PNB Bone Physiology and Articulations

Functions of bone/skeleton

support, protection, allow movement, storage depot for Ca and P salts, hematopoiesis (making blood cells)

classes of bones

long, short, flat, irregular, sesamoid

long bone example

arms/legs

short bone example

feet/hands

flat bone example

sternum/skull

irregular bone example

vertebrae

sesamoid bone example

patella

parts of long bone

diaphysis, metaphysis, epiphysis, marrow cavity x2

diaphysis

long, skinny shaft

metaphysis

neck - where it gets wider

medullary cavity

center of diaphysis - yellow bone marrow (inactive, fat reservoir)

hollow bubbles

in spongy bone - red bone marrow (active, hematopoietic stem cells)

2 types of bone in long bones

compact and spongy

compact bone

osteons w/ concentric layers of lamellae, central canal in middle w/ vessels and nerves

spongy bone

lattice-like network of trabeculae - lighten weight of bone, between is where red bone marrow in epiphysis

layers of long bone

periosteum (fibrous layer and cellular layer) and endosteum

periosteum

wrapping along outside of long bone in two layers - fibrous and cellular

fibrous layer of periosteum

very outside, dense irregular CT - weave around, provide framework, weave bone into tendons/ligaments

cellular layer of periosteum

inside fibrous, contains cells that can deposit calcium salts or take them away — bone remodeling

metaphysis breakdown

contains epiphyseal plate (hyaline cartilage)/epiphyseal line (at 25 yo) — growth plate where bone formation occurs

cartilagenous part of the long bone

articular cartilage - at very end lining of the epiphysis, hyaline cartilage, line the articulations where bones form joint - cushions and reduces frictions

blood supply in bones

very vascularized — blood vessels enter compact bone via Volkmann’s canals (perforating canals) - come in via periosteum, enter perpendicular to central canals

long bone

long bone drawing

compact bone drawing

spongy bone drawing

layers of long bone diagram

two types of bone formation

intramembranous and endochondral

intramembranous ossification

bone forms from mesenchymal cells that differentiate into osteoprogenitor cells that give rise to osteoblasts (forms flat bones)

when skull bones fully ossify

After birth to allow for flexibility through the birth canal — around 2 years

fontanelles

large areas of dense connective tissue on the skull that allow for flexibility during childbirth

endochondral ossification

bone replaces hyaline cartilage (forms most bones in body) — chondrocytes in epiphysis go through hypertrophy, become irregularly shaped, apoptosis, osteoblasts invade empty lacunae made from apoptosis — growth in epiphyseal plate

5 zones of endochondral ossification

1 - resting cartilage, 2 - proliferating cartilage, 3 - hypertrophic cartilage, 4 - calcified cartilage, 5 - ossification

fetal endochondral ossification zones

1 - hyaline cartilage bone model, 2 - periosteal collar, 3 - primary ossification center, 4 - x2 secondary ossification centers, 5 - child bone

periosteal collar

bone added to surface of diaphysis through outside contact with blood vessels — stem cells enter, begin to build matrix around edge = collar)

primary ossification center

source of bone cells — blood vessel invades diaphysis, osteoblasts spreading out with bone matrix (center), diaphysis always transitions into bone first

secondary ossification centers

collar merges with matrix within,blood invading each epiphysis to form 2 more centers

child bone

osteoblasts work to produce matrix until fully enclosed by matrix — lacunae, spongy bone eventually to compact

birth plates

bone maintains ability to grow out length after baby is born because of

2 types of long bone growth

growth in length or growth in width (appositional)

long bone growth in length

cartilage proliferation on epiphyseal side of plate, ossification occurs on diaphyseal side, process continues until chondrocytes stop proliferating and entire growth plate ossifies

appositional growth (width)

adding layers by remodeling marrow cavity, compact bone thickens and strengthens long bone with layers of circumferential lamellae — *can occur in adults if something in lifestyle (ie. weight-training)

bone remodeling in adults

in response to changes in demand (force/load) on bones — weight-training or prolonged bed rest

Wolff’s Law

bones remodel in response to compressive force (higher compressive force=thicker bones and vice versa) — bed rest vs weight-training

calcium reservoir

bones store calcium in excess and break it down in lack of it

two hormones regulating blood calcium homeostasis

parathyroid hormone (PTH) and calcitonin

plasma calcium is low

triggers PTH from thyroid into blood, triggers osteoclasts and reabsorption of calcium, increase Ca to homeostasis

plasma calcium is high

trigger receptors in thyroid, release calcitonin, inhibits osteoclasts, stimulates osteoblasts — create hydroxyapatite, remove Ca from blood, back to homeostasis

osteoporosis

osteoclast activity outpaces osteoblasts as you age— lose bone density, common in older adults and post-menopausal women (lack of estrogen), problematic b/c leads to fractures/decreases calcium reserves/kyphosis

kyphosis

symptom of osteoporosis, excessively curved spine, leads to decrease in lung capacity, decrease in optimal circulation, compress certain nerves

bone repair after break

1 - hematoma (blood vessels throuhgout blood burst and need to contain blood)

