Skeletal muscle Flashcards
How many skeletal muscles are there in the human body?
~640
What are the major types of skeletal muscle fibre arrangements? Which is the most common?
- Parallel (most common): fibres run parallel to the force-generating axis
- Pennate: 1 or more aponeuroses run through the muscle body from the tendon, and the fascicles of muscle fibres attach to these aponeuroses at an angle (= pennation angle).
- Circular: fibres form concentric rings around an opening - act as sphincter to adjust it.
Describe the 3 main categories of parallel muscles and give examples of each.
- Strap
- shaped like strap/belt with fibres running longitudinally, parallel to the direction of contraction
- e.g. sartorius - Fusiform
- cylindrical, wider in the centre with tapering off at ends
- e.g. biceps brachii - Fan shaped
- have fibres that converge at one end
- e.g. pectoralis major
Describe the 3 main types of pennate muscles and give examples of each.
- Unipennate
- all fascicles are on same side as tendon
- e.g. extensor digitorum longus - Bipennate
- fascicles are on both sides of a central tendon
- e.g. rectus femoris - Multipennate
- a central tendon branches off
- e.g. deltoid
To what structures do circular muscles attach? Give examples of such muscles.
- Attach to skin, ligaments and fascia of other muscles rather than bone.
- E.g. orbicularis oculi (around the eye), orbicularis oris (around the mouth)
What is the difference between the origin and insertion of a muscle?
Origin = bone, typically proximal, which has greater mass and is more stable than the muscle’s insertion.
Insertion = structure, typically distal, the muscle attaches to.
- can be bone, tendon or connective tissue (usually tendon to bone)
- tends to be moved by contraction
- greater motion than origin during contraction
How are groups of muscles divided in limbs?
Divided into compartments delineated by fascia.
What are the main functions of skeletal muscle?
- Movement
- Maintain body posture by stabilising joints
- Heat generation
Why does skeletal muscle produce heat?
Tissue is inefficient at converting chemical energy into mechanical work - about 80% of energy lost as heat as a by-product of muscle activity.
What is the difference between agonists and antagonists?
Agonist = prime muscle(s) responsible for a particular movement.
Antagonist = muscles which oppose this movement.
What are synergists?
Muscles that act to assist the prime mover through their angle of pull (but cannot perform the action alone).
What are neutralisers? Give an example.
- 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) acts to cause flexion at the elbow joint.
What are fixators (stabilisers)? Give an example. How are these different to neutralisers?
- Act to hold a body part immobile whilst another body part is moving.
- In most activities, proximal joints are stabilised whilst distal joints move.
- E.g. stabilising the shoulder whilst flexing the elbow. Fixators active in elbow flexion are the muscles that stabilise the position of the scapula and those that stabilise the shoulder joint.
- Neutralisers prevent the unwanted actions of a muscle, fixators stabilise a joint.
How can muscles be classified in terms of ‘levers’? Give examples.
- 1st class levers (“see-saw”)
- muscle and load are at either side of the fulcrum
- usually at mechanical disadvantage in body
- e.g. extension/flexion of head (semispinalis capitas) - 2nd class levers (“wheelbarrow”)
- fulcrum and muscle are at either side of load
- e.g. plantar flexion of foot (gastrocnemius) - 3rd class levers (“fishing rod”)
- load and fulcrum are at either side of muscle
- mechanical disadvantage but most common in body
- e.g. biceps brachii in flexion of elbow when lifting weight
