skeletal system

skeletal system overview

made up of approx 206 bones, connected by joints, organised into the axial skeleton and appendicular skeleton

functions of the skeletal system

support, protection, locomotion, mineral storage, blood cell production

bone tissue types

compact bone and cencellous bone

compact bone (cortical bone)

hard outer layer, strong and dense, greater area of bone than space

cancellous (spongy) bone

spongy inner layer network of trabeculae, less dense than cortical bone, porous, greater area of space than bone, houses bone marrow

bone composition

bone cells (osteoblasts & osteoclasts), osteoids, bone marrow, inorganic mineral salts deposited within matrix

osteoids

non-mineral, organic part of bone matrix made of collagen and non-collagenous proteins

osteoblasts

lay down new bone

osteoclasts

break down old bone

bone marrow

soft tissue inside the bone that produces blood cells and stores fat

types of bone

woven and lamellar

woven bone

collagen fibres are randomly orientated, formed in fetal development or bone repair, remodelled into lamellar bone

lamellar bone

mature bone, collagen fibres organised in parallel, comprised of osteons

why does bone mass decrease with age

Osteoblasts activity decreases, while osteoclasts continue to work at normal levels (more absorption than formation)

what can a decrease in bone mass lead to

weak and porous bones, osteoporosis

axial skeleton

bones of the head and trunk, forms longitudinal axis of the body; consists of the cranium/skull (22 bones) - viscerocranium (14 facial bones) & neurocranium (8 bones around brain), vertebral column (33 bones/vertebrae), rib cage (12 pairs) and sternum

appendicular skeleton

bones that support and form the limbs; upper limb and lower limbs

upper limbs

pectoral girdle (clavicle/scapula), bones of the arms and hands

lower limbs

pelvic girdle (ilium, ischium, pubis), bones of the legs and feet

bone shapes

long, short, flat, irregular, sesamoid

long bones

long and slender; consists of long tube-like diaphysis (shaft) with an epiphysis on either end, epiphyseal growth plates, periosteum, endosteum; e.g. bones of the limbs (femur)

diaphysis

long and tube-like, strong but some flexibility, mostly compact bone

epiphyses

one on either end of diaphysis, articular surface for joints, mostly spongy bone but compact on surface

epiphyseal growth plate

layer of hyaline cartilage separating diaphysis and epiphyses, site of growth, ossifies (solidifies into bone) once growth is complete forming the epiphyseal line

periosteum

dense fibrous connective tissue sheath covering the outer surface of the bone, site of attachment for tendons

endosteum

lines internal surfaces of cavities within bones

short bones

box-like in appearance, similar to long bones, e.g. bones of the wrist and ankle

flat bones

thin, flat, parallel surfaces; usually curved; provide protection for underlying soft tissues and offer extensive surface area for attachment of skeletal muscles, e.g. root of skull, sternum, ribs, scalpula

irregular bones

complex shapes - flat, notched, ridged surfaces; e.g. vertebrae, sacrum, facial bones

sesamoid bones

small, round, flat bones embedded in tendons; protect tendon and increase movement; e.g. patella (kneecap), foot sesamoid, pisiform (located at wrist)

joints

point where two or more bones make contact, classified by structure: fibrous, cartilaginous, synovial

fibrous joints

bones jointed by dense fibrous connective tissue

cartilaginous joints

bones held together by cartilage

synovial joints

bones aren't directly joined - bones have a synovial cavity and are united by an articular capsule, allows movement

vertebral column (spine)

main axis of skeleton; consists of 33 bones: 24 vertebrae (7 cervical, 12 thoracic, 5 lumbar), sacrum (5 fused vertebrae), coccyx (4 fused vertebrae on average); vertebrae are stacked: connected by joints and ligaments, form a stable and flexible comlumn

vertebrae structure

body, pedicle, foramen, arch (lamina and spinous process)

vertebral body

large, flat surfaces facing inferior and superior, transfers weight along the axis of vertebral column

vertebral pedicle

short, thick pillar; connects vertebral body to arch on each side

vertebral foramen

canal through which spinal cord passes

vertebral arch

lateral and posterior walls of the foramen, encloses the spinal cord, lamina and spinous process

