Introduction to the Skeletal System

Structure, function, and classification of bones

Skeletal System

Interconnected system of bones ligaments and tendons

Provide support and protection for body

Composed of 206 bones

Functions of Skeletal System

1)Support – provides solid axis for muscles to act against, creating motion.

2)Protection- bones such as skull provide barrier of protection from external forces

3)Hematopoiesis-production of red blood cells

Types of Bones

Bones are divisible into 5 class.LongShortFlat IrregularSesamoid

Long Bones

Found in the limbsEach bone is made of

a body (diaphysis) and two extremities (epiphyses)

Wall consists of dense tissue

Central canal called medullary canal is filled with marrow

Short Bones

Found in skeleton where strength, compactness, and limited movement are desired

2 main examplesTarsusCarpus

Flat Bones

Used in spots where protection or muscular attachment is desired

Main locations are skull and scapula

Irregular Bones

Bones which don’t fit into other categories due to irregular shapes

Examples: vertebrae;sphenoid; hyoid

Sesamoid (Round)BonesUsually small and

round.Embedded within

tendons adjacent to joints.

Example: patella (knee cap)

Bone Formation and Fractures

Fetal Skeleton

Begins as mainly cartilage

Calcifies in utero

At birth, fontanels remain

Ossification

Bone production process gives bone extreme tensile and compressional strength

Several things contribute to strength

Factors which contribute to bone growth

NutritionExposure to sunlightHormonal SecretionPhysical Exercise

Nutrition

Mainly calcium consumption

Increased blood calcium triggers release of calcitonin

Causes uptake of calcium by osteoblasts (bone builders)

Nutrition (contd)

Decrease in calcium triggers release of Parathyroid hormone

Triggers osteoclasts to break down bone, releasing calcium into blood

Exposure to Sunlight

UV light on the skin causes Vitamin D production

Promotes proper absorption of calcium in the SI

Hormonal Secretion

Human growth hormone

Somatotropin

Both hormones stimulate activity in the epiphyseal plate

Physical Activity

Increase in physical exertion on bone tissue actually increases bone density and strength

Bone maintenance

Osteoblasts-constantly producing new bone tissue

Osteoclasts – clean out old bone tissueCauses holes or

tunnels in bone which osteoblasts then fill in with calcium and phosphate compounds

Fractures

Simple Fracture

Also called closed fracture

Bone breaks cleanly, and does not penetrate skin.

Little chance of infection

Compound Fracture

Bone breaks completely

Bone ends protrude through skin

Major chance of serious bone infection

Comminuted Fracture

Bone breaks into many fragments

Common in elderly

Compression Fracture

Bone is crushed

Common in porous bones

Especially common in vertebrae of osteoporosis patients

Depression fracture

Broken bones are forced inward

Common in skull fractures

Impacted Fracture

Broken bone ends are forced into each other

Common in falls (ie. From ladder) where person attempts to break their fall

Spiral Fracture

Occurs from excessive twisting force on bone

Common in sports injuries

Greenstick Fracture

Bone breaks incompletely

Common in children due to more collagen in bones

Repairing Fractures

Closed reduction = bones are eased back into alignment and “reset”

Open reduction = bones are surgically reset using screws or wires

After either, a cast is usually applied to immobilize the bone; healing begins

Internal Bone Repair

1)Hematoma forms from ruptured blood vessels.

2)After new capillaries form, fibrocartillage callus “splints” broken bone using cartilage and bony matrix.

3)Osteoblasts migrate to area, forming bone “patch” over break. Fibrocartilage is replaced by bony callus.

The Axial SkeletonThe Axial Skeleton

Divisions of the Skeletal SystemDivisions of the Skeletal System

Skeletal system is Skeletal system is divided into two main divided into two main divisiondivisionAxial – central skeleton Axial – central skeleton

that protects and that protects and supports vital organssupports vital organs

Appendicular – Appendicular – skeleton of the skeleton of the extremities extremities

Axial SkeletonAxial SkeletonComposed of skull and Composed of skull and

vertabraevertabrae

Mainly flat and irregular Mainly flat and irregular bonesbones

Serve to protect organs Serve to protect organs such as brain, heart, and such as brain, heart, and lungslungs

Also helps to support Also helps to support body along central axis body along central axis (backbone)(backbone)

Parts of the axial skeletonParts of the axial skeleton

Skull – protects brainSkull – protects brain

Vertebrae – protect Vertebrae – protect spinal chord ;also serves spinal chord ;also serves to keep skeleton uprightto keep skeleton upright

Ribs – protect lungs and Ribs – protect lungs and heart ; gives intercostal heart ; gives intercostal muscles a hard surface muscles a hard surface to move against for to move against for breathingbreathing

