Human Anatomy and Physiology Chapter 10: The Muscular System

Introduction to the Muscular System

  • Chapter Overview   - Learn how skeletal muscle moves bones at joints   - Key questions to address:
        - 10.1 How do skeletal muscles act and interact?
        - 10.2 How are skeletal muscles named?
        - 10.3 Fascicle arrangements
        - 10.4 Lever systems
        - 10.5 The origin, insertion, and actions of important skeletal muscles

Muscle Attachments

  • Every muscle is attached to bone or other connective tissue at 2 points:   1. Origin
         - Definition: The stationary, less movable attachment of the muscle.   2. Insertion
         - Definition: The movable attachment point.
         - Insertion moves towards the origin when the muscle contracts.   

  • Summary: The origin is the least movable end, while the insertion is the more movable end.

Organization Patterns of Skeletal Muscle Fibers

  • Fascicles: Bundles of muscle fibers lying parallel to each other.   - Result in muscles having different shapes and functional capabilities.   - Determine the range of motion and power of muscle contraction.

Interactions of Skeletal Muscles

  • General Principle
      - Skeletal muscles work together or in opposition.
      - Muscles only pull (never push).   - As muscles shorten, the insertion generally moves toward the origin.
      - For every muscle action, there is usually a muscle (or group of muscles) that opposes this action.

Muscle Actions

  • Agonist (or Prime mover): The muscle primarily responsible for producing a specific movement.

  • Antagonist: A muscle that opposes or reverses a particular movement.

  • Synergist: A muscle that assists the agonist by adding force to a movement and reducing unnecessary movement.

  • Fixators: A type of synergist that immobilizes a bone or muscle origin to allow the agonist to work more efficiently.

General Classification of Muscles

  • Classification of muscles based on seven criteria:   1. Direction of Muscle Fibers
         - Rectus: Straight      - Transverse: Right angle      - Oblique: Angled      - Orbicularis: Circular

  2. Relative Size of Muscles      - Maximus: Largest      - Minimus: Smallest      - Major: Larger of two muscles      - Minor: Smaller of two muscles      - Medius: Medium

  3. Specific Body Region
     - Oris: Mouth      - Cervicis: Neck      - Brachial: Arm      - Carpi: Wrist      - Pollicis: Thumb      - Gluteal: Buttocks      - Femoris: Thigh      - Hallucis: Great toe      - Anterior: Toward front of body      - Posterior: Toward back of body      - Inferior: Closer to feet      - Superficialis: Superficial      - Profundus: Deep

  4. Muscle Heads/Tendons of Origin      - Biceps: Two heads      - Triceps: Three heads      - Quadriceps: Four heads      - Example: Sternocleidomastoid (Origin: sternum and clavicle, Insertion: mastoid process of temporal bone)

  5. Muscle Attachments      - Example: Cleido (sternum and clavicle), Intercostal (between ribs)

  6. Shape of Muscle      - Deltoid: Triangular      - Quadratus: Rectangular      - Trapezius: Trapezoid      - Longus: Long      - Brevis: Short

  7. Muscle Action      - Adductor: Adducts body part      - Abductor: Abducts body part      - Flexor: Flexes a joint      - Extensor: Extends a joint

Muscle Naming and Examples

  • Each muscle name generally reflects its characteristics, including action, location, size, shape, and number of origins.

  • Examples of specific muscles:   - Adductor magnus: Adductor   - Abductor pollicis longus: Abductor   - Flexor carpi radialis: Flexor   - Extensor hallucis longus: Extensor   - Sternocleidomastoid: Points to its attachments at the sternum and clavicle.

Major Skeletal Muscles

  • Anterior View
      - Trapezius
      - Deltoid
      - Pectoralis major
      - Triceps brachii
      - Biceps brachii
      - Brachialis   - External oblique
      - Rectus abdominis

  • Posterior View
      - Latissimus dorsi
      - Gluteus maximus
      - Hamstrings: Biceps femoris, Semitendinosus, Semimembranosus
      - Gastrocnemius: Responsible for plantar flexion of foot.

Muscles of Head and Neck

  • Frontalis: Elevates eyebrow

  • Occipitalis: Pulls scalp back

  • Orbicularis oculi: Closes eyelids

  • Levator palpebrae superioris: Opens eyelids

  • Orbicularis oris: Pulls lips together

  • Zygomaticus: Raises corner of mouth   - Origin: Zygomatic bone   - Insertion: Skin/muscles at corner of mouth

Muscles of the Thorax/Abdominal Wall

  • Pectoralis major: Flexion, adduction, rotation of humerus

  • Serratus anterior: Draws scapula forward

  • External intercostals: Enlarge the ribcage (inhalation)

  • Internal intercostals: Depress ribcage (exhalation)

  • Rectus abdominis: Abdominal compression; flexion of vertebral column

Muscles of the Upper Extremity

  • Deltoid: Abduction/flexion of the arm

  • Biceps brachii: Flexion of forearm; supination of hand

  • Triceps brachii: Extension of forearm

  • Brachialis: Flexion of forearm

Muscles of Lower Extremity

  • Gluteus maximus: Extension/lateral rotation of femur

  • Biceps femoris: Extension of femur/flexion of knee

  • Rectus femoris: Flexion of femur/extensions of knee

  • Tibialis anterior: Dorsiflexion; inversion of the foot

End of Chapter Summary

  • Review Chapter Summary at the end of the chapter.

  • Review Chapter Outline.

  • Anticipate questions similar to lab experiences over muscles.