The Neuromuscular (Nerve-Muscle) Connection Help
Introduction to The Neuromuscular (Nerve-Muscle) Connection
This section covers the neuromuscular ( nur -oh- MUS -kyoo-lar) or “nerve” (neur) and “muscle” (muscul) connection. Quite fascinating is that the word muscular ( MUS -kyoo-lar) actually translates to mean “pertaining to a little mouse (muscul)”!
Literally speaking, then, the muscular system of humans is an organ system composed of over 600 individual “little mice” – the skeletal muscle organs. In reality, the skeletal muscle organs are a large group of individual skeletal muscles that get their name from the fact that they are attached to the bones of the skeleton (Figure 14.1). [ Study suggestion: Flex or bend your forearm. Now, extend or straighten it. Observe how your biceps ( BUY -seps) brachii ( BRAY -kee- eye ) muscle bulges, then lengthens, deep to the skin in your upper arm. Try to duplicate the imagination of the early anatomists, by speculating why they called muscles like the biceps brachii the “little mice.” Check your thinking with the diagram in Figure 14.1, below.]
Just as little mice run up-and-down, the skeletal muscles contract and shorten, then relax and lengthen, again. Each of the skeletal muscles is attached to a bone of the skeleton by two or more tendons ( TEN -duns). A tendon is literally a “stretcher.” It is actually a strap of dense fibrous connective tissue that anchors a skeletal muscle to a bone. When the muscle contracts, it exerts a pulling force, P. This pulling force stretches the tendon. The tendon then pulls upon the bone.
The human body has a number of bone–muscle lever ( LEE -ver) systems. A lever is a rigid bar that is acted upon by some force. In a bone–muscle lever system (Figure 14.2), the bone serves as a passive lever or rigid bar that is pulled upon by a contracting skeletal muscle. The pulling force of the muscle is applied to the bone through the attached tendons.
A fulcrum ( FULL -crumb), abbreviated as F, is a place of “support” upon which a lever turns or balances when it moves. Within a muscle–bone lever system, a movable joint generally serves as the fulcrum. For instance, the biceps brachii contracts and provides a pulling force (P) upon its tendons. The tendons raise the bones of the forearm (the levers) at the elbow joint, which serves as the fulcrum (F). A weight (W) or resistance (R) is then lifted, as the forearm is bent or flexed.