IB SEHS B.1.3 Muscular Function

Contractility

The ability of a muscle to contract and generate force.

Extensibility

The ability of a muscle to be stretched beyond its normal resting length.

Elasticity

The ability of a muscle to return to its original shape after being stretched or contracted.

Hypertrophy

The increase in muscle fiber diameter due to resistance training or increased workload.

Atrophy

The decrease in muscle fiber size due to disuse, injury, or disease.

Smooth Muscle

Involuntary, non-striated muscle found in the walls of internal organs and blood vessels.

Skeletal Muscle

Voluntary, striated muscle responsible for movement and posture.

Cardiac Muscle

Involuntary, striated muscle found in the heart, responsible for pumping blood.

Dendrites

Extensions of a neuron that receive signals from other neurons.

Axon

A long projection of a neuron that transmits electrical impulses away from the cell body.

Myelin Sheath

A fatty layer covering axons that speeds up nerve impulse transmission.

Nodes of Ranvier

Gaps in the myelin sheath that allow for faster nerve signal conduction.

Motor Neuron

A nerve cell that carries signals from the central nervous system to muscles to initiate movement.

Neuromuscular Junction

site where a motor neuron communicates with a muscle fiber to stimulate contraction.

Motor End Plate.

The specialized region of the muscle fiber membrane that receives signals from the motor neuron.

Synapse

The junction between two neurons or between a neuron and a muscle fiber where neurotransmitters are released.

Type I Muscle Fiber

Slow-twitch muscle fibers that are fatigue-resistant and rely on aerobic metabolism.

Type IIa Muscle Fiber

muscle fibers that use both aerobic and anaerobic metabolism, providing a balance of power and endurance.

Type IIx Muscle Fiber

Fast-twitch fibers that generate high force quickly but fatigue rapidly, relying primarily on anaerobic metabolism.

Oxidation

The process by which muscles use oxygen to produce energy during aerobic metabolism.

Glycolytic

A term describing energy production that relies on glucose breakdown (anaerobic metabolism) for short bursts of high-intensity effort.

Isometric Contraction

A muscle contraction where force is generated without changing muscle length (e.g., holding a plank).

Isotonic Contraction

A muscle contraction that involves movement and changes in muscle length.

Concentric Contraction

A type of isotonic contraction where the muscle shortens while generating force (e.g., lifting a weight).

Eccentric Contraction

A type of isotonic contraction where the muscle lengthens under tension (e.g., lowering a weight).

Isokinetic Contraction

A contraction where muscle movement occurs at a constant speed, typically using specialized equipment.

Principle of Orderly Recruitment

The process where motor units are recruited in a specific order based on their size: Type I → Type IIa → Type IIx

Agonist

The primary muscle responsible for movement in an exercise (e.g., biceps in a bicep curl). PRIME MOVER

Antagonist

Opposite muscle that relaxes as prime mover contracts (e.g., triceps in a bicep curl).

Fixator

A muscle that stabilizes a joint or body part to allow movement to occur efficiently.

Synergist

A muscle that assists the agonist in performing movement, enhancing force production or stability.

Reciprocal Inhibition

A neuromuscular process where the antagonist muscle relaxes while the agonist contracts to allow smooth movement.