Divisions of the skullDivisions of the skull

Skull is divided into 2 Skull is divided into 2 sets of bonessets of bonesCranium – collection of Cranium – collection of

8 bones which hold and 8 bones which hold and protect brainprotect brain

Facial bones – 14 Facial bones – 14 bones that make up the bones that make up the face; all but 2 are face; all but 2 are pairedpaired

CraniumCranium Frontal Bone – makes up Frontal Bone – makes up

forehead, eyebrows, and forehead, eyebrows, and superior section of eye orbitalsuperior section of eye orbital

Parietal Bone – form most of Parietal Bone – form most of the superior and lateral walls the superior and lateral walls of craniumof cranium

Temporal bones – lie inferior Temporal bones – lie inferior to parietal bonesto parietal bones

Occipital bone – forms back Occipital bone – forms back and floor of cranium; foramen and floor of cranium; foramen magnum (large hole) allows magnum (large hole) allows spinal chord to meet brainspinal chord to meet brain

Facial BonesFacial Bones

Mandible- lower jaw Mandible- lower jaw bonebone

Maxillary bones Maxillary bones (maxillae) fuse (maxillae) fuse together to form together to form upper jawupper jaw

Palatine processes – Palatine processes – directly posterior to directly posterior to maxillae; forms rear maxillae; forms rear of hard palateof hard palate

Facial Bones Contd.Facial Bones Contd.

Zygomatic bones – cheekbonesZygomatic bones – cheekbones

Lacrimal bones – inferior section of orbital Lacrimal bones – inferior section of orbital bones; provides passageway for tearsbones; provides passageway for tears

Ethmoid bone- forms roof of nasal cavityEthmoid bone- forms roof of nasal cavity

More Facial BonesMore Facial Bones

Nasal bones- form Nasal bones- form bridge of nosebridge of nose

Vomer – divides Vomer – divides nasal cavity in halfnasal cavity in half

Inferior conchae- thin Inferior conchae- thin curved bones which curved bones which project from interior of project from interior of nasal cavitynasal cavity

Axial SkeletonAxial Skeleton

Intervertebral DiscsIntervertebral Discs

Spinal curvaturesSpinal curvatures

Bony Thorax Bony Thorax

Intervertebral DiscsIntervertebral DiscsPads of cartilage Pads of cartilage

between each vertebraebetween each vertebraeProvide cushioning; Provide cushioning;

reduce shockreduce shockHigh water contentHigh water contentAs you age, water As you age, water

content lowers, drying content lowers, drying discsdiscs

Can cause herniated Can cause herniated (slipped) disc; where disc (slipped) disc; where disc protrudes from spineprotrudes from spine

Bony ThoraxBony Thorax

Made of bones which Made of bones which connect and protect connect and protect heart and lungsheart and lungs

Ribs, Costal Ribs, Costal Cartilage, and Cartilage, and SternumSternum

RibsRibs12 pairs of ribs, each 12 pairs of ribs, each

connects to a thoracic connects to a thoracic vertebraevertebrae

First 7 pairs = true ribs; First 7 pairs = true ribs; attach directly to sternumattach directly to sternum

Last 5 pairs = false ribs; Last 5 pairs = false ribs; indirect or no attachment; indirect or no attachment; last two are floating (no last two are floating (no sternal attachment)sternal attachment)

SternumSternum

Fusion of three bonesFusion of three bones1) Manubrium (top)1) Manubrium (top)2) Body (middle)2) Body (middle)3) Xiphoid Process 3) Xiphoid Process

(bottom)(bottom)Location for rib Location for rib

attachmentattachmentSurrounded by costal Surrounded by costal

cartilagecartilage

Sternal PunctureSternal Puncture

Process by which Process by which marrow is removed marrow is removed from sternumfrom sternum

Good location Good location because of proximity because of proximity to body surfaceto body surface

The Spinal ColumnThe Spinal Column

Intro Intro

Supports bodySupports bodyConnects skull to Connects skull to

pelvispelvisSends weight down to Sends weight down to

pelvis, where it is pelvis, where it is transmitted through transmitted through the legsthe legs

Surrounds and Surrounds and protects spinal cordprotects spinal cord

26 total bones26 total bones

Divisions of the Spinal ColumnDivisions of the Spinal Column

4 main divisions4 main divisions1) Cervical curvature1) Cervical curvature2)Thoracic curvature2)Thoracic curvature3)Lumbar curvature3)Lumbar curvature4)Pelvic4)Pelvic

