reactions.
When such a muscle is attached to a complex leverage system, like that of the arm, any variation in the force-effect of its contraction will be communicated to its origin, upon which this force will work. Accordingly, the muscles controlling the point of origin will have to contract in proportion to this increase in force, and the muscular spread is the result. This leaves the graded response within a single muscle to be explained.
Question: Do all the fibers contract in response to every stimulus, varying in their degree of response, or does the number of reacting fibers increase with an increase in the stimulus?
Answer: Exercise does not increase the number of muscle-fibers, but increases the size or growth of the fibers themselves. That is to say, a muscle grows, gets stronger, not by the addition of fibers to others, already present, but by an increase in the size of the existing fibers. This points to a physiological unity of muscle which would support the total reaction theory.
The presence of a nerve fibre for each muscle fibre is itself not decisive in either way. Such an arrangement would be as useful for total response as for partial response.

Question: What are the degrees of muscular contraction which exist between the cerebral cortex and the metacarpus?
The neural control of muscle contractions and the degrees of muscular contractions themselves. To provide a comprehensive understanding, both concepts will be discussed.

1. Neural control of muscle contractions: The cerebral cortex, specifically the primary motor cortex, is responsible for initiating and controlling voluntary muscle contractions. It sends signals via upper motor neurons through the spinal cord to lower motor neurons, which in turn stimulate the muscles, including those in the metacarpus (the intermediate part of the hand between the wrist and fingers). The primary motor cortex coordinates the precise timing and intensity of muscle contractions, enabling various types of movements, from fine motor tasks to forceful exertions.
2. Degrees of muscular contractions: Muscle contractions can be categorized into different types or degrees based on their characteristics:
   
   • Isometric contractions: In this type of contraction, the muscle generates tension without changing its length. There is no movement at the joint, but the muscle exerts force to maintain a static position or stabilize a body part.
   • Isotonic contractions: These contractions involve a change in muscle length while maintaining a constant tension. Isotonic contractions can be further divided into two subtypes:
     
     1. Concentric contractions: In this subtype, the muscle shortens as it generates force, such as when lifting a weight or pulling an object.
     2. Eccentric contractions: In this subtype, the muscle lengthens while maintaining tension, such as when lowering a weight or controlling the descent of an object.
   • Isokinetic contractions: These contractions involve the muscle changing its length at a constant velocity while exerting variable tension. Isokinetic contractions are typically facilitated by specialized equipment or therapeutic devices.
   
   

To summarize, the cerebral cortex, specifically the primary motor cortex, plays a crucial role in initiating and controlling muscle contractions, including those affecting the metacarpus. The degrees of muscular contractions, however, are primarily classified as isometric, isotonic, and isokinetic, based on the characteristics of the contractions themselves.