BIOL_250_Chapter_11_-_The_Muscular_System_-_Anatomy_and_Physiology_2e_-_WEB_c9nD9QL

INTRODUCTION TO THE MUSCULAR SYSTEM

Chapter Objectives

• Describe the roles of agonists and antagonists in muscle action.

• Explain muscle fascicle structure and organization in force generation.

• Identify skeletal muscles and their actions on the skeleton.

• Understand muscle origins, insertions, and primary movements.

Skeletal Muscle Functions

• Muscles are essential for a wide range of daily activities including talking, walking, sitting, standing, running, and more. They play a crucial role in bodily movements, posture maintenance, and even breathing.

• Skeletal muscles remain active even during sleep; for example, the diaphragm operates to facilitate the breathing process continuously.

Focus of the Chapter

• This chapter emphasizes the intricacies of skeletal muscle organization, including the naming conventions that are essential for understanding their functions and locations.

• Understanding muscle names enhances memory retention regarding their anatomical placements and roles within the body.

• A thorough examination is provided on how muscles are arranged to facilitate movement, assist in opposing actions, and their anatomical relevance, analyzed regionally from head to toe.

INTERACTIONS OF SKELETAL MUSCLES

Learning Objectives

• Compare and contrast agonist and antagonist muscles.

• Describe fascicle arrangement in skeletal muscle and its implications for strength and function.

• Explain muscle contraction events generating force, including the biochemical processes involved.

Muscle Action Mechanics

Tension and Movement

• Muscle contraction generates tension that is transferred to tendons, which secure muscles to bones and facilitate articulation at joints.

• Understanding the significance of muscle insertion (the moveable end) and origin (the fixed end) is key in enabling effective joint movement.

Agonists and Synergists

• Prime movers (agonists): These are the principal muscles responsible for a particular movement; for example, the biceps brachii are the primary muscles involved in lifting a cup.

• Synergists: These muscles assist the prime movers to perform smoother and more coordinated movements; for example, the brachialis acts to augment the efforts of the biceps during elbow flexion.

• Fixators: These stabilizer muscles help maintain a fixed position at the joint to provide a stable base for the prime movers.

Roles of Antagonists

• Antagonists oppose prime movers during their action, which is critical for controlled movements; for example, the quadriceps and hamstrings work together during knee flexion and extension, respectively.

• This opposition helps maintain body position and aids in the control of rapid movements, preventing injuries.

Examples of Agonist and Antagonist Pairs

• Biceps brachii (agonist) vs Triceps brachii (antagonist): These muscles control the actions of elbow flexion and extension.

• Hamstrings (agonist) vs Quadriceps femoris (antagonist): They play pivotal roles in knee movement and stability.

FASCICLE ORGANIZATION AND MUSCLE TYPES

Fascicle Arrangement

• The structure of fascicles is comprised of several layers including Endomysium (which encases individual muscle fibers), Perimysium (which bundles fibers into fascicles), and Epimysium (which surrounds the entire muscle).

• Types of muscle fascicle arrangements include:

  • Parallel: Fascicles run parallel to the long axis; they provide a greater range of motion but less force (e.g., biceps brachii).

  • Circular (Sphincters): Fascicles are arranged in concentric circles; these muscles control the opening and closing of passages (e.g., orbicularis oris).

  • Convergent: Broad fascicles converge at a single attachment and can direct pull from different angles (e.g., pectoralis major).

  • Pennate: Fascicles are angled relative to a tendon, providing greater force but lesser range of motion (e.g., deltoid).

  • Fusiform: Muscles have a spindle-shaped belly that allows for both force and range of motion (e.g., biceps brachii).

Exercise Guidelines

• Emphasizes the importance of warming up and stretching to prevent injuries associated with muscle strain and joint damage.

• Regular exercise enhances blood flow to skeletal muscles which reduces stiffness in joints and enhances overall flexibility, strength, and endurance.

LEVER SYSTEMS IN MUSCLE AND BONE

Muscle Operations

• Muscles work in conjunction with the skeletal system to produce movement effectively.

• Lever System Analogy: A biological lever consists of:

  • Effort: The force exerted by muscle contraction to move a load (bone).