SacrumSacrumThoraxThorax

Cervical curvatureCervical curvature

Begins where skull Begins where skull meets spinemeets spine

Composed of 7 Composed of 7 vertebraevertebrae

Labeled C1-C7, Labeled C1-C7, starting at skullstarting at skull

First two vertebrae First two vertebrae (C1 and C2)are (C1 and C2)are differentdifferent

C1 and C2C1 and C2

Perform different jobs Perform different jobs than other vertebraethan other vertebrae

C1 (atlas) has C1 (atlas) has depressions that depressions that accept the occipital accept the occipital codyles (codyles (““yes nodyes nod””))

C2 (axis) acts as C2 (axis) acts as pivot point for skull pivot point for skull ((““nono”” head shake) head shake)

Thoracic CurvatureThoracic Curvature

12 bones12 bones

T1-T12T1-T12

Costal demifacet – Costal demifacet – point of attachment of point of attachment of ribsribs

Lumbar VertebraeLumbar Vertebrae

5 vertebrae5 vertebrae

(L1-L5)(L1-L5)

Sturdiest because Sturdiest because under the most stressunder the most stress

SacrumSacrum

1 bone composed of 1 bone composed of 5 fused vertebrae5 fused vertebrae

““wing-likewing-like”” alae alae connect laterally with connect laterally with hip bones (forms hip bones (forms sacroiliac joints)sacroiliac joints)

Makes up posterior Makes up posterior wall of pelviswall of pelvis

CoccyxCoccyx

1 bone formed by 1 bone formed by fusion of 3 vertebraefusion of 3 vertebrae

TailboneTailbone

Thought to be left Thought to be left over from when our over from when our ancestors had tailsancestors had tails

Spinal CurvaturesSpinal CurvaturesScoliosis- lateral Scoliosis- lateral

curvature curvature Lordosis- Apex Lordosis- Apex

towards anterior (ie. towards anterior (ie. Lumbar curvature)Lumbar curvature)

Kyphosis- Apex Kyphosis- Apex towards posterior towards posterior (Osteoporosis (Osteoporosis patients)patients)

Appendicular Skeleton

Pelvic Girdle

PelvisJuncture point for

axial skeleton and lower body

Holds internal organsDistributes weight

down legs3 fused bonesObturator foramen-

large hole through which nerves and muscles pass

Bones of the Pelvis

IliumIschiumPubis

Become fused into “pelvis” at puberty

Ilium

Makes up top of hip (iliac crest)

Lateral portions of the pelvis

Contains hip socket

Features of the Ilium

Iliac crest – rounded projection on superior surface; makes up “hip”

Acetabulum- joint between femure and pelvis

Width from crest to crest = false pelvis

Width of actual inlet = true pelvis

Ischium

Inferior portion of pelvis

Ischial Tuberosity – point of muscle attachment; “sit bones”

Pubis

Anterior portion of pelvisJoined medially by pubic symphysis

Leg bones

Hands and Feet

Appendicular SkeletonAppendicular SkeletonSuperior Extremities Superior Extremities

Shoulder GirdleShoulder Girdle

Also called pectoral Also called pectoral girdlegirdle

Composed of only Composed of only two bonestwo bonesClavicleClavicleScapulaScapula

ClavicleClavicle Collar boneCollar bone

Double-curvedDouble-curved

Attaches medially to manubrium Attaches medially to manubrium of sternumof sternum

Attaches laterally to scapulaAttaches laterally to scapula

Acts as a brace, keeping arm Acts as a brace, keeping arm away from thoraxaway from thorax

Also prevents shoulder Also prevents shoulder dislocationdislocation

ScapulaScapulaShoulder BladeShoulder Blade

Main function is Main function is attachment of shoulderattachment of shoulder

Major point of muscle Major point of muscle attachment for movement attachment for movement of armsof arms

Weakly attached to Weakly attached to thorax, so moves easilythorax, so moves easily

Major Processes of the ScapulaeMajor Processes of the Scapulae

1)Acromion – extends 1)Acromion – extends from spine of from spine of scapulaescapulaePoint of attachment of Point of attachment of

clavicleclavicle

2)Coracoid- main site 2)Coracoid- main site of arm muscle of arm muscle attachmentattachment

Glenoid CavityGlenoid Cavity

Socket of arm jointSocket of arm joint

ShallowShallow

Allows for great range Allows for great range of motionof motion

Also dislocates easilyAlso dislocates easily

Movement in the Shoulder GirdleMovement in the Shoulder Girdle

Very free moving becauseVery free moving because1)Only attaches at one point to axial 1)Only attaches at one point to axial

skeletonskeleton2)Loose attachment of scapula allows it to 2)Loose attachment of scapula allows it to

slideslide3)Glenoid cavity very shallow3)Glenoid cavity very shallow

Arm BonesArm Bones

Arms composed of Arms composed of long boneslong bones

Humerus (upper arm)Humerus (upper arm)

