Week 1 Gross Structure and Function of Skeletal Muscle Part 1&2 Flashcards
Discuss the meaning of the phrase “muscles spared when ligaments suffice” relative to muscle tone and posture using examples form the upper limb.
- non contractile elements of a muscle (CT and tendons) may act as a postural ligament when that muscle is arranged in a way that resists the force of gravity acting across a joint-trapezius and triceps sure may display low level muscle activity to maintain position of body in normal resting posture
- shoulder position: maintained by low grade postural isometric contractions of upper fibers of trapezius
- Glenohumeral joint: downward displacement prevented by locking joint mechanism of humeral head in glenoid cavity
Describe the types of muscle contraction.
- shortening (concentric): muscle becomes shorter, doing active work by generating more force than any external forces there may be
- isometric: whole muscle remains at sam length during contraction, muscular force and external f orcs balanced
- lengthening (eccentric): when whole muscle becomes longer while contracting, muscular force less than external force. two attachments of muscle spread further apart
Force versus movement of muscle.
- force is proportional to cross sectional area of a muscle’s fibers
- movement is proportional to length of a muscle’s fibers
Describe the different types of muscle fiber architecture and effects of adding tendon to the muscles.
- Parallel fibered muscles: adapted for movement as opposed to force. As more tendon is added, movement but not force decreases (reduces fiber length)
- Pennate fibered muscles: adapted for force, not movement. short but numerous muscle fibers. As more tendon is added, force but not movement decreases (reduces number of fibers).
Define prime mover (agonist).
Muscle that is regularly active in initiating and maintaining a particular movement. Gravity can be considered a prime mover.
Define muscle antagonist.
A muscle that is capable of opposing or resisting the action of a mover. E.g. triceps brachii as antagonist to brachialis muscle
Define a muscle fixator or stabilizer.
- acts to stabilize joint position and integrity
e. g. four rotator cuff muscles that stabilize the glenohumeral joint
Define syndergist muscle.
A muscle that acts to eliminate unwanted movements caused by prime movers
e.g. wrist extensors are synergists that act antagonistically while making a fist to prevent wrist flexion caused by finger flexors
Describe the anatomical actions of the deltoid muscle relative to each axis for movements that occur at the shoulder joint.
- Anterior part: passes in front of shoulder joint
- flexion around transverse axis through humeral head
- medial rotation around longitudinal axis
- adduction around AP axis - Lateral part: passes lateral to shoulder joint
- abduction, pennate arrangement - posterior part: passes in back of shoulder joint
- extension around transverse axis
- lateral rotation around longitudinal axis
- adduction around AP axis
Describe the attachments of the biceps brachii muscle.
-long head attaches to scapula at supraglenoid tubercle
-short head attaches to coracoid process
The two head converge and attach to the radial tuberosity
Describe the anatomical actions of the biceps brachii muscle.
- weakly flexes arm at shoulder joint
- powerfully flexes arm at elbow joint
- supination of the pronated forearm-during pronation, radius is rotated so that tendon of biceps wrapped around the radius and attached to radial tuberiosity that is not pointed posteriorly
Describe the muscle function of the biceps brachii.
- primary mover that contracts concentrically when flexing at elbow
- when extending at elbow: acts as antagonist to gravity (primary mover), contracts eccentrically to control extension, triceps not active unless there is resistance.
What are the muscles involved in pronation?
- pronator teres: passes distally from medial epicondyle of the humorous to wrap around lateral side of radial shaft
- pronator quadratus: quandrangular deeps muscle with transversely oriented muscle fibers (by wrist)
They pull radius anteriorly and medially
Describe the muscles involved in supination.
- biceps brachii in anterior compartment
- supinator muscle: arises from lateral epicondyle of the humerus and nearby ulna and inserts on proximal end of radial shaft. Becomes wrapped around radius during pronation
List which muscles are active during different supination activity: supinator (prime mover), biceps (prime mover), triceps (synergist), shoulder (stabilizers)
- slow unresisted supination: supinator only
- fast aspiration with elbow flexed: all four
- fast suppuration with elbow extended: supinator only
- supination against resistance: all four
- biceps brachii recruited as prime mover in supination when speed or power are required
- triceps brachii recruited as synergist to stop the unintended action of elbow flexion caused by biceps
- shoulder muscles activated as stabilizers when biceps involved to counter flexion and extension at shoulder joint caused by biceps and triceps
