Skeleto-muscular System Biology 201 Organismal S&F Dr. Tony Serino Biology Department Misericordia University

Skeletal System Composed of mineralized CT and their supporting structures including: bone, cartilage, ligaments, tendons, and bursae Functions: support, protection, homeostasis (specifically Ca++ regulation) and hempoiesis

General Osteology Composition Cells –originate from mesechyme (undifferentiated mesodermal cells) Extracellular Matrix Ground substances: water, salts, cementing substances, glycoproteins Fibers: collagen and elastin

Cartilage Avascular CT Appositional and interstitial growth possible Perichondrium Chondroblast Lacuna Chondrocyte Matrix

Hyaline Cartilage Most abundant form of cartilage, found in articular cartilages, ribs, tip of nose, tracheal rings, etc. Ground substances dominate matrix with collagen outnumbering elastin fibers

Elastic Cartilage Seen where structure needs to snap back to original shape Located in pinna and epiglottis Matrix dominated by elastin fibers

Fibrocartilage Occurs where great strength is needed, collagen fibers dominate matrix Located in slightly moveable joints; such as, vertebral discs and pubic symphysis

Cartilage in Adult

Bone Heavily mineralized CT Highly vascular Principle storage area of Calcium Provides strength and structural support to body

Long Bone Anatomy

Flat Bone Anatomy Trabeculae

Bone Histology

Haversian System Lamellae

Ossification Development of bony tissues First bone to form is woven (premature) bone This is eventually replace by mature bone (compact or spongy bone) Two methods for creating bones: Intramembraneous (bone replaces mesoderm membrane) Endochondral (bone replaces an intervening cartilage model)

Intramembranous Ossification (Membrane bone formation)

Endochondral Ossification (Replacement Bone formation)

Epiphyseal (Growth) Plate Reserve Cartilage (distal perichondrium) Proliferating Cartilage (Growth zone) Hypertrophic zone (Transforming zone) Calcified matrix (Osteogenic zone)

Fracture Healing

Osteoporosis Normal Osteoporotic

Muscular System Functions: Attributes: Movement –generation of force and/or shortening Maintenance of posture Joint stabilization Heat Generation Attributes: contractility, irritability, extensibility, and elasticity

Types of Muscle Cells Skeletal Muscle –voluntary, striated Cardiac Muscle –involuntary, striated Smooth Muscle –involuntary, no striations

Muscles wrapped with CT, that is continuous with tendon and periosteum

Antagonistic Muscle Arrangement This arrangement plus the series elastic component allows the muscle to return to its original length.

Skeletal Muscle Cells Long, cylindrical, non-branching, multinucleated 10-100 mcm wide and up to 35 cm long Voluntary, no spontaneous depolarization normally Contractile proteins (myosin & actin) arranged in bundles called myofibrils

Each myofibril consists of overlapping thick and thin filaments arranged in units called sarcomeres.

Muscle Contraction: Mechanical Events (Sliding Filaments) When a neuron stimulates a muscle cell with acetylcholine, Calcium ions released from SR flood the myofibrils This causes the thick and thin filaments to bind to each other (generates tension) and may cause them to slide past each other This causes the sarcomere to shorten

Muscles are arranged as Motor Units Motor Unit = 1 motor neuron + all the muscle fibers it controls (innervates) The size of the motor unit depends on the degree of control needed in that particular whole muscle.

Cardiac Muscle Striated, single nucleus, branched cells, connected together by intercalated discs (with many gap junctions) Spontaneously contracts, needs no innervation, involuntary

Smooth Muscle No sarcomeres, therefore, no striations, single nucleated, small spindle shaped cells Spontaneously contracts, involuntary control, can remain contracted for long periods of time without fatiguing Two types: Visceral (single unit) –united by gap junctions Multi-unit –needs innervations, behaves like skeletal muscle (Ex. Iris, Arrector pili muscle)