Functions and Types of Muscular System

Study Notes

Movement: Muscles contract to produce movement, allowing us to walk, talk, and perform various activities.
Posture: Muscles help maintain posture by providing support and stability to the body.
Heat production: Muscle contractions generate heat, which helps regulate body temperature.
Protection: Muscles cover and protect internal organs.

Skeletal Muscle: Attached to bones, responsible for voluntary movements, and appears striated (striped).
- Characteristics: Voluntary control, striated appearance, and multinucleated cells.
- Examples: Biceps brachii, quadriceps femoris.
Smooth Muscle: Found in the walls of internal organs, responsible for involuntary movements, and appears smooth.
- Characteristics: Involuntary control, non-striated appearance, and single nucleus per cell.
- Examples: Muscles in the digestive system, blood vessels, and urinary bladder.
Cardiac Muscle: Found only in the heart, responsible for pumping blood, and appears striated.
- Characteristics: Involuntary control, striated appearance, and branched muscle fibers.
- Examples: Myocardium (heart muscle).

Muscle fiber: A single muscle cell.
Sarcolemma: The plasma membrane of a muscle fiber.
Sarcoplasm: The cytoplasm of a muscle fiber.
Myofibrils: Contractile units within a muscle fiber.
Sarcomeres: Repeating units of myofibrils, responsible for muscle contraction.

The process of muscle contraction.
Actin and myosin filaments slide past each other, shortening the sarcomere and causing muscle contraction.
Requires ATP (adenosine triphosphate) for energy.

The nervous system stimulates muscle contraction.
Neuromuscular junction: The point where a motor neuron meets a muscle fiber.
Acetylcholine (ACh): A neurotransmitter released by the motor neuron, which triggers muscle fiber contraction.

A motor neuron and all the muscle fibers it innervates.
Smaller motor units consist of slow-twitch fibers, while larger motor units have fast-twitch fibers.

When a muscle fiber receives an electrical impulse, it contracts completely (100%) or not at all (0%).
The strength of contraction is determined by the number of motor units recruited.

Red Muscle Fibers (Slow-Twitch):
- Rich in myoglobin, which carries oxygen.
- Used for endurance activities.
White Muscle Fibers (Fast-Twitch):
- Low in myoglobin.
- Used for powerful, short-duration activities.
Motor units within a muscle are homogeneous, meaning they have all red or all white fibers.
Smaller motor units are composed of red slow-twitch fibers.
Large motor units are composed of white fast-twitch fibers.