Anatomy and Physiology Final (Chapter 6-11)

Sutures

"Seams", occur only between bones of skull. Junction is filled by a minimal amount of very short connective tissue fibers that are continuous with periosteum. Allows for growth during youth. In middle age, sutures ossify. Immovable.

Force of muscle contraction is affected by:

- # of muscle fibers stimulated - Relative size of fibers, hypertrophy of cells increase in strength - Frequency of stimulation - Sarcomere length

Bone anatomy and compressive strength

- 60- 70% of dry bone mass: Calcium carbonate and calcium phosphate-> Hydroxyapatite: Makes bone hard and able to resist compressionMi - Arrangement and density: High porosity, 30%- <90% is non mineral -> spongy, trabecular bone (trabeculae) - Low porosity: 5-30% is non mineral, cortical- compact bone

Phase 1 of Muscle Fiber Contraction

- Action potential arrives at axon terminal at neurmuscular junction - ACh released, binds to receptors on sarcolemma - Ion permeability of sarcolemma changes - Local change in membrane voltage (depolarization) occurs - Local depolarization (end plate potential) ignites action potential in sarcolemma

Phase 2 of Muscle Contraction

- Action potential travels across entire sarcolemma - Action potential travels along T tubules - Sarcoplasmic reticulum releases Ca2+, Ca2+ binds to troponin; myosin-binding sites (active sites) on actin exposed - Myosin heads bind to actin; contraction begins

Heat Production During Muscle Activity

- Around 40% is useful as work - Remaining energy is given off as heat - Dangerous heat levels are prevented by radiation of heat through skin by sweating

Skeletal muscle tissue

- Attached to bones and skin - Striated - Voluntary

Functional Classification of Joints

- Based on amount of motility - 3 functional classifications: 1. Synarthroses: Immovable 2. Ampiarthroses: Slightly movable 3. Diarthroses: Freely movable

Saddle Joints

- Biaxial - Each articular surface has both concave and convex areas - Movement allowed: opposition - Example: Carpometacarpal joint in thumb

Condyloid (ellipsoidal) Joint

- Biaxial joints - One articular surface is oval protrusion and other surface is an oval depression - Movement allowed: Flexion, extension, abduction, adduction, circumdiction - Example: metacarpopharngeal joints (knuckles), atlanto-occipital joint (allows us to nod head yes)

Bone remodeling

- Deposits and absorptions near membranes - Bone density remains constant if rate of bone formation (deposits)= rate of bone resorption - Functions of bone remodeling: Calcium homeostasis, adapt to stress, bone repair after fractures

Membranes: Periosteum

- Double layered membrane - Covers external surface of entire bone except at joint surfaces - Outer fibrous layer is dense irregular connective tissue with Sharpey's Fibers (more superficial) - Inner osteogenic layer, next to bone surface, consists primarily of osteogenic cells that give rise to all bone cells except bone destroying cells (more deep) - Richly supplied with nerve fibers and blood vessels

Synovial Joints: Friction Reducting Structure (Tendon Sheath)

- Elongated bursa that wraps completely around a tendon - Common where several tendons are crowded together within narrow canals (Ex: wrist)

Synovial Joints: Friction Reducing Structure (Bursae)

- Flattened fibrous sacs lined with synovial membranes - Contain synovial fluid - Commonly act as "ball bearings" where ligaments, muscles, skin, tendons, or bones rub together

Hormonal Control in Bone Remodeling

- Hypercalcemic conditions: Calcitonin - Hypocalcemic conditions: PTH, Calcitrol

Smooth muscle tissue

- In walls of hollow organs: bladder, stomach, airways - Not striated - Involuntary

Membranes: Endosteum

- Loose irregular connective tissue - Covers trabeculae, lines canals that pass through compact bone -Contains osteogenic cells that can differentiate into other bone cells

Ball and Socket Joints

- Multiaxial joints - One articular surface is spherical head and other is a cup-like socket - Most freely moving synovial joints - Movement allowed: ALL - Example: Glenohumeral joint of shoulder

Plane Joints

- Nonaxial joints - Flat articular surfaces - Moving allowed: Short, gliding movements - Example: Intercarpals, intertarsals

Cardiac muscle tissue

- Only in heart - Striated

Fracture Classification

- Position of the bone ends after fracture. Nondisplaced: Bone ends retain normal position. Displaced: Bone ends out of normal alignment. - Completeness of break. Complete fracture: Bone broken through. Incomplete fracture: Bone not broken through. - Whether the bone ends penetrate skin. Open (compound) fracture: Bone penetrates skin. Closed (simple) fracture: Bone does not penetrate skin. - Also described in terms of location of fracture, external appearance, and/or nature of break.

Pivot Joint

- Rounded end of one bone conforms to a "sleeve" or ring of another bone - Uniaxial movement only - Movement allowed: Rotation - Example: Radiulnar joint, atlanto-axial joint (allows us to shake our heads "no")

Stabilizing Factors at Synovial Joints

- Shapes of articular surfaces (minor role): Determine what movements are allowed, may hinder joint stability or help if articular surface is large and fit snugly together - Ligament number and location (limited role): More ligament, stronger, more ligaments more stable. - Muscle Tone: Keeps tendons that cross the joint taut. Reinforcing shoulder and knee joint and arches of foot.

Functions of bones

- Support - Hormone production - Movement - Protection - Storage - Blood cell formation - Homeostasis

Hinge Joints

- Uniaxial joints - Motion along a single plane - One surface cylindrical and other is a trough - Movement allowed: Flexion and extension - Example: Elbow joint, knee joint

3 Types of Nerve Fibers

-Based on their diameter and degree of myelination Group A fibers - have the largest diameter and heavily myelinated; transmit impulse at the rate of 150 m/s (=300 miles per hour). Ex. Motor neurons Group B fibers - intermediate diameter and lightly myelinated; transmit impulses at a rate of 15 m/s Ex. Preganglionic autonomic fibers Group C fibers - smallest diameters and unmyelinated; transmit impulses at a rate of 1 m/s (= 2 miles per hour). Ex. Postganglionic autonomic fibers

Smooth Muscle

-Found in walls of most hollow organs (except heart) -Usually in two layers (longitudinal and circular) -Slower contraction - Myosin ATPase 10-100 times slower than in skeletal

Difference between primary and secondary ossification center

-In short bones, only primary ossification center is formed. Most irregular bones develop from several distinct ossification centers. -In secondary ossification, almost all steps are repeated except spongy bone in the interior is retained and no medullary cavity forms in the epiphyses.

Peristalsis

-Longitudinal layer contracts; -organ dilates and shortens -Circular layer contracts; -organ constricts and elongates

Isotonic Contractions

-Muscle changes in length and moves the load -Isotonic contractions are either concentric or eccentric: - Concentric contractions: the muscle shortens and does work -Eccentric contractions: the muscle contracts as it lengthens

Effects of resistance (usu. anaerobic) exercise

-Muscle hypertrophy (due to increase in fiber size) - More Myofibrils - More glycogen stores - Muscle strengthens

As a hormone increases, what happens to bone cell activity?

