Muscular System & Contraction Flashcards

Muscular System Functions

Movement: The primary function, achieved through muscle shortening.
Body Stabilization/Posture: Muscles continuously fire to maintain upright posture, even while seated.
Regulate Organ Volume: Primarily performed by smooth muscle, found in hollow organs like the stomach, gallbladder, intestines, uterus, and bladder, controlling their size and contents.
Thermogenesis: The process of generating heat. Muscle contractions, such as shivering, elevate body temperature.
Protection: Muscles cover and protect most body cavities, with the abdominal cavity specifically relying on muscles (e.g., the "six-pack abs") to protect soft organs.

Skeletal Muscle: Striated (striped) and voluntary (under conscious control).
Cardiac Muscle: Found in the heart, striated, and involuntary (not under conscious control).
Smooth Muscle: Non-striated (no stripes) and involuntary.
Note: This unit will primarily focus on skeletal muscle; cardiac and smooth muscle will be covered more extensively with their respective systems.

All muscle tissues possess these five fundamental properties:

Contractility: The ability to shorten and generate force, causing movement. Muscles have a "resting length" and a shorter "working length" during contraction.
Conductivity: The ability to conduct an electrical impulse, also known as an action potential. This impulse is the signal for the muscle to contract.
Excitability: The ability to respond to a nerve impulse (action potential) and become excited.
Extensibility: The ability to extend, stretch, or lengthen.
Elasticity: The ability to return to its original length after being stretched (like elastic in clothing).

There are over 630 skeletal muscles in the human body.
Purpose of Multiple Muscles: Having many muscles (compared to 206 bones) allows for more movement and greater control of precision and direction (e.g., the intricate movements of the hand for playing instruments).

Muscles are primarily made of proteins, which is why meat (muscle) is a rich source of protein.

Contractile Proteins: Directly involved in muscle contraction.
- Myosin: Shaped like a golf club, with heads that bind to actin.
- Actin: Shaped like a string of olives, containing binding sites for myosin heads.
Structural Proteins: Provide structure and support.
- Titin: The most significant structural protein, acting like a coiled spring that runs the length of the sarcomere, providing elasticity and recoil.
Regulatory Proteins: Control whether muscle contraction can occur.
- Troponin: Binds to calcium and changes shape.
- Tropomyosin: In a resting muscle, it covers the binding sites on actin, preventing myosin from attaching.

Sarcomere: The functional unit of muscle contraction, defined as the area between two Z-discs.
In a resting muscle, troponin and tropomyosin cover the binding sites on actin, preventing myosin from attaching.
Binding Site: The specific location on actin that a myosin head must connect to for contraction.
Crossbridge: Formed when a myosin head connects to a binding site on actin.
Sliding Filament Theory: States that during contraction, actin filaments slide over myosin filaments towards the center of the sarcomere.
Walking Theory: Describes how myosin heads act like