Skeletal System Overview

Skeletal System Functions

• Supports the body, protects organs, allows movement, stores minerals and lipids, and produces blood cells.

Bone Growth Types

• Intramembranous ossification: bone develops from fibrous membrane.
• Endochondral ossification: bone develops by replacing hyaline cartilage.

Osteopenia vs. Osteoporosis

• Osteopenia: bone density is lower than normal peak density but not low enough to be classified as osteoporosis.
• Osteoporosis: bone disease where the body loses too much bone, makes too little bone, or both, causing bones to become weak and break easily.

PTH and Calcitonin

• PTH (Parathyroid Hormone): increases blood calcium levels; triggered by low blood calcium.
• Calcitonin: lowers blood calcium levels; triggered by high blood calcium.

Wolff's Law

• Bone adapts to the loads placed on it.

Bone Cells

• Osteoblasts: bone-forming cells.
• Osteoclasts: bone-resorbing cells.
• Osteocytes: mature bone cells.
• Osteoprogenitor cells: stem cells that produce osteoblasts.

Bone Microstructures

• Lacunae: small cavities in bone that contain osteocytes.
• Concentric Lamellae: rings of calcified matrix.
• Circumferential Lamellae: layers of matrix that surround the outer surface of a bone.
• Canaliculi: small channels connecting lacunae.
• Osteon: structural unit of compact bone.
• Osteoid: unmineralized bone matrix composed of collagen.

Bone Types

• Long bones: longer than wide (e.g., femur).
• Flat bones: thin and curved (e.g., sternum).
• Irregular bones: complex shapes (e.g., vertebrae).
• Sesamoid bones: small, round bones embedded in tendons (e.g., patella).
• Sutural bones: small, irregular bones found between the flat bones of the skull.

Cartilage at Bone Tips

• Hyaline cartilage is found at the tips of long bones.

Medullary Cavity

• Bone marrow is found in the medullary cavity.

Bone Structure

• Diaphysis: shaft of a long bone.
• Metaphysis: region between the diaphysis and epiphysis.
• Epiphysis: end of a long bone.

Bone Markings

• Condyles: rounded articular projections.
• Epicondyles: raised areas above condyles.
• Foramen: hole or opening.
• Tubercles: small rounded projections.
• Trochanters: large, blunt, irregular processes (femur only).
• Sulci: grooves or furrows.
• Fossa: shallow depression.

Axial Skeleton Composition

• Skull, vertebral column, and rib cage.

Sutures

• Coronal, sagittal, lambdoid, and squamous. Found in the skull, connecting cranial bones.

Cranial and Facial Bones

• Cranial: frontal, parietal, temporal, occipital, ethmoid, sphenoid.
• Facial: nasal, maxillae, zygomatic, mandible, lacrimal, palatine, inferior nasal conchae, vomer.

Axial Skeleton Landmarks

• Processes, meatus (auditory canal), foramina (openings for nerves/vessels).

Bony Roof of Mouth

• Palatine process of the maxilla and the horizontal plate of the palatine bone.

Mandibular and Mental Foramina

• Mandibular foramen: passage for nerves/vessels to lower teeth.
• Mental foramen: passage for nerves/vessels to the chin.

Paranasal Sinuses

• Frontal, ethmoidal, maxillary, and sphenoidal sinuses. They lighten the skull and provide resonance for speech.

Spinal Curves

• Primary: thoracic and sacral (present at birth).
• Secondary: cervical and lumbar (develop later).
• Lateral: abnormal curves are called scoliosis.

Vertebra Prominens

• The spinous process of C7.

Rib Articulation

• Ribs articulate with the thoracic vertebrae.

Vertebrae Count

• Cervical: 7
• Thoracic: 12
• Lumbar: 5
• Sacral: 5 (fused)
• Coccygeal: 4 (fused).

Sternum

• Manubrium, body, and xiphoid process. Articulates with ribs and clavicles.

Atlas and Axis

• Atlas (C1): responsible for "yes" motion.
• Axis (C2): responsible for "no" motion.

Vertebral Arch

• Formed by the pedicles and laminae.

Fontanels

• Soft spots in the infant skull. Allow for brain growth.

Appendicular Skeleton

• Clavicle, scapula, humerus, radius, ulna, carpals, metacarpals, phalanges, femur, patella, tibia, fibula, tarsals, metatarsals, phalanges.

Appendicular Skeleton Landmarks

• Olecranon fossa, coronoid process, tibial tuberosity, deltoid tuberosity, greater sciatic notch.

Coxal Bones

• Ilium, ischium, and pubis. Ischium bears weight when sitting.

Largest and Longest Bone

• Femur

Malleolus

• Lateral malleolus: distal end of fibula.
• Medial malleolus: distal end of tibia.

Acetabulum

• Hip socket; formed by the ilium, ischium, and pubis.

Articulation Types

• Synarthrosis: immovable (e.g., sutures).
• Amphiarthrosis: slightly movable (e.g., intervertebral discs).
• Diarthrosis: freely movable (e.g., synovial joints).

Synovial Joint Features

• Articular cartilage, joint capsule, synovial membrane, synovial fluid.

Movements

• Dorsiflexion, plantar flexion, adduction, abduction, supination, pronation, eversion, inversion flexion, extension, hyperextension, internal and external rotation.

Mobility and Stability

• Joints with greater mobility have less stability, and vice versa.

Joint Accessory Structures

• Meniscus, joint capsule, ligaments, bursa.

Skeletal Muscle Function

• Movement, posture, heat generation.

Skeletal Muscle Layers

• Epimysium (outer), perimysium (around fascicles), endomysium (around muscle fibers).

Functional Parts of Skeletal Muscle

• A-band, I-band, M-line, Sarcomere

Sliding Filament Theory

• Myosin filaments slide past actin filaments, shortening the sarcomere.

Skeletal Muscle Triad

• T-tubule and two terminal cisternae. Important for transmitting action potentials.

Neuromuscular Junction

• Synaptic terminal, synaptic cleft, motor end plate.

Muscle Cell Action Potential

• Sarcolemma carries the action potential.

Isometric vs. Isotonic Contraction

• Isometric: muscle length does not change.
• Isotonic: muscle length changes.

Aerobic vs. Anaerobic Respiration

• Aerobic: with oxygen.
• Anaerobic: without oxygen.

Oxygen Debt

• The amount of extra oxygen the body needs after exercise to recover.

Muscle Fiber Types

• Type I (slow twitch): fatigue resistant.
• Type II (fast twitch): fatigable.

Rigor Mortis

• Stiffening of muscles after death. Due to lack of ATP.

Muscle Types

• Pennate, circular, parallel, convergent. Parallel is the most common.

Levers

• First, second, and third class. Third class is most common.

Muscles

• Upper extremity, lower extremity, trunk, and face.

Origins and Insertions

• Origin: attachment to immovable bone.
• Insertion: attachment to movable bone.

Muscles of Mastication

• Masseter, temporalis, medial pterygoid, lateral pterygoid.

Muscle Actions

• Agonist: prime mover.
• Antagonist: opposes the agonist.
• Synergist: assists the agonist.

Extrinsic Eye Muscles

• Superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, inferior oblique.

Rotator Cuff Muscles

• Supraspinatus, infraspinatus, teres minor, subscapularis.

Hamstring Muscles

• Biceps femoris, semitendinosus, semimembranosus.

Quadriceps Muscles

• Rectus femoris, vastus lateralis, vastus medialis, vastus intermedius.

Calf Muscles

• Gastrocnemius, soleus.