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The Musculoskeletal System
A comprehensive guide to understanding bones, muscles, and joints
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Understanding the Musculoskeletal Framework
Core Components
The musculoskeletal system comprises bones, muscles, and joints working together harmoniously. Bones provide the structural framework, protecting vital internal organs whilst supporting the body's architecture. They serve as attachment points for muscles, enabling movement and locomotion.
The inner core of bones contains haematopoietic tissue, where red bone marrow manufactures blood cells. Other portions store essential minerals like calcium and phosphorus, crucial for growth and development.
Functional Roles
Joints represent the meeting points of bones, with various types throughout the body determined by flexibility requirements. Muscles, whether attached to bones or internal organs, are responsible for all movement.
Internal movement involves contraction and relaxation of visceral muscles, whilst external movement is accomplished through skeletal muscles attached to bones.
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Three Types of Muscles
Striated Muscles
Also called voluntary or skeletal muscles, these fibres move all bones, face, and eyes. We have conscious control over these muscles through the nervous system.
  • Dark and light bands in cytoplasm
  • Enveloped by fascia tissue
  • Contains blood, lymph, nerve supply
Smooth Muscles
Also called involuntary or visceral muscles, these fibres move internal organs like the digestive tract and blood vessels.
  • Controlled by autonomic nervous system
  • No dark and light fibrils
  • Forms sheets around tubes and vessels
Cardiac Muscle
Striated in appearance but involuntary in action. Movement cannot be consciously controlled.
  • Branching fibres
  • Found exclusively in the heart
  • Automatic contraction
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How Skeletal Muscles Work
Over 400 skeletal muscles in the human body work to move bones through precise attachment points and coordinated contractions.
Muscle Attachment Points
Origin: The point where muscle attaches to the stationary bone, remaining virtually fixed during contraction.
Insertion: The junction point where muscle attaches to the bone that moves during contraction.
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Muscle Actions and Movements
1
Flexion
Decreasing the angle between two bones; bending a limb inward
2
Extension
Increasing the angle between two bones; straightening out a limb
3
Abduction
Movement away from the midline of the body
4
Adduction
Movement toward the midline of the body
5
Rotation
Circular movement around a central axis
6
Dorsiflexion
Decreasing ankle angle so foot bends backward (upward)
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Additional Muscle Movements
Plantar Flexion
The motion that extends the foot downward toward the ground, as when pointing the toes
Supination
As applied to the hand, the act of turning the palm forward
Pronation
As applied to the hand, the act of turning the palm backward
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Bone Structure and Composition
Bones are complete organs composed primarily of osseous tissue, enriched with blood vessels and nerves. This dense connective tissue consists of osteocytes surrounded by calcium-rich intercellular substance.
206
Total Bones
Various types throughout the human body
4
Bone Types
Long, short, flat, and sesamoid
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Anatomy of Long Bones
Key Components
Diaphysis: The shaft or middle region of a long bone, providing structural support.
Epiphysis: Each end of a long bone. The epiphyseal plate represents cartilage tissue constantly being replaced by new bone during growth.
Periosteum: A strong, fibrous, vascular membrane covering the bone surface except at the epiphyses. Contains osteoblasts that deposit calcium phosphate.
Articular Cartilage: Thin layer covering bone ends, cushioning where bones meet at joints.
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Compact vs Cancellous Bone
Compact (Cortical) Bone
A layer of hard, dense tissue lying under the periosteum in all bones, chiefly around the diaphysis of long bones. Contains Haversian canals—minute spaces filled with blood vessels bringing oxygen and nutrients whilst removing waste products like carbon dioxide.
The central medullary cavity in long bone shafts contains yellow bone marrow, primarily composed of fat cells.
Cancellous (Spongy) Bone
Much more porous and less dense than compact bone. Mineral matter is laid down in separated bony fibres called trabeculae, forming a spongy latticework.
Found largely in the epiphyses of long bones and middle portions of other bones. Spaces contain red bone marrow, richly supplied with blood and consisting of immature and mature blood cells in various developmental stages.
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Bone Processes and Depressions
Bone Processes
Enlarged tissues extending from bones as attachment points for muscles and tendons:
  • Bone Head: Round end separated from body by a neck
  • Tubercle: Small, rounded process
  • Trochanter: Large process on femur
  • Tuberosity: Large, rounded process
  • Condyle: Rounded, knuckle-like process at joints
Bone Depressions
Openings or hollow regions serving as passageways:
  • Fossa: Shallow cavity in or on bone
  • Foramen: Opening for vessels and nerves
  • Fissure: Narrow, deep, slit-like opening
  • Sulcus: Groove or furrow
  • Sinus: Hollow cavity within bone
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Cranial Bones: Protecting the Brain
The skull, or cranium, protects the brain and related structures whilst providing attachment points for head and chewing muscles. Cranial bones join at sutures, with fontanelles (soft spots) in newborns allowing for growth.