lamina

posterior part of vertebral arch

spinous process

projects laterally from the point where the vertebral laminae fuse to complete the vertebral arch

joints between vertebrae

zygapophyseal joints and intervertebral discs, inferior and superior notches of two adjacent vertebrae form a foramen in which the spinal nerve emerges

zygapophyseal joints

joint between superior and inferior articular processes, planar joint - allows restricted sliding movements

intervertebral disks

prevent bodies rubbing, acts as shock absorber, enables limited movement in all direction, weakens with age

cervical vertebrae

small body, bifid spinous process, has transverse foramen for the vertebral artery

thoracic vertebrae

long processes, joint facets for ribs on transverse processes

lumbar vertebrae

large, thick body and strong processes

sacrum

5 fused vertebrae; transverse processes fused to form lateral part, spinous processes partially fused to form sacral crest on dorsum

coccyx (tailbone)

5 semifused vertebrae; small vertebrae, no foramen or obvious processes, easily broken if landed on

4 major curvatures of the spine

cervical, thoracic, lumbar, sacral/coccygeal; accommodate upright posture; align body weight with limbs

primary curvatures

thoracic & sacral/coccygeal: outward curve (kyphosis), present in neonates, creates C-shaped curve

secondary curvature

cervical & lumbar, inward curve (lordosis): develops after birth through development

unnatural curvatures of the spine

scoliosis, enhanced kyphosis, enhanced lordosis

scoliosis

abnormal lateral curvature of the spine causes asymmetric posture

enhanced kyphosis

excessive outward curvature of the spine, typically in the thoracic part, causing hunching of the back

enhanced lordosis

increased inward curvature of the spine, typically in the lumbar or cervical part

thoracic cage

consists of thoracic vertebrae, ribs, costal cartilages and sternum

functions of the thoracic cage

protects heart, lungs, thymusand other structures in the thoracic cavity; serves as an attachment point for muscles involved in breathing, maintaining position of vertebral column, and moving pectoral girdles and upper limbs

rib cage

consists of thoracic vertebrae (spine), ribs and sternum

ribs

long, curved, flattened bones, originating on or between the thoracic vertebrae and ending in wall of thoracic cavity

features of the ribs

mobile due to complex musculature, dual articulations at vertebrae and flexible connection to sternum

movements of ribs during breathing

lowering ribs pulls the sternum inward, raising the ribs moves it outwards; movements also change the width and depth of thoracic cage, decreasing/increasing its volume accordingly when breathing in or out

structure of ribs

head, neck, tubercle, angle, shaft, costal cartilage

head of ribs

end of the rib that connects to spine, featuring two articular facets that articulate with vertebral column

neck of ribs

narrow part between head and tubercle

tubercle of ribs

small bump near the head, forms joint with transverse process of vertebrae

angle of ribs

lateral to tubercle, greatest curvature, weakest part

shaft of ribs

main, flat part of rib; costal groove for intercostal nerve and blood vessels

costal cartilage of ribs

forms joint with sternum

sternum

made up of the manubrium, body and ziphoid process

manubrium of sternum

jugular notch on top, articular facets for first and second ribs, joins the body of the sternum at sternal angle with a symphisis

body of sternum

the bony structure that forms the middle portion of the sternum

xiphoid process of sternum

smallest part, attached to inferior surface of the body, diaphragm and rectus abdominis muscle attach to xiphoid process

joints between ribs and vertebrae

costovertebral joints - synovial joints that connect the head of the rib to the costal facets of the thoracic vertebrae, consists of two parts: costocorporeal joint and costotransverse joint

costocorporeal joint

between rib head and vertebrae; two demifacets on each side, two vertebrae together form a socket for the rib head; allow ribs to elevate, descend and rotate during breathing

costotransverse joint

between rib tubercle and transverse process; tubercle of rib connects with transverse costal fact=et f=of the corresponding thoracic vertebrae

joints between ribs and sternum

true ribs (1st-7th pairs) - directly attached to the sternum through the costal cartilage, false ribs (8th-10th pairs) - share a common cartilaginous connection to the sternum, floating ribs (11th & 12th pairs) - don't connect to sternum at all