Anatomy Notes Skeletal System PDF

Skeletal System Composition 1. Bone : hardest structure, composed of minerals 2. Cartilage: reduces friction, model for bone formation 3. Tendons: attach bone to muscle 4. Ligaments : attach bone to bone Background information components of skeletal system are connective tissues...

Skeletal System Composition 1. Bone : hardest structure, composed of minerals 2. Cartilage: reduces friction, model for bone formation 3. Tendons: attach bone to muscle 4. Ligaments : attach bone to bone Background information components of skeletal system are connective tissues ○ different amounts of collagen and elastin fibers which determine hardness extracellular matrix always contain collagen, ground substance and other organic molecules as well as water and minerals Collagen ○ for flexibility, both in the skeletal system and skin Proteoglycans ○ large polysaccharides attached to proteins ○ Store water Part Components Bone Collagen and minerals (ex. Calcium and phosphate) flexible and able to bear weight Cartilage Collagen and proteoglycans (good shock absorbers) Tendon and ligaments Collagen (very tough) *As proteoglycans can store water, the cartilage is very soft. Classification of bones Based on shape: ○ Long: femur, tibia, fibula ○ Short: carpals, tarsals, phalanges ○ Flat: ribs, sternum, skull ○ Irregular: vertebrae, facial Based on bone tissue: compact, spongy (cancellous) Long bone Structures Diaphysis: shaft, compact bone tissue (on outside) Epiphysis: ends, spongy bone tissue as there are large spaces in between articular cartilage ○ Covers epiphyses, reduces friction ○ Thins in older people, leading to arthritis Epiphyseal plate: ○ Site of growth between diaphysis and epiphysis ○ during puberty, this plate is activated, increasing in height Medullary cavity: ○ center of diaphysis, red (blood) or yellow (adipose) marrow ○ when puberty ceases, the epiphyseal plate turns to an epiphyseal line, becoming thinner Periosteum (outside): membrane around bone’s outer surface Endosteum (inside): membrane that lines medullary cavity Bone cells 1. Osteocytes: maintain bone matrix (contain collagen and minerals)  2. osteoblasts : build bone, creates bone matrix 3. Osteoclasts: carve bone Bone Histology 1. Lacunae (plural): spaces between lamellae, osteocytes are found 2. Canaliculus: tiny canals which transport nutrients and removes waste (branching line) 3. Central canal: center of osteon, contains blood vessels which distribute materials especially calcium and phosphorous, has bigger blood vessels 4. Osteon: unit of bone Bone Tissue 1. Compact bone tissue (cortical) ○ cortical bone ○ forms the perimeter of the diaphysis of a long bone and the thinner surfaces of all other bones ○ has more matrix and is denser with fewer pores than spongy bones. ○ Has osteons ○ for strength 2. Spongy bone ○ cancellous bone ○ Location: epiphysis of long bones and center of other bones ○ Trabeculae interconnecting rods, spaces contain marrow ○ No osteons ○ To make bones lighter for mobility Bone physiology Bone formation Ossification: process of bone formation Osteoblast rule ○ Build bone ○ after an osteoblast becomes surrounded by bone matrix it becomes an osteocyte  osteocyte ○ ossification center: where bone formation begins (sides of head because if it's the entire thing, baby would be difficult to remove) ○ primary ossification center where the 1st bone begins to appear forms diaphyses ○ secondary ossification center : forms epiphyses 2 Types of ossification 1. Intramembranous ossification ○ Bone formation within connective tissue membranes ○ osteoblasts build bone Ex. skull bones which is made of different flat bones ○ Osteoblasts begin to produce bone within connective, osteoblast lines up on surface of connective tissues and begins to deposit bone matrix, producing trabeculae (spongy tissue) Intramembranous osteoblast surrounds connective tissue membrane which is not purely cartilage Deposit bone matrix Form trabeculae Trabeculae radiate outwards until they all join to each other trabeculae are remolded and replaced with contact bone 2. Endochondral ossification ○ bone formation inside cartilage ○ cartilage model are replaced by bone Ex. all bones (except some parts of the skull) ○ Hyaline cartilage which is a material of cartilage Cartilage model with the general shape of the mature bone is produced by chondrocytes. A perichondrium surrounds most of the cartilage model. A bone collar is produced, and the perichondrium of the diaphysis becomes the periosteum. The chondrocytes enlarge, and cartilage is calcified. When it has