-Osteoblast activity: PTH hormone- No change. Calcitonin- Higher activity. Calcitrol- No change. - Osteoclast activity: PTH hormone- Higher activity. Calcitonin- Less activity. Calcitrol- More activity.

Hormonal Controls in Bone

-PTH: Parathyroid Hormone - Calcitonin - Leptin - Serotonin

Contraction of Smooth Muscle

-Slow, synchronized contractions -Gap junctions -Electrically couple cells - Some cells are self-excitatory - Pacemakers -change electrical potential without external stimuli -Rate and intensity of contraction may be modified by neural and chemical stimuli -Sliding filament mechanism

Structural Differences between Smooth and Skeletal Muscle

-Spindle-shaped, uninucleate cells: SMOOTH -No striations: SKELETAL -thick filaments and thin filaments arrange diagonally (not alternative pattern): SMOOTH -Lacks sarcomeres & myofibrils: SMOOTH - Thick filaments have heads along their entire lengtH: SKELETAL -Smooth muscle cells lack Z lines -Dense bodies anchor the thin filaments -Attached to the dense bodies: Intermediate filaments -Resist tension -No troponin complex; protein calmodulin binds Ca2+: SMOOTH -Tropomyosin is present in thin filaments, but does not block binding sites: SMOOTH -Sarcolemma of smooth muscle cells lack T-tubules: SMOOTH -shallow cavities called Caveolae (caveoli) that contain extracellular fluid rich in calcium: SMOOTH -Endomysium only: SMOOTH

Isometric Contractions

-The load is greater than the tension the muscle is able to develop -Tension increases to the muscle's capacity, but the muscle neither shortens nor lengthens

Microscopic Anatomy of Bone: Spongy Bone

-Trabeculae (spongy bone) - No osteons - Irregularly arranged lamallae, osteocytes, and canaliculi - Capillaries in endosteum supply nutrients

How many epiphyseal plates are in the long bone of a 22 year old?

0

Steps in endochondral ossification

1. A bone collar forms around the diaphysis of the hyaline cartilage model. 2. Cartilage in the center of the diaphysis calcifies and then develops cavities. 3. The periosteal bud invades the internal cavities and spongy bone forms. 4. The diaphysis elongates and a medullary cavity forms. 5. The epiphysis ossify.

Repair of Simple Fracture Stages

1. A hematoma forms 2. Fibrocartilaginous callus forms 3. Bony callus forms 4. Bone remodeling occurs

Growth of Cartilage: 2 Types

1. Appositional Growth 2. Interstitial Growth 3. Calcification of cartilage (NOT bone)

General Structure of Synovial Joints (6)

1. Articular cartilage 2. Joint (articular) cavity 3. Articular capsule 4. Synovial fluid 5. Reinforcing ligaments 6. Nerves and blood vessels

Steps of Smooth Muscle Contraction

1. Calcium ions (Ca2+) enter cytosol from ECF via voltage-gated or non-voltage gated Ca2+ channels, or from scant SR. 2. Ca2+ binds to and activates calmodulin. 3. Activated calmodulin activates the myosin light chain kinase enzymes. 4. The activated kinase enzymes catalyze transfer of phosphate to myosin, activating the myosin ATPases. 5. Activated myosin forms cross bridges with actin of thin filaments. Shortening begins.

Steps in the Cross-Bridge Cycle

1. Cross bridge formation 2. The power (working) stroke 3. Cross bridge detachment 4. Cocking of the myosin head

Muscle Connective Sheaths from External to Internal

1. Epipmysium 2. Fascicles 3. Perimysium 4. Endomysium

3 Steps of an Action Potential

1. Generation of an end plate potential 2. Depolarization: Generation and propagation of an action potential 3. Repolarization: Restoring the sarcolemma to its initial polarized state

Movements at Synovial Joints

1. Gliding 2. Angular - Flexion, extension, hyperextension - Abduction, adduction - Circumdiction 3. Rotation - Lateral and medial rotation 4. Special movements - Supination, pronation - Dorsiflexion, plantar flexion of foot - Inversion, eversion - Protraction, retraction - Elevation, depression - Opposition

Wolff's Law explains the following observations:

1. Handedness- results in the bones of one upper limb being thicker than the less used limb 2. Vigorous exercise of the most used limb leads to large increases in bone strength 3. Curved bones are thickets where they are most likely to buckle 4. The trabeculae of spongy bone form trusses along lines of compression 5. Large, bony projections occur where heavy, active muscles attach. The bones of weight lifters have enormous thickenings at the attachment sites of the most used muscles. 6. Featureless bones of fetus and atrophied bones of bedridden people (bones not stressed)

Functions of Muscle

1. Movement: Responsible for locomotion and manipulation, and involuntary movement. 2. Maintaining posture and body position: Muscles act continuously to counteract gravity. 3. Stabilize joints: Strengthen and stabilize joints of skeleton. 4. Generate heat: As they contract, maintain normal body temperature.

Process in Initiating Muscle Contraction

1. Nerve impulse reaches axon terminal and opens voltage-gated calcium channels in the axonal membrane. Calcium entry triggers release of ACh into the synaptic cleft. 2. Released ACh binds to ACh receptors in the sarcolemma, opening chemically gated Na+-K+ channels. Greater influx of Na+ causes a local voltage change. 3. Local depolorization opens voltage-gated sodium channels in the neighboring region of the sarcolemma. More sodium enters, which further depolarizes the sarcolemma, generating ATP. 4. Transmission of the action potential along the T tubules changes the shape of voltage-sensitive proteins in the T tubules, which stimulates SR calcium release channels to release Ca2+ into cytosol.

Synovial Joints: Range of Motion

1. Nonaxial: Slipping movements only 2. Uniaxial: Movement in one plane 3. Biaxial: Movement in 2 planes 4. Multiaxial: Movement in or around all 3 planes (Planes: Sagittal, transverse, frontal)

Steps in Intramembranous Ossification

1. Ossification centers appear in the fibrous connective tissue membrane. 2. Osteoid is secreted within the fibrous membrane and calcifies. 3. Woven bone and periosteum form. 4. Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears.

