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The Skeletal System The Skeletal System Parts of the skeletal system Bones (skeleton) – 20% of your body mass Joints – junction of 2 or more bones Cartilages - connective tissue Ligaments – fasten bone to bone Divided into two divisions Axial skeleton – skull, spine and thorax Appendicular skeleton – limbs & girdles 5 Functions of Bones Support of the body Protection of soft organs Movement due to attached skeletal muscles Storage – Ca & P also K, Na, S, Mg, and Cu as well as adipose tissue Blood cell formation - hematopoiesis Bones of the Human Body The skeleton has 206 bones Two basic types of bone tissue Compact bone Dense Homogeneous Spongy bone Small needle-like pieces of bone Many open spaces Figure 5.2b 4 Classifications of Bones Long bones Typically longer than wide Have a shaft with heads at both ends Contain mostly compact bone • Examples: Femur, humerus, bones of fingers Classification of Bones Short bones Generally cube-shape Contain mostly spongy bone Examples: Carpals, tarsals Classification of Bones Flat bones Thin and flattened Usually curved Thin layers of compact bone around a layer of spongy bone Examples: Skull, ribs, sternum Classification of Bones Irregular bones Irregular shape Do not fit into other bone classification categories Example: Vertebrae and hip Gross Anatomy of a Long Bone Diaphysis Shaft – surrounds the medullary cavity Composed of compact bone Epiphysis Ends of the bone Composed mostly of spongy bone Bulbous shape provides space for muscle attachment. Figure 5.2a Gross Anatomy of a Long Bone Medullary cavity Center of long bones Contains yellow marrow (mostly fat) in adults Contains red marrow (for blood cell formation) in infants Figure 5.2a Gross Anatomy of a Long Bone • Epiphysis Line • Found in adult bones • Thin line of bony tissue spanning the epiphysis • Epiphyseal plate • Cartilage in young bone between the diaphysis and the epiphysis for long bone lengthening • AKA : Growth Plate Gross Anatomy of a Long Bone Periosteum Outside covering of the diaphysis Contains nerves, blood vessels, lymph vessels Fibrous connective tissue membrane contains osteoblasts Sharpey’s fibers Secure periosteum to underlying bone Figure 5.2c • Arteries - Supply bone cells with nutrients Gross Anatomy of a Long Bone Endosteum Membrane in medullary cavity Contains osteoclasts and osteoblasts Figure 5.2c • Arteries - Supply bone cells with nutrients Gross Anatomy of a Long Bone Articular cartilage Covers the external surface of the epiphyses Made of hyaline cartilage Decreases friction at joint surfaces Figure 5.2a Slide 5.8a Gross Anatomy of a Long Bone • Hematopoiesis – blood cell formation • Occurs in red marrow cavities of spongy bone • Red Marrow Cavities • Newborn • Medullary cavity and all cavities of spongy bone contain red bone marrow. • Most Adults • Confined to the cavities of spongy bone of flat bones and medullary cavity of some long bones Bone Markings Table 5.1 Surface features of bones Sites of attachments for muscles, tendons, and ligaments Passages for nerves and blood vessels Categories of bone markings Projections and processes – grow out from the bone surface Depressions or cavities – indentations Bone Markings Table 5.1 • On a separate sheet of paper and with a group, examine a collection of bones and determine their type (long, short, flat, irregular), their location, and name any bone markings. • Make a data table and describe each bone. Bone Type Location Markings Microscopic Anatomy of Bone • What do you remember about this picture? • What makes it a connective tissue? Microscopic Anatomy of Bone Bone consists of a few different types of cells Osteoblasts – bone building Osteocytes – mature bone cells Osteoclasts – bone destroying Microscopic Anatomy of Bone Osteoblasts – bone building Found in periosteum and endosteum Secrete matrix Microscopic Anatomy of Bone Osteocytes – mature bone cells Osteoblasts that have become trapped in lacunae Maintain the bone tissue Microscopic Anatomy of Bone Osteoclasts – bone destroying Giant cells that participate in bone resorption Mainly found in endosteum Microscopic Anatomy of Bone Bone also is made up of a hard matrix Organic Component: collagen fibers and other organic materials Inorganic component: 2 salts: calcium phosphate and calcium hydroxide form hydroxyapatite. Microscopic Anatomy of Bone The tissue consists of many units working together Osteon (Haversian System) A unit of microscopic bone; concentric circle & matrix rings Microscopic Anatomy of Bone