A&P Honors - Unit 4: Skeletal System

Function of bones

support against gravity, leverage for muscles, protection of organs, blood cell production, storage of calcium and fat

Bones

solid network of living cells and protein fibers that are surrounded by deposits of calcium salts

Matrix

(2/3 of bone mass): Hydroxyapatite, calcium carbonate, other

Protein fibers

(1/3 of bone mass): collagen is majority of organic matrix mass + others

Periosteum

tough, connective tissue covering (joins with tendons and ligaments)

Bone marrow

inside bone cavities

Bone marrow (hemopoietic tissue)

Produces blood cells, red, in nearly every bone as a child

Adults: skull, vertebrae, ribs, sternum, pelvic gridle, proximal heads of humerus and femur

Bone marrow (fatty connective tissue)

Yellow, most red marrow turns into fatty yellow marrow; no longer produces blood

Shapes

long bones, short bones, irregular bones, flat bones, sesamoid bones

axial skeleton

supports central axis of body and encases viscera (soft organs)

Includes 80 bones

Skull (29)

Vertebral column (26)

Rib cage (25)

The skull

divided into cranial bones(8), facial bones(14), other associated bones(7)

Cranial bones held together by

immorable joints called sutures, flexible in young children (becomes fixed as you age)

Foramina

tiny holes in bones that allow nerves, blood vessels, and other structures to pass through

Foramen magnum

(largest opening) where medulla oblongata projects out from skull, allows for blood vessels and nerves to enter/leave the cranium

Hyoid

associated with voice, fuses from 3 bones in early adulthood, function: provides anchor for muscles of tongue and neck

Vertebral column

vertebrates (irregular bones consisting of several parts)

Spinal chord

runs through the foramen

Humans have __ vertebrae when adult

26

Cervical

Neck, 7 (C1 - C7)

C1 is known as the

atlas vertebra (holds head, nod yes)

C2 is known as the

axis vertebrae (turn head, rotate no)

Thoracic

12, articulate with the ribs, T1 - T2

Lumbar

5, lower back/major weight-bearing, L1 - L5

Sacral

5, fused to form the sacrum

Coccygeal

4, fused to form the coccyx

Intervertebral discs

fibrocartilaginous rings that contain a jelly-like fluid

Major role: bear weight, absorb pressure, prevent bones from rubbing

Thoracic cage

protects the visceral organs

Sternum (protects lungs+heart) made up of these bones

manubrium, body, xiphoid process

Ribs

12 pairs, connected to posteriorly to the vertebrae

Rib pair 1-7 connect to

sternum

Rib pair 8-10 connect to

cartilage

Rib pair 11-12 

floating ribs

Appendicular skeleton

suspended from the axial skeleton, includes bones of limbs, pelvis, shoulder

Pectoral girdle (shoulder) components

clavicles, scapulae

Humerus

head articulates with scapula, distal condyle articulates with forearm

Radius

lines up with thumb, head articulates with humerus, biceps brachii attaches here

Ulna

trochlear notch articulates with humerus

Olecranon forms point of elbow ←Connected to elbow

bones of wrist and hand

two rows of carpal bones (8 per hand), proximal phalanges articulate with metacarpals

phalanges

3 phalanges/finger, 2 phalanges/thumb

Pelvic girdle (hips) components

formed by two coxae (hip bones)

coxa fusion, pubic symphysis

coxa fusion of

ilium, ischium, pubis

pubic symphysis

limits movement, disapates pressure (allows you to jump, helps with child birth for women)

pelvis formed by

coxae, sacrum, coccyx

tibia (thick)

tibial tuberosity, patellar tendon attaches here

anterior crest, medial malleolus

Fibuala (little bone)

articulation of head with tibia, lateral malleolus

Bones of ankle and foot

seven tarsal bones

heel bone (calcaneus)

major load-bearing bone

Osteogenic cells

Stem cells found in endosteum, periosteum, and central canals

Multiply continuously to produce new

Osteoblasts

Cells that create new bone

When surrounded by a calcified matrix, matures into osteocyte

Osteocytes

Mature bone cells, maintain normal bone structure

Osteoclasts (found on bone surface)

Secrete acids & enzymes to break down bony matrix and release minerals

Very large, may contain 50+ nuclei

Compact bone

Dense/tightly packed & arranged in osteons (haversian system)

Outer layer of all bones

Spongy bone

Spaces filled with red bone marrow

Inside bones, reduces weight of bones

Flat bone: Spongy vs Compact

Sandwich-like construction: two layers of compact bone enclosing a middle layer of spongy bone 

Surface covered with periosteum

Ossification

Replacing tissues with bone

Intramembranous

Bone grows in membranes

Baby’s soft spots turn into bone, formation of clavicle

Endochondral

Bone replaces cartilage

Remodeling

Osteoclast activity balanced by osteoblast activity

(exercise)