5 Major Cell Types of Bone Tissue

1. Osteogenic cells 2. Osteoblast 3. Bone lining cells 4. Osteoclasts 5. Osteocytes

Parts of Compact Bone

1. Osteon (Haversian system) 2. Canals and Canaliculi 3. Interstitial and Circumferential Lamellae

Types of Synovial Joints

1. Plane 2. Hinge 3. Pivot 4. Condylar (ellipsoid) 5. Saddle 6. Ball-and-socket

Muscle cell contains the following organelles:

1. Sarcolemma 2. Sarcoplasm 3. Myofibrils 4. Sarcoplasmic reticulum 5. T Tubules

Skeletal muscle contains 2 sets of intracellular tubules that help regulate muscle contraction:

1. Sarcoplasmic Reticulum 2. T Tubules

3 Types of Muscle Tissue

1. Skeletal muscle tissue 2. Cardiac muscle tissue 3. Smooth muscle tissue

As a muscle shortens, all of the following occur:

1. The I bands shorten 2. The distance between successive Z discs shortens 3. The H zones disappear 4. The contigous A bands move closer together, but their length does not change

1st Step of E-C Coupling

1. The action potential propagates along the sarcolemma and down the T Tubules.

Steps in E-C Coupling

1. The action potential propagates along the sarcolemma and down the T tubules 2. Calcium ions are released 3. Calcium binds to troponin and removes the blocking action of tropomyosin 4. Contraction begins

Steps for inducing a skeletal muscle to contract

1. The fiber must be activated by a nerve ending so that a change in membrane potential occurs 2. It must generate an electrical current, "action potential" in its sarcolemma 3. Action potential is automatically propagated along sarcolemma 4. Intracellular calcium ion levels must rise briefly, providing final trigger for contraction

Thin filaments contain several regulatory proteins:

1. Tropomyosin 2. Troponin 3. Elastic Filament 4. Titin 5. Dystrophin 6. Nebulin, myomesin, C proteins

Special Characteristics of Muscle Tissue

1. Vascularized and innervated: 1 artery, 1 nerve, and 1 + veins 2. Excitability: Ability of a cell to receive and respond to a stimulus by changing its membrane potential 3. Contractility: Ability to shorten forcibly when stimulated. 4. Extensibility: Ability to extend or stretch. 5. Elasticity: Ability of a muscle cell to recoil and resume resting length after stretching

Action Potential Questions

1. What is the resting membrane potential?-70 mV 2. At what time is the action potential generated?~2.2ms 3. What causes the change in membrane potential between point C and A?Opening of voltage-gated sodium channels (Sodium ions entering cell) 4. What voltage-gated channel is open at part B? Does it cause ions to move in or out of the cell?Potassium. Out. 5. Is a voltage-gated channel open at point C? No.

How does a motor neuron stimulate a skeletal muscle fiber?

1. When a nerve impulses reaches the end of an axon, the axon terminal releases ACh into the synaptic cleft 2. ACh diffuses across cleft and attaches to ACh receptors on sarcolemma of muscle fiber 3. ACh binding triggers electrical events that ultimately generate an action potential

How many epiphyseal plates are in the long bone of a 4 year old?

2

Synchondroses

A bar or plate of hyaline cartilage unites the bones at a synchondrosis "junction of cartilage". All are immovable. -Most common example: epiphyseal plates in long bones of children.

First step of endochondral ossification

A bone collar forms around the diaphysis of the hyaline cartilage model: Osteoblasts of the newly converted periosteum secrete osteoid against hyaline cartilage diaphysis, encasing it in periosteal bone collar. (Week 9)

Endochondral Ossification

A bone develops by replacing hyaline cartilage; the resulting bone is cartilage or endochondral bone. Except for clavicles, all bones below skull base form this way. Beginning late in second month of development, process uses hyaline cartilage "bones" formed earlier as models for bone construction.

Intramembranous Ossification

A bone develops from a fibrous membrane and the bone is called a membrane bone. Forms the cranial bones (frontal, parietal, occipital, temporal lobes) and clavicles. Most bones formed by this process are flat bones. At about week 8 of development, ossification begins within fibrous connective tissue membranes formed by mesenchymal cells. 4 steps.

Fascicle (portion of muscle)

A discrete bundle of muscle cells, segregated from the rest of the muscle by a connective tissue sheath. Surrounded by perimysum.

Repair of Simple Fracture Step 1

A hematoma forms: When a bone breaks, blood vessels in the bone and periosteum, and sometimes other tissues are torn and hemmorrhage. As a result, a hematoma (mass of clotted blood) forms at fracture site. Soon, bone cells deprived of nutrition die, and tissue becomes swollen, painful, and inflamed.

Symphyses

A joint where fibrocartilage unites bones. Fibrocartilage is compressible and resilient, it acts as a shock absorber and permits a limited amount of movement at the joint. Hyaline cartilage is also present as articular cartilage on bony surfaces. Ampiarthrotic joints designed for strength with flexibility. Slightly movable. Examples: Pubic symphysis, intervertrebal joints.

Hematoma

A mass of clotted blood

Lamallae

A matrix tube made of osteons in a group of hollow tubes of bone matrix, one placed outside the next like a tree trunk. Withstands twisting forces.

Muscle fiber (cell)

A muscle fiber is an elongated multinucleate cell; it has a striated appearance. Surrounded by endomysium.

Striations

A repeating series of dark and light bands are evident along each myofibril. Dark A bands and light I bands are aligned. Each dark A band has a lighter region in its midsection called the H zone. Each H zone is bisected vertically by a dark line called the M line formed by myomesin. Each light I band has a midline interruption, a darker area called Z disc.

Myofibril

A single muscle fiber contains 100's to 1000's of rod-like myofibrils that run parallel to its length. Each myofibril is densely packed in the fiber that mitochondria and other organelles appear to be squeezed between them. Contain sarcomeres and myofilaments.

Second step of cross-bridge formation

ADP and P are released and the myosin head pivots and bends, changing to its bent low-energy state. **As a result it pulls the actin filament toward the M line.**

Opposition

Action taken when you touch your thumb to tips of other fingers on same hand.

Contraction

Activation of myosin's cross bridges (force-generating sites). Shortening occurs if and when cross bridges generate enough tension on thin filaments to exceed forces that oppose shortening.

Third step of cross-bridge formation

After ATP attaches to myosin, the link between myosin and actin weakens and the **myosin head detaches (the cross bridge "breaks")**

T Tubule

An elongated tube at each A band I band junction, where the sarcolemma of the muscle cell protrudes deep into the cell interior. Increase muscle fiber's surface area. Each T Tubule runs between paired terminal cisterns of SR, forming triads.

Secondary Ossification Center

Appear in one or both epiphyses and epiphyses gain bony tissue. Typically, large long bones form secondary centers in both epiphyses, where small long bones form only one. Cartilage in the center of epiphysis calcifies and deteriorates, opening up cavities that allow a periosteal bud to enter. Bone trabeculae appear.

1/6 Structures of Synovial Joints

Articular capsule: Joint cavity is enclosed by a 2-layered articular capsule. Tough external fibrous layer is made of dense irregular connective tissue that is continuous with periostea of articulating bones. Strengthens the joint. Inner layer of joint capsule is a synovial membrane composed of loose connective tissue. It covers all internal joint surface that are not hyaline cartilage. Function is to make synovial fluid.

1/6 Structures of Synovial Joints

Articular cartilage: Hyaline cartilage covers opposing bone surfaces as articular cartilage. Absorb compression and keep bone ends from being crushed.

Synovial Joints

Articulating bones are separated by a fluid-containing joint cavity. All are freely movable diarthroses. Most joints of body and nearly all joints of limbs fall into this class.

