Module 7: Skeletal System

Skeletal System - Functions

• Supportive framework for body

• protect soft tissues/viscera

• Mineral storage

• hematopoiesis

• Facilitates movement w/ skeletal muscles

Osteoblasts

• bone builders

• cells lay down or create osteoid then incorporate mineral salts around themselves

• When active, take Ca out of blood + incorporate into bone ECM

Osteocytes

• Are osteoblasts that have finished laying down osteoid + minerals

• “mature” bone cells

Osteoblast surrounds self w/ calcified matrix + no longer produces → cells become trapped in lacunae within ECM → remains there as osteocyte

Function → plays # of roles in bone maintenance

• comms w/ eachother + other bone cells

• Coordinates bone building + remodelling

Osteoclasts

• Phagocytic cells (bone destroyers)

• break down or absorb ECM of bone

• in bone reabsorption process they release mineral salts (mainly Ca) into blood

Lamelle

Hard, calcified part of bone

made of sheet like layers

hold osteocytes in lucane

make little ring, type structures

Compact Bone

• Dense bone made of many osteons

• Osteons tightly packed together and sit between circumferential lamellae

Circumferential lamellae

Layers of bone tissue

Spongy bone

• Light, porous structure

• Made of trabeculae

  • Bone marrow fulls these spaces

Trabeculae

thin, branching pieces of bone

Hyaline Cartilage

• most abundant

• “joints and growth”

Skeletal locations

• End of bones

• Costal cartilages

• Articular cartilages (inbetween synovial joints)

• respiratory cartilages

• laryngeal cartilages

• Nasal cartilages

Elastic cartilage

• Flexible and springy

• Contains elastin fibres

Skeletal-related locations:

• External ear

• Epiglottis

Fibrocartilage

• Toughest type

• Withstands heavy pressure

• Intermediate between other 2 cartilages

Skeletal locations

• Pads within knee joints

• Between vertebrae

• between pubic bones

Long bone

Bone is longer than it is wide and has an identifiable shaft (diaphysis) and two epiphyses

Short Bone

Bone is not particularly longer in one direction than any other; bone is roughly roundish or cuboidal in shape

Irregular Bone

Bone clearly does not fit any of the other shapes/types and/or has a variety of different proportions, projections or angles…

Flat Bone

Bone has a large, flat (but slightly curved) surface

Endochondral ossification

is the formation of most bones of the body from cartilage precursors.

Osteogenic cells

Mitotically dividing cells that generate new osteoblasts

Axial skeleton

forms the longitudinal axis of the body, therefore consisting of the bones of the skull, vertebrae and ribcage (thoracic cage)

Appendicular skeleton

consists of the bones of the upper and lower limbs and the pectoral and pelvic girdles

Fibrous Joints

Bones connected by dense fibrous CT (mainly collagen)

Little to no movement

• Suture

• Syndemosis

• Gomphosis

Syndemosis - Fibrous joint

Held together by ligaments

Fibia + tibia connect at ankle

Suture - Fibrous joint

Little/no movement

cranial bones held together

Gomphosis - Fibrous joint

“peg in socket” holds tooth in jaw

Cartilaginous joints

Hyaline or fibrocartilage pads

only slightly mobile

• Synchondroses

• Symphasis

Synchondroses - Cartilaginous joints

Bones unified by hyaline cartilage

• Epiphyseal plate

• Sternum

• Joint between sternum and 1st rib

Symphisis - Cartilaginous joints

Bones unified by fibrocartilage

• between 2 pubic bones

  • Pubic symphasis

• between vertebrae

Synovial Joint

A freely movable joint with a joint capsule, synovial fluid, articular cartilage, and surrounding ligaments that provide mobility and stability.

Joint Capsule

A tough outer layer surrounding a synovial joint, providing structure and helping to contain the synovial fluid.

Synovial Fluid

A lubricating fluid secreted by the synovial membrane that reduces friction between the articular cartilages during movement.

Articular Cartilage

Smooth hyaline cartilage covering the ends of bones inside a joint capsule, allowing bones to glide over each other easily.

Synovial Membrane

The inner lining of the joint capsule that produces synovial fluid to lubricate the joint.

Ligaments (in Synovial Joints)

Strong connective tissues outside the capsule that stabilize joints by limiting excessive movement.

Bony Congruence

How well the shapes of the bones in a joint fit together; better fit = more stability, less movement.

Joint Capsule Fit and Ligament Strength

A tight capsule and strong ligaments make a joint more stable but less flexible; a looser capsule allows more movement but less stability.

Muscles and Tendons (in Synovial Joints)

Muscles produce movement across joints and, along with tendons, also help stabilize the joint by supporting it.

Hinge Joint

Description: Allows movement in one direction like a door hinge (flexion and extension).
Example: Elbow, knee, fingers

Pivot Joint

Description: Allows rotational movement around a single axis.
Example: Neck (between atlas and axis), radioulnar joint

Ball-and-Socket Joint

Description: Allows movement in all directions: flexion, extension, rotation, abduction, adduction, circumduction.
Example: Shoulder, hip

Saddle Joint

Description: Allows back-and-forth and side-to-side movement, but limited rotation.
Example: Thumb (carpometacarpal joint)

Condyloid (Ellipsoidal) Joint

Description: Oval-shaped bone fits into a shallow cavity; allows movement in two directions.
Example: Wrist joint, knuckles

Plane (Gliding) Joint

Description: Flat bone surfaces slide over each other with limited movement.
Example: Between small bones in the wrist (carpals) and foot (tarsals)