Basal Humanbiologi Muscle and Skeletal System
Muscle and Skeletal System
(Support and Movement)
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Macro- and microscopic structure of bones
explain depot of minerals, and the structural function of red bone marrow.
- Macroscopic structure
Proximal, Distal epiphyses at each end are covered with articular cartilage, middle is diaphysis. Periosteum encloses expect AC. Diaphysis mainly compact bone, continuous matrix with no gaps. Epiphysis mainly spongy bone, numerous branching bony plates. In medullary cavity, lined by endosteum, middle is loose C. tissue marrow.
- Microscopic structure
Compact bone: Osteocytes in lacunae, with intercellular mats collagen, inorganic salts, form concentric circles, Haversian canals, osteon, extend longitudinally through bone tissue. Osteon contains blood vessels, nerve fibers, loose c. tissue. Volkmann’s canals (perforating canal) connect these transversely. Many osteon cement together and form compact bone material. Collagen gives strength, resilience, salts gives hardness. Osteocytes communicate via cellular process through canaliculi.
- Bone development
- Intramembranous Bones: (the skull) Membrane like c. tissue enlarge, differentiate into osteoblasts, deposit bony matrix around. Mature osteoblasts are called osteocytes, surround completely by matrix.
- Endochondral Bones: (from hyaline cartilage center) Primary ossification center: Periosteum forms, osteoblasts invade center of diaphysis, spongy bone forms. Epiphysis remains cartilaginous and continues to grow. Secondary ossification center: spongy bone form in epiphyses. Epiphyseal plate between the two.Tertiary: osteoclasts, multinucleated fused by monocytes, use lysosomal enzymes digest inner diaphysis form medullary cavity, as compact bone thickens, intromembranous ossification beneath the periosteum.
- E. plate: young cells undergo mitosis, enlarge and matrix forms around, thickens then lengthens.
- Blood cell formation: see Hole's Essential, 8th Edition, §12 or topic 8 (blood)
- Homeostatic mechanism
Deficiency of blood calcium -> hypocalcemia, excess -> hypercalcemia. Bone is major storage site for calcium, and movement of calcium into and out of bone helps to determine blood calcium levels. Calcium moves into bone as osteoblasts build new bone and out of bone as osteoclasts break down bone.
Calcitonin, secreted by the thyroid gland inhibits osteoclasts and stimulates osteoblasts, thus decreasing blood calcium levels. Parathyroid hormone inhibits osteoblasts, stimulates osteoclasts, reduces the output of calcium by the kidneys and promotes the absorption of calcium by the small intestines, thus increasing blood calcium levels.
Joints. Structure, classification
Fibrous joints: bone held together by the collagenous fibre extending the matrix of one bone into the matrix of the next; no joint cavity, immovable eg sutures. Slightly movable eg distal end of tibia and fibula (syndesmosis), gomphosis.
Cartilaginous joints: bones held together by cartilage, no joint cavity. Eg Intervertebral disc, symphysis pubis, costal cartilage of the first rib to sternum (synchondrosis).
Synovial joints: ends of bones covered with hyaline cartilage, enclosed in fibrous joint cavity, outer layer dense c. tissue, ligament, inner layer synovial membrane, secrete synovial fluid, lubricates. Meniscus, fibro cartilage shock absorb. Bursae, fibrous sacs with fluid, extending from skin to nearby bone prominence, aid movement of tendons to glide over bony parts.
Move ability: Diathroses, Amphiathroses, Synarthroses.
Describe 3 different muscle micro, macro structures
Motor unit, all-or-none principle, muscle excitation and contraction.
Skeleton muscle: Series of increasingly smaller parallel units, composed of fascicles, consists of fibers which are multi nuclei cells, are myofibrils composed of sarcomeres, of actin(troponin, tropomyosin) and myosin. Perimysium, epimysium, endomysium. Sarcoplasm reticulum (store Ca2+) – terminal cristerna, T-tubule.
Smooth Muscle: Smaller cells, spindle-shaped, 1 nucleus, fewer actin and myosin myofilaments, not organized into sarcomeres, thus no striated appearance. Single-unit electrically coupled to each other by gap junctions, stimulate each other and a large number of cells contract as a single unit - digestive, reproductive, and urinary tracts. Multiunit occurs as sheets such as in the walls of blood vessels, arrector pili, contracts independently of the others.
Cardiac Muscle: Striated, usually 1 nucleus, branch like a y, at each end form gap junctions with another myocyte ie intercalated disc, allow action potentials to pass from cell to cell. Autorhythmic, one part of the heart normally acts as the pacemaker. Action potentials of cardiac muscle are similar to those in nerve and skeletal muscle but have a much longer duration and refractory period.
Motor unit: 1 motor neuron and all the muscle fibers it stimulates. When a nerve impulse arrives at the end of an axon, stimulates all muscle fibers supplied by that motor neuron to contract in unison.
All-or-none response: muscle fiber exposed to stimulus of threshold strength responds to its fullest extent. If it contracts at all, it contracts fully.
Muscle excitation: 1. action potential arrives at postsynaptic terminal, voltage-gated Ca2+ ion channels open, increase Ca2+ permeability. 2. Ca2+ initiate release of ACH from synaptic vesicles into cleft. 3. ACH diffuse, bind to receptors on postsynaptic membrane, ligand-gated Na+ ion opens. 4. depolarisation of postsynaptic membrane, reaching threshold -> post synaptic action potential.
Muscle contraction: 3.Muscle impulse travel through T-tubules, reach scaroplasmic reticulum. 4. Ca2+ diffuses from SR to sarcoplasm. 5. Ca2+ bind to troponin, tropomyosin moves exposes actin active site, myosin bind to actin. Myosin cross bridge pull actin inward. 6. Muscle fibre shortens.
Muscle Contraction Phenomenon
Concentric: resistance less than max tetanic tension, muscle shortens. Eg. bicep curl
Eccentric: resistance greater than muscle max generated force, even fully activated, muscle lengthens. 1.Absolute tensions achieved are higher than muscle's max tetanic tension generating capacity. 2.Absolute tension relatively independent of lengthening velocity. (Sliding Filament Theory is wrong???)
Isometric: muscle generates force while muscle length remains constant
Isotonic: the muscle is being lengthened while in a passive state (i.e. not being stimulated to contract).
Summation: stimuli of increasing frequency, unable to completely relax till next stimulus arrives.
Tetanus: lacks even partial relaxation, cramps, very high frequency.
State anaerobic, aerobic extraction of energi. Describe the function of creatinphosphate, myoglobin in the muscle.
Anabolism: buildup for larger molecules from smaller ones, requires energy. (dehydration synthesis)
Catabolism: breakdown of larger molecules into smaller ones, releases energy. (hydrolysis)
Anaerobic respiration: glucose converted to pyruvic acid; net of two ATP molecules is produced during glycolysis, in cytosol.
Aerobic respiration: pyruvic acid can enter the mitochondria, go through citric acid cycle and electron transport system, produces H2O, CO2, 34 or 36 ATP molecules.
Creatinphophate: transfer ADP to ATP, stores excess energy from the mitochondria.
Myoglobin: A red oxygen-storage pigment of muscle; supplements hemoglobin in providing oxygen for aerobic muscle metabolism
Source: Hole's Essential, 8th Edition, ISBN 0-07-235118-7, §7 - §8