Movement and Locomotion

This set of vocabulary flashcards covers the anatomical structures of muscles, the biochemical mechanisms of contraction and regulation, and the physical principles and energetic costs of terrestrial, aquatic, and aerial locomotion.

Actin

A microfilament polymer comprising two protofilaments made of 100 globular subunits, found in high concentrations in skeletal and cardiac muscle cells.

Myosin

A long rod-shaped molecule consisting of two protein chains with a globular head that has ATPase activity.

Myosin-1

A term referring to monomeric myosin.

Myosin-2

A term referring to polymerised myosin molecules.

Sarcomere

A highly ordered array of thick myosin and thin actin filaments, bounded by Z lines, which serves as the functional unit of contraction.

A band

The dark band of the sarcomere that contains thick myosin filaments and remains at a constant length during contraction.

I band

The light band of the sarcomere containing only thin actin filaments, which shortens during muscle contraction.

Sarcoplasmic reticulum (SR)

An intracellular membrane system that sequesters $Ca^{2+}$ and releases it to induce muscle contraction.

T-tubules

Sarcotubules that form a ring around each sarcomere to assist in the spread of action potentials.

Triad

The anatomical association of a t-tubule and the sarcoplasmic reticulum (SR) of two adjacent sarcomeres.

Sliding Filament Model

The mechanism for muscle contraction where actin and myosin filaments slide past each other without changing their individual lengths.

Tropomyosin

A regulatory protein that physically covers the myosin-binding sites on actin in a relaxed muscle fiber.

Troponin

A protein with three subunits that, when bound to $Ca^{2+}$, moves tropomyosin to expose actin binding sites.

Excitation-Contraction Coupling

The process where an action potential generated by Acetylcholine (ACh) release triggers $Ca^{2+}$ release and subsequent sarcomere contraction.

Rheobase

The threshold voltage for an impulse of very long duration that is sufficient to elicit a muscle response.

Chronaxie

The minimum duration required for a impulse of $2 \times$ rheobase voltage to elicit a response; used as a measure of cell excitability.

Isometric contraction

A type of contraction where the muscle generates tension without changing its length.

Isotonic contraction

A type of contraction where the muscle changes length while maintaining constant tension.

Latency period

The delay between the application of an electrical stimulus and the first measurable increase in muscle tension.

Summation

A phenomenon occurring when a second muscle twitch is initiated before the first has finished, resulting in increased tension.

Complete tetany

The state where the frequency of stimulation is high enough (the fusion frequency) that individual contractions are no longer discernible.

Cursorial locomotion

An evolutionary trend in limb design and posture specialized for running.

Gait

The specific pattern of limb movement used by an animal during locomotion, which varies with speed.

Duty factor (DF)

The fraction of time during a locomotory cycle that a specific foot remains in contact with the ground.

Plantigrade

A foot posture where the entire sole of the foot makes contact with the ground.

Digitigrade

A foot posture where the animal supports its weight on its digits.

Unguligrade

A foot posture where the animal travels on the tips of its toes.

Net cost of transport ($COT_{net}$)

A measure of the energetic cost of locomotion calculated as the energy required to move a specific distance.

Reynold’s number (Re)

The ratio of inertial forces to viscous forces in a fluid medium, used to characterize fluid flow around an animal.

Friction drag

A component of total drag caused by fluid moving over the surface of an animal's body.

Lift

The force exerted on an object by a fluid perpendicular to the direction of fluid motion.

Aerofoil

A flat or cambered structure that experience aerodynamic forces (lift and drag) when oriented at an angle to a moving fluid.