Osteon (Haversian System) Cells = osteocytes Matrix = lamellae Microscopic Anatomy of Bone Each Osteon contains: Central (Haversian) canal Opening in the center of the osteon Carries blood vessels and nerves Microscopic Anatomy of Bone Each Osteon contains: Lacunae Cavities containing bone cells (osteocytes) Arranged in concentric rings Lamellae Rings around the central canal All collagen fibers run in the same direction Figure 5.3 Microscopic Anatomy of Bone Each Osteon contains: Canaliculi Tiny canals Radiate from the central canal to lacunae Form a transport system Microscopic Anatomy of Bone Each Osteon contains: Volkmann’s canal Canal perpendicular to the central canal Connect blood vessels and nerves of periosteum to Haversian canal Microscopic Anatomy of Bone • Make a concept map of the microscopic structure and anatomy of a long bone. Each section should be connected with a phrase. For example, osteon = contains osteocytes and lacunae Osteon Contains cells and matrix Osteocytes Lamellae Changes in the Human Skeleton In embryos, the skeleton is primarily hyaline cartilage During development, much of this cartilage is replaced by bone Cartilage remains in isolated areas Bridge of the nose Parts of ribs Joints Bone Growth Epiphyseal plates allow for growth of long bone during childhood New cartilage is continuously formed Older cartilage becomes ossified Cartilage is broken down Bone replaces cartilage Hormonal Effects on Bone • Growth hormone, produced by the pituitary gland, and thyroxine, produced by the thyroid gland, stimulate bone growth. • GH stimulates protein synthesis and cell growth throughout the body. • Thyroxine stimulates cell metabolism and increases the rate of osteoblast activity. Hormonal Effects on Bone • At puberty, the rising levels of sex hormones (estrogens in females and androgens in males) cause osteoblasts to produce bone faster than the epiphyseal cartilage can divide. This causes the characteristic growth spurt as well as the ultimate closure of the epiphyseal plate. • Estrogens cause faster closure of the epiphyseal growth plate than do androgens. • Estrogen also acts to stimulate osteoblast activity. Hormonal Effects on Bone • Parathyroid hormone and calcitonin are 2 hormones that antagonistically maintain blood [Ca2+] at homeostatic levels. • Since the skeleton is the body’s major calcium reservoir, the activity of these 2 hormones affects bone resorption and deposition. Growth in Bone Length • Epiphyseal cartilage (close to the epiphysis) of the epiphyseal plate divides to create more cartilage, while the diaphyseal cartilage (close to the diaphysis) of the epiphyseal plate is transformed into bone. This increases the length of the shaft. At puberty, growth in bone length is increased dramatically by the combined activities of growth hormone, thyroid hormone, and the sex hormones. •As a result osteoblasts begin producing bone faster than the rate of epiphyseal cartilage expansion. Thus the bone grows while the epiphyseal plate gets narrower and narrower and ultimately disappears. A remnant (epiphyseal line) is visible on Xrays (do you see them in the adjacent femur, tibia, and fibula?) Bone Fractures A break in a bone Types of bone fractures Closed (simple) fracture – break that does not penetrate the skin Open (compound) fracture – broken bone penetrates through the skin Bone fractures are treated by reduction and immobilization Realignment of the bone Common Types of Fractures Repair of Bone Fractures Hematoma (blood-filled swelling) is formed Break is splinted by fibrocartilage to form a callus Fibrocartilage callus is replaced by a bony callus Bony callus is remodeled to form a permanent patch Stages in the Healing of a Bone Fracture Figure 5.5 Fracture Repair • Step 1: A. B. Immediately after the fracture, extensive bleeding occurs. Over a period of several hours, a large blood clot, or fracture • hematoma, develops. Bone cells at the site become deprived of nutrients and die. The site becomes swollen, painful, and inflamed. Step 2: A. B. C. D. Granulation tissue is formed as the hematoma is infiltrated by capillaries and macrophages, which begin to clean up the debris. Some fibroblasts produce collagen fibers that span the break , while others differentiate into chondroblasts and begin secreting cartilage matrix. Osteoblasts begin forming spongy bone. This entire structure is known as a fibrocartilaginous callus and it splints the broken bone. Fracture Repair • Step 3: A. • Bone trabeculae increase in number and convert the fibrocartilaginous callus