The Skeletal System PDF

The Skeletal System Eric McLearon,MD The Skeletal System We’ll cover: Bone functions Bone structure Bone cells & tissue Hormones and bones 2nd lecture: Axial bones 3rd lecture: Appendicular bones Bone (Osseous tissue) - is alive! (not like stone fossils) Bone functions: 1. Support the body...

The Skeletal System Eric McLearon,MD The Skeletal System We’ll cover: Bone functions Bone structure Bone cells & tissue Hormones and bones 2nd lecture: Axial bones 3rd lecture: Appendicular bones Bone (Osseous tissue) - is alive! (not like stone fossils) Bone functions: 1. Support the body 2. Facilitate movement 3. Protect internal organs 4. Makes blood cells (red marrow) 5. Stores & releases minerals, fat 206 Bones in the Adult Skeleton Classified by Shape: 1. Long bones (arms, legs) 2. Short bones (carpals, tarsals) 3. Flat bones(skull, scapulae, ribs) 4. Irregular bones(vertebrae, face) 5. Sesamoid (patella) Bone Structure (eg. Femur) Diaphysis - the long shaft of a bone -contains medullary cavity (yellow marrow) -made of compact/cortical (dense) bone Epiphysis - at bone ends Diaphysis -contains red marrow -made of spongy/cancellous/trabecular bone Metaphysis - “neck” connecting diaphysis to epiphysis -where growth plate & red marrow is found Bone Structure (eg. Femur) Endosteum - inner membrane of the medullary cavity -bone growth, repair, remodeling all initiated from here Periosteum - fibrous membrane Diaphysis surrounding the bone -contains nerves, blood vessels -where tendons, ligaments attach Articular cartilage - at bone ends, where joints form with other bones -made of hyaline cartilage Bone structure Nutrient foramen - holes in the bone where blood vessels and nerves enter Bone features (Openstax table 6.3) -trochanter, tuberosities, tubercles -condyles -fossa -crests -sinuses -foramen/fissures Bone cells and tissue Bone is the densest body tissue, made of 4 cell types that lie within a matrix of Collagen where salt crystals Calcium phosphate(CaPO4), Calcium carbonate (CaCO3), and other minerals deposit forming Hydroxyapatite (~70% of bone weight) Ca10(PO4)6(OH)2 Bone composition Bone cells Bone cells 1. Osteogenic cells - (aka osteoprogenitor cells) undifferentiated stem cells that have high mitotic activity (dividing often), the only bone cells that divide -found in periosteum or marrow, they become osteoblasts Bone cells 2. Osteoblasts - found in growing portions of bone, they create new bone tissue out of collagen and calcium salts 3.Osteocytes - a mature osteoblast that has surrounded itself with hydroxyapatite -neither of these 2 cells can replicate Bone cells and tissue -Osteocytes sit in lacunae (little spaces) surrounded by bone tissue -they secrete enzymes that maintain mineral concentration in the matrix -can communicate and receive nutrients by channels called canaliculi Bone cells 4. Osteoclasts - break down old, damaged or unnecessary bone("resorption") to release calcium (bone is dynamic!) -found on bone surfaces -multinucleated -arise from a monocyte/macrophage lineage (different cell line than the (osteogenic cell) other 3 bone cells) Bone tissue: Compact vs Spongy Compact/Cortical bone = dense bone tissue -found under periosteum in diaphysis of long bones -made up of Osteons, the structural units of compact bone -each Osteon is made of lamellae (concentric rings) of calcified matrix with a central canal (aka Haversian canal) containing nerves and blood vessels Bone tissue Compact/Cortical bone Bone cells and tissue Spongy(aka Cancellous/Trabecular) bone - less dense, lighter, osteocytes are found in a lattice-like matrix called trabeculae -more trabeculae form under areas of high stress in the bone for support and strength -in some bones (eg. femur), find red or yellow marrow in spongy bone Bone tissue Spongy bone Skeletal formation (Openstax 6.4) Bottom line: Bone starts as cartilage in embryos/fetus/infants and slowly is converted to calcified bone Bone repair Fracture - a break in a bone -bones have excellent ability to heal due to blood vessels (Open) (In multiple pieces) Bone repair After a fracture, a hematoma (collection of blood) forms first, followed by an internal callus (made of cartilage), followed by an external callus(made of bone) -osteoclasts breakdown dead bone, new osteoblasts replace old osteocytes Effects of