calcium, it becomes a hard structure. Primary ossification centers form as blood vessels and osteoblasts invade the calcified cartilage. The osteoblasts lay down bone matrices, forming trabeculae. Secondary ossification centers forms in the epiphyses of long bones Bone Growth Infancy and youth ○ long bones lengthen at epiphyseal plate ○ long bones widen by adding more lamella ○ End of bone growth (in length) ○ epiphyseal plate is replaced by epiphyseal line bone length : endochondral ossification bone widen: appositional growth, diaphyses will be formed, trabeculae will be formed to compact bone and is destroyed by osteocytes Bone remodeling removing of existing bone by osteoclasts and deposition of new bone by osteoblasts occurs in all bone responsible for changes in bone shape, bone repair and adjustment of bone to stress an calcium ion regulation Bone Repair Happen with bone fracture To know there is a fracture, there is a presence of hematoma/bruise Hematoma formation: blood released from damaged blood vessels forms a hematoma Callus formation: the internal cells forms between the ends of the bone and external forms cells around the break (made of cartilage) Callus ossification: osteoblast forms the trabeculae, decomposes, then osteoclast woven,m spongy bones replaces the internal and external calluses (osteoblast when surrounded by bone matrix are considered as osteocytes) Bone remodeling: compact bone replaces woven bone and parts of the internal callus is reserved, restoring the medullary cavity (cast to immobilize, the formed bone should not move or it might break) Bone and calcium homeostasis - blood calcium dictates bone calcium needed Decreased blood Calcium stimulates Parathyroid secretion from parathyroid glands PTH stimulates osteoclasts to break down bone and release Calcium into the blood In the kidneys, PTH increases Calcium reabsorption from the urine. PTH also stimulates active vitamin D formation Vitamin D promotes Calcium absorption from the small intestine into the blood Increased blood Calcium stimulates calcitonin secretion from the thyroid gland Calcitonin inhibits osteoclasts which allows for enhanced osteoblast uptake of calcium from the blood to deposit into the bone Bone Physiology Hematopoietic tissue ○ Makes red blood cells ○ Yellow marrow: mostly flat ○ Red marrow: location of RBC When we were infants, bones were the sites of RBC ○ Location in adults: Red is replaced with yellow marrow red marrow is mainly in epiphysis of femur and humerus General considerations, Axial and Appendicular bones ○ Axial  found in the middle Ex. ribcage, vertebrae, pelvis, skull, sacrum (fused tailbone) ○ Appendicular sides Ex. tribeca, fibera, humerus ○ Articulations where 2 bones come together (joint) 1. Synthesis ○ non movable joints (cobras can move their sutures) ○ Ex. skull 2. Amphiarthrosis ○ slightly movable joint ○ between vertebrae 3. Diarthrosis ○ Freely moveable joint ○ Ex. knee, elbow, wrist Joints are also classified structurally as fibrous, cartilaginous or synovial, according to the major connective tissue type that binds the bone together and whether a fluid-filled joint capsule is present ○ Inside joint cavity = synovial fluid ○ arthritis = less synovial fluid Types of Movement Flexion: bending Extension: straightening Abduction: movement away from the midline Aging and Diseases Why does Osteoporosis mostly happen to women? In women, decreased production of the female reproductive hormone estrogen can cause osteoporosis, mostly in spongy bone, especially in the vertebrae of the spine and the bones of the forearm. Collapse of the vertebrae can cause a decrease in height or, in more severe cases, kyphosis in the upper back. Estrogen levels decrease as a result of menopause; removal of the ovaries; amenorrhea (lack of menstrual cycle) due to extreme exercise or anorexia nervosa (self-starvation); or cigarette smoking. During Pre menopause to menopause, the bone becomes porous, losing bone mass Bone losses 20% of mass due to the decrease of estrogen Osteoblast decreases than osteoclast In men, reduction in testosterone levels can cause loss of bone tissue. However, this is less of a problem in men than in women because men have denser bones than women, and testosterone levels generally don’t decrease significantly until after age 65. To have more estrogen: eat more soybean and vitamin D rich food like canned sardines and leafy grains! Muscles Skeletal Muscle structure All organs are covered by Epimysium ○ A connective tissue that surrounds entire skeletal muscle (outside ) Muscle fasciculus ○ bundle of muscle fibers