TPR Chapter 15: Muscular and Skeletal System

Cartilage

- Cartilage consists of a firm but elastic matrix called chondrin that is secreted by cells called chondrocytes. - Do not contain nerve cells (no innervated) and are avascular (no blood vessels). - Receives nutrient and immune protection from surrounding fluid.

Osteoporosis

A condition in which the body's bones become weak and break easily. Result of increased osteoclast resorption and slowing of bone formation, both of which lead to loss of bone mass. Estrogen is believed to help prevent osteoporosis by stimulating osteoblast activity.

motor unit

A motor neuron and all of the muscle fibers it innervates

rigor mortis.

After death, ATP production ceases. Myosin heads cannot detach from actin, making it impossible for muscles to relax and lengthen.

Bone composition

Bone is a connective tissue derived from embryonic mesoderm. The outermost portions of bone are composed of compact bone, whereas the internal core is made of spongy bone. Compact bone contains organic and inorganic components. - The organic components include collagen, glycoproteins, and other peptides. which gives bone its tensile strength. - The inorganic components include calcium, phosphate, and hydroxide ions, which harden together to form hydroxyapatite crystals (Ca10(PO4)6(OH)2). provides rigidity and density.

Cardiac muscle

Cardiac muscle cells are able to define and maintain their own rhythm through myogenic activity. Starting at the sinoatrial (SA) node, depolarization spreads using conduction pathways to the atrioventricular (AV) node. From there, the depolarization spreads to the bundle of His and its branches, and then to the Purkinje fibers. The gap junctions allow for progressive depolarization to spread via ion flow across the gap junctions between cells. The nervous and endocrine systems also play a role in the regulation of cardiac muscle contraction. The vagus nerve provides parasympathetic outflow to the heart and slows the heart rate. Norepinephrine from sympathetic neurons or epinephrine from the adrenal medulla binds to adrenergic receptors in the heart, causing an increased heart rate and greater contractility. One of the ways epinephrine does this is by increasing intracellular calcium levels within cardiac myocytes.

Muscular System (Types of muscle).

Composed of skeletal muscle, smooth muscle and cardiac muscle.

Muscle contraction: Initiation

Contraction starts at the neuromuscular junction, where the nervous system communicates with muscles via motor (efferent) neurons. This signal travels down the neuron until it reaches the nerve terminal where acetylcholine is released into the synapse. Acetylcholine binds to receptors on the sarcolemma, causing depolarization. Depolarization triggers an action potential, which spreads down the sarcolemma to the T-tubules. The T-tubules travel into the muscle tissues to the sarcoplasmic reticulum. When the action potential reaches the sarcoplasmic reticulum, Ca2+ is ultimately released. The calcium ions bind to a regulatory subunit in troponin, triggering a change in the confirmation of tropomyosin, to which troponin is bound. This change exposes the myosin-binding sites on the actin thin filament.

compact and spongy bone

Cortical bone (compact bone) is very dense and strong. - Its primary purpose is providing structural support to the body and its organs and tissues. - Comprises long bone. - In the center of long bones is a central canal where blood vessels, nerves, and bone marrow are found. - At the ends of the long bones, cortical bone gives way to cancellous bone. Cancellous bone/spongy bone is filled with red bone marrow, important for producing blood cells. - Located at the ends of the long bones (the epiphyses), - It is found in the ends of long bones and in the bones of the pelvis, ribs, vertebrae, and skull. - It is characterized by a lattice-like matrix network called trabeculae. - The bone marrow found in cancellous bones also contains many stem cells that are used to repair damaged or broken bone.

the sliding filament model

During contraction, the thin and thich filament slide across each other, drawing the Z line closer and shortening the length of the muscle cell. The repetitive binding and releasing of myosin heads on actin filaments allows for the thin filament to slide along the thick filament, causing sequential shortening of the sarcomere. This is known as the sliding filament model. When a sarcomere contracts, both the H-zone and I-band shorten while the A-band is unchanged.

Anatomy of a Long Bone (Humerus)

Epiphysis: - Filled with red bone marrow, which produces erythrocytes (red blood cells). - Uses their spongy cores for more effective dispersion of force and pressure at the joints. - Covered with articular cartilage, a thin layer of hyaline cartilage that reduces friction and acts as a shock absorber. - The biochemical breakdown of the articular cartilage results in osteoarthritis. Metaphysis: - Portion of a long bone between the epiphysis and the diaphysis. - It contains the growth plate, the part of the bone that grows during childhood, and as it grows it ossifies into bone. - The growth plate synchronizes chondrogenesis with osteogenesis Diaphysis: - Main section of the long bone. - It is made up of cortical bone and usually contains bone marrow and adipose tissue (fat).

types of cartilage

Hyaline cartilage: - strong and somewhat flexible. - reduces friction and absorbs shock. Elastin cartilage: - Produces shape and support. - outer ear and epiglottis. Fibrous cartilage: - provides rigidity. - found in the pubic symphysis.

