The Musculoskeletal SystemSupport, Protection, Movement and Locomotion

Skeletal Functions

Framework for support Transmits movement Maintains shape Protects internal organs from

mechanical injury Contains and protects the red

bone marrow, one of the hemopoietic (blood-forming) tissues

Mineral reservoir - storage site for excess calcium and phosphorus

Storage of fats – yellow marrow

Cytoskeleton Maintains cell shape

Microfilaments Intermediate filaments Microtubules

Protection Enables motion

Cilia Pseudopodia Flagella

Intracellular transport Cell division

Structural support in plants

Cell walls Collenchyma

and sclerenchyma tissue

Cellulose and lignin

Hydrostatic skeleton

Fluid-filled closed chambers

Internal pressure generated by muscle contraction

e.g. sea anemone and worms

Exoskeleton

Shelled molluscs (CaCO3)

Arthropods (chitin) Hard segments covering

muscles and visceral organs

Muscles are attached to the exoskeleton

Restricts growth and size of insect molting

Endoskeleton

Endoskeleton Internal, often

mineralized, connective tissue

Muscles on the outside Cartilage –

elasmobranchs Other vertebrates –

cartilage replaced by bone as embryo matures and develops

Appendicular and axial skeleton

Axial skeleton (80 bones) axis of the body support and protection of main

organs• Skull • Sternum• Ribs• Vertebral Column + sacrum and

coccyx Appendicular skeleton (126 bones)

anchors appendages to the axial skeleton

• Upper Extremities• Lower Extremities• Pectoral Girdle• Pelvic Girdle

Types of bones

1. Long bones• Long shaft (diaphysis)• Two joint surfaces

(epiphyses)• Mostly compact bone• e.g. femur, tibia, fibula,

radius, ulna 2. Short bones

• Cube-shaped, mostly spongy bone

• e.g. bones of wrist and ankle, patella

3. Flat bones• Thin and curved• e.g. skull and sternum

4. Irregular bones• Irregular and complicated

shapes• e.g. spine and hips

Joints or articulations

Meeting of two bones Types of joints

Immovable Slightly movable Freely movable

Bone Tissue Compact bone

series of Haversian canals concentric layers of bone

cells (osteocytes) new bone formed by

osteocytes Spongy bone

ends of long bones less dense contains red or yellow

marrow Periosteum

outer layer of bone rich in nerve endings, blood,

and lymphatic vessels inner portion forms new

bone or remodels existing bone

Types of bone cells1. Osteoblasts

immature bone cells manufacture hormones

and enzymes that aid in bone mineralization

2. Osteocytes mature osteoblasts in

lacunae (spaces) form bone, maintain

matrix act for calcium

homeostasis3. Osteoclasts

responsible for bone reabsorption and shaping

located on bone surfaces

Bone formation Intramembranous

ossification formation of the flat bones of the skull

Endochondral ossification formation of long bones

Bone remodeling

Resorption of bone (by osteoclasts) followed by replacement of bones (by osteocytes)

Functions to regulate calcium levels, repair damaged bones, and shape and sculpt the skeleton during growth

Rate is regulated by parathyroid hormones (PTH) and Vitamin D

Disorders of the skeletal system

Osteoporosis Reduced bone density

leading to fractures Rickets and

osteomalacia Softening of bones leading

to deformations and fractures

Arthritis Inflammation of joints

Bone fractures Scoliosis, kyphosis