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Anatomy & Physiology - Body Systems

The Muscular System

The branches of science that will help you understand the body parts and functions are anatomy and physiology. Anatomy deals with the study of the human body (the component parts, structure and position) and physiology the study of how the body functions.

Body Systems

The body comprises of a number of systems including the: Cardiovascular system, Digestive system, Endocrine system, Muscular system, Neurological system, Respiratory system and the Skeletal 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:

  • 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:

  • 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.

Heat production

Muscle contractions produce heat and as much as 70% of body heat is produced by energy produced in muscle tissue. Blood is an essential element in temperature control during exercise, taking heat from the body core and working muscles and redirecting it to the skin when the body is overheating. When the internal heat of the body reaches too low a level thermoreceptors in the skin relay a message to the hypothalamus in the brain. In response to this signal, the skeletal muscles contract and relax in an involuntary manner (shivering) increasing muscle activity to generate heat. In turn, muscles are also responsive to exterior heat - cold air increases muscle tone, and hot conditions have a relaxing effect on muscles.

Maintenance of posture

As well as enabling movement, muscles also maintain posture and body position. Sensory receptors in the muscles monitor the tension and length of the muscles and provide the nervous system with crucial information about the position of the body parts, therefore enabling posture to be maintained. Muscles are never completely at rest, nor do they actually have to shorten in length when they contract. The tension or tone produced as a result of these contractions between various opposing groups of muscle helps us remain in a static position, even when we are asleep.

Muscle Origin & Insertion

Each end of a muscle is attached to a bone and these connections are known as the origin and insertion. The muscle's origin is attached to the immovable bone and the muscle's insertion is attached to the movable bone.

Effect of exercise on the muscular system

The effects of regular exercise on the muscular system:

  • Strengthens muscles and the connective tissues
  • Improves muscle control and balance
  • An increase in muscle size and efficiency
  • The amount of myoglobin within skeletal muscle increases
  • Muscles are capable of storing a larger amount of glycogen
  • Muscle became more efficient at disposing of waste products through the bloodstream
  • Increase in muscle recruitment


Related References

The following references provide additional information on this topic:

  • Baldwin, K. M. and Haddad, F. (2014) The Muscular System: Muscle Plasticity. History of Exercise Physiology, p. 337
  • GARY, J. L. et al. (2014) Orthopedic & Muscular System: Current Research
  • BERQUIST, T. H. (Ed.) (2012) MRI of the Musculoskeletal System. Lippincott Williams & Wilkins.

Page Reference

If you quote information from this page in your work then the reference for this page is:

  • MACKENZIE, B. (2001) Physiology - Muscular System [WWW] Available from: https://www.brianmac.co.uk/physiolm.htm [Accessed

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