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Sternocleidomastoid Muscle

• Insertion and Origin

  • Insertion: Mastoid process
  • Origin: Manubrium of the sternum and medial part of the clavicle

• Action

  • When the sternocleidomastoid muscle pulls on the mastoid process, it causes head flexion.
  • It can also assist with forced inhalation by causing elevation of the chest.
  • Used during neck breathing, especially in exercise and respiratory distress situations.

• Clinical Significance

  • Extensive neck breathing can indicate respiratory distress or muscular fatigue and could require intubation.
  • Muscle fatigue can lead to difficulties in breathing.

• Innervation

  • Innervated by the accessory nerve (CN XI) and contributions from cervical nerves C2 and C3.
  • Dysfunction can result in difficulties turning the head or neck.

Serratus Anterior Muscle

• Origin and Insertion

  • Origin: Ribs 1 through 8
  • Insertion: Vertebral border of the scapula

• Function

  • Known as the boxer's muscle because it protracts the scapula and allows for shoulder movement.
  • Important for holding the scapula against the chest wall.

• Clinical Note

  • Injury to the long thoracic nerve can cause a winged scapula.

• Actions

  • Protracts the shoulder/scapula, holds the scapula to the chest wall.

Trapezius Muscle

• Origin and Insertion

  • Origin: Occipital bone, ligamentum nuchae, C7 to T12 vertebrae
  • Insertion: Spine of the scapula, acromion process, acromial end of the clavicle

• Actions

  • Retracts, raises, and rotates the scapula.
  • Engaged in movements such as shoulder shrugs.

• Innervation

  • Innervated by the accessory nerve (CN XI).

Rhomboid Major and Minor Muscles

• Location
  • Minor is located on top of the major muscle.
• Function
  • Elevate and retract scapula.
  • Common source of muscle tension and knots due to protracted posture.

Erector Spinae Muscles

• Function
  • Primary muscle group responsible for extending the back.

Diaphragm

• Function
  • Major muscle for inhalation.
• Innervation
  • Innervated by the phrenic nerve, originating from cervical segments C3, C4, and C5.
  • Mnemonic: "C3, C4, C5 keeps your diaphragm alive."

Intercostal Muscles

• External Intercostals
  • Function: Inhalation.
• Internal Intercostals
  • Function: Exhalation.

Pelvic Floor and Levator Ani

• Function
  • Responsible for pelvic support.
• Kegel Exercises
  • Important for maintaining pelvic floor strength especially after childbirth.
  • Mnemonic: "S2, S3, S4 keeps your pelvis off the floor."

Abdominal Muscles

• Transverse Abdominis
  • Action: Compresses the abdomen.
  • Fiber direction: Transverse (horizontal).
• Rectus Abdominis
  • Action: Flexes the trunk.
  • Fiber direction: Vertical.
• Oblique Muscles
  • Actions:
    • Flex the trunk
    • Rotate the trunk
    • Laterally flex the trunk
  • External obliques flex toward the pockets, whereas internal obliques work oppositely.

Arm Muscles

• Biceps Brachii

  • Heads: Short head (coracoid process), Long head (supraglenoid tubercle).
  • Insertion: Radial tuberosity.
  • Actions: Flexes the arm and elbow, supinates the forearm.
  • Innervation: Musculocutaneous nerve.

• Brachialis

  • Origin: Front distal half of the humerus.
  • Insertion: Coronoid process of the ulna.
  • Action: Flexes the elbow only.
  • Innervation: Both musculocutaneous and radial nerves.

• Brachioradialis

  • Origin: Lateral supracondylar ridge of the humerus.
  • Insertion: Styloid process of the radius.
  • Action: Flexes the elbow; does not cross the shoulder or wrist.
  • Innervation: Radial nerve.

• Triceps Brachii

  • Heads: Long head (infraglenoid tubercle), Lateral head (posterior humerus), Medial head (posterior distal humerus).
  • Insertion: Olecranon of the ulna.
  • Actions: Extension of the arm and elbow.
  • Innervation: Radial nerve.

Patterns in Muscle Function and Innervation

• Extensors tend to be innervated by the radial nerve.
• Flexors typically are innervated by the median and ulnar nerves depending on their location.

General Muscle Action Mnemonics

• FAM: Flex, Add (towards midline), Medial rotation (e.g., hugging muscle: Pectoralis Major).
• Understand the implication of muscle function in terms of posture and injuries (e.g., protraction leading to knots in rhomboids).