into a bony callus of spongy bone. Typically takes about 6-8 weeks for this to occur. Step 4: A. B. During the next several months, the bony callus is continually remodeled. Osteoclasts work to remove the temporary supportive structures while osteoblasts rebuild the compact bone and reconstruct the bone so it returns to its original shape/structure. What kind of fracture is this? It’s kind of tough to tell, but this is a _ _ _ _ _ _ fracture. AXIAL SKELETON • Forms the longitudinal part of the body • 80 bones; Divided into three regions 1. Skull 2. Vertebral column 3. Bony thorax • Protect brain, spinal cord, and organs within the thorax The Axial Skeleton The Skull THE SKULL • 22 bones • Divided into Cranial & Facial bones: • Cranial- Attachment for head muscles and protect brain • Facial- form framework for the face • 1. hold eyes forward • 2. provide cavities for special sense organs (taste and smell) • 3. secure teeth • 4. anchor the facial muscles Bones of the Cranium The Skull – Cranium Bones • Frontal bone • Parietal bones • Meet in the midline of the skull at the sagittal suture • Occipital Bone • Foramen magnum “large hole” • Occipital condyle on either side of foramen articulates with 1st vertebrae- lets nod ! Frontal View Frontal Frontal View Parietal Frontal View Temporal Frontal View Nasal Frontal View Vomer Frontal View Zygomatic Frontal View Maxilla Frontal View Mandible Frontal View Frontal Parietal Temporal Nasal Vomer Zygomatic Maxilla Mandible Frontal View The Skull - Cranium Bones • Temporal bones = “time” • External Auditory Meatus – canal that lead to the eardrums and middle ear. • Mastoid process- anchoring site for neck muscles, lump behind ear, less prominent in females than males • Styloid process- attachment for muscles in neck and ligaments • Zygomatic Process- attachment site for some muscles of the neck • Jugular Foramen – allows jugular vein to pass through; which drains the brain • Carotid Canal – through which internal carotid artery runs, supply blood to the brain. The Skull - Cranium Bones • Sphenoid• looks like a bat, butterfly; inside of the skull • Foramen Ovale – allows fibers of cranial nerve V to pass to the chewing muscles of the lower mandible. • Air cavities that fill the sphenoid bone are called sphenoid sinuses Lateral View Frontal Lateral View Parietal Lateral View Temporal Lateral View Nasal Lateral View Zygomatic Lateral View Maxilla Lateral View Mandible Lateral View Sphenoid Lateral View Occipital Lateral View Mastoid Process Lateral View External Auditory Meatus Lateral View Parietal Frontal Sphenoid Temporal Occipital Mastoid Process Nasal Zygomatic Maxilla Mandible External Auditory Meatus Lateral View The Skull • Most bones are flat bones • Contain interlocking joints called SUTURES • There are 4 types of sutures: 1. Coronal - frontal bone meets parietal 2. Sagittal- parietal bones are paired, separated 3. Squamous-parietal bone meets temporal bone 4. lambdoidal -parietal bones meet occipital bone Sutures Sagittal Sutures Frontal (Coronal) Sutures Squamous Sutures Lambdoid Sutures Sagittal Frontal (Coronal) Squamous Lambdoid Sutures FACIAL BONES • 14 bones form the lower front of the skull and provide the framework for most of the face. • 12 of those bones are paired; Mandible & Vomer are single 1. Mandible - strongest, largest bone in the face (lower jaw) 2. Maxillae - upper jaw 3. Palatine bones – form posterior part of the hard palate. 4. Zygomatic bones = cheekbones FACIAL BONES (Continued) 6. Nasal bones - fused medially, form bridge of nose • Lower part of nose is made of cartilage 7. Lacrimal bones • very small within orbit (eye-socket) 8. Hyoid • Only bone in the entire body that does not articulate to another bone • Not really part of the skull, but is closely related to the mandible and the skull. • Serves as movable base for the tongue • Attachment point for several muscles in the neck, elevates larynx during speech and swallowing • Anchored by ligaments attached to styloid processes of temporal bones Bones of the Skull Figure 5.11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5.22 Human Skull, Superior View Figure 5.8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5.23 Human Skull, Inferior View Figure 5.9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5.24 Pasanasal Sinuses • Clustered around nasal cavity • Lighten the skull & Enhance resonance of voice • Air enters sinuses from nasal cavity; mucous from sinuses drips to nasal cavity VERETBRAL COLUMN • AKA the spine • 70 cm= 28 inches long in average adult • 