Muscle Roles Lecture PDF

ROLE OF THE MUSCLES  ROLE OF THE MUSCLES Muscles rarely act singly; rather, groups of muscles interact in many ways so that the desired movement is accomplished. This interaction may take many different forms so that a muscle may serve in a number of different roles. Agonist...

ROLE OF THE MUSCLES  ROLE OF THE MUSCLES Muscles rarely act singly; rather, groups of muscles interact in many ways so that the desired movement is accomplished. This interaction may take many different forms so that a muscle may serve in a number of different roles. Agonist Antagonist Synergists support  Agonist These are the muscles that can do the action in question Prime movers Secondary movers e.g illiopsoas in hip e.g sartorius in hip flexion flexion Antagonist Is a muscle that can do the opposite action of the action in question. It is usually located on the opposite side of the joint from the movers muscles that can create the action in question. It lengthen when the action in question occurs. They are muscles which oppose the prime movers as they relax and lengthen progressively to allow agonist to contract. So , the movement is controlled but not impeded e.g ; Planter flexors are antagonist for dorsi flexors during ankle dorsiflexion. : elbow extensors are antagonist in elbow flexion Synergists  Muscles which work together in close cooperation as they either contract or relax to modify the action of agonist.  They aim at : - Eliminating the action of undesired movement Types of synergists Conjoint Stabilizer or Fixators Neutralizers  a- Conjoint Synergists = Mutual neutralizers  Two muscles acting together to produce a movement which neither could produce alone.  Flexion of wrist  Or medial and lateral hamstring during pure knee flexion b- Neutralizers  They are muscles which neutralize or cancel the undesired action of other muscles of prime movers or secondary movers.  To oppose the undesired action of the prime movers. e.g. Lateral rotators neutralize undesired motion of adductors and medial rotation ) during hip adduction.  To oppose the undesired action of the secondary movers. e.g. internal rotators neutralize action of sartoruis during hip flexion  Contraction of the finger flexors to grasp an object also tends to flex the wrist. The unwanted wrist flexion is counteracted by the synergic contraction of the wrist extensors.  c- Stabilizers or fixator  A stabilizer muscle is a muscle that can stop an unwanted action of the fixed attachment of the muscle that is working.  They are muscles which surround the proximal joint contract and become firm to allow distal joint to move smoothly. Their contraction is generally isometric.  For example, during straight leg raising from supine lying position the proximal attachment of the psoas major muscle tends to cause anterior tilt of the pelvis, so the rectus abdominis muscle work to stabilize the proximal attachement of the psoas by preventing the anterior pelvic tilt.  Support  The muscles that can hold another part of the body in position while the action in question is occurring.  Do not work directly at the site of the action in question.  Work isometrically to hold body parts in place.  They are muscle which contract in both agonist and antagonist simultaneously and that occur specially under stressful condition.  e.g. longitudinal trunk muscles act as a fixators while the elbow is flexed against heavy weight.   Role of muscles Agonist Antagonist Synergists support Fixators or Conjoint Neutralizers stabilizer Summary chart Take a deep breath Attention  RANGE OF MUSCLE EXTENSIBILITY AND CONTRACTILITY Depends on 1. Length and arrangement of fibers (longitudinal and pennate muscles 2. Number of joints traversed. 3. Resistance of antagonists. 4. Presence of load which oppose the muscle PHYSIOLOGICAL CROSS SECTION OF A MUSCLE  Defined as the area of section that cut every muscle fiber in the muscle perpendicularly. Physiological cross section illustration in fusiform (a), unipennate ( b) and (c) bipennate muscle.  The physiological cross section of a muscle determine its potential force of contraction  Absolute muscle strength is recognized to be 3- 4 kg per cm square cross section.  It is the product of number of muscle fibers making up of the muscle and its level of hypertrophy. Effect of Muscle Architecture on Contraction  longitudinal muscle  Has long muscle fibers  Fibers parallel to long axis of muscle  Creat a large range of motion of body part at the joint with less force  Tends to have smaller physiological cross sectional area  Example: sartorius muscle Effect of Muscle Architecture on Contraction (continued)  Pennate muscle  Has short muscle fibers  Fibers arranged obliquely to long axis of muscle (pennation angle)  Uni-, bi-, and multi-pennate  Creat a short range of motion of body part at the joint with more force ( for strength )  Example: rectus femoris (bi-pennate)  Tends to have larger physiological cross sectional area Pennation angle Increase the pennation angle decrease the strength of the contraction  Differences between one joint muscle and two joint muscle One joint muscle Two joint muscle Suitable when movement is Suitable for performing pattern of desired in one joint only. movement. This muscle is normally Disadvantages active or passive capable of shortening insuffinciency sufficiently to move the body segment to which it is not attached through the maximum angular displacement.  Muscle insufficiency Active insufficiency Passive insufficiency The muscle can not shorten The muscle can not be beyond certain limit without stretched beyond certain loosing tension. limit without causing pain. e.g. maximal hip flexion with knee e.g. when a person try to flex the extension from supine lying hip fully with maximal knee position. extension he usually feels pain in the hamstring if he has tight hamstring Passive insufficiency of the hamstring is manifested by pain.  Tendon action of two joint muscles = Tenodesis  A passive tension without active muscle contraction which may produce movement of the joint if the muscle is elongated over two more than two joint simultaneously. e.g. if the wrist is allowed to flex by the weight of the hand the digits will automatically extend without contraction of the finger extensors. By reversing the wrist movement, the fingers will partially flex.  A 65 years old woman suffers from inability to complete full ROM of elbow flexion what are the possible causes of this problem