2 - cells from endosteum form fibrocartilage around break (internal soft callus), cells from periosteum form hyaline cartilage callus around outside of bone,

3 - osteoclasts reabsorb dead bone fragments and osteoblasts remodel two calli into bony calluses

4 - remodeling (spongy bone back in appropriate places, compact bone in superficial parts)

types of fractures

open/compound (bone breaks through skin - infection), closed (contained w/in skin), and greenstick (bone doesn’t break all way through — children bc not fully ossified)

ALSO includes transverse, spiral, comminuted, impacted, and oblique

articulation

meeting place of 2+ bones

range of motion (ROM)

normal extent of mobility for a specific joint movement — in degrees, differs for everyone (ie. wrist flexion is about 70-90 degrees)

degrees of freedom

number of axes at which movement in a joint occurs, same for everyone (wrist is biaxial joint w/ 2 degrees of freedom and 2 planes of movement)

mobility vs stability

inverse relationship — mobility comes at the risk of stability (ie. shoulder very mobile, more likely to injure)

joint classifications by structure

fibrous, cartilagenous, synovial

joint classifications by function

synarthrosis, amphiarthrosis, diarthrosis

synarthrosis

immoveable (bones meeting in skull)

amphiarthrosis

slightly moveable (public symphesis)

diarthrosis

freely movable (shoulder, hips)

flexion/extension

movements that occur in sagittal plane (front and back)

flexion

bends joint, decreases angle (bend arm)

extension

extends joint, increases angle (extend arm)

ankle movements

dorsiflexion (point up) and plantar flexion (point down)

abduction/adduction

movements that occur in the frontal plane (side to side)

abduction

moving away from midline (raising arm to side)

adduction

moving towards midline (putting arm against body)

circumduction

movement in cone-like shape, both sagittal and frontal plane (moving hand in circle)

rotation

movements that occur around longitudinal axis of moving segment (twisting torso, turning head)

pronation/supination

specialized rotation at the proximal and distal radioulnar joints

supination

palms forward, radius and ulna parallel (anatomical position)

pronation

palms down, radius crosses over ulna

inversion/eversion

special movement of intertarsal joints (ankle)

inversion

bring sole of foot towards midline (in to the body)

eversion

bring sole of foot away from midline (evict from body)

retraction/protraction

forward/backward movement

retraction

pull back (pull in jaw, pull scapula together/back)

protraction

push forward (push out jaw, push scapula forward)

elevation/depression

up and down movement

elevation

move upward (shrug shoulders)

depression

move down (rest shoulders)

opposition

special movement of any finger coming together w/ thumb — pincer grasp, special to few mammals, allows dexterity

joint tidbits

• all fibrous and cartilagenous are either gonna be synarthrosis or amphiarthrosis (bc tissue doesn’t allow for a lot of movement)

• all synovial joints are diarthrosis (fluid-filled sac that allows for lots of movement)

fibrous joints vocab

sutures of skull, fontanels, syndesmosis

sutures of skull

bound together by short, tight fibers, makes strong articulation — interdigitating (interlock/weave, add strength +stability to joint) — synarthrosis

fontanels

special joints in skulls of fetuses/infants - large areas of dense irregular CT that allow for some movement during birth

syndesmosis joint

connects 2 bones together by tight, longer fibers - interosseous ligament that allows for slight give, very stable (ie. distal tibio-fibular articulation that allows for increased ROM for ankle)

cartilagenous joints vocab

synchodrosis and symphisis

synchondrosis joint

hyaline cartilage connects bones, immovable (ie. long bones, epiphyseal plate during growth or first rib + sternum)

symphisis

fibrocartilage discs unite bones, allows slight movement between articulating bones (between pubic bones, bodies of vertebra)

• pubic symphisis during childbirth is special case - opens up a lot more due to estrogen and relaxin that release the ligament itself

synovial joints basic anatomy

joint cavity containing synovial fluid (cushion, lubricate, and nourishes), freely movable joints, contains lots of blood vessels that secrete into fluid, all share common anatomy

other synovial structures

bursa (pillow for synovial fluid, reduces friction and tension) and tendon sheath (synovial fluid-filled structure, forms sleeve around tendons and reduces friction)

types of synovial joints

hinge, pivot, condyloid, saddle, ball-and-socket, and gliding

hinge joint

concave surface articulating with a convex surface, uniaxial, flexion/extension (ie. elbow)

pivot joint

rounder portion of bone rotates w/in a ring of bone/ligament, uniaxial, rotation (ie. atlanto-axial joint)

condyloid joint

shallow depression at one end of one bone articulates w/ rounded structure of other bone, biaxial (ie. wrist)

saddle joint

both bones have saddle shape, concave one direction, convex other, rides on saddle, biaxial (ie. first carpo-metacarpal)

ball-and-socket joint

rounded head of one bone fits into concave articulation of adjacent bone, multiaxial (ie. shoulder, hip)

gliding joint

flat/nearly flat articular surfaces that allow gliding in any direction, nonaxial/multiaxial (ie. sternocostal)