26 irregular bones connected so the flexible, curved spine is formed • Extends from the skull to pelvis • Spinal cord runs through the central canal • Attachment points for ribs and muscles • 33 in fetus and infant- 9 fuse to form sacrum and coccyx • Remaining 24 act as separate vertebrae with connective tissue discs in between each • Ligaments and trunk muscles hold column in place • Intervertebral discs- cushion-like pads- shock Vertebral Column • 5 major divisions: • 7 cervical • 12 thoracic (1 per each pair of ribs) • 5 lumbar • sacrum, coccyx (tiny) • about 5% of otherwise normal people have variations in numbers of thoracic and lumbar vertebrae (cervical # is constant) Abnormal Spinal Curvatures • Scoliosis- abnormal lateral curvature • Result from abnormal vertebral structure or disease involving muscle paralysis, uneven pull of muscles on spine • kyfosis- hunchback• dorsally exaggerated curvature of thoracic vertebrae- osteomalacia, rickets • lordosis- exaggerated lumbar curvature (temporary in prgnant or obese- trying to correct center of gravity Structure of Vertebrae • Body or Centrum – weight bearing • Vertebral arch • Vertebral foramen – canal through which spinal cord passes • Spinous process • Superior and Inferior Articular processes – all vertebrae to form joints • Intervertebral foramina- notched in pedicles of vertebrae to allow space btw vertebrae (from side view)- allows nerves from spinal cord to pass through APPENDICULAR SKELETON • Appendages hang from pectoral and pelvic girdles • Upper and lower limbs differ in their functions and mobility, they have the same structural plan- 3 major segments connected by freely movable joints Regional Characteristics of Vertebrae Atlas – (C1)has no body or spinous process; supports the head; allows the rocking motion of the occipital condyles; allows you to say ‘yes’ Regional Characteristics of Vertebrae Axis- (C2) has a special knoblike feature called the dens; provides a pivot for rotation of the first cervical vertebra and the head; allows you to say ‘no’ The Bony Thorax “The Chest” forms a cage to protect major organs Heart and lungs Looks like an inverted cone Composed of three parts Sternum Thoracic vertebrae 12 ribs Figure 5.19a Slide 5.31a Sternum (breastbone) Manubrium The Bony Thorax Body Xiphoid process Ribs (12) All 12 attach posteriorly to the thoracic vertebra 1-7 = true ribs; attach directly to sternum by costal cartilages 8-12 = false ribs 8-10 attach indirectly to sternum Figure 5.19a Slide 5.31b The Bony Thorax Intercostal spaces are filled with muscles that aid in breathing Figure 5.19a Slide 5.31a Pectoral (shoulder girdle) • 2 Main Bones- clavicle and scapula • medial ends of each clavicle join sternum • distal ends meet scapula • does not quite make a “belt”- scapula only attaches to the thorax and vertebral column by muscles • pectoral girdle attach upper limbs to axial skeleton and insertion points for muscles • girdles are very light, allow flexibility and mobility not seen elsewhere in body Pectoral (shoulder girdle) Reasons upper appendages have flexibility and mobility not seen elsewhere in the body: 1. the only point of attachment of pectoral girdles to axial skeleton is at sternoclavicular joints 2. looseness of scapular attachments allows scapula to move rather freely; can be moved side to side, elevated, depressed 3. socket of shoulder is shallow, small, and poorly reinforced- good for flexibility, bad for stabilityshoulder dislocations are fairly common Pectoral (Shoulder) Girdle Composed of two bones Clavicle (collarbone) Scapula (shoulder blade) These bones are very light and allow, the upper limb to have exceptionally free movement Shoulder girdle is very light and unstable Clavicle is the only part of the girdle that attaches to the axial skeleton Socket of shoulder is shallow and poorly reinforced by ligaments Good for flexibility; bad for stability Shoulder dislocations are common Scapula- shoulder blades • triangular, located btw ribs 2 and 7 • superior border is the shortest • medial border parallels the spinal column • lateral border abuts the armpit (axillary border) • glenoid cavity- small, shallow cavity- articulates with the humerus of the arm • *relatively unstable shoulder joint • anterior surface fairly featureless • posterior- spine- ends laterally in enlarged projection called acromion • acromion articulates with acromial end of clavicle to form acromioclavicular joint • projection anterior from superior border is the coracoid process- beaklike, like a bent little finger- coracoid