perimysium ○ connective tissue around each muscle fasciculus Muscle fiber ○ skeletal muscle cells ○ many nuclei Endomysium ○ connective tissue that surrounds each muscle fiber Muscle fiber structure Microfibril ○ thread like protein that make up muscle fiber Myofilament ○ proteins that make up myofibrils ○ Ex. actin and myosin Sarcoplasm ○ cytoplasm of muscle fiber (cell) Sacroplemma ○ Cell membrane ○ contains T-tubules T-tubules (transverse) ○ Wrap around sarcomeres at A band ○ associated with sarcoplasmic reticulum sarcoplasmic reticulum ○ Type of SER ○ surrounds myosin ○ stores and releases Ca2+ Sarcomere ○ contractile unit ○ contains actin and myosin Z-disk ○ protein fibers form attachment site for actin Sarcomeres I bands: contains only actin A band: actin and myosin overlap M line: myosin is activated H zone ○ center of sarcomere ○ contains only myosin  Cramps happen when sarcoplasmic reticulum releases calcium Actin and Myosin Actin ○ thin myofilament ○ resembles 2 strands of pearls Myosin ○ thick myofilament ○ resemble golf clubs Troponin ○ Attachment site on actin for CA2+ ○ Only seen when you zoom in Tropomyosin ○ filament on groves ofactin ○ Attachment site on actin for myosin Contract ○ Contraction of skeletal muscle tissue occurs as actin and myosin myofilaments slide past one another, causing the sarcomeres to shorten. ○ Many sarcomeres joined end-to-end to form a myofibril. ○ Shortening of the sarcomeres causes myofibrils to shorten, thereby causing the entire muscle to shorten. ○ No H zone Body Movement Muscle Smooth, cardiac, skeletal Functions 1. Movement 2. Maintain posture 3. respiration 4. Production of body heat 5. Communication of body heat 6. Heartbeat 7. Contraction of organs and vessels General properties of muscle tissue contractibility : ability to shorten Excitability : respond to stimulus Extensibility : can stretch Elasticity: recoil Types of muscle 1. Skeletal ○ Moves whole body ○ voluntary  ○ attached to bone ○ has striation and unbranched ○ long cylindrical ○ multiple nuclei (peripheral) 2. Cardiac muscle ○ Involuntary movement in heart ○ branched shape ○ has striations ○ Single nucleus centrally located 3. Smooth ○ digestive system/internal organs ○ spindle shape ○ single nucleus ○ moves food through digestive tract ○ empty urinary bladder ○ regulates blood vessel diameter ○ contracts many gland ducts Skeletal muscle characteristics Make up 40% of body weight Named because it is attached to the bone many nuclei per cell (near periphery) striated longest of muscle types ○ whole muscle organ fats Nerves blood vessels muscle fibers Physiology of Muscle: excitability of muscles Resting membrane potential and action potential Resting: inside is negatively charge, outside is positively charged Action potential: changes intial or flipping of charges Resting membrane potential The electric charge difference across the cell membrane of an unstimulated cell Na+ channels and some but not all K+ channels are closed. K+ diffuses down the concentration gradient through the open K+ channels, making the inside (yellow) of the cell membrane negatively charged compared to th outside. (If more K+, goes outside) Unstimulated outer more Na+, inner more K+ closed Na channels Few K+ channels are open K+ diffuses out Action potential A rapid change in charge across the cell membrane Depolarization. Na+ channels are open. Na+ diffuses down its concentration gradient through the open Na+ channels, making the inside of the cell membrane positively charged compared to the outside Na+ more outside , K+ moreinside Inside (+), outside (-) Repolarization. Na+ channels are closed and NA+ movement in the cell stops. More K+ channels are open > K+ movement out of the cell increases, making the inside of the cell membrane negatively charged compared to the outside, once again. Nerve supply and Muscle fiber stimulation Motor neuron: nerve cells that carry action potentials to muscle fibers Neuromuscular junction (synapse): where nerve cell and muscle fiber meet Presynaptic terminal: end of nerve cell Postsynaptic: muscle fiber membrane Synaptic cleft : space between presynaptic terminal and postsynaptic membrane Synaptic vesicle ○ In presynaptic terminal ○ Store and release neurotransmitters Neurotransmitter ○ chemicals that stimulate or inhibit a muscle fiber ○ Ex. acetylcholine Steps 1. An action potential arrives at the presynaptic terminal causing Ca2+ channels to open 2. Calcium Ions enter the presynaptic terminal and initiate the release of a neurotransmitter acetylcholine (ACl+) form synaptic vesicles into the presynaptic cleft