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Anatomy and Physiology - P4 / M1 / D1 - Structure and Function of the Muscular System

Toby Clark
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Toby Clark

on 13 March 2013

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Transcript of Anatomy and Physiology - P4 / M1 / D1 - Structure and Function of the Muscular System

The Structure and Function of the Muscular System Major Muscles Muscular System You need to know:

the major muscles of the body
3 types of muscle
the function of the muscular system Function of Skeletal Muscle 3 Types of Muscle Cardiac muscle
(Heart Muscle) Smooth Muscle Skeletal Muscle Cardiac muscle is found solely in the walls of the heart. It is similar with skeletal muscles in that it is striated and with smooth muscles in that its contractions are not under conscious control.

It is under control of the autonomic nervous system, however, even without a nervous input contractions can occur due to cells called pacemaker cells.

Cardiac muscles are highly resistant to fatigue due to the presence of a large number of mitochondria, myoglobin and a good blood supply allowing continuous aerobic metabolism. Smooth muscle is also sometimes known as involuntary muscle due to our inability to control its movements, or unstriated as it does not have the stripy appearance of skeletal muscle.

Smooth muscle is found in the walls of hollow organs such as the stomach, oesophagus, bronchi and in the walls of blood vessels.

Smooth muscles have slow, rhythmical contractions and control internal organs, e.g. moving food along the oesophagus or constricting blood vessels during vasoconstriction. Skeletal Muscles are those which attach to bones and have the main function of contracting to facilitate movement of our skeletons. They are also sometimes known as striated muscles due to their appearance. The cause of this 'stripy' appearance is the bands of Actin and Myosin which form the Sarcomere, found within the Myofibrils.

Skeletal muscles are also sometimes called voluntary muscles, because we have direct control over them through nervous impulses from our brains sending messages to the muscle. Contractions can vary to produce powerful, fast movements or small precision actions. Skeletal muscles also have the ability to stretch or contract and still return to their original shape. Skeletal muscle has several important functions within the body:

MOVEMENT: skeletal muscles attach to bones, against which they pull to enable movements. E.g. when running, the hip flexor muscles pull on the femur to lift the leg off the ground, while the quadriceps muscles contract to pull on the tibia to straighten the leg at the knee joint.
SUPPORT & POSTURE: the muscles are seldom fully relaxed and are often in a constant state of slight contraction. In order to adopt an upright position, many muscles within the legs and torso are contracting statically to ensure that the body is balanced. This is also known as muscle tone.
HEAT PRODUCTION: the contraction of skeletal muscle involves the production of energy. In breaking down glycogen to provide this energy, heat is released. This accounts for why the body becomes hot when exercising. When the body is cold, the muscle often goes through a series of involuntary contractions (shivering) in order to release heat and keep the body warm. Functions of the
Muscular System You need to know about:

How the muscles combine to cause movement
Different types of contraction Muscles never work alone. In order for a coordinated movement to be produced, the muscles must work in a group or team, with several muscles working at any one time. Agonist (Prime Mover) A muscle that contracts and is directly responsible for the movement that results at a joint. Antagonist A muscle that has an action opposite to that of an agonist and helps in the production of a coordinated movement. Fixator A muscle that stabilises the origin of the agonist so that an effective contraction can take place. Synergist A muscle that aids the action of the agonist or prevents undesirable movements by stabilizing joints across which the agonist acts. Antagonist Pairings pectorals / latissimus dorsi;
anterior deltoids / posterior deltoids;
trapezius / deltoids;
rectus abdominis / erector spinalis;
quadriceps group / hamstring group;
tibialis anterior / gastrocnemius and soleus;
bicep brachii / triceps brachii;
wrist flexors / wrist extensors. There are four main types of muscle contraction:

Concentric
Eccentric
Isometric
Isokinetic CONCENTRIC CONTRACTION: The shortening of a muscle while contracting. E.g. during the upward phase of a biceps curl, the biceps contracts concentrically. ECCENTRIC CONTRACTION: The lengthening of a muscle while contracting. E.g. during the downward phase of a biceps curl, the biceps contracts eccentrically. ISOMETRIC CONTRACTION: Where a muscle contracts, yet there is no visible shortening or lengthening. It is also known as static contraction. E.g. when holding a barbell with the elbows flexed at 90°, the biceps contracts isometrically. ISOKINETIC CONTRACTION: An isokinetic muscle contraction is one in which the muscle contracts and shortens at constant rate of speed. Examples of this type of contraction in day-to-day and sporting activities are rare. The best is breast stroke in swimming, where the water provides a constant, even resistance to the movement of adduction.
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