SKELETAL SYSTEM NOTES

Chapter 6: Functions of Bone and the Skeletal System

  • Bone tissue constitutes approximately 18% of body weight and performs six primary functions.

1. Support

  • The skeleton provides structure and supports soft tissues.

  • Functions as attachment points for tendons of skeletal muscles.

2. Protection

  • Bones safeguard vital organs:

    • Skull → protects the brain

    • Vertebrae → safeguard the spinal cord

    • Ribs → protect the heart and lungs

3. Movement

  • Muscles connect to bones and pull on them to produce motion upon contraction.

4. Mineral Homeostasis

  • Bones store calcium and phosphorus, contributing to strength and maintaining mineral balance in blood.

  • Bones contain about 99% of total body calcium.

5. Blood Cell Production

  • Red bone marrow generates red blood cells (RBCs), white blood cells (WBCs), and platelets through a process known as hemopoiesis.

  • Locations of red bone marrow include hip bones, ribs, sternum, vertebrae, skull, and the ends of the humerus and femur.

  • In newborns, all marrow is red, but much converts to yellow marrow with age.

6. Triglyceride Storage

  • Yellow bone marrow serves as a fat storage site (triglycerides) for energy.

Chapter 6.2: Structure of a Long Bone

1. Diaphysis

  • The diaphysis, or the shaft, is the main part of the bone, providing strength and structural integrity.

2. Epiphyses

  • The epiphyses are the ends of the bone where joints form.

3. Metaphyses

  • The metaphyses lie between the diaphysis and epiphyses.

  • Contains the epiphyseal (growth) plate, allowing for lengthwise growth; becomes the epiphyseal line once growth ceases.

4. Articular Cartilage

  • Hyaline cartilage covering the ends of bones at joints.

  • Functions to reduce friction and absorb shock; however, it heals poorly due to an absence of blood vessels.

5. Periosteum

  • A tough outer membrane encapsulating the bone (excluding joints).

  • Comprises an outer fibrous layer and an inner osteogenic layer for growth and repair.

  • Attached by Sharpey’s fibers, providing a point for tendon and ligament attachment.

6. Medullary Cavity

  • A hollow space in the diaphysis containing yellow marrow and blood vessels.

  • Reduces bone weight while maintaining strength.

7. Endosteum

  • A thin inner lining of the medullary cavity that contains bone-forming cells.

Chapter 6.3: Histology of Bone Tissue

  • Bone is classified as a connective tissue made up of a combination of cells, collagen fibers, and mineral salts.

Bone Composition

  • Bone tissue consists of:

    • 15% water

    • 30% collagen

    • 55% mineral salts (primarily calcium phosphate)

  • Minerals contribute to the hardening process of bone (calcification), whereas collagen provides flexibility and strength.

  • This process is conducted by osteoblasts.

Types of Bone Cells

  1. Osteogenic Cells

    • Stem cells that divide and differentiate into osteoblasts; found in the periosteum and endosteum.

  2. Osteoblasts

    • Cells that build bone by secreting collagen and initiating calcification.

  3. Osteocytes

    • Mature bone cells that maintain bone tissue; do not undergo division.

  4. Osteoclasts

    • Cells that break down bone (resorption) using enzymes and acids, aiding in remodeling and regulating calcium levels.

Bone Remodeling

  • Bone continuously undergoes renewal via remodeling:

    • Resorption: Osteoclasts eliminate the old matrix and minerals.

    • Deposition: Osteoblasts incorporate new collagen and minerals.

  • Approximately 5% of bone is remodeled at any given time:

    • Compact bone % remodeled: ~4% yearly.

    • Spongy bone % remodeled: ~20% yearly.

  • Remodeling is pivotal for removing damaged bone, reinforcing bone structure, and adapting to stress or physical activity.

  • Stressed bone tends to become thicker and stronger, while bones subjected to less stress become thinner.

Osteoclast Process

  • Osteoclasts attach to the bone surface, forming a sealed zone, and release enzymes and acids that digest bone.

  • Minerals are released into the bloodstream, after which osteoblasts rebuild the bone.

Factors Affecting Bone Growth and Remodeling

Minerals

  • Essential minerals include calcium, phosphorus, magnesium, fluoride, and manganese.

Vitamins

  • Vitamin A: Activates osteoblasts.

  • Vitamin C: Vital for collagen synthesis.

  • Vitamin D: Necessary for calcium absorption.

  • Vitamins K & B12: Required for bone protein formation.

Hormones

  • Childhood: Insulin-like growth factors (IGFs), human growth hormone (hGH), thyroid hormones, and insulin stimulate osteoblast activity and growth.

  • Puberty: Estrogen and testosterone induce growth spurts, bone shaping, and eventually lead to the closure of growth plates.

  • Adulthood: Hormones help maintain bone density and reduce resorption; estrogen promotes osteoclast apoptosis.

Exercise

  • Weight-bearing exercises enhance bone strength, while inactivity results in bone weakening.

Fractures and Repair

Fracture Definition

  • A fracture is defined as any break in bone.

  • Stress fractures: Microscopic cracks caused by overuse or osteoporosis.

Repair Steps

  1. Hematoma Formation (6–8 hours): A blood clot is generated, inflammation occurs, and debris is cleaned up.

  2. Soft Callus Formation (~3 weeks): Fibroblasts and chondroblasts bridge the ends of the bone with collagen and cartilage.

