Lecture Notes: Muscles of the Head, Neck, and Trunk

Introduction

• Facial expressions are unique to humans, not common in the animal kingdom.
  • Example: Turtles and dolphins do not display emotions through facial expressions.
  • Clinical correlation: Strokes or ischemic events can impair facial muscles, affecting non-verbal communication.

Importance of Facial Muscles

• Facial muscles are crucial for non-verbal communication.
  • Unique to humans compared to other animals.
• Common frustrations for patients with impaired facial muscles include feeling misunderstood.

Lab Overview

• Focus on muscles of the head, neck, and trunk.
• Four categories for grouping muscles.

Muscles of the Neck

• Landmarks: Thyroid and hyoid (floating bone in the axial skeleton).
• Naming: Often based on structures they connect, except for levator scapulae (named for action) and digastric (two bellies).
• Key Muscles:
  • Levator scapulae: Elevates scapula.
  • Sternocleidomastoid (SCM): Connects sternum, clavicle, and mastoid process and turns the head.
  • Scalenes (middle, anterior, posterior): Stabilize the neck.
  • Platysma: Visible when making a disgusted face.
  • Sternohyoid, Omohyoid, Mylohyoid, Digastric, Stylohyoid: Various connections between neck structures.

Muscles of the Face

• Key Muscles:
  • Orbicularis oculi: Circular muscle around the eye.
  • Levator labii: Elevates the lip.
  • Zygomaticus minor and major: Associated with zygomatic arches.
  • Risorius: Helps in laughing.
  • Occipitofrontalis: Extends from back to front of cranium.
  • Buccinator: Muscle of the cheek.
  • Depressor labii: Lowers the lips.
• Clinical Note: Strokes can impair facial muscles, affecting non-verbal communication and speech.

Muscles of Chewing

• Key Muscles:
  • Masseter: Powers canines.
  • Temporalis: Powers molars.
  • Pterygoids (medial and lateral): Associated with grinding motion of molars.
• Nerve Innervation:
  • Facial and trigeminal nerves responsible for facial and chewing muscles.

Muscles of the Trunk

• Anterior Muscles:
  • Rectus abdominus: "Six-pack" muscles.
  • Obliques (external and internal): Assist in lateral rotation of the trunk.
  • Transverse abdominus: Deep core muscle.
  • Serratus anterior: Known as the punching muscle.
• Breathing Muscles:
  • Diaphragm: Moves downward during contraction for inhalation.
  • Intercostals: Assist in inhalation and exhalation.
• Posterior Muscles:
  • Rhomboid minor and major: Retract scapula.
  • Spinal erector muscles: Spinalis, longissimus thoracis, iliocostalis.
  • Splenius muscles: Capitus and cervicus help turn the head.
  • Spinal erectors facilitate upright posture.

Conclusion

• High-yield concepts for the lab include facial muscles, breathing, and skeletal structures like the hyoid and thyroid.
• Resources: Labs 15 and 16 in the lab manual.
• Importance of reviewing muscular and skeletal systems for lab tests.