Fourth step of cross-bridge formation

As ATP is hydrolyzed to ADP and P, the **myosin head returns to its prestroke high energy, or cocked position**

Epiphyseal plate closure

As adolescence ends, the chondroblasts of the epiphyseal plates divide less often. The plates become thinner and thinner until they are entirely replaced by bone tissue. Longitudinal bone growth ends when the bone of the epiphysis and diaphysis fuses. Happens at about 18 in females, and 21 years in males. Only articular cartilage remains in bones.

Classification of Bones

Axial and appendicular skeleton

Structural Classification of Joints

Based on: Binding material, presence of a joint cavity. 1. Fibrous 2. Cartilaginous 3. Synovial

Flexion

Bending movement, usually along sagittal plane, that DECREASES ANGLE of the joint and brings articulating bones closer together. Example: Bending head toward chest.

Epiphyseal Line

Between the diaphysis and each epiphysis of an adult long bone; a remnant of the epiphyseal plate, a disc of hyaline cartilage that grows during childhood to lengthen the bone. The flared portion of the bone where the diaphysis and epiphysis meet is sometimes called the metaphysis.

1st step of an action potential

Binding of ACh molecules to ACh receptors at the neuromuscular junctions opens chemically gated ion channels that allow Na+ and K+ to pass. Since the driving force for Na+ is greater than that for K+, more Na+ diffuses IN than K+ diffuses out. A transient change in membrane potential occurs as the interior of the sarcolemma becomes less negative (depolarization). Initially, depolarization is a local event called an end plate potential.

H Zone

Bisected vertically by a dark line called M Line

Greenstick fracture

Bone breaks incompletely, one side of shaft breaks; other side bends

Open (internal) reduction

Bone ends secured together surgically with pins and wires

Epiphyses

Bone ends; in many cases they are broader than the diaphysis. An outer shell of compact bone forms epiphysis exterior and the interior contains spongy bone. A thin layer of articular (hyaline) cartilage covers the joint surface of each epiphyses, cushioning opposing bone ends during movement and stress.

Comminuted fracture

Bone fragments into 3+ pieces, particularly common in aged.

Mineral and growth factor storage in bone

Bone is a resevoir for minerals, most importantly calcium and phosphate. The stored minerals are released into the bloodstream as needed. Deposits and withdrawals go on continuously in the bones. Mineralized bone matrix stores important growth factors.

Compression fracture

Bone is crushed. Common in porous bones.

Repair in Simple Fracture Step 4

Bone remodeling occurs. Beginning during bony callus formation and continuing for several months after, the bony callus is remodeled. The excess material on diaphysis exterior and within medullary cavity is removed and compact bone laid down to reconstruct the shaft walls. The final structure of remodeled area resembles the original unbroken bony region because it responds to same set of mechanical stressors.

Response to Mechanical Stress- Wolff's Law

Bone's response to mechanical stress (muscle pull) and gravity, keeps bones strong when stressors are acting. Wolff's law states that a bone grows or remodels in response to the demands placed on it. For example, a bone is stressed whenever weight bears down on it, which tends to bend the bone and stretch it. This results in long bones being thickest midway along diaphysis, exactly where bending stresses are greatest. Compression and tension are minimal toward center of the bone.

Osteoblasts

Bone-forming cells that secrete bone matrix. They are actively mitotic. The unmineralized bone matrix they secrete includes collagen, and calcium-binding proteins that make up the initial unmineralized bone or osteoid.

Syndesmoses

Bones are connected exclusively by ligaments, cords, or bands of fibrous tissue. Amount of movement depends on length of connective fibers. If short fibers, little or no movement. If long fibers, large amount of movement.

Fibrous Joints

Bones are joined by collagen fibers of connective tissue. No joint cavity present. Amount of movement depends on length of connective tissue fibers. Most are immovable. The 3 types are: 1. Sutures 2. Syndemoses 3. Gomphoses

Cartilaginous Joints

Bones are united by cartilage. No joint cavity and are not highly movable. 2 types: 1. Synchondroses 2. Symphyses

Hormone production in bone

Bones produce OSTEOCALCIN, a hormone that helps to regulate insulin secretion, glucose homeostasis, and energy expenditure

Bones provide support

Bones provide a framework that supports the body and cradles soft organs. For example, the rib cage protects the thoracic wall.

Haglund's Deformity AKA Pump Bump

Bony enlargement in calcaneus from wearing heels

Fractures

Breaking a bone, during youth; most fractures are a result of trauma. In old age, most fractures occur as bones weaken.

Depressed fracture

Broken bone portion depressed inward (skull)

What is the role of Calcium in skeletal muscle contractions?

By BONDING to the TROPONIN it causes the TROPOMYOSIN to MOVE from its blocking position on the active sites on the actin filaments SO the CROSS BRIDGES CAN ATTACH

Third Step of E-C Coupling

Calcium binds to troponin and removes the blocking action of tropomyosin. When Ca2+ binds, troponin changes shape, exposing binding sites for myosin (active sites) on the thin filaments.

2nd Step of E-C Coupling

Calcium ions are released. Transmission of the action potential along the T tubules of the triads causes the voltage-sensitive tubule proteins to change shape. This shape change opens the Ca2+ release channels in the terminal cisterns of the sarcoplasmic reticulum, allowing Ca2+ to flow into the cytosol.

Volkmann's canals

Canals of a second type (in compact bone) called perforating canals or Volkmann's canals lie at right angles to long axis of bone and connect blood and nerve supply of medullary cavity to central canals. Unlike central canals of osteons, perforating canals are not surrounded by lamellae, but are lined with endosteum.

Second step of endochondral ossification

Cartilage in the center of the diaphysis calcifies and then develops cavities: As bone collar forms, chondrocytes within the shaft enlarge and signal surrounding cartilage matrix to calcify. Then, because calcified cartilage matrix is impermeable to diffusing nutrients, chondrocytes die and matrix begins to deteriorate. The deterioration opens up cavities, but bone collar stabilizes the hyaline cartilage model. Elsewhere, cartilage remains healthy and continues to grow briskly causing the cartilage model to elongate. (Between Week 9 and Month 3)

Appositional Growth

Cartilage-forming cells in the perichondrium secrete new matrix against the external face of the existing cartilage tissue.

Thick Filaments

Central, containing myosin, extend entire length of the A band. Connected in the middle of the sarcomere at the M line.

Elastic Filament

Composed of giant protein Titin. Extends from Z disc to thick filament and runs within thick filament to attach to M line. Holds thick filaments in place, maintaining organization of A band and helps muscle cell spring back into shape.

Actin

Composes thin filaments. Has kidney-shaped polypeptide subunits called globular actin or G actin which have active sites to which myosin heads attach during contraction. In thin filaments, G actin subunits are polymerized into long actin filaments, "filamentous" or F actin. 2 intertwined actin filaments form backbone of each thin filament.

Muscle (organ)

Consists of hundreds to thousands of muscle cells, plus connective tissue wrappings, blood vessels, and nerve fibers. Covered externally by the epimysium.