  3. Hard Callus Formation (3–4 months): Osteoblasts create spongy bone that gradually replaces cartilage.

  4. Remodeling: Osteoclasts remove dead bone, compact bone shapes are restored, and healing may leave slight thickening.

Bone and Calcium Homeostasis

  • Bones house 99% of body calcium, which is essential for nerves, muscles, blood clotting, and enzyme activity.

  • Blood calcium levels must be maintained between 9-11 mg/100 mL. Elevated levels can cause cardiac arrest, while decreased levels can lead to respiratory failure.

  • Mechanisms:

    • Osteoclasts release calcium into the bloodstream when levels are low.

    • Osteoblasts absorb calcium when blood calcium levels are high.

Hormones Involved

  1. Parathyroid Hormone (PTH): Increases blood calcium by activating osteoclasts, curtailing calcium loss through the kidneys, and enhancing vitamin D for gut absorption.

  2. Calcitonin: Decreases blood calcium levels by inhibiting osteoclast function; utilized in osteoporosis treatment.

  3. Calcitriol (Vitamin D): Promotes calcium absorption from dietary sources.

Exercise and Bone Health

  • Mechanical stress reinforces bone strength; osteoblasts deposit additional minerals and collagen.

  • High-impact activities (e.g., running, jumping) are superior to low-impact activities (e.g., walking) for bone health.

  • Lack of stress leads to bone atrophy (e.g., immobilization, sedentary lifestyle, space travel).

  • Engaging in weight-bearing exercise prior to the closure of growth plates optimally maximizes bone mass. Benefits persist at any age.

Aging and Bone Health

  • In youth, bone formation outpaces resorption, resulting in growth.

  • In adulthood, formation and resorption enter equilibrium, sustaining bone mass.

  • After middle age, resorption surpasses formation, leading to bone loss, osteoporosis, and increased risk of fractures.

  • The decline in bone mass correlates with demineralization and reduced collagen content, complicating bone strength.

  • Women typically experience more pronounced effects, facing a higher risk for osteoporosis.

Bone Disorders

  • Osteoporosis: A condition characterized by fragile and brittle bones that can be managed with weight-bearing exercise, calcium and vitamin D supplementation, and sometimes pharmacological interventions (e.g., calcitonin).

  • Rickets/Osteomalacia: Conditions tied to vitamin D deficiency that result in soft, weak bones in children (rickets) and adults (osteomalacia).

Cranial Bones

Frontal Bone

  • Forms the forehead, roofs of eye sockets, and much of the anterior cranial floor.

  • The metopic suture fuses the halves by about age 6-8.

  • Contains the supraorbital margin, which is a thickened edge above the orbit that includes the supraorbital foramen/notch for nerves and blood vessels.

  • Houses frontal sinuses that are air-filled and lined by mucosa.

Parietal Bones

  • Constitute the sides and roof of the cranial cavity.

  • The internal surface displays grooves for blood vessels supplying the dura mater.

Temporal Bones

  • Form the inferior lateral cranium and part of the cranial floor.

  • The temporal squama is the flat area of the temple.

  • Houses the zygomatic process, which makes up the zygomatic arch in conjunction with the zygomatic bone.

  • Features the mandibular fossa and articular tubercle, which together form the temporal-mandibular joint (TMJ).

  • Contains the mastoid process for neck muscle attachment and includes mastoid air cells which pose a risk for mastoiditis.

  • The styloid process provides attachments for the tongue and neck muscles, while the petrous portion houses components of the middle and inner ear, as well as the carotid and jugular foramina.

Occipital Bone

  • Forms the posterior and base of the skull.

  • The foramen magnum allows passage for the spinal cord and vertebral arteries, and the XI nerve.

  • Occipital condyles articulate with the first cervical vertebra (C1) enabling the nodding motion (“yes”).

  • The external occipital protuberance serves as an attachment point for the ligamentum nuchae (neck ligament).

  • Contains superior and inferior nuchal lines for muscle attachments.

Sphenoid Bone

  • The keystone of the cranial floor, it articulates with all cranial bones.

  • Identifiable by its butterfly shape, consisting of a body, greater and lesser wings, and pterygoid processes.

  • Houses the sella turcica, where the pituitary gland is situated, and contains the optic foramen for the optic nerve and ophthalmic artery.

  • Features superior orbital fissure, foramen ovale, foramen rotundum, and foramen lacerum which allow passage for nerves and blood vessels.

Ethmoid Bone

  • Located at the anterior cranial floor, it forms part of the medial wall of the orbit, the superior nasal septum, and later nasal walls.

  • Contains the cribriform plate that permits passage for olfactory nerves.

  • The crista galli anchors the falx cerebri, while the perpendicular plate forms a part of the superior nasal septum.

  • Contains ethmoidal cells/sinuses, which are involved in mucus production, as well as superior and middle nasal conchae, which aid in air circulation and olfactory functions.

Facial Bones

Nasal Bones

  • Comprise the bridge of the nose and provide support for nasal cartilage.

Lacrimal Bones

  • Form part of the medial orbital wall; contain lacrimal fossa for tear ducts.

Palatine Bones

  • Contribute to the posterior hard palate and parts of the nasal cavity and orbit floors.

