Lecture Notes: Muscle Labeling and Physiology

Announcements

• New muscle labeling packet available with muscle pictures included.
• The chapter involves intense study of physiology and muscle models.

Muscle Structure Basics

• Belly of the Muscle: Fleshy part allowing contraction (shortening with force).
  • Contains muscle cells, myofibrils, sarcomeres.
• Tendons: Attach muscle to bones, focusing on origins and insertions.
  • Origin: Stationary bone attachment.
  • Insertion: Movable bone attachment.

Example: Elbow Flexion

• Flexion and Extension: Biceps allow flexion, triceps allow extension.
• Biceps: Originate on scapula, insertion on radius.
• Triceps: Originate on scapula, insertion on ulna.

Muscle Naming

• Muscle names indicate characteristics such as shape, action, location, and number of origins.
• Examples:
  • Biceps brachii: Two origins.
  • Triceps brachii: Three origins.
  • Quadriceps: Four parts.

Lever Systems in Muscles

• Lever systems describe muscle-bone cooperation to produce movement.
• Components: Effort (muscle), Fulcrum (joint), Load (resistance).
• Types of Lever Systems:
  1. First-Class: Fulcrum between effort and load (e.g., neck joint for nodding).
  2. Second-Class: Load between effort and fulcrum (e.g., standing on tiptoes).
  3. Third-Class: Effort between fulcrum and load (e.g., elbow flexion when lifting).

Muscle Cell Model

• Sarcolemma: Muscle cell membrane.
• Endomysium: Connective tissue cover, forms tendons.
• Myofibrils: Contain contractile units.
• Sarcoplasmic Reticulum (SR): Stores calcium, releases it upon excitation.
• Transverse Tubules (T Tubules): Conduct electrical signals.

Neuromuscular Junction

• Components: End bulbs, synaptic cleft, sarcolemma.
• Neuron: Sends electrical signals to muscle cells.

Sarcomere Model

• Enlarged view showing myofibrils.
• Terminal Cisterns: Part of the SR.
• Actin and Myosin: Important for contraction (not tested on model recognition).

Non-Muscular Structures

• Epicranial Aponeurosis: Covers the skull.
• Thoracolumbar Fascia: Covers lower back.
• Retinaculum: Bands at wrist (extensor and flexor).
• Iliotibial Tract (IT Band): Runs from ilium to tibia.

Facial and Neck Muscles

• Facial Muscles: Orbicularis oculi (eye), orbicularis oris (mouth), buccinator (cheek), etc.
• Neck Muscles: Sternocleidomastoid, omohyoid, sternohyoid.

Thoracic and Abdominal Muscles

• Pectorals: Major and minor.
• Serratus Anterior: Serrated edges.
• Rectus Abdominis: Up and down fibers, "six-pack".
• Intercostals: External and internal, essential for breathing.

Hip and Leg Muscles

• Gluteus Maximus: Main butt muscle.
• Hamstrings: Biceps femoris (lateral), semitendinosus, semimembranosus (medial).
• Quadriceps: Rectus femoris, vastus lateralis, vastus medialis.
• Adductors and Gracilis: Medial thigh muscles.

Arm and Back Muscles (To be recorded separately)

• Back Muscles: Trapezius, latissimus dorsi, infraspinatus, teres minor/major.

Note: Arm muscles not covered yet, will be recorded separately. Review models and textbook pages for visualization and memorization.