Skeletal Muscle System

Structure of a Muscle
- Muscles are composed of bundles of muscle fibers called fascicles.
- Each fascicle consists of elongated striated muscle cells (muscle fibers).

Primary Functions:
- Give Shape: Provides form to the body.
- Produce Movement: Enables body motion through contraction.
- Maintain Posture: Keeps body upright and aligned.
- Support Other Structures: Provides support for organs and tissues.
- Produce Heat: Generates heat through metabolic processes.

Connective Tissue Components:
- Epimysium: Surrounds the entire muscle.
- Perimysium: Surrounds individual fascicles.
- Endomysium: Surrounds individual muscle fibers.
All connective tissue layers extend beyond the muscle belly to form tendons or aponeurosis, which attaches muscle to bone or muscle to muscle.

Muscle Fiber Characteristics:
- Long, cylindrical, multinucleated cells.
- Contains sarcoplasm: Occupies most of the muscle fiber volume and contains glycogen and myoglobin (a red-colored protein that binds oxygen).
Myofibrils:
- Components that are contractile elements of skeletal muscle.
- Myofibrils extend the entire length of the muscle fiber and are made of long chains of sarcomeres.

Basic Functional Unit of Striated Muscle:
- Composed of thick and thin filaments.
- Overlapping pattern creates striations (dark A bands and light I bands).
- Z-discs: Boundaries at either end of the sarcomere.
- M-line: Midsection where thick filaments are anchored.

Sarcomere Shortening:
- Types of Contractions:
- Relaxed Muscle: Sarcomeres at rest.
- Partially Contracted Muscle: Moderate overlap of filaments.
- Maximally Contracted Muscle: Maximum overlap, reduced length of sarcomeres.

Stimulus for Muscle Contraction:
- A neuron stimulates muscle cells; together, they form a motor unit.

Attachment Points:
- All muscles cross at least one joint.
- Muscles have two attachments: Origin and Insertion.
- Origin: Attached to an immovable or less movable bone.
- Insertion: Attached to a movable bone, moves toward the origin during contraction.

Muscle Classifications:
- Prime Mover: Primary muscle responsible for a movement.
- Antagonist: Opposes the action of the prime mover.
- Synergist: Aids the prime mover; stabilizing muscles.
- Fixator: Stabilizes the origin of the prime mover.

Important Skeletal Muscles (Anterior View):
- Masseter, Sternocleidomastoid, Trapezius, Deltoid, Pectoralis major, Biceps brachii, Tibialis anterior, Rectus abdominis, External oblique, Adductor longus, Sartorius, Vastus lateralis, Rectus femoris, Vastus medialis, Gastrocnemius, Soleus.
Important Skeletal Muscles (Posterior View):
- Trapezius, Deltoid, Triceps brachii, Gastrocnemius, Latissimus dorsi, External oblique, Gluteus medius, Gluteus maximus, Gracilis, Adductor magnus, Semitendinosus, Semimembranosus, Soleus, Sternocleidomastoid.