The Skeletal System

BONES

hard elements of the skeleton

consist of nonliving extracellular calcium minerals

gives bones hard + rigid appearance

actually a living tissue containing several cells, nerves + blood vessels

Contains 5 Functions

Support

Protection

Movement

Blood cell formation

Mineral storage

dense compact bone forms the shaft + covers each end

nearly a solid structure w/ central canals containing nerves + blood vessels

made up of extracellular deposits of calcium phosphate surrounding + enclosing cells called osteocytes

arranged in rings in osteons

also called Haversian Systems

ones near the center of an osteon receive nutrients by diffusion from blood vessels that pass through a central canal

as bone develops + becomes hard, osteocytes become trapped in lacunae

remain in contact with each other via canaliculi

within it are extensions of the cell cytoplasm in adjacent osteocytes joined together by gap junctions

channels that permit movement of ions, water + other molecules b/w adjacent cells

by exchanging nutrients across gap junctions, osteocytes can be supplied with nutrients even though most osteocytes are not located near a blood vessel

waste products are exchanged in in opposite direction + removed by blood vessels

less dense spongy bone fills inner region of epiphysis

latticework of hard + strong trabeculae

as hard as compact bone, but is less dense + allows for bone to be light + strong

osteocytes do not need to rely on central canals for nutrients + waste removal

slender trabecular structure of spongy bone gives each osteocyte access to nearby blood vessels in red bone marrow

central cavity in diaphysis is filled with yellow bone marrow

primarily fat that can be used for energy

long bones like the arms and legs contain red bone marrow

stem cells in red bone marrow produce red + white blood cells + platelets

outer surface is called the periosteum

tough layer of connective tissue that contains specialized bone forming cells

LIGAMENTS

consist of dense fibrous connective tissue + bind bones to each other

attach bone to bone

confer strength to certain joints while still permitting movement in relation to each other

CARTILAGE

specialized connective tissue made of collagen + elastin in a ground substance + reduces friction in joints

smoother + more flexible than bone

found where support under pressure is needed + movement is necessary

FIBROCARTILAGE

collagen arranged in thick bundles

withstands pressure + tension

intervertebral disks + menisci

HYALINE CARTILAGE

smooth glossy cartilage of thin collagen

forms embryonic structures that then become bone

1. chondroblasts form hyaline cartilage, creating a rudimentary model of future bone

chondroblast activity is concentrated OUTSIDE growth plate

2. cartilage starts to dissolve + periosteum begins to develop, new blood vessels transport osteoblasts into area to form periosteum

3. osteoblasts secrete osteoid + enzymes, facilitating the deposition of hydroxyapatite crystals

conversion of cartilage to bone is concentrated INSIDE growth plate

4. growth plates in long bones move farther apart + the bone lengthens + widens

controlled by hormones (growth hormone)

covers ends of mature bones in joints creating smooth low friction surface

ELASTIC CARTILAGE

mostly elastin

highly flexible

lends structure to outer ear + epiglottis

bone is a dynamic tissue that undergoes constant replacement, remodeling + repair

compression stress on a bone causes electrical currents within the bone that stimulate the bone forming activity of osteoblasts

weight bearing exercise increases overall bone mass + strength

homeostasis of bone structure depends on the balance of osteoclast + osteoblast activity

OSTEOPOROSIS

condition in which bones lose great deal of mass because of an imbalance over many years in the rates of osteoclasts + osteoblasts

Cells Involved In Bone Development

Chondroblasts

cartilage-forming cells that build a model of future bone

Osteoblasts

young bone forming cells that cause hard extracellular matrix of bone to develop

Osteocytes

mature bone cells that maintain the structure of a bone

Osteoclasts

bone dissolving cells

1. blood vessels create a hematoma at site of fracture, inflammation, swelling + pain happen

2. fibroblasts migrate to area + some become chondroblasts that produce a callus b/w the broken ends of the bone

3. osteoclasts arrive + remove dead fragments of bone + hematoma

4. osteoblasts arrive + deposit osteoid matrix + encourage crystallization of CaP minerals + convert the callus into bone

The Skull

cranial bones

flat bones that enclose + protect the brain

frontal bone

forehead + upper eye sockets

parietal bones

upper left + right sides of the skull

temporal bones

lower left + right sides of the skull

sphenoid bones

b/w frontal + temporal bones

forms back of both eye sockets

ethmoid bone

eye sockets + supports the nose

facial bones

front of the skull

maxilla

part of the eye sockets + anchor upper teeth

palatine bones

roof of the mouth

also formed by maxilla bones

vomer bone

part of the nasal septum

divides nose into left + right

zygomatic bones

cheekbones + outer portion of eye sockets

nasal bones

upper bridge of nose

lacrimal bones

tiny opening where the tear ducts drain tears from the eye sockets into the nasal cavity

mandible

lower jaw + teeth

attached to the temporal bone only

occipital bone

back + base of skull

foramen magnum

large opening at base of skull

where vertebral column connects to the skull + spinal cord enters skull to communicate w/ brain

