The Human Body - Muscular System (1952)

[Music] thank you [Music] lifting a 150 pound weight all of us will agree depends upon strong well-coordinated muscles actions that involve the muscles of the body are practically endless standing running dancing playing a musical instrument masticating food in fact any body move the action of breathing is the beating of the heart involves certain muscles so do the movements of the small intestine consider together the many muscles of the human body make up the muscular system the system however is actually made up of three kinds of muscles cardiac muscle found only in the heart is one kind of muscle by taking a specimen of cardiac muscle from this animal heart and placing it under the microscope we see it is feather-like in appearance the function of the cardiac muscle is to maintain the pumping action of the heart the beating of the heart is an involuntary action so cardiac muscle is sometimes called involuntary muscle throughout the body there are many other involuntary muscles muscles that we cannot consciously control these muscles are found in such internal organs as the esophagus the stomach the large and small intestines and other structures whose movements are essential to internal body processes this is a specimen of involuntary muscle from the stomach by placing a section of this muscle under the microscope we see that it appears quite smooth muscle is another name given most of the involuntary muscles of the body here is a magnified view of the Third Kind of muscle it is striped or striated striped muscles are voluntary muscles muscles we can consciously control the voluntary muscles generally control body movement large groups of voluntary muscles are found in the face the neck the trunk the arms and the legs although a particular muscle may be of a voluntary type it may also be controlled in an involuntary manner an example of such muscles are those which control the movement of the eyelids we can open or close our eyelids at will but our eyelids will close involuntarily if the eyes are subjected suddenly to Bright Light this involuntary reaction is also called a reflex response normally we can move a leg at will but the voluntary muscles here will also respond in a reflex fashion a light tap with a hammer will produce involuntary reflex movement in this film we are concerned with the voluntary muscles the muscles that perform work by moving the body's skeleton here we have dissected from an experimental animal a typical striped or voluntary muscle the first thing we notice about the muscle is its glossy hard outer covering this covering of tough tissue is called the sheath by dissecting the muscle we see that the outer sheath encloses a number of smaller sheaves these sheaths in turn bind together and connect much smaller bundles of striped or voluntary muscle cells such as those we saw under the microscope as in this simplified drawing groups of muscle cells are attached to a nerve cell which provides the stimulus necessary for the muscle cells to perform their work in this drawing of a single group of voluntary muscle cells we see that they are fibers when stimulated by nerve impulses a chemical reaction causes these fibers to contract when an entire muscle moves thousands of such groups of voluntary muscle cells are Contracting the importance of the nerve impulse to muscular contraction or movement can be demonstrated we have here part of a dissected frog's leg including the muscle called the gastrocnemius a comfortable muscle in the human is the calf muscle which extends or depresses the foot the lower end of the Frog's muscle is held stationary the other end is attached to a bar which is movable any movements of this bar can be traced on a revolving drum in addition the muscle is wired to an electronic stimulator electric charges from the stimulator can produce nerve impulses in the muscle this knob controls the number of electric impulses produced by the stimulator this knob controls the voltage of the impulses sending a few low voltage impulses through to the muscle causes only a few of the many muscle fibers to contract so small contractions of the entire muscle are produced but as the number of impulses is increased and a higher voltage is used more muscle fibers are stimulated and the muscle undergoes greater contractions on the tracing we can compare the contractions of the muscle produced by strong nerve impulses with those produced by a weak nerve impulses as shown in this schematic drawing of several groups of muscle cells and their attached nerve fibers weak stimuli may cause only one of groups of muscle cells to contract hunger stimuli affect more groups of cells thus producing a stronger contraction of the muscle this action takes place within hundreds of muscle cells having thousands of fibers so continuous contraction of the muscle can take place as some muscle cell fibers contract and others relax this basically is how the muscle cells perform the physiological or mechanical work of voluntary muscle contraction it is these contractions which produce movement of the body skeleton voluntary muscles are usually attached to two jointed bones in the human body the greater majority of muscles such as this one located in the upper thigh are attached to the bones by means of tendons dense bands of inelastic tissue the large muscle in the upper arm the biceps is also attached by tendons to the bones the work of the biceps is to raise the forearm let's look at the arm in cross section here we see the biceps and the tendons of the muscle that attach it to the bones in this case the bones of the forearm the end of the tendon or muscle that is attached to the stationary bone is called the origin the end of the muscle or tendon attached to the movable bone is called the insertion all voluntary muscles of the body are paired the triceps is the muscle paired with the biceps one of the pair of muscles contracts when stimulated by nerve impulses to raise the jointed bone flexor is the name given to muscles which raise jointed bones the other of the pair of muscles has an opposite action it contracts to lower the jointed bone extensor is the name given to muscles which lower jointed bones note that as the flexor raises the bone the extensor relaxes and that as the extensor lowers the bone the flexor relaxes this action is true of all pairs of voluntary muscles in the body we know that muscular action results from stimulation of the muscle cells but what happens in the muscle cells when they are stimulated physiologists have discovered that muscular contraction is by and large a chemical process they have discovered that muscle cells contain a variety of chemical compounds which break down to provide energy some of this energy is used for muscular contraction some energy is used to re-synthesize or put together again essential chemicals to yield energy for contraction muscle cells contain many chemicals among them are three major compounds having complex names which indicate their complex chemical structure adenosine triphosphate the first of these chemicals abbreviated as ATP yields energy for muscular contraction the second and third chemicals phosphocreatine and glycogen yield energy to re-synthesize ATP let's look at this process in a bit more detail as we've said the energy for muscular contraction is yielded from the breakdown of ATP a complex chemical compound at the very same time this breakdown occurs phosphocreatine the second chemical compound breaks down to yield energy to re-synthesize ATP simultaneously the third chemical compound glycogen breaks down to yield energy to re-synthesize phosphocreatine in addition a breakdown of glycogen produces another chemical compound called lactic acid part of the lactic acid produced combines with oxygen to yield energy from the remainder of the lactic acid to re-synthesize glycogen the important thing we should remember about this complex process is that the breakdown of certain chemicals yields energy for muscular contraction and energy to re-synthesize essential chemicals but even from this brief indication of the chemistry of the voluntary muscles it is evident that these highly complex organs which direct the movement of the human body and skeleton should be well cared for if the body is to function properly to accomplish this a muscle should be exercised daily proper body posture and competitive sports are among the many ways we can exercise our muscles by strengthening and stimulating them we soon see the infinite variety of work these versatile organs of the muscular system are capable of carrying out in our bodies [Music]