Inferior Nasal Conchae

  • Located on the lateral walls of the nasal cavity; serve to swirl/filter air.

Vomer

  • Forms the inferior portion of the nasal septum.

Maxillae

  • Comprise the upper jaw, hard palate, parts of the nasal and orbital floor, and house the maxillary sinus, as well as alveoli for the upper teeth.

Zygomatic Bones

  • Known as the cheekbones; form the lateral wall and floor of the orbit.

Mandible

  • The lower jaw, the only movable bone in the skull.

  • Contains alveoli for lower teeth and features the mental and mandibular foramina for nerve and vessel passage.

Orbits

  • Orbital cavities are formed by seven bones: frontal, sphenoid, ethmoid (cranial) and palatine, zygomatic, lacrimal, and maxilla (facial).

Unique Skull Features

Sutures

  • Immovable joints crucial for skull growth in infants:

    • Coronal Suture: Between frontal and parietal bones

    • Sagittal Suture: Between parietal bones

    • Lambdoid Suture: Between parietal and occipital bones

    • Squamous Suture: Between parietal and temporal bones

Paranasal Sinuses

  • Frontal, sphenoid, ethmoid, and maxillary sinuses; mucus lined and function to lighten the skull, resonate the voice, and moisten inhaled air.

Fontanels

  • Soft spots on infant skulls:

    • Anterior Fontanel: Largest; closes around 18-24 months

    • Posterior Fontanel: Closes roughly at 2 months

    • Anterolateral Fontanel: Closes around 3 months

    • Posterolateral Fontanel: Closes between 1-12 months

  • Serve to provide skull flexibility during birth and allow for brain growth; the anterior fontanel can be used for blood sampling.

Vertebral Column (Spine)

Structure & Function

  • Approximately 2/5 of body height, protects the spinal cord, supports the head, and serves as an attachment point for ribs, pelvis, and muscles.

  • It possesses flexibility allowing for forward/backward bending, sideways flexion, and rotation.

  • Average adult length is about 71 cm in males and 61 cm in females.

Vertebral Count

  • There are 33 vertebrae in children, which fuse to form 26 in adults:

    • Cervical: 7 (neck)

    • Thoracic: 12 (chest)

    • Lumbar: 5 (lower back)

    • Sacrum: 1 (5 fused)

    • Coccyx: 1 (typically 4 fused)

  • Cervical, thoracic, and lumbar vertebrae are movable; sacrum and coccyx are fused.

Normal Curves

Side View

  • Cervical & Lumbar Curves: Convex (curving outward)

  • Thoracic & Sacral Curves: Concave (curving inward)

  • Primary Curves: Thoracic and sacral curves are present from fetal development.

  • Secondary Curves: Cervical develops around 3 months old, and lumbar develops when a child begins to walk.

  • The curves provide strength, balance, and serve as shock absorbers.

Intervertebral Discs

  • Located between vertebrae from C2 to the sacrum, constituting ~25% of the entire column height.

  • Outer Layer: Annulus fibrosus (fibrocartilage).

  • Inner Layer: Nucleus pulposus (elastic pulp).

  • Functions include shock absorption and allowance for mobility.

  • Daily height fluctuations may occur; compression occurs during the day and rehydration occurs at night.

Typical Vertebra Structure

  • Vertebral Body: Weight-bearing component; contains nutrient foramina.

  • Vertebral Arch: Composed of pedicles and laminae that enclose the spinal cord (vertebral foramen).

  • Processes: There are seven total:

    • 2 transverse + 1 spinous for muscle attachment

    • 4 articular processes form joints with adjacent vertebrae (facets)

Intervertebral Joints

  • Formed between vertebral bodies and facets of neighboring vertebrae.

Age-Related Changes

  • Decreased bone mass and density results in increased brittleness.

  • Loss of cartilage expresses as osteophytes, vertebral stenosis, and can lead to nerve compression causing pain and muscle weakness.

Regions of Vertebral Column

  1. Cervical: Neck, comprising 7 vertebrae.

  2. Thoracic: Chest region, comprising 12 vertebrae.

  3. Lumbar: Lower back, comprising 5 vertebrae.

  4. Sacral: Comprised of 5 fused vertebrae.

  5. Coccygeal: Comprised of 4 fused vertebrae.

Thorax

Structure

  • Composed of the chest region, with the thoracic cage formed by the sternum, ribs, costal cartilages, and thoracic vertebrae.

  • Costal cartilages attach the ribs to the sternum.

  • The thoracic cage is narrow at the top and broad at the bottom; it is flattened from front to back.

Function

  • Provides protection for thoracic and upper abdominal organs.

  • Supports upper limbs.

  • Assists in respiration.

Cervical Vertebrae (C1–C7)

  • Anatomically characterized by small bodies and large arches; the vertebral foramina are the largest among the spinal vertebrae.

  • Each cervical vertebra features three foramina: one vertebral foramen and two transverse foramina for the passage of vertebral arteries, veins, and nerves.

  • Spinous processes for vertebrae C2 to C6 are commonly bifid.

  • C1 (Atlas): Lacks a body and spinous process; forms a ring with anterior and posterior arches where lateral masses form the atlanto-occipital joint, allowing the “yes” motion.

  • C2 (Axis): Contains the dens (odontoid process), which enables pivoting for the atlanto-axial joint, allowing for the “no” motion.

