Unraveling the Secrets of Muscle Tension Quiz 4 (p 16-21)

Muscle Contraction

• During relaxation phase, actin filaments slide back to their original position.
• Maximum strength of tetanic contraction of a muscle operating at a normal muscle length is 4-5 times the maximum strength of a single twitch.

Muscle Physiology

• Treppe, also known as the 'staircase effect', is a gradual increase in muscle contraction force due to repeated stimulation.
• After the first five stimuli during temporal summation, the muscle contraction force increases.
• Factors that contribute to muscle fatigue include depletion of ATP and CP, increase in lactic acid, and decrease in pH.

Muscle Mechanics

• Forcefulness of muscle contraction depends on the length of the sarcomeres within a muscle, with optimal force generated at resting length.
• Slow-twitch motor units are recruited first during a muscle contraction.
• The size principle of motor unit recruitment ensures that the smallest motor units are recruited first to achieve precise movements.
• When a nerve is damaged, muscle tone decreases.

Muscle Twitch

• During the latent phase of muscle twitch, there is a delay between the stimulation and the contraction of the muscle.
• Mechanism of tetanization involves the rapid stimulation of a muscle, resulting in the summation of individual muscle twitches.

Muscle Fibers

• Frequency summation contributes to muscle contraction by increasing the force of contraction through rapid stimulation.
• Parallel fiber arrangement is found in muscles capable of greater range of motion.
• Oblique fiber arrangement, resembling that found in a feather, is found in muscles with a complex architecture.
• Rotatory muscles, responsible for mobility, have their proximal attachment far from the joint axis.
• Superficial muscles with a high proportion of FG fibers have a high proportion of fast-twitch fibers.

Muscle Architecture

• The amount of shortening or lengthening of a muscle fiber is directly determined by its architectural characteristic.
• Cross-sectional area of a muscle perpendicular to the orientation of the muscle fibers is known as the physiological cross-sectional area (PCSA).

Muscle Strength

• Factors that can affect muscle strength include muscle length, muscle fiber type, and neural drive.
• In a first-class lever, the two resultant forces are applied on either side of the fulcrum.
• Second-class lever has the moving force closer to the axis than the weight or resistance, providing a force advantage.
• The formula for mechanical advantage in a lever system is output force / input force = distance of effort arm / distance of resistance arm.
• Third-class lever provides a force advantage, allowing large things to be moved by a small force.
• An example of a second-class lever in the human body is the wheelbarrow-like movement of the foot during plantarflexion.

Muscle Tension

• In an unstretched muscle that is stimulated, tension increases rapidly to a maximum and then plateaus.
• In a moderately stretched muscle that is stimulated, tension increases to a maximum and then decreases as the muscle shortens.
• In an overstretched muscle that is stimulated, tension is minimal due to the decreased overlap of actin and myosin filaments.
• Isotonic contraction is a type of muscle contraction where the muscle shortens while generating a constant tension.
• Hypertrophy occurs when muscle fibers increase in size, leading to an increase in muscle strength.
• Atrophy occurs when muscle fibers decrease in size, leading to a decrease in muscle strength.