Appendicular skeleton

Consists of the bones of the upper and lower limbs and girdles (shoulder and hip bones) that attach limbs to axial skeleton. Bones of limbs help us move (locomotion) and manipulate our environment.

Hyperextension

Continuing angular movements beyond anatomical position

Myofilament/filament (extended macromolecular structure)

Contractile myofilaments are of 2 types: thick and thin. Thick filaments contain bundled myosin molecules, thin filaments contain actin molecules (plus other proteins). The sliding of thin filaments past thick filaments produces muscle shortening. Elastic filaments maintain the organization of the A band and provide elastic recoil when tension is released.

Fourth Step of E-C Coupling

Contraction begins. Myosin binding to actin forms cross bridges and contraction (cross bridge cycling) begins. E-C Coupling is over.

What is the role of Calcium in smooth muscle contractions?

Contraction is initiated by a calcium-regulated phosphorylation of myosin

Refractory Period

Describes a muscle fiber during repolarization; because the cell cannot be stimulated again until repolarization is complete.

Plantar Flexion

Downward movement of foot (pointing toes) (en pointe)

When does cartilage growth typically end?

During adolescence, when the skeleton stops growing

The Sliding Filament Model of Contraction

During contraction, the thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree. Neither the thick nor thin filaments change length during contraction. - When nervous system stimulates muscle fibers, myosin heads on thick filaments latch onto myosin-binding sites on actin in thin filaments, and sliding begins. - These cross bridge attachments form and break several times during a contraction, generating tension and propeling thin filaments toward center of sarcomere - As this event occurs simultaneously in sarcomeres throughout cell, muscle shortens - As thin filaments slide centrally, Z discs to which they attach are pulled toward M line

Crosss Bridges

During contraction, when globular heads of thick and thin filaments link together and swivel around their point of attachment acting as motors to generate force.

Synostoses

During middle age, fibrous tissue ossifies and skull bones fuse into a single unit. At this stage, closed sutures are called synotoses. (Forming a single bone from 2+ bones).

Which of the following are present in the long bone of a 42 year old. A. Epiphyseal line B. Diaphysis C. Epiphyses D. 2 of the above E. All of the above

E: All of the above

Neuromuscular Junction

Each axon of somatic motor neuron forms an elliptical neuromuscular junction or motor end plate with a single muscle fiber.

Sarcoplasmic Reticulum (SR)

Elaborate smooth endoplasmic reticulum. Interconnecting tubules surround each myofibril. Most SR tubules run longitudinally along the myofibril, communicating with each other at H zone. Stores Calcium and releases it on demand when muscle fiber is stimulated to contract.

Axon terminal

End of axon

Synaptic cleft

End of axon and muscle fiber are separated by synaptic cleft, which is filled with extracellular substance rich in glycoproteins and collagen fibers

Osteogenic cells from the periosteum specialize into osteoblasts which then begin creating the bone collar. This is part of:

Endochondrial Ossification

Cross Bridge Formation

Energized myosin head attaches to an actin myofilament, **forming a cross bridge**

Acetylcholinesterase

Enzyme in the synaptic cleft, terminates ACh to its building blocks- prevents continued muscle fiber contraction in absence of added stimulation

Epiphyseal fracture

Epiphysis separates from diaphysis along epiphyseal plate

Triglyceride (fat) storage in bone

Fat, a source of energy, is stored in bone cavities

Repair in Simple Fracture Step 2

Fibrocartilaginous callus forms. Within several days, events lead to the formation of soft "granulation tissue", also called "soft callus". Capillaries grow into hematoma and phagocytic cells invade area and clean debris. Fibroblasts, cartilage, and osteogenic cells invade fracture site from periosteum and endosteum and begin reconstructing bone. Fibroblasts produce collagen fibers that span break and connect broken bone ends. Some precursor cells differentiate into chondroblasts that secrete cartilage matrix. Within this mass of repair tissue, osteoblasts begin forming spongy bone. The cartilage cells farthest from the capillaries secrete an externally bulging cartilagnious matrix that later calcifies. This entire mass of repair tissue, the FIBROCARTILAGINOUS CALLUS, splints the broken bone.

Small motor units

Fine movements (fingers, eye movements)

Bone lining cells

Flat cells found on bone surfaces where bone remodeling is not going on, help maintain matrix, bone lining cells on external bone surface are also called periosteal cells, and lining internal bone surfaces are called endosteal cells.

Muscle tension

Force exerted by a contracting muscle

Pronation

Forearm rotates medially and palm faces posteriorly or inferiorly. Moves distal end of radius across ulna so bones form an X. Example: dribbling a ball. RADIUS ROTATES OVER ULNA.

Axial skeleton

Forms the long axis of the body and includes the bones of the skull, verterbral column, and rib cage.

Diarthroses

Freely movable joints; predominate in limbs

Osteoclasts

Giant multinucleate cells located at sites of bone resorption. When actively resorbing bone, osteoclasts rest in a shallow depression (resorption bay) and exhibit a distinctive ruffled border that contacts the bone. The deep plasma membrane infoldings of the ruffled border tremendously increase the surface area for degrading bones and seal off area from surrounding matrix.

Osteoporosis

Group of diseases in which bone resorption outpaces bone deposit. Bone becomes very fragile. Matrix composition stays the same but bone mass decline and bones become porous and light. Spongy bone of spine is most vulnerable, and femur, compression fractures are common. Occurs mostly in aged, white women. Sex hormones maintain health and normal density of skeleton by restraining osteoclasts and promoting deposit of new bone. After menopause, estrogen secretion wanes and estrogen deficiency can cause osteoporosis.

Triads

Groupings of 3 membranous structures: terminal cistern, T tubule and terminal cistern. As they pass from one myofibril to the next, the T tubules also encircle each sarcomere. Muscle contraction is controlled by electrical impulses that travel along sarcolemma, release Calcium from terminal cisterns.

Growth in Width (Thickness)

Growing bones widen as they lengthen. Bones increase in thickness, or in long bones, diameter, by appositional growth. Osteoblasts beneath periosteum secrete bone matrix on external bone surface as osteoclasts on the endosteal surface of the diaphysis remove bone.

Canaliculi

Hairlike canals connect lacunae to each other and to the central canal.

A Band

Has a lighter region in its midsection, the H Zone

Hormonal controls vs mechanical stress in remodeling

Hormonal controls determine WHETHER and WHEN remodeling occurs in response to changing blood calcium levels. Mechanical stress determines WHERE remodeling occurs.

Leptin in Bone

Hormone released by adipose tissue, plays a role in regulating bone density. Best known for its effects on weight and energy balance, may also inhibit osteoblasts through a brain (hypothalamus) pathway that activates sympathetic nerves serving bones.

The articular surface contains:

Hyaline Cartilage

Synarthroses

Immovable joints; largely restricted to axial skeleton

Lacunae

In compact bone, osteocytes occupy lacunae at junctions of lamellae.

Trabeculae

In living bone, the open spaces between the honeycomb like trabeculae or spongy bone are filled with red or yellow bone marrow. NO OSTEONS.