The Hyoid Bone

does not make direct contact with other bones

attached to temporal bone by ligaments

serves as point of attachment for muscles of tongue, larynx + pharynx

The Vertebral Column

main axis of body

supports head, protects spinal cord + serves as site of attachment for limbs + muscles

contains 33 vertebrae

7 cervical

12 thoracic

5 lumbar

5 fused sacral

4 fused coccygeal

vestigial structure

Intervertebral Disks

separate vertebrae

composed of fibrocartilage

shock absorbers

permit limited degree of movement

strong impacts can cause herniated disks

The Ribs + Sternum

have 12 ribs

1-7 are true ribs

attach directly to sternum

8-10 are false ribs

attach via cartilage

11-12 are floating ribs

have no attachment

helps us breathe by expanding + contracting

shields heart, lungs + other thoracic region organs

Fibrous Joints

immovable

fontanels

soft spots on baby's heads that change shape

Cartilaginous Joints

bones are connected to hyaline cartilage

slightly moveable + allow some flexibility

vertebrae + ribs

Synovial Joints

bones are separated by thin fluid filled cavity

interior is lined with synovial membrane secretes synovial fluid to lubricate + cushion joint

synovial membrane + surrounding hyaline cartilage create a joint capsule

articulating surfaces of two bones covered with tough smooth layer of hyaline cartilage

two bones are fastened together + stabilized by ligaments

Hinge Joint

knee + elbow

to reduce friction, there are small disks on either side of knee joint called menisci

knee also includes 13 bursae sacs

allows movement in one plane

Ball + Socket Joint

wide range of movement

can withstand tremendous use

held tightly together by ligaments + stabilized by tendons

regulated by hormones

when Ca levels FALL

PTH stimulates osteoclasts to secrete bone-dissolving enzymes to release Ca + P into bloodstream

when Ca levels RISE

calcitonin stimulates osteoblast activity which causes Ca + P to be removed from blood + deposited into bone

serves as structural framework for support of soft organs

protects certain organs from physical injury

permits flexible movement of most parts of the body

long bones

bones of limbs + fingers

short bones

wide as they are long

wrist bones

flat bones

cranial bones + sternum

thin, flattened bones with small amount of spongy bone b/w compact bone

irregular bones

coxal bones + vertebrae

don't fit into the other categories

flat + irregular bones (sternum + hips) contain red bone marrow

Pectoral Girdle

supportive frame for upper limbs

Right + Left Clavicles

extend across top of our chest

Right + Left Scapulas

triangular bones in upper back

Humerus

fits into a socket in the scapula

upper arm

long bone

Ulna + Radius

forearm bones

Carpal Bones

8 small bones that make up the wrist

held together by sheath of connective tissue

Carpal Tunnel Syndrome

repetitive stress syndrome

often due to repetitive typing on a computer keyboard

Metacarpal Bones

5 bones that form the palm of the hand

Phalanges

14 bones that form the fingers + thumb

Pelvic Girdle

primary function is to support weight of upper body against force of gravity

protects organs inside pelvic cavity + is attachment site for legs

Coxal Bones

attach to sacral region of vertebral column + then curve forward to meet in front at the pubic symphysis where they are joined by cartilage

Femur

longest + strongest bone in body

rounded upper end of each fits into socket in coxal bone

Tibia

larger lower bone that is in contact w/ femur

Fibula

smaller lower bone

Patella

kneecap

triangular bone that protects + stabilizes knee joint

Tarsal Bones

7 ankle + heel bones

Metatarsal Bones

5 long bones that form the foot

Phalanges

14 bones that form the toes

broader in women

Osteoporosis

caused by excessive bone loss

slight imbalance b/w rates of osteoclasts (breaking down bone) + osteoblasts (making new bone)

decline in estrogen after menopause can cause it

Sprains

damage to ligaments

accompanies by internal bleeding, bruising, swelling + pain

take long time to heal because the ligaments have few cells + poor blood supply

Bursitis + Tendinitis

inflammation

response to injury characterized by redness, warmth, swelling + pain

caused by injuries, blows to the joints or bacterial infections

do not heal quickly due to low blood supply

Arthritis

inflammation of joints

cartilage covering the ends of bones wear out, results in increased friction b/w bones