  • Load: The resistance faced, such as an object being lifted or the body's own weight.

  • Fulcrum: The joint around which movement occurs, serving as the pivot point.

• A simple example is the use of a hammer. When swinging a hammer, the muscles contract (effort) against resistance (load) to drive a nail into wood.

NAMING SKELETAL MUSCLES

Criteria for Muscle Naming

• Understanding the etymology of muscle names is pivotal for effective learning and retention of muscle names.

• These criteria include:

  • Shape: e.g., deltoid (triangular), rhomboid (diamond-shaped).

  • Size: e.g., maximus (largest), minimus (smallest).

  • Location: e.g., pectoralis (chest area).

  • Number of Origins: e.g., biceps (two origins), triceps (three origins).

  • Action: e.g., flexor (muscle that helps bend a joint).

Examples:

• Masseter: The principal muscle responsible for chewing; its contraction raises the mandible.

• Gluteus Maximus, Medius, Minimus: Named based on size and location within the gluteal region.

Etymological Connections

• Muscle names stem from Latin and Greek origins that enhance understanding:

  • ad: toward (as in ADvance)

  • ab: away from

  • longus: long

  • maximus: largest

Application of Muscle Names

• Familiarity with muscle roles can be derived from their names (e.g., flexors are involved in flexing movements while extensors help extend limbs).

• Specific naming conventions allow for instant recognition of a muscle's function and its anatomical relationships with surrounding structures (e.g., sternocleidomastoid, which helps in rotating and flexing the head).

AXIAL MUSCLES OF HEAD, NECK, AND BACK

Grouping and Functions

• Axial Muscles: These are categorized based on their functions and roles in stabilizing the trunk and head, vital for balance and postural control.

• Facial Muscles: These muscles insert into the skin and are responsible for facial expressions, such as smiling or frowning (e.g., orbicularis oris).

• Neck and Back Muscles: These muscles stabilize the head and facilitate the movement of the vertebral column, crucial for everyday activities such as nodding or turning.

Muscle Examples:

• Sternocleidomastoid: Noted for its role in flexing and rotating the head.

• Erector Spinae: Plays a significant role in extending and stabilizing the spine, allowing for an upright posture.

ABDOMINAL WALL AND THORAX

Abdominal Muscle Groups

• Major muscles include the external obliques, internal obliques, transversus abdominis, and rectus abdominis.

• These muscles collectively support abdominal organs, assist with movement, and maintain posture, offering protection to internal structures.

• Thoracic Muscles: These include muscles crucial for breathing; the diaphragm is the primary muscle responsible for ventilating the lungs.

Diaphragm Function

• It actively regulates thoracic cavity volume, allowing for effective inhalation and exhalation.

• Associated muscles like the external and internal intercostals support deep inhalation and exhalation, aiding the respiratory process.

PECTORAL GIRDLE AND UPPER LIMBS

Muscle Groupings

• Pectoral Girdle Muscles: These muscles play essential roles in stabilizing and positioning the scapula, ensuring correct shoulder function and mobility.

• Muscles that Move the Arm: Muscles originating on the scapula or axial skeleton are engaged in the action of the arm (e.g., latissimus dorsi for arms lowering and raising).

Action of Arm Muscles

• Muscle actions include flexion and extension:

  • Major muscles like the biceps brachii are responsible for flexion while the triceps brachii are engaged during extension.

  • Supinators assist in actions involving turning the palm upward, showcasing the collaborative work of different muscle groups.

MUSCLES OF THE LOWER BODY

Thigh Muscles

• Muscle groups include gluteal region muscles, as well as muscles within the anterior, posterior, and medial compartments of the thigh.

• Functions of these muscles vary significantly and include flexion, extension, and stabilization of the lower limbs.

Leg Muscles for Movement

• Anterior Compartment: Responsible for dorsiflexing the foot (e.g., tibialis anterior).

• Posterior Compartment: Plays a key role in plantarflexing the foot (e.g., gastrocnemius).

• Intrinsic Foot Muscles: Crucial for supporting the arch of the foot and facilitating toe movements, enabling balance and mobility during walking and running.