Skeletal, Muscular & Integumentary Systems

Skeletal System FUNCTIONS: Supports the body Protects internal organs Provides for movement – levers act with muscles Stores mineral reserves Provides a site for blood formation An adult has 206 bones in their body

Skeletal System Divisions Axial – supports the central axis of the body (skull, vertebral column, rib cage Appendicular – bones of the arms, legs, pelvis & shoulder

Bone Structure Bones are living tissue – a solid network of cells & protein fibers that are surrounded by hardened deposits of calcium salts Outer layer = periosteum (tough connective tissue) Thick inner layer = compact bone with Haversian canals Second inner layer = spongy bone At birth, most bone marrow is red. Adults have about 50% yellow marrow. About 8 million rbc’s are created every second. Yellow marrow is mostly fat, and as we age, it can be found in places where red marrow once resided -- some of the bones in our arms, legs, fingers and toes, for instance. If the body needs more blood cells, yellow marrow can transform back into red marrow and produce them. Some bones have a lot more red marrow than others -- the pelvic bone, the spine's vertebrae and our ribs are all rich with it. The body also stores iron in bone marrow. Innermost layer = bone marrow Yellow marrow – mostly fat cells Red marrow – produces rbc, some wbc, platelets, contains stem cells

Bone Development An embryo skeleton is almost entirely cartilage Strong, flexible connective tissue No blood vessels Cartilage is replaced by bone during the process of ossification Ossification begins 6-7 months before birth Bone growth occurs at the ends of long bones

Bone Connections Joint – place where one bone connects to another bone Bones connect to bones through ligaments Joint Types: Immovable joint (fixed joints) – allow no movement between bones that touch each other (skull) Slightly movable joint – small amount of restricted movement (slight separation from each other) (vertebrae) Freely movable joint – permit movement - ball-and-socket - hinge - saddle - pivot Bones connect to bones with tough connective tissue called ligaments. Joints are enclosed in sacs called bursa filled with liquid (synovial fluid) to allow smooth movement.

Muscular System Muscles are specialized tissue that can contract and relax. Muscles work with the skeletal system to allow movement. Three types of muscles: Skeletal – attached to bones to allow voluntary movement Smooth – usually not under voluntary control Cardiac – heart muscle

Skeletal Muscle Alternating light & dark bands (striation) Usually voluntary control Large cells that can have many nuclei Found all over the body – usually attached to bones

Smooth Muscle Spindle –shaped cells One nucleus Found in walls of hollow structures (blood vessels, stomach, intestines) Involuntary control

Cardiac Muscle Striated Has one or two nuclei per cell Usually involuntary control Found ONLY in the heart

Skeletal Muscle Anatomy Skeletal muscle consists of bundles of muscle fibers Bundles of muscle fibers are composed of individual muscle fiber cells Each muscle fiber consists of myofibrils that have light & dark bands (striations) Each myofibril is made up of thick filaments (myosin protein) & thin filaments (actin protein) A unit of alternating actin & myosin = sarcomere, separated by a dense “Z band” matter

(Click)

Muscle Contraction Control The axon terminal contains vesicles with the neurotransmitter Acetylcholine (Ach). An action potential causes the vesicles to release the Ach across the neuromuscular synapse. This causes the release of Ca+ in the muscle fiber causing actin & myosin to interact. As long as Ach is released, the muscle will contract. As soon as the Ach is stopped, the muscle relaxes. A strong muscle contraction is the result of MANY muscle fibers contracting. The greater the number of muscle fibers activated, the stronger the muscle contraction.

Muscles and bones Skeletal muscles connect to bones through tendons. There are usually several tendons connecting many muscles around a joint. Muscles usually act in opposing pairs.

Integumentary System Integument = “covering” Skin Hair Nails Some glands (found in skin) Skin primary functions: Barrier against infection & injury Helps regulate body temperature Removes waste products Protection against UV radiation

Skin Anatomy Epidermis Dermis Hypodermis Two layers: dead outermost layer & inner living layer Keratin Melanin No blood vessels Dermis Next inner layer Collagen Many blood vessels Nerve endings Sensory receptors Glands: sweat & sebaceous Smooth muscles Hair follicles Skin cancer can be caused by excessive exposure to UV radiation from the sun. Hypodermis Mainly fat storage Contains larger blood vessels & larger nerve fibers

Hair & Nails Formed from keratin (fibrous protein) Forms horns, reptile scales, bird feathers, porcupine quills Hair is produced at the base by hair follicles Sebaceous (oil) glands help maintain hair health

Nails grow from an area of rapidly dividing cells = nail root. Nails grow at an average of 3mm per month (fingernails grow more rapidly than toenails)