Skeletal and Muscular Systems: Study Guide for BIOL 2113L Unit 2 Exam

The Skeletal System

Cartilage and Bone Tissue Types

The skeletal system is composed of various connective tissues, primarily cartilage and bone, each with unique properties and functions.

• Cartilage Tissue Types:

  • Hyaline Cartilage: Most common; provides support with flexibility. Found in the nose, trachea, larynx, and at the ends of long bones (articular cartilage).

  • Elastic Cartilage: Contains more elastic fibers; maintains shape and flexibility. Found in the ear and epiglottis.

  • Fibrocartilage: Contains thick collagen fibers; resists compression. Found in intervertebral discs, pubic symphysis, and menisci of the knee.

• Bone Tissue Types:

  • Compact Bone: Dense and strong; forms the outer layer of bones.

  • Spongy (Cancellous) Bone: Porous and lighter; found at the ends of long bones and inside flat bones.

• Extracellular Matrix (ECM): Non-cellular component providing structural support. In bone, ECM is hard due to mineralization; in cartilage, it is semi-solid or firm but flexible.

• Rigidity: Bone is more rigid due to calcium salts; cartilage is more bendy due to collagen and elastic fibers.

Structural Classes of Bones

Bones are classified by shape and structure, which relate to their function.

• Long Bones: Longer than wide (e.g., femur, humerus).

• Short Bones: Cube-shaped (e.g., carpals, tarsals).

• Flat Bones: Thin, often curved (e.g., sternum, skull bones).

• Irregular Bones: Complex shapes (e.g., vertebrae, hip bones).

• Sesamoid Bones: Embedded in tendons (e.g., patella).

• Sutural Bones: Small bones within cranial sutures.

Compact Bone vs. Spongy Bone

Bone tissue is organized into two main types, each with distinct substructures and functions.

• Compact Bone:

  • Composed of osteons (Haversian systems), which are cylindrical structures containing concentric lamellae (layers of bone matrix).

  • Central canal: Contains blood vessels and nerves.

  • Provides strength for weight-bearing.

• Spongy Bone:

  • Composed of a network of trabeculae (thin columns and plates).

  • Spaces between trabeculae contain red marrow for hematopoiesis.

  • Reduces bone weight while maintaining strength.

Bone Marrow and Hematopoiesis

• Yellow Marrow: Stores fat; found in the medullary cavity of long bones in adults.

• Red Marrow: Site of blood cell formation (hematopoiesis); found in spongy bone of flat bones and epiphyses of long bones.

• Hematopoiesis: The process of forming blood cells, occurring primarily in red marrow.

Structure of a Long Bone

• Diaphysis: Shaft; composed mainly of compact bone.

• Epiphysis: Ends of the bone; mostly spongy bone covered by compact bone.

• Metaphysis: Region between diaphysis and epiphysis; contains the epiphyseal plate/line.

• Epiphyseal Plate: Hyaline cartilage in growing bones; site of lengthwise growth.

• Epiphyseal Line: Remnant of the plate in adults; marks where growth has stopped.

• Medullary Cavity: Central cavity containing yellow marrow.

Bone Markings

Bones have various markings that serve as sites for muscle attachment, joint formation, or passage of nerves and blood vessels.

Type	Examples	Function
Articulations/Joint Surfaces	Condyle, Facet, Head	Form joints with other bones
Projections/Elevations	Crest, Line, Tuberosity, Tubercle, Epicondyle, Spine, Trochanter, Process	Attachment points for muscles/ligaments
Holes/Depressions	Foramen, Fissure, Meatus, Fossa, Sulcus/Groove, Sinus	Passage for nerves/vessels; reduce bone weight

Other Bone Terms

• Ramus: Arm-like bar of bone.

• Angle: Corner or bend in a bone.

• Body/Diaphysis: Main shaft of a long bone.

• Metaphysis: Growth zone between diaphysis and epiphysis.

• Epiphysis: End part of a long bone.

Bone and Cartilage Cell Types

• Osteoprogenitor Cells: Stem cells that differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells; secrete bone matrix.

• Osteocytes: Mature bone cells; maintain bone tissue.

• Osteoclasts: Bone-resorbing cells; break down bone matrix.

• Chondroblasts: Cartilage-forming cells.

• Chondrocytes: Mature cartilage cells.

• Cell Maturation: Osteoprogenitor cells become osteoblasts, which mature into osteocytes. Osteoclasts arise from a different lineage (monocyte/macrophage).

• Hormones: Parathyroid hormone (PTH), calcitonin, and growth hormone regulate bone remodeling and growth.

Functions of the Skeletal System

• Support and protection of organs

• Leverage for movement

• Mineral storage (calcium, phosphate)

• Blood cell production (hematopoiesis)

• Fat storage (yellow marrow)

• Hormone production (osteocalcin)

Axial Skeleton

• Skull: Protects brain; includes cranial and facial bones (e.g., frontal, parietal, temporal, occipital, sphenoid, ethmoid, zygomatic, maxilla, mandible).

