Lecture Outline - Chapter 18

18.1. Bone Structure and Growth (p. 329)

1. Bone Structure (Fig. 18.1)
   • a. Long bones contain a medullary cavity.
   • b. Thin side shell of compact bone provides strength.
     • i. Compact bone has concentric circles around Haversian canals.
     • ii. Bone cells are within tiny chambers called lacunae.
     • iii. Lacunae separated by a matrix containing collagen and mineral deposits of calcium and phosphorus salts.
   • c. Ends contain spongy bone.
     • i. Spongy bone has numerous bony bars and plates separated by irregular spaces.
     • ii. Solid portion follows lines of stress for strength.
     • iii. Spaces between plates filled with red marrow that produces blood cells.
   • d. Cavity of long bone contains yellow marrow which is fat-storage tissue.
2. Bones Grow and Are Renewed
   • a. Most cartilage in prenatal development is replaced by bone by process of endochondral ossification.
   • b. Osteoblasts are bone-forming cells.
     • i. Secrete calcium salts in matrix of earlier cartilage and bone.
     • ii. Form primary ossification center, then secondary centers at ends of bones; finally cartilaginous disks become ossified and bone stops growing.
     • iii. Osteoblasts that get trapped in matrix become osteocytes, mature bone cells located in lacunae of osteons.
     c. Osteoclasts are bone-absorbing cells that break down bone matrix, remove worn cells, and deposit calcium into blood.
   • d. Physical use and hormone balance affects thickness of bones.
   • e. Calcium requirements remain high in adults due to constant buildup and breakdown.

1. Functions of Skeleton:
   • a. supports the body.
   • b. protects soft body parts.
   • c. produces red blood cells.
   • d. stores inorganic salts.
   • e. provides sites for muscle attachment.
   • f. permits flexible body movement.
2. The Axial Skeleton
   • a. Skull formed by the cranium and facial bones
     • i. Cranium:
       - protects brain.
       - has eight bones in adults.
       - in newborns, membranous regions (fontanels) are between bones.
       - contains sinuses (air spaces lined with mucous membrane) are found in several bones, such as the mastoid, and reduce weight of skull, resonate voice.

       ii. Cranial bones include:

       - frontal bone at forehead.

       - parietal bones at sides.

       - occipital bone at back and base.

       - foramen magnum is opening at base where brain stem enters.

       iii. Fourteen facial bones include:

       - mandible is lower jaw with lower teeth.

       - maxillae is upper jaw with upper teeth and hard palate.

       - palatine bones form back of hard palate and floor of nasal cavity.

       - zygomatic bones form cheekbones and bridge of nose.
3. Vertebral Column Supports
   • a. Extends from skull to pelvis; protects spinal cord.
   • b. Vertebrae are named for their locations: cervical (7), thoracic (12), lumbar (5), sacrum, and coccyx. (Fig. 18.3)
   • c. Intervertebral disks between vertebrae provide padding, prevent grinding, and absorb shock due to normal movements; can rupture if vertebrae slip.
4. Ribs
   • a. All twelve pairs connect directly to thoracic vertebrae in back.
   • b. Lower two pairs called "floating ribs" because they do not attach to sternum.
   • c. Sternum is called the breastbone; attaches to ribs by cartilage or bone.
5. Appendicular Skeleton is Girdles and Limbs (p. 332)
   • a. Pectoral (shoulder) Girdle and Arm (Fig. 18.4)
     • i. Loosely linked by ligaments.
     • ii. Clavicle (collar bone) connects to sternum in front and scapula in back.
     • iii. Scapula is shoulder blade; held in place by muscles.
     • iv. Arm consists of long upper bone, the humerus, with small socket allowing it to dislocate sometimes.
     • v. Forearm consists of:
       - radius that allows forearm to twist.
       - ulna running parallel to radius at outside of forearm.

       vi. Hand consists of:

       - eight carpal bones of wrist

       - five metacarpal bones that form the palm

       - phalanges in fingers and thumb
   • b. Pelvic Girdle and Leg (Fig. 18.5)
     • i. Two large coxal bones (hipbones) anchored to sacrum to form pelvis; wider in females to permit childbirth.
     • ii. Upper leg bone, the femur, is largest and strongest bone in body.
     • iii. Lower leg consists of:
       - larger tibia (forms shin leading to inside part of ankle)
       - smaller fibula (leading down to outside of ankle).

       iv. Foot consists of:

       - seven tarsal bones (ankle)

       - metatarsals (form arch of foot)

       - phalanges forming the sturdy toes
6. Joints Join Bones (p. 334)
   • a. Bones join at joints classified as:
     • i. Fibrous joints that are immovable; example: sutures between cranial bones.
     • ii. Cartilaginous joints are slightly movable; example: joints between the vertebrae or coxal bones for childbirth.
     • iii. Synovial joints are freely movable. (Fig. 18.6)
       - two bones contained in separate fluid-filled cavities.
       - joint capsule is lined by synovial membrane lubricated by synovial fluid.
       - two bones are held together by ligaments.
       - edges capped by crescent-shaped cartilage termed menisci for support and stability.
       - fluid-filled sacs called bursae ease friction between tendons and ligaments or bones; inflammation of bursae is called bursitis (tennis elbow).

       iv. Types of joints:

       - hinge joints (knee and elbow) swing in one direction.

       - ball-and-socket joints (femur at coxal bone) allow rotation.
   • b. Medical Problems
     • i. Synovial joints subject to rheumatoid arthritis where membrane becomes inflamed and thickens; probably an autoimmune reaction.
     • ii. In osteoarthritis, cartilage at ends of bones disintegrates creating a rough surface during old age.

