4.3 Part 2

Muscle Structure

• Muscles are composed of muscle fibers bundled into fascicles
• Fascicles are surrounded by connective tissue, nerves, and blood vessels
• Fascicle arrangement determines muscle classification

Parallel Muscle

• Muscle fibers run parallel to the long axis of the muscle
• Most muscles are parallel
• Tendons on each end
• Contraction shortens and widens the muscle
• Example: Biceps brachii

Convergent Muscle

• Fan-shaped with a narrow tendon attachment at one end
• Broad attachment at the opposite end
• Example: Pectoralis muscle in the chest

Pennate Muscle

• Muscle fibers form an angle with the tendon
• Direction of pull is not parallel to the muscle body
• Generate less movement but more force
• Example: Rectus femoris muscle of the knee

Circular Muscle

• Arranged circumferentially
• Also known as a sphincter muscle
• Contraction closes an opening
• Example: Orbicularis oris (mouth)

Lever Systems

• Improve muscle function
• Classified based on the location of the:
  • Load (what is moved)
  • Fulcrum (pivot point)
  • Applied Force (muscle pull)

First Class Lever

• Fulcrum is in the center
• Example: Seesaw, Head on neck

Second Class Lever

• Load is between the fulcrum and applied force
• Example: Wheelbarrow

Third Class Lever

• Applied force is between the fulcrum and load
• Majority of levers in the body
• Example: Biceps brachii (elbow flexion)

Muscle Arrangement

• Muscles are made up of bundles of muscle fibers called fascicles
• Muscle types are classified by how fascicles are arranged
• Parallel muscle type is the most common type
• Parallel muscles have fibers parallel to muscle's long axis
• Parallel muscles contract, shortening, and widening the muscle
• Biceps brachii is a good example
• Convergent muscles are fan-shaped, with a wide origin and a narrow attachment, like the chest muscle pectoralis
• Pennate muscles have fibers at an angle to the tendon. They generate more force than parallel muscles, but less movement.
• Rectis femoris, a knee muscle, is a good example of a bipennate muscle
• Circular muscles (sphincters) are arranged in a circle, contracting to close openings
• Example of circular muscle: obicularis oris (mouth)

Lever Systems

• Lever systems are fundamental to muscle function
• Lever system classification:
• Load: The object being moved.
• Fulcrum: The pivot point.
• Applied Force: The muscle pull.
• Most levers in the body are third class, where the applied force is between the load and the fulcrum.
• First-class levers have the fulcrum between the load and the applied force, like a seesaw or the head moving on the neck.

Explore the fascinating world of muscle structure and classification in this quiz. From parallel to circular muscles, learn about the different types of muscle arrangements and their functions. Test your understanding of muscle anatomy with examples of specific muscles.