Chapter 10: The Muscular System

10.1 General Function of Axial and Appendicular Muscles

The muscular system is divided into axial and appendicular muscles, each serving distinct roles in movement and stability.

• Axial Muscles: These muscles are located along the central axis of the body and are primarily responsible for movements of the head, neck, and trunk, as well as maintaining posture and supporting the organs.

• Appendicular Muscles: These muscles are attached to the limbs and girdles, facilitating movement of the arms and legs, and enabling locomotion and manipulation of objects.

• Example: The rectus abdominis (axial) stabilizes the trunk, while the biceps brachii (appendicular) flexes the forearm.

10.2 Fascicle Organization and Levers in Muscle Efficiency

Muscle fascicles are bundles of muscle fibers whose arrangement affects muscle function and force production. Muscles act on bones as levers, influencing movement efficiency.

• Fascicle Arrangements: Types include parallel, convergent, pennate, and circular, each affecting contraction strength and range of motion.

• Levers: Bones act as levers, with muscles providing the force. Levers are classified as first, second, or third class, depending on the relative positions of the fulcrum, load, and effort.

• Equation:

• Example: The biceps brachii acts as a third-class lever when flexing the forearm.

10.3 Muscle Naming: Location, Appearance, and Function

The names of muscles often provide clues about their characteristics, including location, shape, size, and function.

• Location: Muscles may be named for their anatomical position (e.g., brachialis in the arm).

• Appearance: Names may reflect shape (e.g., deltoid for triangular shape) or size (e.g., maximus for largest).

• Function: Names may indicate action (e.g., flexor for flexion).

• Example: The sternocleidomastoid muscle is named for its origin and insertion points.

10.4 Axial vs. Appendicular Muscle Divisions

Muscles are grouped into axial and appendicular divisions based on their location and function.

• Axial Division: Includes muscles of the head, neck, vertebral column, and thoracic-abdominal regions.

• Appendicular Division: Includes muscles of the shoulders, arms, forearms, hands, hips, thighs, legs, and feet.

• Example: The trapezius (axial) and the quadriceps femoris (appendicular).

10.5 Four Groups of Axial Muscles and Their Functions

Axial muscles are categorized into four main groups, each with specific functions.

• Muscles of the Head and Neck: Facilitate facial expression, mastication, and movement of the head.

• Muscles of the Vertebral Column: Maintain posture and allow movement of the spine.

• Muscles of the Thoracic Region: Assist in breathing and support the thoracic cavity.

• Muscles of the Abdominal Region: Support abdominal organs and enable trunk movement.

• Example: The diaphragm (thoracic) is essential for respiration.

10.6-7 Muscles of the Face and Jaw: Origins, Insertions, Actions

Facial and jaw muscles are responsible for expressions and mastication. Each muscle has a specific origin, insertion, and action.

• Origin: The fixed attachment point of the muscle.

• Insertion: The movable attachment point.

• Action: The movement produced when the muscle contracts.

• Example: The masseter originates from the zygomatic arch, inserts on the mandible, and elevates the jaw.

10.10 Trunk Muscles: Origins, Insertions, Actions

Trunk muscles stabilize and move the vertebral column and thorax.

• Example: The rectus abdominis originates from the pubic bone, inserts on the sternum and ribs, and flexes the vertebral column.

10.12 Functions of Upper and Lower Limb Muscles

Muscles of the limbs enable complex movements and provide strength and dexterity.

• Upper Limb Muscles: Allow manipulation, lifting, and fine motor skills.

• Lower Limb Muscles: Support locomotion, balance, and posture.

• Example: The gluteus maximus extends the thigh, while the flexor digitorum profundus flexes the fingers.

10.13 Principal Appendicular Muscles: Origins, Insertions, Actions

Key appendicular muscles are responsible for major movements of the limbs.

• Example: The biceps brachii originates from the scapula, inserts on the radius, and flexes the forearm.

10.14 Pectoral Girdle Muscles: Origins, Insertions, Actions

Pectoral girdle muscles stabilize and move the shoulder.

• Example: The trapezius originates from the occipital bone and vertebrae, inserts on the clavicle and scapula, and elevates, retracts, and rotates the scapula.

10.15 Muscles That Move the Arm: Origins, Insertions, Actions

Arm muscles facilitate movement at the shoulder and elbow joints.

• Example: The deltoid originates from the clavicle and scapula, inserts on the humerus, and abducts the arm.

10.16 Forearm Muscles: Origins, Insertions, Actions

Forearm muscles control wrist, hand, and finger movements.

• Example: The flexor carpi radialis originates from the humerus, inserts on the metacarpals, and flexes the wrist.

10.17 Muscles of the Hand and Fingers: Origins, Insertions, Actions

These muscles enable fine motor skills and dexterity.

• Example: The flexor pollicis longus originates from the radius, inserts on the thumb, and flexes the thumb.

10.19 Muscles That Move the Thigh: Origins, Insertions, Actions

Thigh muscles are essential for walking, running, and maintaining posture.

• Example: The iliopsoas originates from the lumbar vertebrae and ilium, inserts on the femur, and flexes the thigh.

10.20 Muscles That Move the Leg: Origins, Insertions, Actions

Leg muscles control knee movement and stability.

• Example: The quadriceps femoris originates from the femur and pelvis, inserts on the tibia, and extends the leg.

10.21 Muscles That Move the Foot: Origins, Insertions, Actions

Foot muscles are involved in movements such as dorsiflexion, plantarflexion, inversion, and eversion.

• Example: The tibialis anterior originates from the tibia, inserts on the metatarsals, and dorsiflexes the foot.

Additional info: For detailed muscle names, origins, insertions, and actions, refer to the separate Muscle List document as indicated in the syllabus. The above notes provide a structured overview of the main topics and concepts for Chapter 10: The Muscular System.