Bone Remodeling

In the adult skeleton, bone deposit and bone resorption occur at the surfaces of both the periosteum and the endosteum. Together, the two processes constitute bone remodeling. Packets of adjacent osteoblasts and osteoclasts called remodeling units coordinate bone remodeling.

Interstital Lamellae

Incomplete lamellae lying between osteons. They either fill gaps between forming osteons or are remnants of osteons that have been cut through by bone remodeling.

Angular Movements

Increase or decrease angle between 2 bones

Aerobic (endurance) exercise leads to:

Increased -Muscle capillaries -Number of mitochondria -Myoglobin synthesis -May convert fast glycolytic fibers into fast oxidative fibers - More endurance

1/6 Structures of Synovial Joints

Joint (articular) cavity: Unique to synovial joints, joint cavity is a potential space with a small amount of synovial fluid.

Interstitial Growth

Lacunae-bound chondrocytes divide and secrete new matrix, expanding the cartilage from within.

Intramembranous Ossification: Step 4

Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. Trabeculae just deep to the periosteum thicken. Mature lamellar bone replaces them, forming compact bone plates. Spongy bone consisting of distinct trabeculae persists internally and its vascular tissue becomes red marrow.

Large motor units

Large weight-bearing muscles and gross movement (thigh, hip movement)

Perimysium

Layer of dense irregular connective tissue that surrounds each fascicle

Ossification Zone

Leaves long slender spicules of calcified cartilage at the epiphysis-diaphysis junction which look like stalactites. These calcified spicules ultimately become part of ossification/osteogenic zone and are invaded by marrow elements from medullary cavity. Osteoclasts partly erode the cartilage spicules, then osteoblasts quickly cover them with new bone. Ultimately spongy bone replaces them. Eventually as osteoclasts digest spicule tips, medullary cavity also lengthens.

H zone of A band appear ______ because thin filaments do not extend into this region

Less dense

Elevation

Lifting a body part superiorly. Example: closing mouth.

Dorsiflexion

Lifting the foot so that its superior surface approaches the shin (upward movement) (putting weight on heels)

Dystrophin

Links thin filaments to integral proteins of sarcolemma, which are anchored to extracellular matrix.

Circumferential lammellae

Located just deep to periosteum, superficial to endosteum, extend around entire circumference of diaphysis and resist long bone twisting.

Other proteins that bind filaments or sarcomeres:

Maintain alignment; nebulin, myomesin, C proteins.

Osteocytes

Mature bone cells that occupy spaces (lacunae) that conform to their shape. Osteocytes monitor and maintain the bone matrix. If they die, surrounding matrix is resorbed. Also act as stress "sensors" and respond to mechanical stimuli. They communicate info to cells responsible for bone remodeling (osteoblasts and osteoclasts) so that bone matrix can be made or degraded to preserve calcium homeostasis.

Hypertrophic Zone

Meanwhile, the older chondrocytes in the stack, which are closer to the diaphysis hypertrophy, and their lacunae erode and enlarge, leaving large interconnecting spaces.

I Band

Midline interruption, darker area called Z Disc

Growth in Length of Long Bones (Longitudinal Bone Growth) + Steps

Mimics many of the events of endochondral ossification and depends on the presence of epiphyseal cartilage. The cartilage is relatively inactive on the side of the epiphyseal plate facing epiphysis, a region called the resting zone. But the epiphyseal plate cartilage next to the diaphysis organizes into a pattern that allows fast, efficient growth. The cartilage cells here form tall columns, like coins in a stack. 1. Proliferation zone (growth zone, cells divide quickly) 2. Hypertrophic zone (lacunae erode and enlarge, leaving large spaces) 3. Calcification zone (Surrounding cartilage matrix calcifies, chondrocytes die and deteriorate) 4. Ossification zone (Osteoclasts partly erode cartilagteg, osteoblasts quickly cover them with new bone, spongy bone replaces them, medullary cavity lengthens)

Osteogenic cells

Mitotically active stem cells in membranous periosteum and endosteum. In growing bone they are flattened or squamos cells. When stimulated, these cells differentiate into osteoblasts or bone lining cells while others persist as osteogenic cells.

Thin Filaments

More lateral, contain actin extending across the I band and partway into the A band. The Z disc anchors the thin filaments. Intermediate filaments extend from Z disc and connect myfobrils.

Blood cell formation in bone

Most blood cell formation, or hematopoiesis, occurs in red marrow cavities of certain bones

Proteins actin and myosin play a role in...

Motility and shape change in almost every body cell

Circumdiction

Moving a limb so that it makes a cone in space. Distal end of limb moves in a circle, while point of cone is stationary. Example: winding up to pitch.

Abduction

Moving away, movement of a limb away from the midline or median plane of the body, along the frontal plane. Example: raising thigh or arm laterally.

Depression

Moving elevated part inferiorly. Example, opening mouth.

Adduction

Moving toward, movement of a limb toward the body midline.

Movement allowed by Synovial Joints

Muscle attachments across a joint: Origin: site of attachment to immovable bone. Insertion: site of attachment to movable bone. Muscle contraction leads to insertion to move toward origin. Movements can be described relative to lines; transverse, frontal, or sagittal.

Fascicles

Muscle fibers that are grouped within each skeletal muscle

1/6 Structures of Synovial Joints

Nerves and blood vessels: Synovial joints are richly supplied with sensory nerve fibers and blood vessels that supply synovial membrane.

Serotonin in bone

Neurotransmitter made in the gut; when we eat, serotonin is secreted and circulated via the blood to the bones where it interferes with osteoblast activity.

Protaction

Nonangular anterior movement in a transverse plane. Example: Moving jaw out.

Each muscle fiber has _____ neuromuscular junction located _____

ONLY ONE, approximately midway its length

Muscle Load

Opposing force exerted on the muscle by the weight of the object being moved

Extension

Opposite of flexion; occurs at same joints. Involves movement along sagittal plane that INCREASES ANGLE between articulating bones and straightens flexed limb or body part. Example: straightening flexed neck, body trunk, elbow or knee.

Intramembranous Ossification: Step 1

Ossification centers appear in the fibrous connective tissue membrane: Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center that produces the first trabeculae of spongy bone.

Bone resorption

Osteoclasts move along bone surface, digging depressions or grooves as they break down bone matrix. The border of osteoclast clings to bone, sealing off area of bone destruction that digest organix matrix. Resulting acidic brew in resorption bay converts calcium salts into forms that pass easily into solution. Osteoclasts may also phagocytize demineralized matrix and dead osteocytes. Digested matrix end products, growth factors, and dissolved mienrals are endocytosed, transported across osteoclast, and released at opposite side. There they enter interstitial fluid and then blood. When resorption is complete, osteoclasts undergo apoptosis. PTH and proteins by T cells are important.

Intramembranous Ossification: Step 2

Osteoid is secreted within the fibrous membrane and calcifies: Osteoblasts continue to secrete osteoid, which calcifies in a few days. Trapped osteoblasts become osteocytes.

