Muscle Identification and Anatomy

Observations under Microscope

• Intercalated Discs:

  • Important for identifying cardiac muscle.

  • Dark lines that separate individual muscle cells.

• Striations:

  • Visible light and dark stripes in cardiac or skeletal muscle tissue.

  • In cardiac muscle: nuclei are spaced out, not clustered, contrasting with skeletal muscle where nuclei are numerous and centrally located.

• Cardiac Muscle Characteristics:

  • Clear cell perimeters with visible striations.

  • Cells often branch, indicating their nature.

  • Intercalated discs identified by dark lines between cells.

Identification of Muscle Types

• Skeletal Muscle:

  • Must be able to recognize the striations and multiple nuclei (multinucleated cells).

  • Tendons connect to skeletal muscles but not to cardiac or smooth muscles.

  • Striations are more difficult to see under a high magnification, suggesting caution when identifying them on slides.

• Smooth Muscle:

  • Cells are fusiform (spindle-shaped) with a single nucleus.

  • No visible striations.

  • Check edged structures to identify tissue shape.

Muscle Naming Conventions

• By Number of Heads/Tendons:

  • Biceps: 2 tendons/heads (e.g., biceps brachii).

  • Triceps: 3 tendons/heads (e.g., triceps brachii).

  • Quadriceps: 4 tendons/heads (e.g., quadriceps femoris) consists of:

  • Rectus Femoris: central part of quadriceps.

  • Vastus Lateralis: lateral section.

  • Vastus Medialis: medial section.

  • Vastus Intermedius: between medial and lateral sections.

Muscle Size Categories

• Major vs. Minor:

  • Major: Larger muscle (e.g., pectoralis major).

  • Minor: Smaller muscle (e.g., pectoralis minor).

• Maximus, Medius, Minimus:

  • Gluteus Maximus: Largest muscle.

  • Gluteus Medius: Moderate size.

  • Gluteus Minimus: Smallest muscle.

Muscle Shape Categories

• Deltoid: Shaped like a triangle.

• Longus and Brevis for Tendons:

  • Refers to tendon length, not muscle length.

  • Example: Abductor pollicis brevis (short tendon) vs. longus (long tendon).

• Muscle Functions:

  • Anterior muscles: Flexors

  • Posterior: Extensors

  • Abduction: Movement away from the body's midline (e.g., abductor pollicis abducts the thumb).

Important Takeaways

1. Identifying Muscle Types: Use molecular characteristics (nuclei, striations) when observing slides.

2. Understanding Naming Conventions: Clarifies muscle structure and attachment.

3. Interpreting Visual Structures: Recognizing shapes and striation patterns is key in muscle identification.