Radius and Ulna Radius and Ulna (forearm)(forearm)

HumerusHumerus

Simple long boneSimple long bone

Greater and lesser Greater and lesser tubercle allow for tubercle allow for muscle attachmentmuscle attachment

Deltoid tuberosity-Deltoid tuberosity-place of attachment place of attachment for deltoid musclefor deltoid muscle

Attachment to the forearmAttachment to the forearm

Trochlea articulates Trochlea articulates against bones of against bones of forearmforearm

Olecranon fossa Olecranon fossa shaped like spoonshaped like spoon

Forearm bonesForearm bones

Ulna – pinkie-side of Ulna – pinkie-side of forearmforearm

Radius – Thumb side Radius – Thumb side of forearmof forearm

Processes of the ulnaProcesses of the ulna

Olecranon process Olecranon process attaches to humerus attaches to humerus at olecranon fossaat olecranon fossa

Allows for articulation Allows for articulation between upper and between upper and lower armlower arm

Hands and Feet

Joints

Intro

Any point where bones meet

Also called articulations

Every bone (except hyoid) articulates with at least 1 other bone

Classifications of Joints

Can be classified by mobility, or by the type of tissue which connects the bones

Joint classification by Mobility

Can be one of three types.1) Synarthroses –

immovable joint2)amphiarthroses- slightly

moveable joint3)diarthroses- freely

movable

Classification by connective tissue type

Joints are connected by either fibrous, cartilage, or synovial connective tissue.

Fibrous is usually synarthroses,

Synovial – diarthroses

Fibrous Joints

Fibrous tissueExample= sutures of

the skullTight fibrous tissue

allows for essentially no movement

Cartilaginous Joints

Cartilage

Example= intervertebral joints

Can express either type of movement

Synovial Joints

Bones separated by synovial cavity

Empty pocket serves to reduce friction between moving bones

Usually located in extremities, where movement is necessary

So… What does it mean to be double-jointed?

Usually not actually two joint cavities

Ligaments are simply less taut than normal, allowing for more flexibility

Can be indicative of serious genetic defects

Joint Problems

Osteoarthritis – general break-down of joints, leading to ossification, and then pain.

Rheumatoid Arthritis – autoimmune disease where body attacks its own tissues; cause unknown

Features of the Skull

Sutures of the craniumSuture – location

where flat bones of the cranium meet and fuse

Squamous- fuses temporal and parietal

Coronal – fuses frontal to parietal

Saggital – fuses plates of parietal bones

Lambdoid – fuses occipital to parietal

Bone markings of the Temporal Bones

1) external auditory meatus – canal which leads to inner ear

2) styloid process – sharp, needlelike projections inferior to the e.a.m.;location of muscle attachment

3) zygomatic process- forms cheek bones;forms large hole which allows jaw muscles to pass through to mandible

Temporal bone markings (contd.)4) mastoid process –

posterior and inferior to e.a.m.;location of muscle attachment for muscles of the neck

5) jugular foramen- at junction of occipital and temporal bones; allows jugular vein to pass through from brain

6) carotid canal – anterior to j.f. Allows carotid artery to pass to brain

Occipital Condyles

Lie lateral to the foramen magnum

Rest upon the spinal column

Provides point of attachment for skull to spinal column

Cribriform Bones

Cribriform bones – “holey” bone plates which make up roof of nasal cavity;allow for olfactory sensors to pass from nose to brain

Sinuses

Empty pocket inside bones which are lines with mucous membranes

Paranasal sinus- surrounds nasal cavity

Lighten skull, and thought to amplify sounds when speaking

Deformations

Cleft palate = when palatine bones fail to properly or completely fuse.

Leads to inability to nurse, due to failure to form a vacuum.

Male vs. Female Skeleton

In general

Male skeleton is larger, with thicker bones

Female bones maintain many characteristics of prepubescent skeleton

Male features change at puberty (usually at points of muscular attachment)

Skull

Male mastoid process more pronounced

Superior portion of female orbital (brow ridge) less pronounced

Female mandible is pointed, while male is squared

Facial Differences

Female face wider than male

Females have more pointed nose, while males are more blunt

Female forehead less sloping

Eyebrows positioned higher in females

Pelvis

Female Pelvis wider and more shallow

Male iliac crests more pointed

Male pelvis more narrow

SacrumFemale sacrum wider and flatter

Usually more rounded than male

Forensic anthropology

Most will say that there is no exact way to determine sex from skeleton (not exact science)

Pelvis is probably most reliable feature to analyze, followed by mandible