Bones, Joints and Muscles

Bones: 206 in human body n Function: – support (eg) pelvic bowl, legs – protect (eg) skull, vertebrae – mineral storage (eg) calcium, phosphate, inorganic component – movement (eg) walk, grasp objects – blood-cell formation (eg) red bone marrow n Osteoblasts: secrete organic part of bone matrix = osteoid n Osteocytes: mature bone cells, maintain bone matrix

Some Reminders about Bones n Bone = bone tissue (type of CT) n A Bone = an organ n Compact vs. Spongy Bone n Composition: Hydroxyapatite, protoplasm, collagen, blood vessels, marrow n Skeleton = bones, cartilage (avascular, no nerves, 80% H 2 O), joints, ligaments n Shapes of Bones – Long, Flat, Irregular, Short n Before 8 weeks, embryo is all cartilage

Structure of Bone

Anatomy of a Long Bone n Diaphysis – Medullary Cavity – Nutrient Art & Vein n 2 Epiphyses – Epiphyseal Plates – Epiphyseal Art & Vein n Periosteum – Outer: Dense irregular CT – Inner: Osteoblasts, osteoclasts – Does not cover epiphyses – Attaches to bone matrix via collagen fibers n Endosteum – Osteoblasts, osteoclasts – Covers trabeculae, lines medullary cavity

2 Types of Bone Formation n 1) Intramembranous Ossification – Membrane bones: most skull bones and clavicle – Osteoblasts in membrane secrete osteoid that mineralizes – Osteocytes maintain new bone tissue – Trabeculae forms between blood vessels – Grows into thickened plates at periphery = compact bone – Periosteum forms over it

2 Types of Bone Formation : n 2) Endochondral Ossification: All other bones – Begins with a cartilaginous model – Perichondrium becomes replaced by periosteum – Cartilage in diaphysis calcifies – Trabeculae forms from Periosteal bud n Periosteal bud = arteries & veins, cells forming bone marrow, osteoblasts, osteoclasts – Medullary cavity is formed by action of osteoclasts – Epiphyses grow and eventually calcify n Epiphyseal plates remain cartilage for up to 20 years

Bone Growth & Remodeling n GROWTH n Appositional Growth = widening of bone – Bone tissue added on surface by osteoblasts of periosteum – Medullary cavity maintained by osteoclasts n Lengthening of Bone – Epiphyseal plates enlarge by chondroblasts – Matrix calcifies (chondrocytes die and disintegrate) – Bone tissue replaces cartilage on diaphysis side n REMODELING n Due to mechanical stresses on bones, their tissue needs to be replaced – Osteoclasts-take up bone ( = breakdown) n release Ca 2++, PO 4 to body fluids from bone – Osteoblasts-lay down bone n secrete osteoid to form new bone n Ideally osteoclasts and osteoblasts work at the same rate!

Joints (articulations) n Where parts of skeleton meet n Allows varying amounts of mobility n Classified by structure or function n Arthrology: study of joints

Classification of Joints n Function: – Synarthroses = no/little movement – Amphiarthroses = slight movement – Diarthroses = great movement

Joints by Functional Classification TypeMovementExample SynarthrosisNone (minimal) Sutures, Teeth, Epiphyseal plates, 1 st rib and costal cart. AmphiarthrosisSlightDistal Tibia/fibula Intervertebral discs Pubic symphysis DiarthrosisGreatGlenohumeral joint Knee joint TMJ

Joint Classification n Structure – Cartilagenous n Synchondrosis: connected by hyaline cartilage (synarthroses) n Symphysis: connected by fibrocartilage (amphiarthroses) – Fibrous n Sutures: connected by short strands of dense CT (synarthroses) n Syndesmoses: connected by ligaments (varies) n Gomphosis: peg in socket w/short ligament (synarthroses) – Synovial (diarthroses)

Joints by Structural Classification StructureTypeExample CartilagenousSynchondrosis Symphysis Epiphyseal plates Intervertebral discs FibrousSutures Syndesmoses Gomphosis Skull Distal Tibia/fibula Teeth in sockets SynovialGlenohumeral joint Knee joint TMJ

Components of SYNOVIAL JOINTS: ( Structural Joint Classification continued) n Articular cartilage: hyaline; covers ends of both bones articulating n Synovial (joint) cavity: space holding synovial fluid n Articular capsule: Made of 2 layers – Fibrous: external, dense CT for strength – Synovial membrane: internal, produces synovial fluid n Synovial fluid: viscous; lubricates and nourishes; contained in capsule and articular cartilages n Reinforcing ligaments: extracapsular/intracapsular n Nerves + vessels: Highly innervated, Highly vascular n Meniscus (some): fibrocartilage; improves the fit of 2 bones to increase stability

Synovial Joint pg 215

Bursae & Tendon Sheaths n Bursae: flat, fibrous sac w/synovial membrane lining n Tendon Sheaths: elongated bursae that wraps around tendons n 3 Factors in Joint Stability: – Muscle Tone – Ligaments – Fit of Articular Surface pg 219

