MBLEx

The skeletal system consists of bones, cartilage, ligaments, and joints. Its functions are support, protection, movement, mineral storage, blood cell production, and energy storage. Bone tissue is connective tissue with a calcified extracellular matrix. Compact bone is dense and forms the outer layer; spongy (cancellous) bone is porous and lies inside. The periosteum covers bone surfaces except at joints, and the endosteum lines the medullary cavity.

Osteoblasts					Osteocytes					Osteoclasts
Bone-forming cells					Maturebonecellsthatmaintainthe					Bone-resorbing cells; remodeling
					matrix					balancesresorptionandformation
										continuously

A long bone has a diaphysis (shaft), epiphyses (ends), metaphyses (growth regions), and a medullary cavity containing yellow marrow in adults. The epiphyseal plate (growth plate) drives lengthwise growth and becomes the epiphyseal line when growth stops. Bones are classified by shape as long (femur), short (carpals), flat (sternum, scapula), irregular (vertebrae), or sesamoid (patella).

Theadultskeleton(206Bones)

Division	Components
Axialskeleton(80)	Skull(22):8cranialbones(frontal 2parietal 2temporal occipital sphenoid ethmoid)and14facial , , , , ,
	bones(2maxillae mandible 2zygomatic 2nasal 2lacrimal 2palatine 2inferiornasalconchae , , , , , , ,
	vomer) Vertebralcolumn(26):7cervical 12thoracic 5lumbar thesacrum(5fused) andthe . , , , ,
	coccyx (4 fused) Thoracic cage (25): sternum and 12 pairs of ribs; true ribs 1–7 attach directly to the .
	sternum false ribs 8–10 attach through costal cartilage and floating ribs 11–12 have no anterior , ,
	attachment Thehyoidandsixauditoryossiclescompletethecount . .
Appendicularskeleton(126)	Pectoralgirdle:clavicleandscapula Upperlimb:humerus radius ulna 8carpals 5metacarpals 14 . , , , , ,
	phalanges Pelvicgirdle:twohipbones(oscoxae) eachformedbythefusedilium ischium and . , , ,
	pubis Lowerlimb:femur patella tibia fibula 7tarsals 5metatarsals 14phalanges . , , , , , , .

Joints (articulations) are classified structurally as fibrous (mostly immovable), cartilaginous (slightly movable), or synovial (freely movable), and functionally as synarthroses (immovable), amphiarthroses (slightly movable), or diarthroses (freely movable). Synovial joints have a joint cavity with synovial fluid, articular cartilage over the bone ends, a joint capsule, and ligaments. Their types and movements are reviewed in Section 2.

The body has three muscle types. Skeletal muscle is striated, voluntary, and multinucleated, and attaches to bone through tendons; it is the primary focus of massage. Cardiac muscle is striated and involuntary, found only in the heart. Smooth muscle is nonstriated and involuntary, found in the walls of organs and blood vessels. Muscle functions include movement, posture, heat production, and protection.

➜

➜

➜

surrounds the whole muscle

surrounds each fascicle (bundle

surrounds each muscle fiber

chains of sarcomeres, the

of fibers)

(cell)

contractile units

The sliding filament mechanism explains contraction: calcium ions expose binding sites on actin, myosin heads attach, pull the thin filaments toward the center of the sarcomere, release, and repeat, using energy from ATP. A motor unit is one motor neuron and all the fibers it innervates; small motor units allow fine control and large ones generate greater force. Slow-twitch (Type I) fibers resist fatigue and use aerobic metabolism for endurance; fast-twitch (Type II) fibers fatigue quickly and use anaerobic metabolism for power.

Region	MusclesandActions
Headandneck	Frontalis(raiseseyebrows);orbicularisoculi(closeseyes);orbicularisoris(closeslips);masseterand
	temporalis(closethejaw);sternocleidomastoid(flexesandrotatesthehead);scalenes(flextheneck assist ,
	breathing)
Trunk	Trapezius(movesthescapula extendsthehead);latissimusdorsi(extends adducts andmediallyrotatesthe , , ,
	arm);erectorspinae(extendsthespine);quadratuslumborum(laterallyflexesthetrunk);pectoralismajor
	(flexes adducts andmediallyrotatesthearm);rectusabdominis(flexesthetrunk);externalandinternal , ,
	obliques(rotateandlaterallyflexthetrunk);transversusabdominis(compressestheabdomen)
Upperlimb	Deltoid(abductsthearm);rotatorcuff(supraspinatus infraspinatus teresminor subscapularis;stabilizesthe , , ,
	shoulder);bicepsbrachii(flexestheelbow supinates);tricepsbrachii(extendstheelbow);brachialisand ,
	brachioradialis(flextheelbow);pronatorteres(pronates);supinator(supinates)
Lowerlimb	Iliopsoas(flexesthehip);gluteusmaximus(extendsthehip);gluteusmedius(abductsthehip);tensorfasciae
	latae(flexesandabductsthehip);quadricepsfemoris(extendstheknee);hamstrings(flextheknee extendthe ,
	hip);adductorgroup(adductsthehip);gastrocnemiusandsoleus(plantarflex);tibialisanterior(dorsiflexes)