Lab Practical 2 Study Notes: Bones, Joints, and Muscles (Chapters 6–10)

Bones and Skeletal Tissue

Microscopic Anatomy & Bone Growth

The growth and development of bones involve specialized structures and cellular processes, particularly at the epiphyseal plate, which is crucial for longitudinal bone growth during childhood and adolescence.

• Epiphyseal Plate: Also known as the growth plate, this is a layer of hyaline cartilage found between the epiphysis (end) and diaphysis (shaft) of long bones. It is responsible for the lengthwise growth of bones.

• Zones of the Epiphyseal Plate:

  • Resting (Quiescent) Zone: Closest to the epiphysis; contains small, inactive chondrocytes.

  • Proliferation Zone: Chondrocytes undergo rapid mitosis, stacking in columns and pushing the epiphysis away from the diaphysis.

  • Hypertrophic Zone: Chondrocytes enlarge (hypertrophy), and their lacunae (spaces) expand.

  • Calcification Zone: Matrix becomes calcified; chondrocytes die, leaving behind cavities.

  • Ossification (Osteogenic) Zone: Osteoblasts invade the area, depositing bone matrix and forming new bone tissue.

• Chondrocytes: These are cartilage cells found within the epiphyseal plate. They appear as rounded or oval cells within lacunae and are essential for cartilage growth and subsequent bone elongation.

• Role in Bone Growth: Chondrocytes proliferate, enlarge, and eventually die, allowing osteoblasts to replace cartilage with bone tissue, thus enabling bone lengthening.

The Skeleton

Bone Identification & Landmarks

The human skeleton consists of 206 bones, each with unique features and landmarks that serve as points of attachment, passageways for nerves and blood vessels, or articulation sites.

• Bone Names: Students should be able to identify all major bones, such as the femur, humerus, skull bones, vertebrae, etc.

• Landmark Features: Each bone has characteristic landmarks. Examples include:

  • Foramen Magnum (occipital bone): Large opening for the spinal cord.

  • Olecranon Process (ulna): Prominent elbow projection.

  • Greater Trochanter (femur): Large lateral projection for muscle attachment.

Joints (Articulations)

General Joint Concepts

Joints are connections between bones that allow for movement and flexibility. They are classified by structure and function.

• Bursae: Small, fluid-filled sacs lined by synovial membrane. They reduce friction between moving structures, such as tendons and bones.

• Location: Commonly found in areas of high friction, such as the shoulder, elbow, and knee.

• Bursitis: Inflammation of a bursa, often due to repetitive movement or trauma. The shoulder is particularly susceptible due to its wide range of motion.

Specific Joints: Identification & Key Structures

• Temporomandibular Joint (TMJ):

  • Location: Between the temporal bone of the skull and the mandible (jawbone).

  • Articulating Bones: Mandibular condyle and mandibular fossa of the temporal bone.

• Knee Joint (Tibiofemoral Joint):

  • Key Structures:

    • Patella (kneecap)

    • Medial meniscus (cartilage pad)

    • Fibular collateral ligament (LCL)

    • Tibial collateral ligament (MCL)

    • Posterior cruciate ligament (PCL)

    • Anterior cruciate ligament (ACL)

    • Quadriceps femoris tendon

• Shoulder Joint (Glenohumeral Joint):

  • Key Structures:

    • Clavicle

    • Scapula

    • Humerus

    • Glenoid fossa (of scapula)

    • Glenohumeral ligament

    • Acromioclavicular ligament

    • Subscapularis tendon (rotator cuff)

• Hip Joint (Coxal Joint):

  • Key Structures:

    • Acetabulum (of coxal bone)

    • Head of the femur

    • Ischiofemoral ligament

    • Pubofemoral ligament

    • Pubis & Pubic Ramus (parts of coxal bone)

    • Ilium (part of coxal bone)

    • Ischium (part of coxal bone)

Muscle and Muscle Tissue

Microscopic Anatomy & Connective Tissue Coverings

Muscle tissue is organized into bundles and covered by layers of connective tissue, each with a specific function.

• Endomysium: Surrounds each individual muscle fiber (cell).

• Perimysium: Surrounds a fascicle, which is a bundle of muscle fibers.

• Epimysium: Surrounds the entire muscle, which is composed of multiple fascicles.

• Fascicle: A bundle of muscle fibers visible in cross-section as a group of cells surrounded by perimysium.

Muscle Contraction & Myograms

Myograms are graphical representations of muscle contractions, showing the response of a muscle to stimulation over time.

• Myogram: A plot of muscle tension (force) versus time.

• Phases of a Muscle Twitch (on a myogram):

  • Stimulus: The point at which the muscle is stimulated.

  • Latent Period: Short delay after stimulus before contraction begins; corresponds to excitation-contraction coupling.