Joint Shapes n Hinge: cylindrical end of 1 bone fits into trough shape of other – angular movement-1 plane (eg) elbow, ankle, interphalangal n Plane: articular surface in flat plane – Short gliding movement – (eg) intertarsal, articular processes of vertebrae pg 224

Joint Shapes n Condyloid: egg-shape articular surface + oval concavity – side-to-side, back+forth movement – (eg) metacarpophalangeal (knuckle) n Pivot: round end fits into ring of bone + ligament – rotation on long axis – (eg) prox. radius/ulna, atlas/dens pg 225

Joint Shapes n Saddle: articular surface both concave + convex – side-to-side, back-forth movement – (eg) carpometacarpal jt of thumb – n Ball + Socket: spherical head + round socket – multiaxial movement – (eg) shoulder, femur pg 225

!Muscles! Function: 1) movement 2) maintain posture 3) joint stability 4) generate heat !Muscles!

Special Features of Muscle n Contractibility = cells generate pulling force n Excitibility = nervous impulses travel through muscle plasma membrane to stimulate contraction n Extensibility = after contraction muscle can be stretched back to original length by opposing muscle action n Elasticity = after being stretched, muscle passively recoils to resume its resting length

Muscle System: uses levers to move objects n How it works: A rigid bar moves on fixed point when a force is applied to it, to move object n Lever = rigid bar = bone n Fulcrum = fixed point = joint n Effort = force applied = muscle contraction n Load = object being moved = bone

Movements of Muscles n Extension: increasing angle between body parts n Flexion: decreasing angle between body parts – Dorsiflexion vs. Plantarflexion – Inversion vs. Eversion n Abduction: moving away from the median plane n Adduction: moving towards the median plane n Rotation: moving around the long axis n Circumduction: moving around in circles

n Elevation: lifting body part superiorly n Depression: moving body part inferiorly n Supination: rotating forearm laterally n Pronation: rotating forearm medially n Protraction: Anterior movement n Retraction: Posterior movement Movements of Muscles

Muscle Basics to Remember n 3 Types: Skeletal, Cardiac, Smooth n Origin vs. Insertion n Direct vs. Indirect Attachments – direct = right onto bone – indirect = via tendon/aponeurosis n more common n leave bony markings = tubercle, crest, ridge, etc. n Sometimes attach to skin

Functional Muscle Groups n Agonist = primary mover of a muscle, major response produces particular movement – (eg) biceps brachii is main flexor of forearm n Antagonists = oppose/reverse particular movement, prevent overshooting agonistic motion – (eg) triceps brachii is antagonist to biceps brachii

Functional Muscle Groups n Synergists = muscles work together, adds extra force to agonistic movement, reduce undesirable extra movement – (eg) muscles crossing 2 joints n Fixators = a synergist that holds bone in place to provide stable base for movement – (eg) joint stablilizers

Naming Muscles n Location: (eg) brachialis = arm n Shape: (eg) deltoid = triangle n Relative Size: (eg) minimus, maximus, longus n Direction of Fascicles: (eg) oblique, rectus n Location of Attachment: (eg) brachioradialis n Number of Origins: (eg) biceps, quadriceps n Action: (eg) flexor, adductor, extensor

Arrangement of Muscle Fibers n Parallel: long axis of fascicles parallel to axis of muscle; straplike (eg) biceps, sternocleidomastoid n Convergent: O = broad, I = narrow, via tendon; fan or triangle shaped (eg) pectoralis major n Circular: fascicles arranged in concentric circles; sphincter (eg) around mouth

Arrangement of Muscle Fibers n Pennate: fascicles short + attached obliquely to tendon running length of muscle; featherlike – Unipennate = fascicles insert on only 1 side n (eg) flexor pollicis longus – Bipennate = fascicles insert both sides n (eg) rectus femoris – Multipennate = many bundles inserting together n (eg) deltoid

Arrangements of Muscle Fascicles pg 269

STOP More on Levers on the following pages

First Class Lever n Effort at 1 end n Load at other end n Fulcrum in middle n (eg) scissors n (eg) moving head up and down pg 267

Second Class Lever n Effort at 1 end n Fulcrum at other end n Load in middle n (eg) wheelbarrel n (eg) standing on tip toes (not common in body) pg 267

Third Class Lever n Load at 1 end n Fulcrum at other end n Force in middle n (eg) using a tweezers n (eg) lifting w/biceps pg 267

Mechanical Advantage n When the load is close to the fulcrum, effort is applied far from fulcrum n Small effort over large distance = move large load over short distance n (eg) Using a jack on a car pg 266

Mechanical Disadvantage n When the load is farther from the fulcrum than the effort, the effort applied must be greater than the load being moved n Load moved quickly over large distance n (eg) using a shovel pg 266