Troponin

Other major protein in thin filaments, is a globular 3 polypeptide complex. One of its polypepties is an inhibitory subunit that binds to actin, another binds to tropomyosin and helps position it on actin, another binds calcium ions.

Epimysium

Overcoat of dense irregular connective tissue that surrounds entire muscle

In a relaxed muscle fiber, the thin and thick filaments ____

Overlap only at the ends of the A Band

Gomphosis

Peg-in-socket fibrous joint. Only example: articulation of a tooth with bony alveolar socket. Fibrous connection is the short periodontal ligament.

Phases leading to muscle fiber contraction:

Phase 1: Motor neuron stimulates muscle fiber. Phase 2: Excitation-contraction coupling occurs.

Closed (external) reduction

Physicians hands coax bone ends into position

Sarcolemma

Plasma membrane of a skeletal muscle fiber

Tropomyosin

Polypeptide strands, a rod-shaped protein, spiral about actin core and stiffen and stabilize it. Arranged end to end along actin filaments, and in relaxed muscle fiber, BLOCK myosin-binding sites on actin so that myosin heads on thick filaments cannot bind to thin filaments.

Retraction

Posterior movement in a transverse plane. Example: Retracting, bringing jaw back.

Ossification/Osteogensis

Process of bone formation. In embryos, the formation leads to bony skeleton. Later, another form, bone growth, occurs during early adulthood. In adults, it serves mainly for bone remodeling/repair.

Calcitonin in Bone

Produced by C cells of thyroid gland. Appears to be a hormone in search of a function because its effects on Calcium homeostasis are negligible. When administered pharmacologically, it lowers blood calcium levels temporarily.

Myosin

Protein that makes up thick filaments. Each consists of 2 heavy and 4 light polypeptide chains and has a rodlike tail attached by a flexible hinge to 2 globular heads. The tail has 2 intertwined helical polypeptide heavy chains.

Spiral fracture

Ragged break from excessive twisting forces

Reduction

Realignment of broken bone ends

Primary Ossification Center

Region of a long bone where formation typically begins; in the center of the hyaline cartilage shaft. First, blood vessels infiltrate the perichondrium covering the hyaline cartilage "bone" converting it to a vascularized periosteum. Then, the underlying mesenchymal cells specialize into osteoblasts and ossification can begin.

Sarcomere

Region of a myofibril between 2 successive Z discs. Smallest contractile unit of a muscle fiber; functional unit of skeletal muscle. Contains an A band flanked by half an I band at each end. Sarcomeres align end to end.

1/6 Structures of Synovial Joints

Reinforcing ligaments: Synovial joints are reinforced by a number of bandlike ligaments.

Action Potential

Result of a sequence of electrical changes along the entire surface of the sarcolemma, includes 3 steps.

Myofibril or Fibril (complex organelle composed of bundles of myofilaments)

Rodlike contractile elements that occupy most of muscle cell volume. Composed of sarcomeres arranged end to end, appear banded, and bands of adjacent myofibrils are aligned.

Supination

Rotating the forearm laterally so that the palm faces anteriorly or superiorly. RADIUS AND ULNA ARE PARALLEL.

Canals and Canaliculi

Running through core of each osteon is central canal or Haversian canal, with small blood vessels and nerve fibers that serve osteon's cells. Lined with endosteum.

Terminal cistern

SR tubule that forms a larger, perpendicular cross channel at the A band-I band junctions, and always occur in pairs.

The myofilaments are connected to the _____ and held in alignment at the Z discs and M Lines

Sarcolemma

How does time until rigor mortis differ if saxitoxin or anatoxin is involved?

Saxitoxin: same Anatoxin: Sooner

Excitation-Contraction (E-C) Coupling

Sequence of events by which transmission of an action potential along the sarcolemma causes myofilaments to slide. Causes the rise in intracellular levels of calcium ions which allows filaments to slide.

Cross- Bridge Cycle

Series of events during which myosin heads pull thin filaments toward the center of the sarcomere. The cycle continues as long as ATP is available and Ca2+ is bound to troponin. If ATP is unavailable, the cycle stops between steps 2 and 3.

Bones provide anchorage

Skeletal muscles use bones as levers to move the body and its parts. The result makes movement possible.

The M line in the center of the H zone is ______ because of the fine protein strands that hold adjacent thick filaments together

Slightly darker

Ampiarthroses

Slightly movable joints; largely restricted to axial skeleton

Myofilaments

Smaller structures within a myofibril, muscle equivalents of the actin- or myosin- containing microfilaments.

Eversion

Sole of foot faces laterally (away from body, points sideways)

Inversion

Sole of foot turns medially (toward body, sideways)

Skeletal Muscle Fiber Types

Speed and ATP pathways -Speed of Contraction -Speed at which Myosin ATPase hydrolyzes ATP -Slow -Fast -Major Pathway for ATP production -aerobic respiration ---> oxidative fiber -anaerobic respiration using more glycogen ---> glycolytic fiber - 3 major skeletal muscle types: i) Slow Oxidative Fibers ii)Fast Oxidative Fibers iii) Fast Glycolytic fibers

Gliding

Synovial Joint; when one flat or nearly flat bone surface glides or slips over another (back and forth and side to side) without angulation or rotation. Example: intercarpal and intertarsal joints, between processes of verterbrae.

1/6 Structures of Synovial Joints

Synovial fluid: Occupies all free spaces within joint capsule. Fluid is derived largely by filtration from blood flowing through capillaries in synovial membrane. Also found within articular cartilages, provides lubrication for joint surfaces to meet. Fluid is forced from cartilages when a joint is compressed, so pressure is relieved (weeping lubrication) lubricates free surfaces of cartilages and nourishes cells. Also contains phagocytic cells.

Proliferation Zone

The cells at the "top" (epiphysis-facing) side of the stack next to the resting zone comprise the proliferation or growth zone. These cells divide quickly, pushing the epiphysis away from the diaphysis and lengthening the entire long bone.

Sarcomere (segment of a myofibril)

The contractile unit, composed of myofilaments made up of contractile units

Sarcoplasm

The cytoplasm of a muscle cell; contains large amounts of glycosomes (granules of stored glycogen that provide glucose during muscle cell activity for ATP production) and myoglobin (red pigment that stores oxygen)

Fourth step of endochondral ossification

The diaphysis elongates and a medullary cavity forms: As the primary ossification center enlarges, osteoclasts break down newly formed spongy bone and open a medullary cavity in the center of the diaphysis. Throughout the fetal period (week 9-birth) the rapidly growing epiphyses consist only of cartilage and hyaline cartilage models continue to elongate by division of viable cartilage cells at epiphyses. Ossification "chases" cartilage formation along length of shaft as cartilage calcifies, erodes, and is replaced by bony spikes on epiphyseal surfaces facing medullary cavity. At birth, most long bones have a bony diaphysis surrounding remnants of spongy bone, a widening medullary cavity, and 2 cartilaginous epiphyses. Shortly before or after birth, secondary ossification centers appear in one or both epiphyses, and they gain bony tissue. The cartilage in center of epiphysis calcifies and deteriorates, opening up cavities that allow periosteal bud to enter. Bone trabeculae appear just as they did in primary ossification center.