Frontal Bone
Forms the forehead and bony sockets containing the eyes
Parietal Bones
Two bones forming the roof and upper sides of the cranium
Temporal Bones
Two bones forming lower sides and base, enclosing ears and containing the temporomandibular joint (TMJ)
Occipital Bone
Forms back and base of skull with foramen magnum for spinal cord passage
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Additional Cranial Bones
Sphenoid Bone
Bat-shaped bone extending behind the eyes, forming part of the skull base. Serves as an anchor joining frontal, occipital, and ethmoid bones together.
Ethmoid Bone
Thin, delicate bone composed primarily of spongy, cancellous bone. Supports the nasal cavity and forms part of the eye orbits.
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Facial Bones Structure
All facial bones except the mandible are joined by immovable sutures. The mandible is the only movable facial bone, essential for mastication (chewing) and speaking.
01
Nasal Bones
Two slender bones supporting the bridge of the nose, joining with the frontal bone and forming part of the nasal septum
02
Lacrimal Bones
Two thin, small bones at each eye corner, containing fossae for lacrimal glands and canals for tear duct passage
03
Maxillary Bones
Two large bones composing the massive upper jaw (maxillae), joined by a median suture. Cleft palate occurs when they don't unite before birth
04
Mandibular Bone
The lower jaw bone containing alveoli (tooth sockets). Joins the skull at the temporal bone, forming the TMJ
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The Vertebral Column
The spinal column comprises 26 bone segments called vertebrae, arranged in five divisions from the skull base to the tailbone.
1
Cervical (C1-C7)
First 7 vertebrae forming the neck bones. These do not articulate with ribs.
2
Thoracic (T1-T12)
12 vertebrae articulating with the 12 pairs of ribs.
3
Lumbar (L1-L5)
5 strongest and largest vertebrae in the lower back.
4
Sacrum
Slightly curved, triangular bone formed from 5 fused sacral bones.
5
Coccyx
The tailbone, fused from 4 small coccygeal bones.
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Vertebra Structure
Common Components
Whilst vertebrae in different regions vary slightly, they share several common parts:
  • Vertebral Body: Inner, thick, disc-shaped portion
  • Intervertebral Discs: Cartilaginous pads between bodies providing flexibility and shock absorption
  • Vertebral Arch: Posterior part with spinous process, transverse processes, and laminae
  • Neural Canal: Space between body and arch for spinal cord passage
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Bones of the Thorax
Clavicle
Collar bone; slender bone connecting the breastbone to each shoulder bone
Scapula
Shoulder bone; two flat, triangular bones on each dorsal side. The acromion extension joins with the clavicle
Sternum
Breastbone; flat bone extending down the chest midline. Lower portion is the xiphoid process
Ribs
12 pairs: True ribs (1-7) join sternum; False ribs (8-10) join 7th rib; Floating ribs (11-12) are free anteriorly
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Bones of the Arm and Hand
Humerus
Upper arm bone with large, rounded head joining scapula and clavicle
Ulna & Radius
Ulna: medial lower arm bone with olecranon (elbow). Radius: lateral lower arm bone
Carpals
8 wrist bones arranged in two rows of 4 each
Metacarpals
5 bones radiating to the fingers
Phalanges
Finger bones: 3 per finger (proximal, middle, distal); 2 in thumb
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The Pelvic Girdle
The pelvic girdle (hip bone) supports the trunk and articulates with the thigh bone and sacrum. The adult pelvic bone comprises three pairs of fused bones.
Components
Ilium: Uppermost and largest portion. The two iliac parts join the sacrum dorsally, forming the sacroiliac joint. The iliac crest is filled with red bone marrow and serves as attachment for abdominal wall muscles.
Ischium: Posterior part of the pelvis. The ischium and attached muscles form what you sit on.
Pubis: Anterior part joining via cartilaginous disc at the pubic symphysis.
Acetabulum: Socket in the hip bone where the femur head fits, named after a Roman vinegar cup.
Pelvic Cavity: The region within the ring of bone, containing the rectum, sigmoid colon, bladder, and female reproductive organs.
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Bones of the Leg and Foot
Femur
Thigh bone—longest bone in the body. Rounded head fits into the acetabulum socket
Patella
Knee cap—small, flat bone in front of femur-tibia articulation, held by muscle attachments
Tibia
Largest lower leg bone (shin bone). Forms medial malleolus at ankle's inside prominence
Fibula
Smaller lower leg bone, hidden under muscles. Forms lateral malleolus at ankle's outside prominence
Tarsals
7 ankle bones including the calcaneus (heel bone)—largest tarsal bone
Metatarsals & Phalanges
5 metatarsals leading to toe phalanges: 2 in big toe, 3 in each other toe
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Understanding Joints
A joint (articulation) represents the coming together of two or more bones. Different joint types provide varying degrees of movement throughout the body.
Immovable Joints
Suture joints between skull bones providing rigid protection
Partially Movable
Joints between vertebrae allowing limited flexibility
Ball-and-Socket
Freely movable synovial joints like the hip, where femur head fits into acetabular fossa
Hinge Type
Freely movable synovial joints found in elbow, knee, and ankle
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Synovial Joint Structure
Key Components
Joint Capsule: Fibrous cartilage tissue separating bones in synovial joints.
