Download The Muscular System

The Muscular System
Muscle tissue has four main properties: Excitability (ability to respond to
stimuli), Contractibility (ability to contract),Extensibility (ability of a muscle to be
stretched without tearing) and Elasticity (ability to return to its normal shape).
Through contraction, the muscular system performs three important functions:
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Motion - walking, running etc.
Heat production - maintain normal body temperature
Maintenance of posture - standing, sitting etc.
Motion
To understand how the muscles combine with the skeleton in providing motion we must
look at the basic mechanics of movement. The main framework of the body is covered
by muscle, whose function is to permit movement. We know that to move or lift a load
against another force, it is easier to use levers, and it is this principle which the
musculoskeletal system adopts and which we must examine.
The component parts that are used in a lever are as follows:
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Lever - nearly always the bone
Fulcrum - pivot point of the lever, which is usually the joint
Muscle Force - force that draws the opposite ends of the muscles together
Resistive Force - force generated by a factor external to the body (e.g. gravity,
friction etc.) that acts against muscle force
Torque - the degree to which a force tends to rotate an object about a specified
fulcrum
There are different types of levers dependent upon the position of fulcrum, effort and
resistive force.
First Class lever: Muscle force and resistive force is on different sides of the fulcrum
e.g. the head resting on the vertebral column. As the head is raised, the facial portion of
the skull is the resistance, the fulcrum is between the atlas and occipital bone, and the
effort is the contraction of the muscles of the back.
Second Class lever: Muscle force and resistive force act on the same side of the
fulcrum, with the muscle force acting through the level longer than that through which
the resistive force acts - e.g. raising the body up onto the toes. The body is the
resistance, the ball of the foot is the fulcrum, and the effort is the contraction of the calf
muscle.
Third Class lever: Muscle force and resistive force act on the same side of the fulcrum,
with the muscle force acting through the lever shorter than that through which the
resistive force acts - e.g. adduction of the thigh. The weight of the thigh is the
resistance, the hip joint is the fulcrum, and the contraction of the adductor muscle is the
effort.
Most of the limbs of the human body are articulated by third class levers.
Agonist, Antagonist, Fixator & Synergist Muscles
Muscles can only exert a pulling force so work in pairs. When we move a limb one
muscle, the agonist muscle also known as the prime mover, causes the movement and
an antagonist muscle works in opposition to the agonist muscle.
Example: Biceps curl – the biceps is the agonist muscle causing the movement and the
triceps are the antagonist muscle working in opposition to the biceps.
The function of a fixator muscle is to stabilize the origin of the agonist muscle so that it
can move efficiently.
Other muscles, known as synergist muscles, stabilize muscle movements to keep them
even, and control the movement so that it falls within a range of motion which is safe
and desired.