The Muscular System and Muscle Contraction

Vocabulary practice flashcards covering muscle anatomy, functional classification, sliding filament mechanisms, neuromuscular signaling, and musculoskeletal levers.

Insertion

The point where a muscle is attached to a movable bone.

Origin

The point where a muscle is attached to an immovable bone.

Prime Movers (Agonists)

Muscles that are most responsible for producing a certain movement.

Antagonists

Muscles that oppose or do the reverse of a certain movement, located on the opposite side of a joint from the prime mover.

Synergists

Muscles that assist the prime mover by stabilizing across a joint or adding additional force.

Fixators

Synergist muscles that specifically immobilize a muscle's origin bone to increase the prime mover's effectiveness and maintain posture.

Tropomyosin

A regulatory protein that blocks actin from binding with myosin heads until displaced by troponin.

Troponin

A regulatory protein that binds with $Ca^{+2}$ and pulls tropomyosin out of the way to expose actin active sites.

Cross-Bridge

The structural connection formed when a myosin head attaches to an exposed active site on an actin filament.

Power Stroke

The movement during contraction where energy stored in the myosin head is used to pull actin filaments toward the M line as ADP and P are released.

Somatic Motor Neurons

Neurons utilized by the nervous system to connect with skeletal muscles and signal them to contract.

Excitable Cells

Cells, such as neurons and muscle cells, that respond to external stimuli by changing their resting membrane potential.

Resting Membrane Potential

The voltage difference across a cell membrane, typically measuring between $-50\,mV$ and $-90\,mV$.

Action Potential (AP)

A large change in membrane potential that spreads rapidly over long distances within an excitable cell.

Neuromuscular Junction (Motor End Plate)

The site where the axon terminals of a somatic motor neuron meet a muscle fiber, including the intervening synaptic cleft.

Synaptic Cleft

The gap between cells across which chemical neurotransmitters diffuse to transmit electrical signals.

Acetylcholine (ACh)

The specific neurotransmitter chemical messenger that motor neurons release to signal skeletal muscle contraction.

Lever

A rigid bar that moves on a fixed point when a force is applied to it, functionally represented by bones in the human body.

Fulcrum

The fixed point on which a lever bar moves, functionally represented by joints in the human body.

Effort

The applied force used to move a resistance or load, generated by muscle contractions acting upon insertion bones.

Mechanical Advantage

A mechanical state achieved in a lever system when the effort is applied farther from the fulcrum than the load is.

Mechanical Disadvantage

A mechanical state occurring in a lever system when the effort is applied nearer to the fulcrum than the load is.

First-Class Lever

A lever system where effort is applied at one end and the load at the other, with the fulcrum situated in between, such as raising the head from the chest.

Second-Class Lever

A lever system where effort is applied at one end and the fulcrum is at the other, with the load in between, such as standing on one's toes.

Third-Class Lever

A lever system where the applied effort is positioned between the load and the fulcrum, such as performing a bicep curl.