Forms and Actions at Joints Flashcards
How does skeletal muscle cause movement at synovial joints?
- Attaches to bone
- Muscle structure
- Types of contraction
- Crosses joint
What are the classes of levers with muscle attachments
- First : stabilises joint position e.g. nodding head (cranium joined to vertebrae keeps position balanced)
- Second : effective at overcoming loads e.g. plantar flex foot (body pushes up against gravity when we are on tip toes)
- Third : large ROM and speed e.g. biceps brachii (causes flexion at elbow - huge ROM) (lower weight larger ROM)
What functions are determined by muscle form?
- Length of muscle fibres
- Number of muscle fibres
- Arrangement of muscle fibres
How does length affect muscle form/function?
- Fibres can shorten up to 50% max of resting length
- Large ROM required = long muscle fibres
How does number of muscle fibres affect muscle form/function?
- Tension is directly proportional to cross-sectional area
- Greater number of fibres = greater CSA = greater tension
How does muscle fibre arrangement affect muscle form/function?
- Fibres arranged vertically between muscle tendons - parallel (more tension, overcome heavier weight)
- Fibres oblique to muscle tendon - pennate, more fibres into same space = reduced shortening but greater CSA
What is concentric action?
- Tension is greater than the load
- Muscle shortens (brings bones closer together)
Example : elbow flexion (biceps brachii contracts concentrically - angle decreases)
What is eccentric action?
- Tension less than load
- Muscle elongates (pull in opposite direction, bones move further apart)
Example : elbow extension (biceps brachii contracts eccentrically - angle increases)
What is isometric action?
- Tension does not outweigh load (stays equal)
- No change in length of muscle or joint position
Example : holding elbow joint still (bicep brachii contracts isomentrically - no change to angle)
What are the four types of muscle roles at a joint?
- Agonist
- Antagonist
- Stabiliser
- Neutraliser
What are the three types of muscle action?
- Concentric
- Eccentric
- Isometric
What is an agonist?
- Agonists act concentrically to create a movement at a joint
Example : Biceps brachii shorten - flexion
What is an antagonist ?
- Antagonists act eccentrically to oppose and control the movement
Example : Triceps brachii lengths - extension
What is a Stabiliser?
- When a muscle is active to hold a joint still - isometric action
Example : holding a heavy book - your bicep brachii’ s role is a stabiliser and the action is isometric (no change in length)
What is a Neutraliser?
- Muscle eliminates an unwanted movement caused by another muscle
Example : Biceps Brachii will flex when you drink from a glass, not supinate. Pronator muscles neutralise supinating effect