helps anchor biceps • suprascapular notch- a nerve passgeway Scapula (shoulder blade) Connects the clavicle and humerus Lie on the dorsal surface of the rib cage over ribs 2-7 Flat bone, roughly triangular in shape Attached to the thorax and vertebral column only by muscles Scapular Bone Markings Glenoid cavity Shallow, articular surface that articulates with the head of the humerus forming the shoulder joint Acromion Articulates with the clavicle to form the acromioclavicular joint Forms the summit of the shoulder Coracoid process Small, hook-like structure on the lateral edge of the superior portion of the scapula Assists in stabilizing shoulder joint and anchors biceps Spine Raised region on the posterior side for attachment of trapezius Clavicle (collar bone) Extend horizontally across the superior thorax Functions as an anchor for muscles and ligaments and acts as a brace Articulates with the scapula (acromion) at the acromioclavicular joint Articulates with the manubrium (sternum) on the medial (sternal) end Clavicles- collarbones • rounded on sternal end- attaches to manubrium • flat on acormial end- attaches to acromion of scapula • resist compression poorly- use outstretch arms to break a fall, clavicles break • sensitive to muscle pull, become larger and stronger in people who do a lot of manual labor involving shoulder and arm muscles Arm • Upper arm- humerus • articulates with scapula and radius and ulna • Proximal end- smooth head, fits into glenoid cavityanatomical neck- slight constriction • greater and lesser tuberclesmuscle attachment points • intertubercular groove- serves as a guide for tendon of biceps Bones of the Upper Limb The Upper Limb Pectoral girdle (Shoulder) Humerus (Arm) Radius and Ulna (Forearm) Carpals, metacarpals, phalanges (Hand) Arm Bone Markings •surgical neck- most frequently fractured portion of the humerus •medial and lateral epicondyles •trochlea- medial- articulates with ulna •capitulum- lateral, ball likearticulates with radius ulnar nerve runs behind medial epicondyle, it’s responsible for tingling sensation when you hit you elbow coranoid fossa- anterior olecranon fossa- posterior- allow unla to rotate freely ForearmUlna & Radius • Articulate with each other proximally and distally at radioulnar joints • in anatomical positionradius lateral • palm faces backpronation- radius and ulna form an X Forearm • ulna- slightly longer, primarily responsible for forming elbow joint • coranoid and olecranon processes fit into fossa of humerus (grip the trochlea) • olecranon locks into olecranon fossa to prevent hyperextension • radius- styloid process • major contributor to the wrist HAND- carpals, metacarpals, phalanges • Carpals- bones of wrist • 8, marble sized short bones • Arranged into 2 irregular rows • Metacarpals- bones of palm • 5- numbered 1-5 from thumb to pinkie • heads of metacarpals are knuckles • phalanges- bones of fingers • each hand has 14 phalanges • except for thumb, each finger has 3 bones • distal, middle, and proximal phalanges • (thumb has no middle) • proximal articulate with the heads of metacarpals The Hand (27 bones) Carpals – wrist (8) Arranged in two rows of four Articulate with the radius to form the radiocarpal joint Articulate with each other and united by ligaments Metacarpals – palm (5) When you clinch your fist the heads are your “knuckles” Articulates between each phalanx called metacarpophalangeal joints Phalanges (phalanx bones) – fingers (14) Each finger has 3 bones (distal, middle, and proximal) except for the thumb that has 2 bones Articulates between each phalanx called interphalangeal joints Pelvic Girdle • attaches lower limbs to axial skeleton and supports visceral organs of pelvic cavity • pelvic girdle secured to axial skeleton by some of the strongest ligaments in the body • sockets are deep and cuplike • pelvic girdle made up of 2 coxal (hip) bones • each unites anteriorly (with each other) and posteriorly (with sacrum) • pelvis= both coxal bones plus sacrum and coccyx Pelvic Girdle • during childhood, 3 separate bones- ilium, ischium, and pubis • these fuse firmly by adulthood • point where the three fuse is a deep socket called acetabulum- vinegar cupacetabulum articulates with the head of the femur • ilium= hands on hip bone • sacroiliac joint • ischium- the sitting down bone • pubis- bladder rests upon it • obturator foramen- blood vessels and nerves pass through • pubic symphysis- fibrocartilage • pubic arch- sharpness helps us determine male or female Bony Pelvis Both hip (coxal) bones, sacrum and coccyx