  • C7 (Vertebra Prominens): Notable for its large, non-bifid spinous process, which is distinctively palpable at the neck's base.

Thoracic Vertebrae (T1–T12)

  • These vertebrae are larger and stronger than cervical ones.

  • Spinous processes for T1 to T10 are long, flat, and pointed inferiorly.

  • The spinous processes for T11 to T12 are shorter, broader, and point posteriorly.

  • Transverse and vertebral body facets articulate with ribs, establishing vertebrocostal joints.

  • Mobility is limited by rib-sternum attachment.

Lumbar Vertebrae (L1–L5)

  • The largest and strongest vertebrae, identified by short and thick projections.

  • Spinous processes have a quadrilateral shape and extend straight posteriorly to attach large back muscles.

  • Articular processes are classified as superior (medial) and inferior (lateral).

Sacrum

  • Shapes a triangular structure formed by five fused vertebrae (S1-S5); fusion typically occurs between 16 and 30 years.

  • It provides support for the pelvic girdle and consists of features:

    • Anterior: Concave with four transverse ridges and pairs of anterior foramina.

    • Posterior: Comprises median and lateral sacral crests, posterior foramina, sacral hiatus, and sacral cornua.

    • Superior: Base that articulates with L5 (lumbosacral joint).

    • Lateral: Auricular surfaces which form the sacroiliac joints.

Coccyx

  • Typically a triangular structure made of four fused vertebrae (Co1-Co4); fuses during the ages of 20 to 30 years.

  • Articulates with the sacral apex; the cornua connect to the sacral cornua.

  • The female coccyx points inferiorly to facilitate childbirth, while the male coccyx points anteriorly.

Sternum

  • Flat in shape and measures approximately 15 cm; comprises three parts:

    • Manubrium: Superior part connecting with clavicles and the first two ribs; includes a suprasternal notch.

    • Body: The largest, central component articulating with ribs 2 to 10.

    • Xiphoid Process: Inferior part that is cartilage in youth but ossifies around 40 years of age; serves as an attachment for abdominal muscles.

  • The sternal angle marks the junction between the manubrium and body.

Ribs (12 pairs)

  • Rib lengths increase from ribs 1–7 and then decrease from ribs 8–12.

  • Posteriorly connects with thoracic vertebrae; anteriorly connects to the sternum via costal cartilage.

  • True Ribs (1–7): Directly attach to the sternum (vertebrosternal).

  • False Ribs (8–12):

    • Vertebrochondral Ribs (8–10): Indirect sternum attachment.

    • Floating Ribs (11–12): Lack anterior attachment.

  • Rib Parts:

    • Head: Articulates with vertebrae at facet/demifacet.

    • Neck: Connects the head to the body; tubercle articulates with the transverse process.

    • Body (Shaft): Main section; the costal angle marks the curvature point; costal groove offers protection for vessels and nerves.

  • Intercostal Spaces: Houses muscles, blood vessels, and nerves; commonly used for thoracic surgery access.

Pectoral (Shoulder) Girdle

Function

  • The girdle connects the upper limbs to the axial skeleton and facilitates arm mobility.

Components

  • Composed of the clavicle and scapula (on each side).

Clavicle (Collarbone)

  • Exhibits an S-shape, lying horizontally, and is subcutaneous.

  • Medial (sternal) End: Rounded, articulates with the manubrium at the sternoclavicular joint.

  • Lateral (acromial) End: Flat, connects with scapula at the acromion, forming the acromioclavicular joint.

  • Important features include the conoid tubercle for ligament attachment (clavicle to scapula) and the costoclavicular ligament impression.

Scapula (Shoulder Blade)

  • A large, triangular flat bone located in the posterior thorax (2nd to 7th ribs).

  • Spine: A diagonal ridge; the lateral end extends to form the acromion, the shoulder's highest point, articulating with the clavicle.

  • Glenoid Cavity: Articulates with the humerus, forming the shoulder joint.

  • Borders:

    • Medial (vertebral): Near the spine.

    • Lateral (axillary): Near the arm.

    • Superior: Meets the medial border at the superior angle.

  • Processes:

    • Coracoid Process: Serves as an attachment for muscles and ligaments (pectoralis minor, biceps brachii, coracobrachialis).

  • Fossae:

    • Supraspinous Fossa: Attachment site for supraspinatus muscle.

    • Infraspinous Fossa: Attachment site for infraspinatus muscle.

    • Subscapular Fossa: Attachment site for subscapularis muscle.

Upper Limb (30 Bones per Limb)

Humerus (Arm)

  • Proximal End: Head connects to the glenoid cavity (shoulder joint).

  • Neck:

    • Anatomical Neck: Former site of the epiphyseal plate.

    • Surgical Neck: A common site for fractures.

  • Tubercles:

    • Greater Tubercle: Lateral prominence situated inferior to the acromion; easily palpable.

    • Lesser Tubercle: Located anteriorly.

    • Intertubercular Sulcus: Groove between the tubercles.

  • Shaft: Contains the deltoid tuberosity for muscle attachment; features a radial groove for the radial nerve.

  • Distal End:

    • Capitulum: Articulates with the radius.

    • Trochlea: Articulates with the ulna.

