Muscle Anatomy and Physiology Quiz

Muscular System Anatomy & Physiology

• The muscular system is responsible for all types of body movement.
• There are approximately 650 muscles in the human body.
• Different muscles have different functions when it comes to movement.
• Muscle cells are elongated and are known as muscle fibers.
• Muscle contractions are due to proteins called myofilaments.

Functions of Muscles

• Muscles produce movement or generate tension.
• Muscles help with skeletal movement, communication, body position, posture, protect soft tissues, and guard entrances and exits. They also maintain body temperature.
• Muscles are attached to bones at least at two points.
• Origin is the attachment to an immovable bone.
• Insertion is the attachment to a movable bone.

Lever Systems

• Lever systems involve a rigid bar (lever) that moves on a fixed point (fulcrum) when a force is applied (effort).
• Bones and muscles act as lever systems in the body. The resistance (load) is the weight and tissues the muscles need to move.

Types of Levers

• First-Class Levers: The fulcrum is in between the effort and the load (e.g., seesaw).
• Second-Class Levers: The load is between the effort and the fulcrum (e.g., wheelbarrow).
• Third-Class Levers: The effort is between the load and the fulcrum. Most skeletal muscles are of this type.

Muscle Actions and Types of Muscles

• Agonist: The primary muscle that moves a bone.

• Antagonist: The muscle that opposes the agonist.

• Synergists: Assist the prime mover muscles.

• Fixators: Help to hold bones in place.

• Tendons are thick and rope-like structures that connect muscle to bones.

• Aponeuroses are flat sheet-like structures that also connect muscle to bones

Five Golden Rules of Skeletal Muscle Activity

• All muscles cross at least one joint.
• The bulk of muscles lies proximal to the joint crossed.
• All muscles have at least two attachments (origin and insertion).
• Muscles only pull (never push).
• During contraction, the muscle insertion moves towards the origin.

Muscle Contraction

• The process of muscle contraction is called the sliding filament model.
• Nerve impulses trigger myosin to pull actin filaments closer together.

Sliding Filament Model Parts

• Part 1: Shows the release of calcium removes guard proteins around actin to reveal binding sites.
• Part 2: Shows how myosin heads break down ATP and use energy to bind and pull on the actin.

Neuromuscular Junction

• The neuromuscular junction is where a motor neuron meets a muscle cell.
• The end of the motor neuron meets the muscle cell at a motor end plate.
• Nerve impulses are sent through a neuron to the muscle to begin contraction.
• Acetylcholine (ACh) is released from the neuron and binds to receptors on the motor end plate.

Muscle Fiber Contraction

• Muscle fiber contraction is "all or none," meaning either all fibers contract or none do.
• Different combinations of fiber contractions cause different responses.

Energy for Muscle Contraction

• Initially, muscles use stored ATP for energy.
• After initial energy, other pathways are used to produce ATP.
• Aerobic respiration involves a series of metabolic pathways occurring in the mitochondria, where glucose is broken down.
• In anaerobic glycolysis glucose is broken down.
• Muscle fatigue occurs when a muscle is unable to contract.

Muscle Fatigue and Oxygen Debt

• The common reason for muscle fatigue is oxygen debt--oxygen is required to get rid of accumulated lactic acid.
• Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less.

Effects of Exercise on Muscles

• Aerobic exercise increases blood supply to the muscles. It also increases mitochondria and oxygen storage in the muscle fibers and increases muscle fatigue resistance.
• Anaerobic exercise increases the amount of contractile filaments and connective tissue.
• Stretching increases flexibility and helps avoid injuries.

Aging Muscles

• During aging, muscle tissue decreases, and connective tissue increases.
• Muscles become stringier.
• Body weight declines due to loss of muscle mass.
• Strength usually decreases by 50% by age 80 if no weight training is done.

Muscle Complications

• Muscle cramps are painful, uncontrollable muscle contractions, often caused by dehydration and ion imbalance.
• Pulled muscles (torn muscles) occur from stretching muscles too far, resulting in tearing of fibers.

Muscle Diseases & Disorders

• Atrophy is muscle wasting away due to disintegrating protein in the muscles, which is commonly from lack of use.
• Tetanus is a bacterial infection that causes maximal muscle contraction due to overstimulation of nerves.

Muscle Types

• Skeletal muscle: striated, voluntary, attached to bones, multinucleated, surrounded and bundled by connective tissue.
• Cardiac muscle: striated, involuntary, only in the heart, single nucleus, contracts at a steady rate.
• Smooth muscle: non-striated, involuntary, in hollow organs (intestines, stomach, bladder), spindle-shaped cells, single nucleus, pushes food and other substances through body.