Pelvic Girdle (Hip) Functions Connects the vertebral column to the femurs Bear the full weight of the upper body when sitting and standing Transfer the weight from the axial skeleton to the lower limbs Provides attachments for powerful muscles, ligaments and tendons which makes it the most stable joint but lacks mobility Protects some of the urinary, reproductive and digestive organs Coxal Bones Ilium (hands on hip) Uppermost and largest bone of the pelvis Large flaring bones that forms the superior region Anteriorly it joins the pubis Inferiorly it joins the ischium Extends upward from the acetabulum Coxal Bones Ischium (sit down bone) Lower, back portion of the hip bone Proceeds downward from the acetabulum below the ilium and behind the pubis Expands into a large tuberosity and curves forward and forms the top of the obturator foramen Coxal Bones Pubis (bladder rests on it) Anterior portion of the hip bone Extends medially and inferiorly from the acetabulum Articulates with the opposite side at the pubic symphysis Forms the front of the pelvis and supports the organs Pelvic Girdle Bone Markings Acetabulum All three bones fuse together to form a deep socket Located on the lateral surface of the bone Articulates with the head of the femur for the hip joint Iliac crest Superior border of the wing of ilium Attachment for many muscles Ischial tuberosity Inferior surface of ischium Weight is placed on this Pelvic Girdle Bone Markings Pubic symphysis Pubis bones articulate together by a fibrocartilage disc Pubic arch Inferior to the joint is an inverted V-arch Sharpness determines male versus female True pelvis (lesser pelvis) Inferior region surrounded by bone False pelvis (greater pelvis) Superior, expanded portion of the cavity Gender Differences of the Pelvis Female pelvis is modified for childbearing 1. Wider, shallower, lighter and rounder 2. Tilted forward 3. True pelvis defines the birth canal 4. True pelvis and false pelvis are wider in females 5. Pubic arch more than 90 degrees in females FEMUR • Femur • head, fovea capitis • patella Femur (Thigh) Largest and longest bone in the body Length is ¼ of a person’s height It can support up to 30 times the weight of an adult Articulates with hip proximally and tibia distally Patella Kneecap Bone enclosed in the quadriceps tendon that secures the thigh muscles to the tibia Femur Bone Markings Head Articulates with coxal bone at acetabulum Greater and lesser trochanter Sites of attachment for thigh and buttocks muscles Gluteal tuberosity Lateral ridge that runs vertically upward to the base of the greater trochanter Attachment site for gluteus maximus Lateral and Medial condyle Distal projections that articulate with the tibia TIBIA & FIBULA • Tibia- shin bone • medial malleolus • Fibula- little white bone • lateral malleolus Tibia and Fibula (Lower leg) Located from the ankle to the knee Both ends of the two bones articulate at tibiofibular joint Bones are connected by an interosseous membrane Tibia (Shinbone) Receives the weight of the body and the bigger of the two Second largest bone in the body Articulates with the femur superiorly, the fibula laterally and with the talus (ankle) inferiorly Tibia Bone Markings Tibial tuberosity Crest to which the patellar ligament attaches from the patella and the quadriceps muscle Medial malleolus Medial surface of the distal tibia Articulates with the talus bone to form the ankle joint Fibula Located on the lateral side of the tibia Stick-like bone with expanded ends Articulates with the tibia on both ends Does not articulate with the femur Fibula Bone Marking: lateral malleolus Distal end of the fibula that articulates with talus Causes the ankle to bulge laterally METATARSALS & TARSALS • Foot is composed of tarsals, metatarsals and phalanges. • Supports weight & serves as lever • Calcaneus and Talus are the two bones that support most of the body’s weight • Metatarsals form sole • 14 phalanges form toes; distal, middle & proximal Sesmoid bone The Foot (26 bones) Functions Supports body weight Acts as a level to propel the body forward in locomotion Adapts to uneven ground Ankle and Foot (26 bones) Tarsals (7) – ankle Posterior half of the foot Forms the arches of the foot which serves as a shock absorber Body weight is carried by two large bones – talus and calcaneus Talus (ankle bone) Articulates with tibia and fibula Calcaneus (heel bone) Attachment site for Achilles tendon Metatarsals (5) – sole Phalanges – toes (14) Each toe has 3 bones (distal, middle, and proximal) except for the big toe which has 2