  • Contraction Phase: Muscle tension increases as cross-bridges form.

  • Relaxation Phase: Muscle tension decreases as calcium ions are reabsorbed and cross-bridges detach.

  • Repolarization: Restoration of the resting membrane potential after contraction.

  • Refractory Period: Time during which the muscle cannot respond to a new stimulus.

  • Resting State: Baseline muscle tension before and after contraction.

Cardiac Muscle

Cardiac muscle is found only in the heart and has unique structural features that distinguish it from skeletal and smooth muscle.

• Microscopic Appearance: Striated like skeletal muscle but with shorter, branched fibers.

• Distinguishing Feature: Presence of intercalated discs, which are specialized cell junctions that allow rapid electrical communication between cells.

• Comparison: Skeletal muscle fibers are long, cylindrical, and multinucleated; smooth muscle fibers are spindle-shaped and lack striations.

Sarcomere Structure

The sarcomere is the fundamental contractile unit of striated muscle, responsible for muscle contraction.

• Sarcomere: The segment between two Z discs in a myofibril.

• Thick Filaments: Composed primarily of the protein myosin.

• Thin Filaments: Composed mainly of actin, along with troponin and tropomyosin.

The Muscular System

Human Muscle Identification & Actions

Understanding the location, origin, and insertion of major muscles is essential for identifying their actions and functions.

• Head & Neck Muscles:

  • Frontalis: Raises eyebrows; origin: epicranial aponeurosis, insertion: skin of forehead.

  • Platysma: Tenses skin of neck; origin: fascia of chest, insertion: lower mandible.

  • Orbicularis oris: Closes and protrudes lips; origin: maxilla and mandible, insertion: skin around lips.

  • Orbicularis oculi: Closes eyelids; origin: frontal and maxillary bones, insertion: eyelid tissue.

  • Masseter: Elevates mandible (chewing); origin: zygomatic arch, insertion: mandible.

• Torso Muscles:

  • Intercostal Muscles: Muscles between the ribs; include external (elevate ribs) and internal (depress ribs) intercostals.

  • Rectus abdominis: Flexes vertebral column; origin: pubic crest, insertion: xiphoid process and costal cartilages.

  • Pectoralis major: Adducts and flexes humerus; origin: clavicle/sternum, insertion: humerus.

  • External oblique: Compresses abdomen; origin: lower ribs, insertion: iliac crest.

  • Sternocleidomastoid: Rotates and flexes neck; origin: sternum/clavicle, insertion: mastoid process.

  • Latissimus dorsi: Extends and adducts arm; origin: lower spine/iliac crest, insertion: humerus.

• Upper Limb Muscles:

  • Deltoid: Abducts arm; origin: clavicle/scapula, insertion: humerus.

  • Biceps brachii: Flexes elbow; origin: scapula, insertion: radius.

  • Triceps brachii: Extends elbow; origin: scapula/humerus, insertion: ulna.

  • Palmaris longus: Flexes wrist; origin: humerus, insertion: palmar aponeurosis.

  • Brachioradialis: Flexes forearm; origin: humerus, insertion: radius.

• Lower Limb Muscles:

  • Gastrocnemius: Plantar flexes foot; origin: femur, insertion: calcaneus via Achilles tendon.

  • Soleus: Plantar flexes foot; origin: tibia/fibula, insertion: calcaneus.

  • Vastus lateralis: Extends knee; origin: femur, insertion: patella/tibia.

  • Rectus femoris: Extends knee, flexes hip; origin: ilium, insertion: patella/tibia.

  • Biceps femoris: Flexes knee; origin: ischial tuberosity/femur, insertion: fibula/tibia.

  • Sartorius: Flexes, abducts, and laterally rotates thigh; origin: ilium, insertion: tibia.

Table: Connective Tissue Coverings of Muscle

Covering	Structure Covered
Endomysium	Individual muscle fiber (cell)
Perimysium	Fascicle (bundle of fibers)
Epimysium	Entire muscle (bundle of fascicles)

Table: Phases of a Muscle Twitch (Myogram)

Phase	Description
Latent Period	Time between stimulus and onset of contraction
Contraction	Muscle tension increases to peak
Relaxation	Muscle tension decreases to baseline

Key Equations

• Force of Muscle Contraction: $F = m \times a$ Where F is force, m is mass, and a is acceleration.

• Resting Membrane Potential (for muscle fibers): $V_m = V_{in} - V_{out}$ Where $V_m$ is membrane potential, $V_{in}$ is intracellular potential, and $V_{out}$ is extracellular potential.

Additional info: For muscle identification, students should also be familiar with the actions, origins, and insertions of each muscle, as well as their appearance in anatomical models and diagrams. For joint structures, understanding the function and clinical relevance (e.g., common injuries) is beneficial for practical exams.