    • Fossae:

    • Radial fossa (anterior)

    • Coronoid fossa (anterior)

    • Olecranon fossa (posterior)

    • Epicondyles:

    • Medial and lateral for muscle attachments; the ulnar nerve runs close to the medial epicondyle.

Ulna (Medial Forearm / Pinky Side)

  • Typically longer than the radius.

  • Proximal End:

    • Olecranon: Prominence of the elbow.

    • Coronoid Process: Forms part of the trochlear notch.

  • Distal End:

    • Features a head and styloid process (ligament attachment for the wrist).

  • Articulates with the humerus (elbow) and radius (proximal and distal radioulnar joints).

Radius (Lateral Forearm / Thumb Side)

  • Narrow at the proximal end and widens at the distal end.

  • Proximal End: Head articulates with the capitulum of the humerus and the radial notch of the ulna.

  • Distal End: Features a styloid process for ligament attachment and articulates with wrist bones (scaphoid, lunate, triquetrum).

  • Shaft: contains a radial tuberosity (biceps brachii attachment).

Joints

  • Elbow Joint: Formed by humerus, ulna, and radius.

  • Proximal Radioulnar Joint: Between the radius head and the ulna's radial notch.

  • Distal Radioulnar Joint: Between the ulna head and the radius's ulnar notch.

  • Wrist Joint (Radiocarpal): Between the radius and carpal bones (scaphoid, lunate, triquetrum).

Carpals (Wrist, 8)

  • Proximal Row (lateral to medial): Scaphoid, Lunate, Triquetrum, Pisiform

  • Distal Row (lateral to medial): Trapezium, Trapezoid, Capitate, Hamate

  • Carpal Tunnel: Formed by the pisiform and hamate (on the ulnar side) and scaphoid and trapezium (on the radial side) through which the median nerve and flexor tendons pass.

Metacarpals (Palm, 5)

  • They extend from the base to the distal head; numbered I–V from the thumb to the little finger.

  • Distal heads of metacarpals form the knuckles.

Phalanges (Fingers, 14)

  • The thumb has two phalanges, while other fingers have three each.

  • Phalanges consist of proximal, middle, and distal sections; interphalangeal joints connect the segments.

Pelvic (Hip) Girdle

Function

  • The girdle connects the lower limbs to the axial skeleton, supports weight, and protects pelvic organs.

Components

  • Composed of two hip bones (coxae) and a sacrum; they unite anteriorly at the pubic symphysis and posteriorly at the sacroiliac joints.

  • The hip bone consists of three parts that fuse by age 23: ilium, ischium, and pubis.

Ilium

  • Features a superior ala and an inferior body, contributing to the acetabulum.

  • Iliac Crest: The superior border features anterior superior and posterior superior spines for muscle attachment.

  • Greater Sciatic Notch: A passageway for the sciatic nerve.

  • Iliac Fossa: Attachment site for the iliacus muscle.

  • Arcuate Line & Gluteal Lines: Serve as landmarks for gluteal muscle attachment.

Ischium

  • Positionally located at the inferior posterior aspect; comprises a superior body and an inferior ramus that fuses with the pubis.

  • Ischial Spine and Tuberosity: Sites for ligament and muscle attachment that endure pressure during sitting.

  • Lesser Sciatic Notch & Obturator Foramen: Provide passage for nerves and vessels.

Pubis

  • Anterior and inferior, containing a superior ramus, inferior ramus, and body.

  • Pubic Crest & Tubercle: Landmarks for muscle attachment; the pectineal line aids in identifying bone structure.

  • Acetabulum: The socket for femoral head.

  • Pelvic Brim: Differentiates the false (superior) from the true (inferior) pelvis.

Lower Limb (30 Bones per Limb)

Femur (Thigh)

  • The longest and most robust bone in the body.

  • Proximal End: Head fits into the acetabulum; the neck is a frequent fracture site alongside greater and lesser trochanters.

  • Shaft: Contains a gluteal tuberosity and linea aspera for muscle attachment.

  • Distal End:

    • Medial & Lateral Condyles: Articulate with the tibia.

    • Epicondyles: Provide sites for ligament attachment alongside an intercondylar fossa and patellar surface for interaction with the patella during knee flexion.

Patella (Kneecap)

  • Recognized as a sesamoid bone situated within the quadriceps tendon.

  • Base (proximal) and Apex (distal) identified; the posterior facets articulate with the femur; it enhances leverage and provides protection for the knee.

Tibia (Shin)

  • The larger and more medial bone of the leg responsible for weight-bearing.

  • Proximal End: Features medial and lateral condyles for articulation with the femur and an intercondylar eminence.

  • Anterior Aspect: Notable for the tibial tuberosity (attachment for the patellar ligament).

  • Distal End: Contains the medial malleolus (ankle region).

Fibula

  • Smaller and lateral, providing stabilization for the ankle joint.

  • Proximal End: The head articulates with the tibia.

  • Distal End: Features a lateral malleolus contributing to ankle integrity.

Tarsals (Ankle, 7)

  • Comprising several bones, including:

    • Posterior: Talus (articulates with the tibia and fibula) and calcaneus (the heel, largest bone).

    • Anterior: Navicular bone, three cuneiforms (medial, intermediate, lateral), and cuboid.

Metatarsals (5)

  • Extending from base to head, with the first metatarsal being the thickest due to its weight-bearing role.