Ligaments: Fibrous bands or sheets of connective tissue anchoring bones together around the joint capsule for strength.
Articular Cartilage: Smooth cartilage surface covering bones at the joint.
Synovial Membrane: Lines the synovial cavity beneath the joint capsule.
Synovial Fluid: Special lubricating fluid containing water and nutrients that nourish and lubricate joints, minimising friction on articular cartilage.
Bursae: Closed sacs of synovial fluid near joints, lubricating areas between tendons, ligaments, and bones where friction would develop.
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Pathological Conditions: Bone Disorders
Ewing's Sarcoma
Malignant bone tumour requiring immediate medical attention
Exostosis
Bony growth arising from the bone surface
Osteogenic Sarcoma
Malignant tumour arising from bone (osteosarcoma)
Osteomalacia
Softening of bone with inadequate calcium amounts
Osteomyelitis
Inflammation of bone and bone marrow
Osteoporosis
Decrease in bone density (mass); thinning and weakening of bone
Talipes
Clubfoot—congenital deformity of foot bones
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Types of Bone Fractures
A fracture is the sudden breaking of a bone. Crepitus is the crackling sound produced when bone ends rub together or against roughened cartilage.
Simple (Closed) Fracture
Bone is broken but there is no open wound in the skin
Compound (Open) Fracture
Bone is broken with an open wound in the skin
Comminuted Fracture
Bone is broken into multiple fragments
Greenstick Fracture
Incomplete fracture common in children where bone bends
Compression Fracture
Bone is crushed, common in vertebrae
Impacted Fracture
Bone fragments are driven into each other
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Fracture Treatment Methods
Reduction Techniques
Reduction: Restoration of the bone to its normal position.
Closed Reduction: Manipulative reduction without an incision, typically performed for simple fractures.
Open Reduction: An incision is made into the fracture site, often necessary for complex fractures requiring internal fixation.
Immobilisation
Cast Application: A solid mould of the bone is applied to fractures to immobilise the injured bone, allowing proper healing.
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Joint Disorders: Arthritis Types
Ankylosing Spondylitis
Chronic, progressive arthritis with stiffening of joints, primarily affecting the spine
Gouty Arthritis
Inflammation of joints caused by excessive uric acid in the body
Osteoarthritis
Progressive, degenerative joint disease characterised by loss of articular cartilage and hypertrophy of bone at articular surfaces
Rheumatoid Arthritis
Chronic disease where joints become inflamed and painful, believed to be caused by an autoimmune reaction against joint tissues
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Additional Joint Conditions
Bunion
Abnormal swelling of the joint between the big toe and first metatarsal bone
Carpal Tunnel Syndrome (CTS)
Compression of the median nerve by a wrist ligament as it passes through the carpal tunnel
Dislocation
Displacement of a bone from its joint
Ganglion
Cystic mass arising from a tendon in the wrist
Herniated Intervertebral Disc
Abnormal protrusion of cartilaginous pad into the neural canal or spinal nerves
Sprain
Trauma to a joint with pain, swelling, and injury to ligaments
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Systemic Musculoskeletal Disorders
Lyme Disease
A recurrent disorder marked by severe arthritis, myalgia (muscle pain), malaise, and neurological and cardiac symptoms. Transmitted through tick bites and requires prompt antibiotic treatment.
Systemic Lupus Erythematosus
A chronic inflammatory disease involving joints, skin, kidneys, nervous system, heart, and lungs. This autoimmune condition requires comprehensive management and monitoring.
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Laboratory Tests for Musculoskeletal Disorders
Antinuclear Antibody Test (ANA)
Plasma tested for antibodies found in systemic lupus erythematosus patients
Erythrocyte Sedimentation Rate (ESR)
Measures rate of erythrocyte settling. Elevated rates indicate inflammatory disorders like rheumatoid arthritis
Rheumatoid Factor Test
Blood tested for rheumatoid factor antibody found in rheumatoid arthritis patients
Serum Calcium (Ca)
Measurement of calcium amount in blood serum
Serum Creatine Phosphokinase (CPK)
Enzyme levels elevated in muscular dystrophy, myocardial infarction, and skeletal muscle disorders
Serum Phosphorus (P)
Measurement of phosphorus amount in serum sample
Uric Acid Test
Measures uric acid in blood. High values associated with gouty arthritis
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Clinical Procedures and Diagnostics
1
Arthrocentesis
Surgical puncture of joint space with a needle. Synovial fluid is removed for analysis
2
Arthrography
X-ray pictures of a joint after injection of opaque contrast material
3
Arthroplasty
Surgical repair of a joint. Total hip arthroplasty replaces femoral head and acetabulum with cemented prostheses
4
Arthroscopy
Visual examination inside a joint with an endoscope. Primarily used for knee, ankle, and shoulder visualisation
5
Bone Scan
Radioactive phosphate injected intravenously; uptake measured by scanning device to detect tumours, infection, or inflammation
6
Electromyography
Recording muscle contraction strength resulting from electrical stimulation
7
Muscle Biopsy
Removal of muscle tissue for microscopic examination
8
Photon Absorptiometry
Rays passed through bones to measure density, detecting osteoporosis
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