exercise, nutrition & hormones on bone Exercise: makes bones more dense -gravity and the physical stress placed on bones during exercise stimulates osteoblasts to reinforce certain areas(eg. trabeculae) with more calcium salts CC: weight lifting good for old folk's bones Bone nutrition Calcium(Ca+2) - must be in diet for bone growth & maintenance Vitamin D - a vitamin and hormone, it promotes Ca+2 and phosphate (PO4) absorption from the small intestine and kidney -can be made from cholesterol and UV light in the skin in a pathway involving the liver and kidneys -promotes Ca+2 deposition onto bone and Ca+2 homeostasis in body -Vitamin K works with Vitamin D to promote bone growth -Minerals like Magnesium (Mg) and Fluoride(F) also contribute to bone density and strength Bones and hormones Growth Hormone - from the pituitary gland (brain) -stimulates chondrocyte (cartilage cells) mitosis at the epiphyses of long bones, enhances calcium mineralization of bones and increases osteoblast activity Bones and hormones Thyroid hormones(T3, T4) and Sex hormones (Estrogen, Testosterone) also stimulate osteoblasts to create new bone tissue Bones and hormones Parathyroid hormone (PTH) - released in response response to low Ca+2 in bloodstream, it stimulates osteoclasts to break down bone to release Ca+2 Calcitonin - inhibits osteoclasts, stimulates osteoblasts to deposit Ca+2 onto bones Ca+2 Homeostasis -the 3 major hormones regulating Calcium are Vitamin D, Parathyroid Hormone (PTH) and Calcitonin The Axial Skeleton - the head, neck, chest and back 80 of the 206 bones in adult Skull-28(22 skull & 6 Ossicles) Hyoid-1 Vertebrae, Sacrum, Coccyx-26 Ribs-24 Sternum-1 (Appendicular = arms/legs) Ossicles - Malleus, Incus, Stapes -3 little bones in each middle ear The Skull (aka Cranium) -divided into Facial bones and Brain case(aka Cranial bones) -21 of the 22 skull bones are immobile, only the mandible moves The Skull - Brain case/Cranial bones: protects the brain! Two Parietal bones (right and left) form the lateral walls and top of skull Two Temporal bones (R/L) joins the zygoma to form an arch (cheek) -have a cluster of air Mastoid process cells in a mastoid process -houses the middle and inner ears The Temporal bones: landmarks -external auditory meatus -mandibular fossa -mastoid process The Cranial bones Frontal bone - it’s in the front, single Glabella = small depression between eyebrows -forms the superior part of the orbit -thickened above orbit to form ridges (protective) The Cranial bones Occipital bone - posterior skull, single -ligaments and muscles of the neck and back attach here -has opening called Foramen Magnum - where the spinal cord enters/exits skull -condyles form a joint with 1st cervical vertebrae (C1, the Atlas) The Cranial bones Sphenoid bone - bat-shaped, single, central skull bone, joined to most other skull bones -divided into “wings”, forms much of the skull base -has small, central saddle-shaped depression called the sella turcica which houses the pituitary gland Greater wing The Cranial bones Sphenoid bone - has medial/lateral pterygoid plates(processes) that form the posterior/lateral nasal cavity -these plates are also muscle attachment points -has many important foramen (holes) for nerves to exit/enter The Cranial bones Ethmoid bone - single, midline bone that forms the roof and lateral walls of upper nasal cavity -has superior and middle “conchae” (aka turbinates) on each side inside the nasal cavity -has a cribriform plate with many small openings for the Olfactory nerve endings (cranial nerve I, provides sense of smell) The Cranial bones Ethmoid bone has “Crista galli” projecting upwards, attaches to connective tissue called falx cerebri (separates brain hemispheres) The Skull Sutures - where the bones meet Sagittal suture Pterion (weak spot) The Skull : Facial Bones Maxillary bones - form the upper jaw, much of the hard palate(roof of mouth), part of the orbit, lateral base of nose -has an Alveolar process/ridge which houses the upper teeth The Skull : Facial Bones Palatine bones - a pair of irregular bones that form part of the nasal cavity and orbits -form the posterior portion of hard palate (roof of mouth) The Skull : Facial Bones Zygomatic (aka zygoma or cheekbone) -forms lateral portion of orbit and the zygomatic arch The Skull : Facial Bones Nasal Bones - two small bones that join together at the bridge of the nose, support the nasal cartilage The Skull - Facial Bones Lacrimal bones - small bones that contribute to the medial wall of the orbit -form the nasolacrimal canal, where tears drain The Skull - Facial Bones Inferior Nasal Conchae (concha (sing.) aka turbinate) -curved bony plates, project inferior into the nasal cavity, below the Ethmoid The Skull - Facial Bones The Vomer - a single, midline, triangular bone, it forms the posterior portion of the nasal septum The Skull : Facial Bones Mandible - forms the lower jaw, only mobile skull bone -the posterior portion is called the ramus, has a condylar process that articulates with the Temporal bone to form the Temporomandibular joint (TMJ) -the body is the horizontal portion extending forward from the angle -the Alveolar crest/ridge houses the lower teeth The Skull: Important features The Orbit -seven bones contribute to forming the orbit, which surrounds and protects the eye and associated structures: Frontal, Lacrimal, Sphenoid, Ethmoid, Palatine, Maxillary and Zygomatic The Skull: Important features Nasal Septum - The bony portion of the nasal septum is made up of the Ethmoid and Vomer, the rest of the nasal septum is septal cartilage The Skull: Important features Nasal Conchae(aka Turbinates) - three curved downward projections in the nasal cavity that warm and moisturize incoming air, allow contact with mucus to capture debris -the superior and middle conchae are part of the Ethmoid, the Inferior nasal conchae are independent bones Cranial fossa - Anterior, Middle and Posterior The Skull: Important features Anterior cranial fossa - shallowest fossa, overlies orbits, contains Frontal lobes of brain Made up of Frontal, Sphenoid and Ethmoid bones The Skull: Important features Middle cranial fossa - made of sphenoid, temporal bones, the temporal lobes of brain found here -many important openings: Optic canal - where optic nerve passes through the sphenoid Superior Orbital fissure - nerves to eye muscles and sensory nerves pass through here Carotid canal - carotid arteries enter here The Skull: Important features Posterior cranial fossa - deepest fossa, contains the cerebellum, formed by the temporal and occipital bone Foramen magnum - large opening where spinal cord enters/exits Internal acoustic meatus - where Vestibulocochlear (CN8) nerve enters Jugular foramen - cranial nerves and jugular veins exit skull The Skull: Important features Paranasal Sinuses - all communicate with the nasal cavity, give resonance to voice -four bones have sinuses: Frontal, Maxillary, Sphenoid, Ethmoid Skull summary: 6 Ossicles (MIS) 8 Cranial bones, 14 Facial bones (28 total) The Hyoid - Not part of skull, doesn’t contact other bones - Attached to tongue, larynx and pharynx muscles thus involved in speaking and swallowing - has central body, greater and lesser horns for muscle attachment The Vertebral Column(aka Spinal column) - Protects the spinal cord, supports neck, provides rib attachment, carries weight - Three major regions made of 24 vertebrae: Cervical(7), Thoracic(12), Lumbar(5) - Inferior to the vertebrae are the Sacrum and Coccyx (aka tailbone) - Has 4 curvatures that provide strength and flexibility The Vertebral Column - Curvatures - The Thoracic and Sacral curvatures are primary, i.e. develop as a fetus so we're born with them - The Cervical curvature develops as an infant(with head raising) and the Lumbar curvature develops as a toddler(with walking) The Vertebral Structure Body - thick, rounded portion in anterior of vertebrae Pedicles - extend posterior from body, together with Lamina form the Vertebral arch and Foramen where spinal cord passes through Spinous, Transverse processes - Important attachment points for muscles, ligaments Superior, Inferior articular processes - Attach to vertebrae above and below The Cervical Vertebrae(7) - C1, the first cervical vertebrae is called the Atlas, which is ring shaped, has no body or spinous process (allows one to nod) - C2 is called the Axis, has an upward projection called the Dens (aka odontoid process), allows you to shake your head side to side The Cervical Vertebrae -the remaining cervical vertebrae (C3-7) are unnamed, have small bodies -have transverse foramen (holes in the transverse process) where vertebral arteries run The