2Skeletal System FUNCTIONS: Supports the body Protects internal organs Provides for movement – levers act with musclesStores mineral reservesProvides a site for blood formationAn adult has 206 bones in their body
3Skeletal System Divisions Axial – supports the central axis of the body (skull, vertebral column, rib cageAppendicular – bones of the arms, legs, pelvis & shoulder
4Bone StructureBones are living tissue – a solid network of cells & protein fibers that are surrounded by hardened deposits of calcium saltsOuter layer = periosteum (tough connective tissue)Thick inner layer = compact bone with Haversian canalsSecond inner layer = spongy boneAt 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 marrowYellow marrow – mostly fat cellsRed marrow – produces rbc, some wbc, platelets, contains stem cells
5Bone Development An embryo skeleton is almost entirely cartilage Strong, flexible connective tissueNo blood vesselsCartilage is replaced by bone during the process of ossificationOssificationbegins 6-7 monthsbefore birthBone growth occursat the ends of long bones
6Bone Connections Joint – place where one bone connects to another bone Bones connect to bones through ligamentsJoint 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 - pivotBones 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.
8Muscular SystemMuscles are specialized tissue that can contract and relax.Muscles work with the skeletalsystem to allow movement.Three types of muscles:Skeletal – attached to bonesto allow voluntary movementSmooth – usually not under voluntary controlCardiac – heart muscle
9Skeletal Muscle Alternating light & dark bands (striation) Usually voluntary controlLarge cells that can have many nucleiFound all over the body – usually attached to bones
10Smooth Muscle Spindle –shaped cells One nucleus Found in walls of hollow structures (blood vessels, stomach, intestines)Involuntary control
11Cardiac Muscle Striated Has one or two nuclei per cell Usually involuntary controlFound ONLY in the heart
12Skeletal Muscle Anatomy Skeletal muscle consists of bundles of muscle fibersBundles of muscle fibers are composed of individual muscle fiber cellsEach 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
14Muscle Contraction Control The axon terminal containsvesicles with theneurotransmitterAcetylcholine (Ach).An action potential causesthe vesicles to release theAch across theneuromuscular synapse.This causes the releaseof Ca+ in the muscle fibercausing actin & myosinto interact.As long as Ach is released, themuscle 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.
15Muscles and bones Skeletal muscles connect to bones through tendons. There are usuallyseveral tendonsconnecting manymuscles around a joint.Muscles usually act inopposing pairs.
16Integumentary System Integument = “covering” Skin Hair Nails Some glands (found in skin)Skin primary functions:Barrier against infection & injuryHelps regulate body temperatureRemoves waste productsProtection against UV radiation
17Skin Anatomy Epidermis Dermis Hypodermis Two layers: dead outermost layer & inner living layerKeratinMelaninNo blood vesselsDermisNext inner layerCollagenMany blood vesselsNerve endingsSensory receptorsGlands: sweat &sebaceousSmooth musclesHair folliclesSkin cancer can be caused by excessive exposure to UV radiation from the sun.HypodermisMainly fat storageContains larger blood vessels & larger nerve fibers
18Hair & Nails Formed from keratin (fibrous protein) Forms horns, reptile scales, bird feathers, porcupine quillsHair is produced at the base by hair folliclesSebaceous (oil) glands help maintain hair health
19Nails 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)