Muscle Types and Physiology

Skeletal Muscle
- Voluntary control
- Striated appearance
- Multinucleated cells
- Responsible for movement of bones
- Examples: Biceps, quadriceps
Cardiac Muscle
- Involuntary control
- Striated appearance
- Single nucleus per cell
- Found only in the heart
- Functions to pump blood
Smooth Muscle
- Involuntary control
- Non-striated appearance
- Single nucleus per cell
- Lines hollow organs (e.g., intestines, blood vessels)
- Involved in peristalsis and blood vessel regulation

Muscle Contraction
- Triggered by electrical impulses from the nervous system
- Involves sliding filament theory:
  - Actin and myosin filaments slide past each other
  - Shortening of the sarcomere leads to contraction
Energy Sources
- Adenosine triphosphate (ATP) is primary energy source
- Creatine phosphate provides quick energy
- Anaerobic respiration (glycolysis) for short bursts of activity
- Aerobic respiration for endurance activities
Muscle Fiber Types
- Type I (Slow-Twitch)
  - High endurance, low power
  - Aerobic metabolism
  - Found in postural muscles
- Type II (Fast-Twitch)
  - Type IIa: Moderate endurance, power, and speed
  - Type IIb: Low endurance, high power and speed
  - Anaerobic metabolism

Movement
- Enables locomotion and movement of body parts
- Works in pairs (agonist and antagonist muscles)
Posture Maintenance
- Stabilizes joints and maintains body position
- Continuous muscle contractions allow for upright posture
Heat Production
- Muscle contractions generate heat
- Important for maintaining body temperature
Circulation Assistance
- Skeletal muscles assist in venous return of blood to the heart during contraction
Support and Protection
- Provides structural support to the body
- Protects internal organs through surrounding muscle layers

Skeletal Muscle: Under voluntary control with a striated look, develops movement of bones; notable examples include biceps and quadriceps.
Cardiac Muscle: Operates involuntarily, also striated, has a single nucleus, and is exclusive to the heart where it is responsible for pumping blood.
Smooth Muscle: Involuntary and non-striated, contains one nucleus per cell, found in hollow organs like intestines and blood vessels; plays a role in peristalsis and regulating blood flow.

Muscle Contraction: Initiated by electrical signals from the nervous system, employing the sliding filament theory where actin and myosin filaments slide together, shortening the sarcomeres for contraction.
Energy Sources:
- ATP serves as the main energy source.
- Creatine phosphate supplies immediate energy.
- Anaerobic respiration (glycolysis) supports short, high-intensity efforts.
- Aerobic respiration is crucial for prolonged endurance activities.
Muscle Fiber Types:
- Type I (Slow-Twitch): Characterized by high endurance and low power, relies on aerobic metabolism, typically found in muscles that maintain posture.
- Type II (Fast-Twitch):
  - Type IIa: Offers moderate endurance, power, and speed.
  - Type IIb: Provides low endurance but high power and speed, dependent on anaerobic pathways.

Movement: Facilitates locomotion and different body movements through coordinated actions of agonist and antagonist muscle pairs.
Posture Maintenance: Stabilizes joints and upholds body position via continuous muscle contractions, essential for balanced standing.
Heat Production: Generates heat during muscle contractions, playing a vital role in regulating body temperature.
Circulation Assistance: Aids the return of venous blood to the heart, particularly through skeletal muscle contractions.
Support and Protection: Offers structural integrity and safeguards internal organs by enveloping them with muscle layers.

Skeletal Muscle
- Characterized by a striated appearance, allowing for easy identification under a microscope.
- Under voluntary control, enabling conscious movement.
- Composed of multi-nucleated cells, which help muscle fibers grow and repair.
- Primarily attached to bones, facilitating skeletal movement and locomotion.
Smooth Muscle
- Displays a non-striated appearance, making it distinct from skeletal and cardiac muscle.
- Operates under involuntary control, functioning without conscious effort.
- Each cell contains a single nucleus, which is typical of smooth muscle.
- Located in the walls of hollow organs, such as the intestines and blood vessels, playing a role in involuntary actions like digestion and circulation.
Cardiac Muscle
- Exhibits a striated appearance, similar to skeletal muscle, but functions involuntarily.
- Composed of single-nucleated cells that are interconnected by intercalated discs, promoting synchronized contractions.
- Exclusively found in the heart, crucial for the pumping of blood throughout the body.

Movement
- Essential for locomotion and the movement of body parts, facilitating daily activities.
- Works in pairs through agonist (primary muscle) and antagonist (opposing muscle) actions for coordinated motion.
Posture Maintenance
- Stabilizes joints and maintains body posture against gravitational forces.
- Continuous muscle contraction is necessary to keep an upright position, preventing falls.
Heat Production
- Generates heat as a byproduct of muscle contractions, important for maintaining body temperature.
- Shivering serves as an involuntary response to produce additional heat, particularly in cold conditions.
Joint Stability
- Provides support and stability to joints, helping to maintain alignment during movement.
- Protects joints from dislocation and injury, enhancing overall mobility and physical activity.
Circulation Assistance
- Skeletal muscles aid in venous return, facilitating blood flow back to the heart through muscle contractions.
- Important for promoting blood circulation, especially in the limbs, helping maintain cardiovascular health.