Thoracic vertebrae (12) -larger than cervical vertebrae -have costal facets to attach to ribs -spinous processes angle inferiorly The Lumbar vertebrae(5) -large and thick bodies, carry the weight of the thorax -intervertebral discs (exist between all the vertebrae) are most often displaced (herniated) in the lumbar spine The Sacrum -triangular shaped bone, forms from the fusion of 5 bones, fused by age 20 -attached to L5 superiorly, coccyx inferiorly and ilium bones laterally -has many foramina for nerve passage L5 The Coccyx -aka tailbone, formed by fusion of 4 small bones -doesn’t do much (we don’t have tails anymore) Intervertebral discs of spine -fibrocartilage pads that fill the gap between adjacent vertebral bodies, are flexible and allow some movement of the vertebrae -thickest in the lumbar spine -account for 25% of your height 2 parts: Anulus Fibrosus - thick fibrous outer layer anchored to the vertebral body and the Nucleus Pulposus - soft, gel-like inside the disc, allows some compression Spinal Ligaments 1. Anterior longitudinal ligament - runs the entire length of the spinal column on the anterior vertebral bodies’ surfaces, prevents excess posterior movement (hurt in whiplash) 2. Supraspinous ligament - connects the spinous processes along the posterior aspect of the spine -becomes “Nuchal ligament” in cervical spine, attaches to occipital skull The Thoracic cage -made of 12 pairs of ribs (24 bones), the sternum and the costal cartilage -ribs are anchored to thoracic vertebrae (T1-12) -protects the heart and lungs The Sternum -found in the anterior thoracic cage, it has 3 parts: Manubrium - superior portion, has a jugular notch/depression Sternal body - long central portion, attaches to ribs 1-7 by cartilage Xiphoid process - inferior tip of sternum (don’t break it during CPR!) The Ribs : 12 pairs = 24 bones -numbered 1 through 12 (superior to inferior), Left and Right -have heads that articulate with their respective thoracic vertebrae (Rib 1 attaches to T1, etc) -have a costal groove on the underside where blood vessels and nerves run -Ribs 1-7 attach to the sternum by a costal cartilage ("true ribs") -Ribs 8-12 ("false ribs") don’t directly attach to sternum, but the rib cartilage above it -Ribs 11&12 are “floating”: have cartilages that attach to lateral abdominal wall The Appendicular Skeletal System - the other 126 bones The Pectoral (Shoulder) Girdle = Clavicle and Scapula Clavicle - what attaches your arm to the body (via the scapula) -divided into 3 regions: medial (sternal) end which articulates with the manubrium,the shaft, and the lateral (acromial) end which articulates with the acromion of the Scapula -protects nerves and blood vessels beneath it -highly mobile, easily fractured The Scapula -a dense triangular bone surrounded by muscle -has a Glenoid fossa on its lateral aspect to articulate with the Humerus -Coracoid process - an important bony projection for chest/arm muscles -Spine of scapula - runs along the posterior side, ends at the Acromion which articulates with the Clavicle (AC joint) Scapula -has three fossae: above(supraspinous fossa) and below(infraspinous fossa) the spine, and the whole anterior surface(subscapular fossa) -a dense bone, fractures usually require high energy impact Scapula and Clavicle The Humerus : proximal -single bone of upper arm -humeral head is proximal, articulates with the glenoid fossa of the scapula to make the shoulder joint (dislocates inferior/anterior 90%) -has greater/lesser tuberosities - important for muscle attachments -anatomic(proximal) vs surgical neck(distal) The Humerus : distal -has medial and lateral Epicondyles for tendon attachments (golf vs tennis elbow) -the Trochlea articulates with the Ulna -the Capitulum articulates with the Radius -has 3 fossa to receive the radius and ulna when Posterior Anterior fully flexed (coronoid, radial) or extended (olecranon fossa) The Humerus The Ulna -the medial forearm bone, it’s proximal end has a large curved Trochlear notch to articulate with the humerus (the elbow joint) -also forms joints with the Radius proximally and distally -the Olecranon process - what we know as the “elbow” -linked to the Radius along the shaft by a thick fibrous interosseous membrane -Styloid process is distal at the wrist The Radius -the lateral forearm bone, it’s Head is disc-shaped