1. Skeletal muscles enable organism to respond to a stimulus. (Fig. 18.2)
2. Muscle Pairs:
   • a. Are attached to bone by tendons made of fibrous connective tissue.
   • b. When a muscle contracts, origin of the muscle is on stationary bone.
   • c. Insertion is on bone that moves.
   • d. Because muscles can only contract or shorten, they always pull and never push.
   • e. Therefore, they generally work in antagonistic pairs to flex or extend a limb.
     • i. Biceps contract to flex or bring up the lower arm.
     • ii. Triceps contract and cause extension of lower arm.
3. Physiology: When Whole Muscles Contract
   • a. Muscle can be attached to a physiograph and mechanical force of stimulated muscle is measured. (Fig. 18.8a)
   • b. Myogram is visual representation of muscle contraction when muscle is stimulated to shorten.
4. Response to Stimulus
   • a. A single muscle fiber will contract completely or not at all when threshold stimulus is applied.
   • b. Force of contraction of whole muscle depends upon number of fibers contracting.
   • c. Maximum stimulus is one beyond which the degree of contraction does not increase.
5. Muscle Twitch
   • a. When muscle is given maximum stimulus, it contracts and then relaxes; this is a muscle twitch. (Fig. 18.8b)
   • b. Latent period is time between stimulation and initiation of contraction.
   • c. Contraction period is time of contraction.
   • d. Relaxation period follows contraction.
   • e. Refractory period is time during which a muscle, if given two maximum stimuli very quickly, will not respond to second stimulus.
6. Summation and Tetanus: Blending Twitches
   • a. If frequency of threshold stimulation is increased, muscle tension will summate until a maximal sustained contraction, called tetanus, is achieved without any relaxation phase occurring; myogram no longer shows twitches.
   • b. Continued stimulation brings on muscle fatigue by depleting energy reserves.
   • c. Intact muscles rarely fatigue because while some fibers are contracting, others are relaxing.

1. Muscle fibers (cells) are arranged in bundles. (Fig. 18.9)
   • a. Muscle fibers are multinucleated because they formed by uniting many cells.
   • b. Muscle fiber cells have many mitochondria to supply energy to contract.
2. Muscle Fibers Contain Filaments
   • a. Sarcolemma (plasma membrane) dips into cytoplasm to form T (tubule) system that is in contact with portions of endoplasmic reticulum called calcium storage sacs.
   • b. These storage sacs, containing calcium ions essential in muscle contraction, surround myofibrils within muscle fiber.
3. Myofibrils
   • a. Are banded cylinders that run the length of fibers.
   • b. Have light and dark bands (striations) causing skeletal muscle to appear striated.
   • c. Sarcomere is contractile unit of myofibril. (Fig. 18.10)
     • i. Extends from one Z line to the next Z line.
     • ii. I bands have thin actin filaments.
     • iii. Dark A band of sarcomere is composed of the thick myosin filaments and some overlapping actin filaments.
     • iv. H zone has only thick myosin filaments.
4. The Filaments Slide (Table 18.1) (p. 337)
   • a. Actin filaments slide past myosin filaments as sarcomere distance shortens.
   • b. The cross-bridges of myosin pull actin filaments inward. (Fig. 18.9)
   • c. In presence of calcium ions, myosin cross-bridges combine with actin.
   • d. Detachment occurs when myosin accepts ATP molecules.
   • e. After myosin breaks down ATP, cross-bridges are ready to attach to actin filament again.
   • f. Cross-bridges attach-and-release 50 - 100 times as filaments pull to center of sarcomere.
   • g. Creatine phosphate, a storage form of high-energy phosphate in muscle fiber, is used to regenerate ATP.
5. Oxygen Debt
   • a. If creatine phosphate is depleted and no oxygen is available, fermentation can supply some ATP.
   • b. Fermentation converts glucose to pyruvic acid to lactate (lactic acid).
   • c. Lactate builds up and produces muscular aching and fatigue.
   • d. Continued intake of oxygen after exercise is required to complete metabolism of lactate; this represents an oxygen debt.
   • e. Lactate is transported to liver where one-fifth is broken down and four-fifths is converted back to glucose.
6. Nerves Stimulate Muscles
   • a. Nerve impulses cause muscles to contract.
   • b. A motor unit represents a motor nerve axon and the several muscle fibers that it triggers.
   • c. The axon knob from each branch contains synaptic vesicles containing acetylcholine (Ach).
   • d. Region where axon bulb nearly touches sarcolemma of muscle fiber is neuromuscular junction, similar to synapse.
   • e. Nerve impulses cause acetylcholine (ACh) to release from synaptic vesicles.
   • f. ACh causes sarcolemma to be depolarized, which results in a muscle action potential that spreads over the sarcolemma and down the T tubule system.
   • g. The action potential causes calcium to be released from sarcoplasmic reticulum, and calcium now binds to troponin, a protein located along the actintropomyosin unit.
   • h. The position of troponin is shifted so that myosin cross-bridges can bind to actin binding sites. (Fig. 18.11)
   • i. When nerve impulses no longer stimulate muscle fiber, contraction ceases; calcium ions are pumped back into their storage sacs, cross-bridges detach and the muscle relaxes.
7. Exercise: Variety of Benefits (p. 340)
   • a. Endurance is length of time muscle can work without fatiguing.
   • b. Strength is force muscle can exert against a resistance.
   • c. Regular exercise also:
     • i. enlarges muscle.
     • ii. increases work heart can accomplish and decreases resting heart rate.
     • iii. increases lung capacity.
     • iv. decreases body fat.
     • v. increases bone density.
     • vi. decreases cholesterol level.
     • vii. decreases blood pressure.