Muscle Structure And Function Flashcards
Active vs passive force of a muscle
Active- when a nerve stimulates a muscle
Ex: when flexing the wrist, the fingers curl up- they use passive tension to produce movement
Passive- when a muscle is stretched
Can a paralyzed muscle develop passive tension?
Can passive tension in muscle produce movement?
Yes! The connective tissue can still be stretched
Yes, minimal
Structure of a muscle: what is the contractile unit? What is the non contractile unit?
Contractile- muscle tissue
Non contractile- connective tissue (passive tension when stressed)
Sarcomere
The active force generating portion of the muscle
Cross-bridge
Bonding of actin and myosin within a sarcomere
The basic unit of active muscle tension!!
Generation of force at sarcomeres: 4 key points
- Tension is generated by cross bridges
- No cross bridges can be formed and no generation of active tension can occur unless there is overlap of actin and myosin
- Maximum # of cross bridges can be formed when there is maximum overlap of actin and myosin
- The greater the amount of cross bridges, the greater the amount of force generated in the sarcomere
Active insufficiency
Diminished ability of a muscle to produce or maintain active tension
Occurs when the muscle has shortened to a point where no further cross bridges are available
Why doesn’t active insufficiency occur all of the time?
Which joints are most susceptible to active insufficiency?
Joints work to preserve energy and minimize the amount of shortening of a muscle
Activation of antagonistic muscles on the other side of the joint offset the amount of muscle shortening, by rotating in the opposite direction (lengthening)
The higher number of joints a muscle crosses, the greater the susceptibility to active insufficiency
Types of muscle activation
Isometric: muscle produces force while maintaining constant length
Concentric: muscle produces force as it shortens
Ex: Biceps while bringing hand to mouth
Eccentric: muscle produces force as it lengthens
Ex: Deltoid while lowering arm down to the side
Agonist
muscle (or group) directly responsible for the movement being performed
Ex: anterior deltoid during shoulder flexion
Antagonist
muscle (or group) that has the opposite action of the agonist
Ex: brachialis is an antagonist to triceps
Synergist
A pair of muscles producing force in the same linear direction, cooperating to perform a particular action
Ex: flexors/extensors of the wrist
Force couple
A type of synergy where 2 or more muscles simultaneously work to produce force in DIFFERENT LINEAR directions but with torques acting in the SAME ROTARY direction
Ex: turning a steering wheel, walking through a revolving door, hip flexors and back extensors
Recruitment vs Rate Coding
The nervous system recruits (activates) motor neurons as needed OR increase stimulation of original neuron through rate coding
Rate coding: once a specific motor neuron is recruited, muscle force increases in the rate of its excitation
As a muscle fatigue increases, the nervous system will often increase rate of activation (rate coding) or recruit additional motor units (recruitment)
Differential analysis in movement
Essential for OT to be able to accurately identify the true cause/source of the limitation (why won’t the elbow flex)
Ex: “patient has full passive range of motion but little to no active range of motion” In order for a joint to go through full range of motion, consider:
