Anatomy and Physiology Chapter 12: The Muscular System

Chapter 12: The Muscular System

Icebreaker

  • Many daily activities require the use of skeletal muscles.
  • Common questions include:
    • How does a baseball player throw a ball?
    • How does the human body breathe?
  • This chapter explores the arrangement and names of skeletal muscles and investigates their actions.

Interactions of Skeletal Muscles

Section 12.1 Learning Objectives

  • Outline key concepts regarding skeletal muscle interactions, their fascicle arrangements, and their lever systems.

Interactions of Skeletal Muscles in the Body

  • Muscles may have multiple sites of attachments.
  • Tendons are structures that attach muscles to bones.
    • Tendons pull on the periosteum, which causes the bones to move.
  • Definitions:
    • Origin: Point of attachment that does not move during muscle action.
    • Insertion: Point of attachment that moves during muscle action.
    • Prime Mover: The principal muscle involved in a specific action.
    • Example: The biceps brachii acts as the prime mover for elbow flexion.

Synergists and Fixators

  • Synergists: Muscles that assist the prime mover in accomplishing a movement.
    • Example: Brachioradialis and Brachialis during elbow flexion.
  • Fixators: Muscles that stabilize the insertion points during a movement.

Agonists and Antagonists

  • Agonist: Muscle that is primarily responsible for producing an action; also referred to as the prime mover.
  • Antagonist: Muscle that produces the opposite movement of the agonist.
    • Example: The triceps brachii is the antagonist to the biceps brachii.

Patterns of Fascicle Organization

Section 12.1 Patterns of Fascicle Organization

  • Fascicle: A bundled group of muscle fibers, surrounded by perimysium.
  • The arrangement of fascicles influences the force generated and the range of motion of the muscle.

Types of Fascicle Arrangements

  1. Parallel: Fascicles arranged in the same direction as the long axis of the muscle.
  2. Fusiform: A parallel arrangement with a large muscle belly in the center and narrowing ends.
  3. Circular: Fibers wrap around in a circle.
  4. Convergent: Fascicles converge onto a single, narrow insertion point.
  5. Pennate:
    • Unipennate: Fascicles on one side of the tendon.
    • Bipennate: Fascicles on both sides of the tendon.
    • Multipennate: Muscle branches within the muscle to resemble multiple feathers arranged together.

Characteristics of Muscle Bellies

  • Muscle bellies of fusiform muscles enlarge when the muscle contracts, forming an even larger muscle belly.

Definitions and Terms for Muscle Actions

Matching Activity 1

  • Terms and their respective definitions:
    • Origin: Attachment site that does not move.
    • Agonist: Muscle that is primarily responsible for a movement.
    • Synergist: Muscle that assists in accomplishing a movement.
    • Antagonist: Muscle that produces the opposite movement.
    • Insertion: Attachment site that moves.

Knowledge Check Activity 1

  • Principal muscle involved in accomplishing an action is known as the:
    • Answer: C. Prime mover.

Naming Skeletal Muscles

Section 12.2 Learning Objective

  • Explore the origins and terminology used for naming skeletal muscles.

Origins of Skeletal Muscle Names

  • Derived from Greek and Latin root words, based on observable characteristics:
    • Shape
    • Size comparison
    • Orientation of fibers
    • Number of origins
    • Action of muscle
    • Location of attachment
    • Grouping of muscle.

Characteristics Used to Name Muscles (1 of 2)

  • Muscle Shape: Named for resemblance to a specific shape.
  • Muscle Size: Some muscles are named based on their size relative to other muscles in a group.
  • Location: Muscles are often named for the region they occupy.
  • Orientation of Fibers: Used to describe some muscles based on fiber arrangement.

Characteristics Used to Name Muscles (2 of 2)

  • Number of Origins: The quantity of origins aids in differentiating nearby muscles.
  • Action: Some muscles are named for the specific action they achieve.
  • Attachment: The attachment location is often represented in muscle names, with the origin typically listed first.
  • Grouping: Some muscles belong to groups which can influence their naming.

Words Pertaining to Muscle Size (Table 12.1)

  • Common terms include:
    • Maximus: Largest
    • Medius: Medium
    • Minimus: Smallest
    • Brevis: Short
    • Longus: Long
    • Major: Larger
    • Minor: Smaller
    • Longissimus: Longest

Shape-Based Muscle Names

  • Example: Rhomboid muscles resemble a rhombus.
  • Example: Deltoid muscle resembles an upside-down Greek letter delta.

Prefixes Indicating Number (Table 12.2)

  • Greek and Latin prefixes relevant to numbers:
    • Uni = 1
    • Bi/Di = 2
    • Tri = 3
    • Quad = 4
    • Multi = many.

Anatomy of a Muscle Name

  • Example 1: Biceps brachii; "Bi" means two, "ceps" derived from Latin for "head," and "brachii" indicates the location.
  • Example 2: Flexor carpi ulnaris; "Flexor" indicates the action (flexes the wrist), "carpi" means wrist, and "ulnaris" refers to its location along the ulna.

Muscle Actions (Figure 12.6)

  • Muscle actions vary based on location:
    • Lateral side of a joint: Abduction of limbs, lateral flexion of trunk or neck.
    • Medial side of a joint: Adduction.
    • Anterior portion of a joint: Flexion.
    • Posterior portion of a joint: Extension.

Muscles of the Human Body

  • Muscles of Facial Expression originate on skull bones and insert on skin.
  • Examples include:
    • Orbicularis oculi: Closes eyes.
    • Zygomaticus major/minor: Involved in smiling.

Muscles That Move the Eyes

  • Origins on the outside of the eye, inserting onto the outer eye surface include:
    • Superior and inferior obliques and rectus muscles (lateral, medial, inferior, superior).

Muscles That Move the Lower Jaw

  • Enable mastication (chewing) include:
    • Masseter, Temporalis, Pterygoid muscles.

Muscles That Move the Tongue

  • Aid in speech and swallowing; categorized into:
    • Extrinsic muscles: Originating outside the tongue (e.g., genioglossus).
    • Intrinsic muscles: Originating within the tongue.

Muscles of the Anterior Neck

  • Assist in swallowing and speech, including:
    • Suprahyoid muscles: Above hyoid bone (e.g., digastric).
    • Infrahyoid muscles: Below hyoid bone (e.g., sternohyoid).

Muscles That Move the Head

  • Neck muscles that balance, move, and rotate the head:
    • Sternocleidomastoid: Involved in lateral flexion and rotation of the head.
    • Scalenes: Synergists of sternocleidomastoid.

Muscles of the Posterior Neck and Back

  • Allow for lateral flexion, extension, and rotation of the head:
    • Splenius capitis, splenius cervicis.
  • Extension of the vertebral column:
    • Erector spinae group: (Iliocostalis, longissimus, spinalis).

Muscles of the Abdomen

  • Anterior Muscles:
    • External oblique, Internal oblique, Transversus abdominis, Rectus abdominis: Enclosed by rectus sheaths (linea alba).
  • Posterior Muscles: Help form the posterior wall of the abdomen and maintain posture:
    • Psoas major, Iliacus, Quadratus lumborum.

Muscles of the Thorax

  • Diaphragm: Divides abdominal and thoracic cavities; major muscle for breathing.
  • Intercostal muscles located between ribs assist with breathing.

Muscles of the Pelvic Floor

  • Pelvic diaphragm: Forms the base of the pelvic cavity, including:
    • Levator ani (comprising pubococcygeus and iliococcygeus).

Muscles of the Perineum

  • Perineum: Region between pubic symphysis and coccyx, consists of:
    • Urogenital triangle (anterior, includes external genitalia).
    • Anal triangle (posterior, includes anus).

Breakout Group Activities

Activity 1

  • List common facial expressions like smiling or closing eyes; identify responsible muscles:
    • Smiling: Zygomaticus major.
    • Closing eyes: Orbicularis oculi.
    • Pursing lips: Orbicularis oris.
    • Raising eyebrows: Frontalis.

Activity 2

  • Research the names of human muscles; determine origins of names based on shapes, actions, or locations.

Major Muscular Functions Based on Groups

  • Advantages of grouping appendicular muscles:
    • Increases strength and organization; allows muscles with similar functions to work together.
  • Disadvantages:
    • Injury to one muscle in a compartment may affect all muscles in that compartment, leading to potential loss of function.

Knowledge Check Activity 2

  • The muscles located between the ribs are the:
    • Intercostal muscles (Answer: C).

Values of Lifting Techniques

  • The reason given for lifting heavy objects with the legs is:
    • It utilizes the largest, strongest muscles of the body, located in the thigh.

Appendix

Remember to Review:

  • Definitions of muscle points of attachment, naming of skeletal muscles, location, origin, insertion, and action of significant skeletal muscles to solidify knowledge by the end of the chapter.