S1) Skeletal Muscle Morphology, Structure & Mechanics Flashcards
What are the 3 types of muscle cells?
- Skeletal
- Cardiac
- Smooth
State the structure and function of skeletal muscle
- Structure: striated muscle due to the ordered arrangement of the myofibrillar apparatus producing a characteristic banding pattern
- Function: permit movement through voluntary contractions
Describe the role of skeletal muscle in heat generation
- Approximately 80% of chemical energy is lost as heat as a by-product of muscle activity
- This inefficiency is used by the physiological process of shivering to raise core body temperature by the involuntary activation of skeletal muscle
Describe the numerical distribution of skeletal muscles in the body
- Approximately 640 skeletal muscles
- Most of which are present as bilateral pairs
The most common arrangement of skeletal muscle is for the fibres to run parallel to the force-generating axis.
Identify the three types of parallel muscles
Describe the structure of strap muscles
Strap muscles are shaped like a strap with the fibres running longitudinally, parallel to the direction of contraction e.g. sartorius
Describe the structure of fusiform muscles
Fusiform muscles are cylindrical and wider in the centre while tapering off at the ends e.g. biceps brachii
Describe the structure of fan-shaped muscles
Fan shaped muscles have fibres that converge at one end e.g. pectoralis major
What are pennate muscles?
Pennate muscles are muscles which 1/more aponeuroses running through the muscle body from the tendon and fascicles which attach to these aponeuroses obliquely to the direction of movement
Identify and describe the different kinds of pennate muscles
- Unipennate where all the fascicles are on the same side as the tendon
- Bipennate where fascicles are on both sides of a central tendon
- Multipennate where a central tendon branches
What is a pennation angle?
The pennation angle is the angle between a fascicle’s orientation and the tendon axis
What are circular muscles?
Circular muscles are muscles where fibres form concentric rings around a sphincter or opening by attaching to skin, ligaments and fascia of other muscles rather than to bone
E.g. orbicularis oculi around the eye, orbicularis oris around the mouth
What are agonist and antagonist muscles?
- An agonist is the prime muscle(s) responsible for a particular movement
- An antagonist is the muscle(s) which opposes this movement
What are synergists?
Synergists are muscles which act to assist the prime mover as they cannot act alone to perform the movement e.g. brachioradialis and pronator teres in elbow flexion
What are neutralisers?
Neutralisers are muscles which prevent the unwanted actions that an agonist can perform
E.g. rotator cuff muscles stabilise the glenohumeral joint whilst biceps, (whose long head acts to cause shoulder flexion) cause elbow flexion
What are fixators?
Fixators are muscles which act to hold a body part (proximal joint) immobile whilst another body part (distal joint) is moving
E.g. elbow flexion – fixators are the muscles that stabilise the scapula and those that stabilise the shoulder joint
Distinguish between neutraliser and fixator muscles
- Neutralisers prevent the unwanted actions of a muscle
- Fixators stabilise a joint
What is muscle contraction?
Muscle contraction refers to the active cycling of cross-bridges between the actin thin filaments and the myosin thick filaments within the sarcomeres