• Movable Bones: Mandible is the only movable skull bone; strongest facial bone.

• Skull Sutures: Lambdoid, sagittal, squamosal, coronal, occipitomastoid, metopic; connect specific skull bones.

• Vertebral Column: Cervical, thoracic, lumbar, sacral, coccygeal regions; cervical and lumbar are more mobile, sacral and coccygeal are fused.

• Intervertebral Discs: Fibrocartilage pads; absorb shock and allow flexibility.

• Abnormal Curves: Scoliosis (lateral), kyphosis (excess thoracic), lordosis (excess lumbar).

• Thoracic Cage: Ribs, sternum (manubrium, body, xiphoid process), costal cartilages.

Appendicular Skeleton

• Pectoral (Shoulder) Girdle: Clavicle and scapula; allows wide range of motion.

• Pelvic (Hip) Girdle: Two hip bones (os coxae); supports body weight, less mobile but more stable.

• Sex Differences: Female pelvis is wider and shallower for childbirth.

• Limbs: Humerus, radius, ulna (upper limb); femur, tibia, fibula (lower limb). Femur is the strongest bone.

Joints (Articulations)

• Functional Classification:

  • Synarthroses: Immovable (e.g., skull sutures).

  • Amphiarthroses: Slightly movable (e.g., intervertebral discs).

  • Diarthroses: Freely movable (e.g., shoulder, knee).

• Structural Classification:

  • Fibrous Joints: Bones joined by dense connective tissue; includes sutures, syndesmoses, gomphoses.

  • Cartilaginous Joints: Bones joined by cartilage; includes synchondroses (hyaline cartilage), symphyses (fibrocartilage).

  • Synovial Joints: Bones separated by a fluid-filled cavity; subclasses include hinge, ball-and-socket, condylar (ellipsoid), pivot, saddle, plane.

Major Types of Movement

• Flexion/Extension

• Abduction/Adduction

• Pronation/Supination

• Rotation, Circumduction, Elevation, Depression, Protraction, Retraction, Opposition, etc.

• Movements occur at synovial joints; specific movements depend on joint structure.

The Muscular System

Muscle Tissue Types

Type	Location	Striated?	Voluntary?	Function
Skeletal Muscle	Attached to bones	Yes	Yes	Movement, posture, heat production (shivering)
Cardiac Muscle	Heart	Yes	No	Pumps blood
Smooth Muscle	Walls of hollow organs	No	No	Moves substances (peristalsis)

Structure of Skeletal Muscle

• Muscle (Organ): Composed of bundles of fascicles.

• Fascicle: Bundle of muscle fibers (cells).

• Muscle Fiber: Single muscle cell; contains myofibrils.

• Myofibril: Rod-like unit within muscle fiber; made of sarcomeres.

• Sarcomere: Smallest contractile unit; defined by Z-discs.

Sarcomere Structure

• Bands and Lines:

  • A Band: Dark region; contains thick (myosin) filaments.

  • I Band: Light region; contains thin (actin) filaments only.

  • H Zone: Center of A band; only thick filaments.

  • M Line: Center of H zone; holds thick filaments together.

  • Z Disc: Boundary of sarcomere; anchors thin filaments.

• During Contraction: I band and H zone shrink; A band remains the same.

Muscle Cell Organelles and Substructures

• Sarcoplasmic Reticulum (SR): Stores and releases calcium ions.

• T Tubules (Transverse Tubules): Invaginations of the sarcolemma; transmit action potentials into the muscle fiber, triggering calcium release from SR.

• Myofibrils: Found in striated muscle; composed of repeating sarcomeres.

Muscle Contraction: Sliding Filament Model

• Muscle contraction occurs when myosin heads pull actin filaments toward the center of the sarcomere.

• Requires ATP and calcium ions.

• Overlap of filaments is essential for contraction; without overlap, cross-bridges cannot form.

Neuromuscular Junction and Contraction Trigger

• Acetylcholine (ACh): Neurotransmitter released by motor neuron; binds to receptors on muscle fiber, initiating action potential.

• Neuromuscular Junction: Synapse between motor neuron and muscle fiber.

• T Tubules: Conduct action potential to SR, causing calcium release and muscle contraction.

Gross Muscle Terms

• Agonist (Prime Mover): Main muscle responsible for movement.

• Antagonist: Opposes the action of the agonist.

• Synergist: Assists the agonist.

• Fixator: Stabilizes the origin of the agonist.

• Origin: Attachment site that remains relatively stationary.

• Insertion: Attachment site that moves during contraction.

• Biceps, Triceps, Quadriceps: Indicate number of origins (2, 3, 4 respectively).

Major Muscles

• Be able to identify major muscles by name, function, or in diagrams (refer to Exercise 13: Figures 13.2 and 13.7).

Additional info: For diagrams and further visual references, consult your lab manual and recommended videos. The above guide covers all major topics listed in the exam study guide and provides foundational knowledge for exam preparation.