Phalanges (Toes, 14)

  • The big toe comprises two phalanges while the other toes contain three each, connected by interphalangeal joints.

Arches of the Foot

  • Comprise two longitudinal arches (medial and lateral) and one transverse arch across the tarsals/metatarsals.

  • Functions include supporting weight, absorbing shock, and providing leverage.

  • Weight distribution during standing is about 40% on the ball of the foot and 60% on the heel—this ratio shifts when using high-heeled shoes.

Chapter 9.1: Joint Classifications

Objective

  • To delineate the structural and functional classifications of joints.

Structural Classification (Anatomy-Based)

  1. Fibrous Joints

    • No synovial cavity; bones are joined by dense irregular connective tissue.

  2. Cartilaginous Joints

    • Also lacking a synovial cavity; constructed of cartilage tissue.

  3. Synovial Joints

    • Include a synovial cavity; bonded by an articular capsule typically reinforced with ligaments.

Chapter 9.2: Fibrous Joints

Objective

  • To illustrate the structure and functionality of fibrous joints.

Characteristics

  • Lacking synovial cavities; connected closely by dense connective tissue; exhibit little to no movement.

Types of Fibrous Joints

  1. Sutures

    • Comprised of a thin layer of connective tissue between skull bones.

    • Immovable in adults (synarthrosis); slightly movable in children (amphiarthrosis).

    • Synostosis: Occurs when a suture transitions into bone, rendering it immovable.

  2. Syndesmoses

    • Bones linked by ligaments.

    • Allow slight movement (amphiarthrosis).

    • Example: distal tibiofibular joint.

    • Gomphosis: Tooth anchored in its socket; no movement occurs (synarthrosis).

  3. Interosseous Membranes

    • A sheet of connective tissue positioned between long bones, permitting slight movement.

    • Examples include the radius and ulna, and the tibia and fibula.

examples: tibia/fibula and radius/ulna

Chapter 9.3: Cartilaginous Joints

Objective

  • To examine the structure and function of cartilaginous joints.

Characteristics

  • Absence of synovial cavities, with bones adhered by cartilage; exhibit little to no movement.

Types of Cartilaginous Joints

  1. Synchondroses

    • Joints where bones are joined by hyaline cartilage; are immovable (synarthrosis).

    • Examples: epiphyseal plate, first rib with the sternum.

    • These may ossify into a synostosis.

  2. Symphyses

    • Covered with hyaline cartilage and interconnected by fibrocartilage; permit slight movement (amphiarthrosis).

    • Examples: pubic symphysis, intervertebral joints, and the manubrium-body connection of the sternum.

Chapter 9.4: Synovial Joints

Objectives

  • To explicate synovial joint structure alongside bursae and tendon sheaths.

Structure

  • Includes a synovial cavity facilitating the freedom of movement (diarthrosis).

  • Articular Cartilage: Covers bone surfaces, reducing friction while absorbing shock.

  • Articular Capsule:

    • Outer Fibrous Membrane: Dense connective tissue that imparts strength and resilience.

    • Inner Synovial Membrane: Areolar connective tissue that secretes synovial fluid.

Labrum: A fibrocartilaginous rim in ball-and-socket joints (shoulder and hip) that enhances stability.

Nerve & Blood Supply

  • Nerves relay sensations such as pain, motion, and stretch.

  • Arteries deliver oxygen and nutrients; synovial fluid nourishes the cartilage.

Bursae & Tendon Sheaths

  • Bursae: Fluid-filled sacs that mitigate friction between moving components.

  • Tendon Sheaths: Tubular bursae envelopes that surround tendons to minimize friction.

examples: elbow, knee, hip joint

Chapter 9.5: Types of Movements at Synovial Joints

  1. Gliding

    • Occurs when flat surfaces slide back and forth or side to side (e.g., intercarpal/tarsal joints).

  2. Angular Movements

    • Flexion: Reduces the angle between bones (e.g., bending the elbow, knee, or trunk).

    • Extension: Increases the angle (e.g., straightening a limb).

    • Hyperextension: Extension occurring beyond the anatomical position.

    • Lateral Flexion: Sideward bending of the trunk or neck.

    • Abduction: Moving a bone away from the midline.

    • Adduction: Moving a bone towards the midline.

    • Circumduction: Circular movement that is a combination of flexion, extension, abduction, and adduction.

  3. Rotation

    • Medial (Internal) Rotation: Rotating towards the midline.

    • Lateral (External) Rotation: Rotating away from the midline.

    • Illustrations include head movements and limb rotations.

  4. Special Movements

    • Elevation/Depression: Movement upward or downward (shrugging shoulders).

    • Protraction/Retration: Movement forward or backward (e.g., jaw or clavicle).

    • Inversion/Eversion: Turning the sole of the foot inward/outward.

    • Dorsiflexion/Plantar Flexion: Flexing or pointing the foot at the ankle.

    • Supination/Pronation: Rotating the forearm (palm facing up/down).

    • Opposition: Thumb to fingertip contact (grasping).

Chapter 9.7: Factors Affecting Range of Motion (ROM)

  1. Bone Structure/Shape

    • Determines fitting and motion capabilities.

  2. Ligament Strength/Tension

    • Limits or guides movement through restrictions.

