CHAPTER 9

Three types of muscle

Skeletal, Cardiac, Smooth muscle.

Location of Skeletal Muscle

Attached to bones throughout the body.

Location of Cardiac Muscle

Found in the walls of the heart.

Location of Smooth Muscle

Found in the walls of hollow organs (e.g., intestines, blood vessels).

Is skeletal muscle striated?

Yes, skeletal muscle is striated.

Is cardiac muscle branched?

Yes, cardiac muscle is branched.

Is smooth muscle voluntary?

No, smooth muscle is involuntary.

Four important functions of muscle tissue

Movement, stability, heat production, and posture.

Connective tissue sheath surrounding each muscle fiber

Endomysium.

Connective tissue sheath surrounding each muscle fascicle

Perimysium.

Connective tissue sheath surrounding each muscle

Epimysium.

Plasma membrane of a muscle fiber

Sarcolemma.

Bundles of myofilaments inside muscle fibers

Myofibrils.

What overlaps to create a sarcomere?

Thick (myosin) filaments and thin (actin) filaments.

What is found in a relaxed muscle segment of a sarcomere?

Only thin filaments.

Protein that makes up thick filaments

Myosin.

Protein that makes up thin filaments

Actin.

Structure of a thick filament binding to actin

Myosin heads.

Function of the sarcoplasmic reticulum

Regulates calcium ion release for muscle contraction.

Function of T tubules

Conduct action potentials into the muscle fiber.

Function of sarcomeres in contraction

Shortens during muscle contraction.

What happens to distance between Z-discs during contraction?

Decreases.

Four stages of skeletal muscle contraction

Excitation, contraction, relaxation, and recovery.

What is an action potential?

A rapid rise and fall in membrane potential.

Three phases of an action potential

Depolarization, repolarization, and hyperpolarization.

What is end plate potential?

A local depolarization that triggers an action potential.

Excitation-contraction coupling relationship

Links electrical activity to mechanical muscle contraction.

Four steps of EC coupling

AP travels down T tubules, Ca2+ is released from SR, Ca2+ binds to troponin, contraction occurs.

Five types of ion channels in muscle excitation

Voltage-gated Na+, voltage-gated K+, Ca2+ channels, ligand-gated channels, and stretch-sensitive channels.

Purpose of the cross-bridge cycle

Contraction of muscle through repetitive attachment and detachment of myosin to actin.

Four steps of the cross-bridge cycle

Cross-bridge formation, power stroke, cross-bridge detachment, reactivation of the myosin head.

What does ATP binding trigger?

Detachment of myosin from actin.

What does ATP hydrolysis trigger?

Re-cocking of the myosin head.

Condition occurring without ATP

Rigidity or rigor mortis.

Skeletal muscle fiber's tiny response to a single action potential

Muscle twitch.

Three phases of a muscle twitch

Latent, contraction, relaxation.

What is a motor unit?

A motor neuron and all the muscle fibers it innervates.

Molecular event during latent period

Calcium is released from the sarcoplasmic reticulum.

Molecular event during contraction period

Cross-bridge cycling occurs.

What happens during the relaxation period?

Calcium is reabsorbed, tension decreases.

Summation in muscle contractions

Increased muscle tension through rapid successive twitches.

How do motor unit activations relate to tension?

More motor units produce more tension.

Isometric vs isotonic contraction

Isometric: tension increases without length change; Isotonic: muscle changes length and produces movement.

Two types of isotonic contractions

Concentric (shortening) and eccentric (lengthening).

Three mechanisms for ATP regeneration

Direct phosphorylation, anaerobic glycolysis, aerobic respiration.

What are substrates for direct phosphorylation?

Creatine phosphate and ADP.

Sugar needed for anaerobic metabolism

Glucose.

Oxygen’s role in ATP regeneration by aerobic metabolism

Yes, oxygen is required, and mitochondria are needed.

Dominant mechanism during first 6 seconds of exercise

Direct phosphorylation.

What does EPOC stand for?

Excess post-exercise oxygen consumption.

Four events during EPOC

Lactic acid removal, replenishing oxygen, restoring ATP, and restoring creatine phosphate levels.

Muscle fatigue definition

Inability to maintain force; protects against injury.

Major causes of muscle fatigue

Lactic acid buildup and depletion of energy reserves.

Factors increasing force of muscle contraction

Number of motor units recruited, muscle size, muscle stretching, and frequency of stimulation.

Factors increasing velocity and duration of contraction

Muscle fiber type, load, and frequency of stimulation.

Three types of skeletal muscle fibers

Slow oxidative, fast oxidative, fast glycolytic.

Which type contracts the quickest?

Fast glycolytic fibers.

Which type fatigues the slowest?

Slow oxidative fibers.

Which type produces the most force?

Fast glycolytic fibers.