and articulates with the Capitulum of the humerus -forms joints with the ulna proximally and distally -articulates with two carpal bones at the wrist -also has a Styloid process at the wrist The Radius and Ulna The Carpals - 8 of them in 2 rows Proximal row: Scaphoid, Lunate, Triquetrum, Pisiform The Carpals - 8 of them in 2 rows Distal row: Trapezium, Trapezoid, Capitate, Hamate The Carpals -held together by the Flexor retinaculum, a strong ligament which forms a tunnel with the carpal bones called the Carpal tunnel -many tendons and the Median nerve pass through the tunnel The Metacarpals -Five elongated bones spanning the palm/dorsum of hand -Numbered 1(thumb side, lateral) through 5(pinky side, medial) -articulate with the carpals proximally, the phalanges distally -Boxer’s fracture - 5th MC neck The Phalanges (singular = phalanx) -found in the fingers (digits) -14 in both hands, only two found in the thumb(1st digit) DIP -numbered by digit and called PIP proximal, middle(intermediate) or distal phalanx based on location MCP -form Metacarpophalangeal joints(MCP), Proximal Interphalangeal joints (PIP), and Distal Interphalangeal joints (DIP) The Hand Sesamoid bone The Pelvic Girdle - made of Hip aka Coxal bones -A "Hip" bone is formed by the fusion of 3 bones: Ilium, Ischium and Pubis bones(=1) -Attached to the Sacrum via the Sacroiliac joint -All 3 bones contribute to the Acetabulum, where the femur articulates Hip (aka Coxal bones) Ilium - largest hip bone, can feel crest at base of back -has large, smooth fossa on anterior side -many muscle attachments Hip (aka Coxal bones) Ischium - posterior/inferior hip bone, it’s tuberosity is what we sit on Pubis - anterior, forms pubic symphysis with other pubis bone, composed of 2 “rami” The 3 bones fused together =1 Hip bone The Pelvis = the Hip bones+Sacrum and Coccyx -supports the weight of the torso when sitting, transfers the weight to the legs when standing -protects pelvic organs, many muscle attachments -supported by many ligaments -have foramen for nerves & blood vessels The Pelvis -female pelvic outlet is larger than male pelvic outlet The Femur (proximal) -the single bone of the thigh, longest and strongest bone of the body -it’s head articulates with acetabulum of the hip bone to form the hip joint -has a “neck” and greater and lesser trochanters - (muscle attachment sites) The Femur (distal) -has lateral and medial condyles that articulate with the tibia to form the knee joint -has lateral and medial epicondyles for muscle/ligament attachment The Patella (aka kneecap) -largest sesamoid bone (floating, looks like a sesame seed) -completely enclosed in the quadriceps tendon -articulates with patellar surface of femur, protecting the knee joint The Tibia (aka “shin”) -the medial lower leg bone, bears weight -has medial and lateral condyles covered with menisci that articulate with the femur to form the knee joint -proximally has tibial tuberosity, where patellar ligament attaches -connected to the fibula via an interosseous membrane -medial malleolus - bony prominence at ankle The Fibula -smaller, lateral bone of lower leg -important for muscle attachments and balance -articulates with the tibia proximally and the tibia and talus distally (contributes to ankle joint, but not knee joint) -forms lateral malleolus at ankle The Tibia and Fibula Tibial tuberosity The Tarsals : 7 of them Talus - squared superior portion articulates with the tibia and fibula to form the ankle joint The Tarsals : 7 of them Calcaneus (aka the heel) - largest tarsal, bears weight from tibia via the talus Calcaneus The Tarsals : 7 of them Cuboid(lateral), Navicular(medial), Medial Cuneiform, Intermediate Cuneiform and Lateral Cuneiform form a cluster proximal to the metatarsals Metatarsals -five elongated bones that form the dorsum of the foot -articulate with tarsals proximally and phalanges distally -numbered 1 through 5, medial to lateral, the first is thickest, the 2nd is longest Phalanges (of the foot) -14 in all (like the hand) -numbered like the metatarsals, and named proximal, middle and distal phalanges based on location -large toe (1st) has only proximal and distal phalanges The Foot Bone summary References: Openstax Chapter 6 Researchgate NCBI - Pubmed Google images: Physiopedia, Encyclopedia Britannica, Biology online, Alamy, Nature