  3. Muscle Tension

    • Reinforces ligaments, thereby controlling movement.

  4. Contact of Soft Tissues

    • Limits movement if body parts touch.

  5. Hormones

    • Hormonal changes such as relaxin in pregnancy enhance flexibility.

  6. Disuse

    • Immobilization leads to reduced ROM, fluid retention, flexibility, and muscle size.

Classification of Joints

A. Structural Classification

1. Fibrous- bones are held together by fibrous connective tissue (sutures)

2. Cartilaginous- bones are held together by cartilage (ribs)

3. Synovial- the space between the articulating bones of a synovial joint, filled with synovial fluid

B. Functional Classification

1. Synarthrosis- joints do not move (sutures in skull)

2. Amphiarthrosis- slightly movable joints (pubic symphysis)

3. Diarthrosis- freely movable joints (mostly anything)

II. Synarthrosis (Immovable Joint)

A. Suture- an immovable fibrous joint in the skull where bone surfaces are closely united.

B. Gomphosis- a fibrous joint in which a cone-shaped peg fits into a socket (roots of teeth with the alveoli of the maxillae and mandible)

C. Synchondrosis- a cartilaginous joint in which the connecting material is hyaline cartilage. (Joint between the epiphysis and diaphysis of a growing bone)

III. Amphiarthrosis (Slightly movable Joint)

A. Syndesmosis- a fibrous joint in which articulating bones are united by dense fibrous tissue. (distal articulation of the tibia and fibula)

B. Symphysis- a line of union. A slightly movable cartilaginous joint such as the symphysis pubis between the anterior surfaces of the coxal (hip) bones. (Bodies of vertebrae pubic symphysis)

The acromioclavicular and sternoclavicular joints are amphiarthroses

IV. Diarthrosis (Freely movable Joint)

A. Structure of Diarthrosis

1. Synovial Cavity- the space between the articulating bones of a synovial joint, filled with

synovial fluid

2. Articular cartilage- hyaline cartilage attached to articular bone surfaces

3. Articular capsule- sleeve-like structure around a synovial joint composed of a fibrous capsule and synovial membrane. Capsule makes a cavity

a. Fibrous capsule

i. Ligaments- dense, regularly arranged connective tissue that attaches bone to bone

b. Synovial membrane- the inner of the two layers of the articular capsule of a synovial

joint, composed of loose connective tissue that secretes synovial fluid into the synovial (joint) cavity

c. Synovial fluid- secretion of synovial membranes that lubricates the joints and nourishes articular cartilage

4. Accessory ligaments

a. Extra-capsular ligaments that lie outside the joint capsule, providing additional support and stability to the joint.

b. Intra-capsular ligaments that are located within the joint capsule and help to stabilize the joint by connecting the bones internally.

5. Articular discs (cartilage)- fibro-cartilage pad between articular surfaces of bones of some synovial joints, (meniscus)

6. Cracking sound- noise produced during joint movement, often due to the rapid release of gas bubbles in the synovial fluid.

B. Types of Diarthrosis

2. Hinge Joint (ginglymus)- a synovial joint in which a convex surface of one bone fits into a concave surface of another bone, such as the elbow, knee, ankle, and inter-phalangeal joints

3. Pivot Joint (trochoid)- a synovial joint in which a rounded, pointed, or conical surface of one bone articulates with a ring formed partly by another bone and partly by a ligament, as in the joint between the atlas and axis. Pivot point is the dens on the axis. Humerus and radius are also examples

6. Ball-and-Socket Joint (spheroid)- a synovial joint in which the rounded surface of one bone moves within a cup-shaped depression or fossa of another bone, as in the shoulder or hip joint. Examples: shoulder and hip

ADD ONS:

Fractures in the metaphysis will cause premature ossification closure (bone stops growing)

C1 (Atlas) allows for when you say yes; C2 and C1 allow for when you say no; Dens on C2 is the axis for C1 to allow left/right rotation

Where the clavicle changes directions is usually where it fractures (it’s proximal)

The humeral-radial joint enables supination and pronation, facilitating the rotation of the forearm and allowing for a wide range of motion during daily activities.

2 os coxae and sacrum make up the full pelvis, providing stability and support for the upper body while also accommodating for the transferring of weight through the hips during movement.

Auditory Ossicles: malleus, incus, stapes

4 main bones in the nasal septum: perpendicular plate of the ethmoid, which forms the superior part of the bony septum

  • Perpendicular Plate of the Ethmoid: It supports the structure of the nasal cavity and helps define its shape, contributing to the overall anatomy of the face.

  • Vomer: This bone aids in separating the nasal passages and allows for airflow regulation, also playing a role in olfactory function by supporting the structure that houses the olfactory bulb.

  • Maxillary Crest: It provides structural integrity to the upper jaw and helps support the nasal cavity, thereby influencing both ventilation and drainage systems within the nasal structure.

  • Palatine Crest: It reinforces the back partition of the nasal cavity while serving as an attachment point for the soft palate muscles, which are essential for swallowing and speech.

  • Frontal Sinus: Located in the forehead region, it aids in voice resonance and reduces skull weight, while contributing to the overall structure of the forehead.

  • Sphenoid Sinus: Found within the sphenoid bone, it plays a role in the drainage of mucus from the nasal cavity and influences the airflow patterns in the nasal passages.