2nd step of action potential

The end plate potential ignites an action potential by spreading to adjacent membrane areas and opening voltage-gated sodium channels there. Na+ enters, and once a certain threshold is reached, an action potential is generated. The action potential moves along the length of the sarcolemma, as it moves, the local depolarization wave of the action potential spreads to adjacent areas of the sarcolemma and opens voltage-gated sodium channels. Again, Na+ diffuses INTO t he cell following its electrochemical gradient.

Fifth step of endochondral ossification

The epiphyses ossify. Bone trabeculae appear, just as they did earlier in the primary ossification center. Hyaline cartilage remains in 2 places: on the epiphyseal surfaces as articular cartilages and at the junction of the diaphysis and epiphysis as epiphyseal plates. (Childhood to adolescence).

Bones provide protection

The fused bones of the skull protect the brain.

What is and isn't contraction

The generation of force (tension) -Does not necessarily cause shortening of the fiber - Hold out a book - Rigor mortis -Shortening occurs when tension generated by crossbridges on the thin filament exceeds forces opposing shortening

Motor Unit

The motor neuron and all of the skeletal muscle fibers it innervates - 1 motor neuron innervates many fibers - 1 fiber only innervated by 1 motor neuron

Somatic motor neurons

The nerve cells that activate skeletal muscle fibers; reside in brain or spinal cord. Axons extend to muscle cells.

Third step of endochondral ossification

The periosteal bud invades the internal cavities and spongy bone forms. In month 3, the forming cavities are invaded by the periosteal bud which contains a nutrient artery and vein, nerve fibers, red marrow elements, osteogenic cells, and osteoclasts. The entering osteoclasts partially erode the calcified cartilage matrix and the osteogenic cells become osteoblasts and secrete osteoid around the remaining calcified fragments of hyaline cartilage. In this way, bone covered cartilage trabeculae, the earliest version of spongy bone, is formed.

Saltatory Conduction

The propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials - Faster, more energy efficient

3rd Step of Action Potential

The repolarization wave is a consequence of changes in membrane permeability. Na+ channels close and voltage-gated K+ channels open. Since Potassium ion concentration is substantially higher inside the cell than in extracellular fluid; K+ diffuses rapidly out of the muscle fiber, restoring negatively charged conditions inside.

Osteon (Haversian) System

The structural unit of compact bone. Each osteon is an elongated cylinder parallel to long axis of the bone. Functionally, osteons are tiny weight-bearing pillars. Contains lamella (osteons are group of hollow tubes of bone matrix, one placed outside other like growth rings in a tree trunk), each matrix tube is a lamella. Often called lamellar bone. Resist twisting forces.

Calcification Zone

The surrounding cartilage matrix calcifies and chondrocytes die and deteriorate, producing the calcification zone.

Why is spongy bone necessary?

Trabeculae in spongy bone align along lines of stress and help bone resist stress. NO OSTEONS ARE PRESENT. Nutrients reach osteocytes by diffusing through canaliculi from capillaries surrounding trabeculae.

Diaphysis

Tubular shaft that forms the long axis of the long bone. It is constructed of a thick collar of compact bone that surrounds a central medullary cavity aka marrow cavity. In adults, the medullary cavity contains fat (yellow marrow) and is called the yellow marrow cavity.

Perforating Sharpey's Fibers

Tufts of collagen fibers that extend from fibrous layer into bone matrix, secure periosteum to underlying bone

Rotation

Turning of a bone around its own long axis. Only movement between first 2 cervical vertebrae and common at the hip and shoulder joints. May be directed toward or away from midline.

PTH in Bone

When blood levels of ionic calcium decline, PTH is released and stimulates osteoclasts to resorb bone, releasing calcium into blood. Osteoclasts break down new and old matrix. As blood concentrations of Ca rise, the stimulus for PTH ends. Decline of PTH reverses its effectss and causes blood Ca to fall.

How canaliculi are formed

When bone is forming, osteoblasts secreting bone matrix surround blood vessels and maintain contact. As newly secreted matrix hardens and maturing cells become trapped, a system of tiny canals, canaliculi, filled with tissue fluid is formed. Tie all osteocytes in a mature osteon together, allowing them to communicate.

How are binding sites on Actin exposed?

When intracellular Calcium levels are low, the muscle cell is relaxed, and tropomyosin molecules physically block the active (myosin-binding) sites on actin. As Ca2+ levels rise, the ions bind to regulatory sites on troponin. 2 Calcium ions must bind to a troponin causing it to change shape and roll tropomyosin into the groove of the actin helix, away from the myosin-binding sites. **The tropomyosin "blockade" is removed when enough Calcium is present.**

Aftermath of E-C Coupling

When the muscle action potential stops, the voltage-sensitive tubule proteins return to their original shape, closing the Ca2+ release channels of the SR. Ca2+ levels in the sarcoplasm fall as Ca2+ is continuinally pumped back into the SR by active transport. Without Ca2+, the blocking action of tropomyosin is restored, myosin-actin interaction is inhibited, and relaxation occurs. Each time an AP arrives at the neuromuscular junction, E-C coupling is repeated.

Repair in Simple Fracture Step 3

Within a week, new bone trabeculae appear in fibrocartilaginous callus and gradually convert it to a bony (hard) callus of spongy bone. Bony callus formation continues until a firm union forms about 2 months later. This process generally repeats events of endochondral ossification.

Synaptic vesicles

Within axon terminal; small membranous sacs containing neurotransmitter acetylcholine (ACh)

Intramembranous Ossification: Step 3

Woven bone and periosteum form: Acculumating osteoid is laid down between embryonic blood vessels in a manner that results in a network (instead of concentric lamellae) of trabeculae called woven bone. Vacularized mesenchyme condenses on external face of woven bone and becomes periosteum.

Multiple Sclerosis (MS)

autoimmune disease -demyelination of axons in the CNS -impulse transmission slows down -interferes with communication/control between the brain and the rest of the body.

Cardiac Muscle

o Intercalated Disks o Gap junctions o Desmosomes o Aerobic muscle o Coronary circulation o Minimal cell division after infancy o Hypertrophy o Can have spontaneous electrical changes o pacemaker cells/autorhythmic cells o 1% autorhythmic cells o 99% contractile cells

A resting sarcolemma is ___

polarized

Cardiac muscle with Smooth Muscle

❁ Gap junctions ❁ Pacemaker cells: autorhythmic ❁ Innervated by autonomic nervous system (involuntary) ❁ Influenced by hormones

Cardiac Muscle Similarities with Skeletal Muscle

❁ Striated with sarcomeres ❁ Troponin & Tropomyosin ❁ T tubules ❁ Sarcoplasmic reticulum ❁ Similar to slow oxidative fibers myoglobin mitochondria slow to fatigue