Chapter 7: Skeletal System

Classification of Bones Axial skeleton – bones of the skull, vertebral column,

& rib cage

Appendicular skeleton – bones of the upper and lower limbs, shoulder, & hip

Bones contain several tissues – bone tissue, nervous tissue, cartilage, blood, epithelium around vessels

Classification of Bones: By Shape

Long bones – longer than they are wide (humerus, femur, radius, ulna, tibia, fibula, fingers, & toes)

Short bones – cube-shaped bones of the wrist & ankle Bones that form within tendons (patella)

Flat bones – thin, flattened, and a bit curved (sternum, scapula, ribs, & most skull bones)

Irregular bones – bones with complicated shapes (vertebrae & hip bones)

Function of Bones Support – form the framework that supports the body

and cradles soft organs

Protection – provide a protective case for the brain, spinal cord, and vital organs

Movement – provide levers for muscles

Function of Bones Mineral storage – reservoir for minerals, especially

calcium & phosphorus release into blood with needed

Blood cell formation – hematopoiesis occurs within the marrow cavities in bones Red marrow – make blood cells Yellow marrow – store fat

Bone Markings Bulges, depressions, and holes that serve as

Sites of attachment for muscles, ligaments, and tendons

Joint surfaces Conduits for blood vessels and nerves

Bone Markings: Projections-Sites of Muscle & Ligament

Attachment Tuberosity – rounded projection

Crest – narrow, prominent ridge of bone

Trochanter – large, blunt, irregular surface

Line – narrow ridge of bone

Bone Markings: Projections – Sites of Muscle & Ligament Attachment

Tubercle – small rounded projection

Epicondyle – raised area above a condyle

Spine – sharp, slender projection

Process – any bony promenence

Bone Markings: Projections – Projections That Help to Form

Joints Head – bony expansion carried on a narrow neck

Facet – smooth, nearly flat articular surface

Condyle – rounded articular projection

Ramus – arm-like bar of bone

Bone Markings: Depressions & Openings

Meatus – canal-like passageway

Sinus – cavity within a bone

Fossa – shallow, basin-like depression

Groove – furrow

Fissure – narrow, slit-like opening

Foramen – round or oval opening through a bone

Gross Anatomy of Bones: Bone Texture

Compact bone – dense outer layer

Spongy bone – honeycomb of trabecular filled with yellow bone marrow

Structure of Long Bone Long bones consist of a diaphysis and an epiphysis

Diaphysis Tubular shaft that forms the axis of long bones Composed of compact bone that surrounds the

medullary cavity Yellow bone marrow (fat) is contained in the medullary

cavity

Structure of Long Bone Epiphyses

Expanded ends of long bones Exterior is compact bone, and the interior is spongy

bone Joint surface is covered with articular (hyaline)

cartilage Epiphyseal line separates the diaphysis from the

epiphyses

Structure of Short, Irregular, & Flat Bones

Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone on the inside

Have no diaphysis or epiphysis

Contain bone marrow between the traveculae

No medullary cavity

Response to Mechanical Stress

Wolff’s law – a bone grows or remodels in response to the forces or demands placed upon it

Observations supporting Wolff’s law include: Long bones are thickest midway along the diaphysis

(where bending stress in the greatest) Curved bones are thickest where they are most likely

to buckle

Response to Mechanical Stress

Trabeculae form along lines of stress

Large, bony projections occur where heavy, active muscles attach

Bone Fractures (Breaks) Bone fractures are classified by:

The position of the bone ends after fracture The completeness of the break The orientation of the bone to the long axis Whether or not the bone ends penetrate the skin

Types of Bone Fractures Nondisplaced – bone ends retain their normal

position

Displaced – bone ends are out of normal alignment

Types of Bone Fractures Complete – bone is broken all the way through

Incomplete – bone is not broken all the way through

Linear – the fracture is parallel to the long axis of the bone

Types of Bone Fractures Transverse – the fracture is perpendicular to the long

axis of the bone

Compound (open) – bone ends penetrate the skin

Simple (closed) – Bone ends do not penetrate the skin

Common Types of Fractures

Comminuted – bone fragments into three or more pieces ( common in the elderly)

Spiral – ragged break when bone is excessively twisted (common sports injury)

Depressed – broken bone portion pressed inward (typical skull fracture)

Common Types of Fractures

Compression – bone is crushed (common in porous bones)

Epiphyseal – epiphysis separates from diaphysis along epiphyseal line; can hinder growth (occurs where cartilage cells are dying)

Greenstick – incomplete fracture where one side of the bone breaks and the other side bends (common in children)