  • Ethmoid Sinus: Comprising multiple small air cells, it helps with air filtration, humidity, and the olfactory sensory function, as it is in close proximity to the olfactory bulbs.

  • Maxillary Sinus: The largest of the paranasal sinuses, it contributes to voice resonance and aids in the drainage of secretions from the maxilla region, while also affecting the overall shape and structure of the face.

The vertebral column, also known as the spine, serves several crucial functions, including providing structural support for the body, protecting the spinal cord, allowing for flexibility and movement in the torso, as well as serving as an attachment point for muscles and ligaments.

Intramembranous ossification occurs directly within mesenchymal tissue and is responsible for the formation of flat bones, such as those in the skull, where bone develops from connective tissue membranes. In contrast, endochondral ossification involves the replacement of hyaline cartilage with bone and is critical for the formation of long bones, such as the femur, where a cartilage model is formed first before being replaced by bony tissue

Compact Bone

Structure:

Dense and solid, forming the hard outer shell of bones.

Structural unit is the osteon (Haversian system).

Osteons are composed of concentric rings of calcified matrix called lamellae.

A central (Haversian) canal runs through each osteon, housing blood vessels and nerves.

Mature bone cells (osteocytes) reside in spaces called lacunae.

Tiny channels called canaliculi connect lacunae to each other and the central canal.

Function:

Provides strength, support, and protection to the body and internal organs.

Withstands significant mechanical stress and compressive forces.

Resists bending and fracturing along the long axis of the bone.

Location:

Forms the outer layer of all bones.

Makes up the majority of the diaphysis (shaft) of long bones.

Spongy Bone

Structure:

Porous, with a lattice-like network of bony plates or rods called trabeculae.

Does not contain osteons or central canals.

Spaces between trabeculae are filled with bone marrow (specifically red marrow in certain locations) and blood vessels.

Osteocytes are present in lacunae within the trabeculae and receive nutrients via diffusion from the marrow spaces.

Function:

Reduces the overall weight of the skeleton, allowing for easier muscle movement.

Provides flexibility and acts as a shock absorber against forces from multiple directions.

The spaces between trabeculae house red bone marrow, the site of hematopoiesis (production of blood cells).

Location:

Found on the interior of all bones, deep to the compact bone layer.

Most abundant in the epiphyses (ends) of long bones.

The primary component of flat bones (skull, ribs), irregular bones (vertebrae), and short bones (carpals/tarsals).

Long Bones:

Explanation: Longer than they are wide; act as levers for movement and support weight.

Examples: Femur, humerus, tibia, fibula, radius, ulna, phalanges.

Short Bones:

Explanation: Cube-shaped, roughly equal in length, width, and thickness; provide stability and limited motion.

Examples: Carpal bones (wrist), tarsal bones (ankle).

Flat Bones:

Explanation: Thin, flattened, and often curved; provide protection for organs and broad surfaces for muscle attachment.

Examples: Cranial bones (skull), sternum, ribs, scapulae.

Irregular Bones:

Explanation: Complex, unique shapes; protect nervous tissue and provide muscle attachment points.

Examples: Vertebrae (spine), pelvic bones, facial bones.

Sesamoid Bones:

Explanation: Small, round bones embedded within tendons; protect tendons and increase muscle leverage.

Examples: Patella (kneecap), sesamoid bones under the big toe.

Process of Intramembranous Ossification (Short Explanation)

Centers Form: Mesenchymal cells cluster and become osteoblasts (bone builders).

Bone Secreted: Osteoblasts make osteoid (unmineralized bone matrix) which then calcifies, trapping cells as osteocytes.

Spongy Bone and Periosteum Form: Bony spicules fuse into a network of spongy bone; surrounding tissue becomes the periosteum (outer covering).

Compact Bone Forms: Outer layer of spongy bone is replaced by compact bone.

Process of Endochondral Ossification (Short Explanation)

Cartilage Model: A miniature hyaline cartilage model of the bone is formed by chondroblasts.

Calcification: Cartilage in the center of the shaft calcifies; blood vessels invade.

Primary Ossification Center: Osteoblasts arrive and form spongy bone in the center of the shaft (diaphysis). A bone collar of compact bone forms around the outside.

Medullary Cavity: Osteoclasts break down the central spongy bone to create the marrow cavity.

Secondary Centers: Spongy bone forms in the ends (epiphyses) of the bone.

Growth Plates: Cartilage remains at the joint surfaces (articular cartilage) and the epiphyseal (growth) plate, allowing the bone to lengthen.

Intramembranous Ossification:

Starts with mesenchymal connective tissue (a fibrous membrane).

Bone forms directly from this tissue.

Forms flat bones like the skull and clavicles.

Endochondral Ossification:

Starts with a hyaline cartilage model.

The cartilage is formed first, then replaced by bone tissue.

Forms most bones in the body, especially long bones, short bones, and vertebrae.

Mechanical Stress:

Osteocytes (mechanosensors) detect the physical stress (bending/compression).

In response to stress, osteocytes signal osteoblasts (bone builders) to increase activity and form new bone matrix, strengthening the bone in high-stress areas.

Stress generally inhibits osteoclasts (bone resorbers), preventing excessive bone breakdown.

Lack of stress (e.g., bed rest, space travel) reverses this process, leading to increased osteoclast activity and net bone loss.