Comminuted Fracture

Spiral Fracture

Depressed Fracture

Compression Fracture

Epiphyseal Fracture

Greenstick Fracture

Stages in the Healing of a Bone Fracture

Hematoma formation: Torn blood vessels hemorrhage

A mass of clotted blood (hematoma) forms at the fracture site

Site becomes swollen, painful, and inflamed

Stages in the Healing of a Bone Fracture

Fibrocartilaginous callus forms

Granulation tissue (soft callus) forms a few days after the fracture

Capillaries grow into the tissue and phagocytic cells begin cleaning debris

Stages in the Healing of a Bone Fracture

The fibrocartilaginous callus forms when: Osteoblasts and fibroblasts migrate to the fracture and

begin reconstructing the bone

Fibroblasts secrete collagen fibers that connect broken bone ends

Osteoblasts begin forming spongy bone

Osteoblasts furthest from capillaries secrete an externally bulging cartilaginous matrix that later calcifies

Stages in the Healing of a Bone Fracture

Bony callus formation: New bone trabeculae appear in the fibrocartilaginous

callus

Fibrocartilaginous callus coverts into a bony (hard) callus

Bone callus begins 3-4 weeks after injury & continues until firm union is formed 2-3 months later

Stages in the Healing of a Bone Fracture

Bone remodeling: Excess material on the bone shaft exterior and in the

medullary canal is removed

Compact bone is laid down to reconstruct shaft walls

Stages in the Healing of a Bone Fracture

Joints Weakest parts of the skeleton

Articulation – site where two or more bones meet

Functions of joints Give the skeleton mobility Hold the skeleton together

Joints A joint is a junction between bones

Joints have differences in degree of motion Immovable Slightly movable Freely movable

More commonly classified by their structure or the material that binds the joints together: Fibrous joints Cartilaginous joints Synovial joints

Fibrous Joints Lie between bones that closely contact one another

There is no joint cavity

Thin layer of dense connective tissue joins the bones at such joints

Most are immovable some can move slightly

There are 3 types: Sutures – occur between the bones of the skull Syndesmoses – connection between the distal end of

the tibia & fibula and radius & ulna Gomphoses – peg-in-socket fibrous joint between a

tooth and its alveolar socket

Cartilaginous Joints Articulating bones are united by cartilage

Lack a joint cavity

Two types: Synchondroses

Bar or plate of hyaline cartilage unties the bones Immovable Ex) joint between first rib and the sternum

Symphyses Hyaline cartilage covers the articulating surface of the

bone Joint is designed for strength and flexibility Ex) intervertebral joints & pubic symphysis of the pelvis

Synovial Joints Those joints in which the articulating bones are

separated by a fluid-containing joint cavity

All are freely movable diarthroses

Ex) all limb joints & most joints of the body

Synovial joints all have the following: Articular cartilage Joint (synovial) cavity Articular capsule Synovial fluid Reinforcing ligaments

Types of Synovial Joints Ball-and-socket joints

Consists of a bone w/ a ball-shaped head than articulates with a cup-shaped cavity of another bone

Allows the widest range of motion that any other joint

Ex) shoulder & hip

Types of Synovial Joints Condyloid joints

Oval-shaped condyle of one bone fits into an elliptical cavity of another bone

This joint allows for flexion, extension, adduction, abduction, & circumduction movements

Ex) Joints between the metacarpals and phalanges

Types of Synovial Joints Gliding joints

Articulating surfaces are nearly flat or slightly curved

Allow sliding and twisting movements

Ex) Joints in the wrist, ankle, and between the articular processes of adjacent vertebrae

Types of Synovial Joints Hinge joints

Convex surface of one bone fits into the concave surface of another

Resembles the hinge of a door

Ex) Elbow, knee, joints of the phalanges

Types of Synovial Joints Pivot joints

Cylindrical surface of one bone rotates within a ring formed of bone and ligament

Movement is limited to the rotation around a central axis

Ex) joint between the proximal ends of the radius and the ulna

Types of Synovial Joints Saddle joints

Forms between bones whose articulating surfaces have both concave and convex regions

Surface of one bone fits the complementary surface of the other

Permits a variety of movements

Ex) joint between the trapezium and the metacarpal of the thumb

Types of Joint Movements

Flexion – bending parts at a joint so that the angle decreases at the joint

Extension – straightening parts at a joint so that the angle of the joint increases

Dorsiflexion – bending the foot at the ankle toward the shin

Plantar flexion – bending the foot at the ankle toward the sole

Hyperextension – excess extension of the parts at a joint beyond the anatomical position

Types of Joint Movements

Abduction – moving a part away from the midline

Adduction – moving a part toward the midline

Rotation – moving a part around an axis

Circumduction – moving a part so that its end follows a circular path

Types of Joint Movement Pronation – turning the hand so that the palm is

downward or turning the foot so that the medial margin is lowered

Supination – turning the hand so that the palm is upward or turning the foot so that the medial margin is raised

Eversion – turning the foot so that the sole is outward

Inversion – turning the foot so that the sole is inward

Retraction – moving a part backward

Protraction – moving a part forward

Elevation – raising a part

Depression – lowering a part