Hypercalcemia

Hypercalcemia can cause the bones to release too much calcium, leaving them deficient. This abnormal bone activity can lead to pain and muscle weakness, confusion, lethargy, and fatigue.

Frequency Summation and Tetanus

If a muscle fiber is exposed to frequent and prolonged stimulation, it will have insufficient time to relax. The contractions will combine, become stronger and more prolonged. This is known as frequency summation. If the contractions become so frequent that the muscle is unable to relax at all, this is known as tetanus. Prolonged tetanus will result in muscle fatigue.

Cardiac Myogenic activity: Describe graph of cardiac myogenic activity: P wave: PR interval: QRS complex: ST segment: T wave:

One of the unique characteristics of cardiac muscle is how each cardiac myocyte communicates. Cardiac muscle cells are connected by intercalated discs, which contain many gap junctions.

Bone Growth and Development

Osteogenesis/ossification. Bone is formed by one of two processes: endochondral ossification or intramembranous ossification. Endochondral ossification is the process of bone development from hyaline cartilage. All of the bones of the body, except for the flat bones of the skull, mandible, and clavicles, are formed through endochondral ossification. Intramembranous ossification is the process of bone development from fibrous membranes in which undifferentiated embryonic connective tissue (mesenchymal tissue) is transformed into, and replaced by, bone. It is involved in the formation of the flat bones of the skull, the mandible, and the clavicles.

Microscopic bone Structure: osteons, lamellae, harversian canal, canaliculi, volksmann's canal.

Osteons: - The structural unit of the compact bone. - Also called a Haversian system. Lamellae: - Layers of osteon is called a lamella. - The collagen fibers of adjacent lamallae run at perpendicular angles to each other, allowing osteons to resist twisting forces in multiple directions. Haversian canal: -Central canal, or Haversian canal contains blood vessels, nerves, and lymphatic vessels. Canaliculi: - Allow for the exchange of nutrients and wastes between osteocytes and the Haversian and Volkmann's canals. Lacunae: - House mature bone cells known as osteocytes. Volkamann's canal: - Channels that run perpendicular to the central canal to connect osteons.

Bone Cells: osteoprogenitor cells, osteoblasts, osteocytes, osteoclast.

Osteoprogenitor cells: -Undifferentiated cells with high mitotic activity and they are the only bone cells that divide. - They differentiate and develop into osteoblasts. Osteoblasts: - synthesizes collagen and proteins (osteoids). - produces alkaline phosphate: enzyme that forms hydroxyapatite. - Matures into osteocytes (Bone formation). Osteocytes: - Located in the lacunae, matures into bone cell. Osteoclast: - Phagocytic cousin of macrophage. - Derived from monocytes. - Participates in bone reabsorption by dissolving hydroxyapatite crystals. - located in Howship's lacunae. Osteoblasts build bone. Osteoclasts chew bone.

slow twitch muscle fibers

Other name: Type 1 Colour: red. Contraction speed: Slow. Force generated: Low. Mitochondria: High. Activity: Aerobic. Fatigue resistance: High. Source of energy: triglyceride.

fast twich muscle fibers

Other name: Type 2B. Colour: white. Contraction speed: Fast. Force generated: High. Mitochondria: Low. Activity: Anaerobic. Fatigue resistance: Low. Source of energy: ATP and creatine phosphate.

Skeletal endocrine control: PTH, calcitonin, calcitriol: Effect on bone: Effect on kidneys: Effect on small intestine:

PTH: - Effect on bone: stimulates osteoclast activity. - Effect on kidneys: increases reabsorption of calcium and conversion of vitamin D to calcitrol. - Effect on small intestine: increased calcium reaborption. Calcitrol: - Effect on bone: stimulates osteoclast activity. - Effect on kidneys: increases reabsorption of phosphorous. - Effect on small intestine: increased calcium reabsorption. Calcitonin: - Effect on bone: stimulates osteoblast activity. - Effect on kidneys: decreases reabsorption of calcium. - Effect on small intestine: N/a

Gross Structure of Myocytes. Definition and function: Sarcomere. Sarcolemma. Sarcoplasmic reticulum Sarcoplasm.

Sarcomeres are attached end-to-end to form myofibrils. Myofibrils are surrounded by a covering known as the sarcoplasmic reticulum. The sarcoplasmic reticulum is a modified endoplasmic reticulum that contains a high concentration of Ca2+ ions. The sarcoplasm is a modified cytoplasm located just outside the sarcoplasmic reticulum. The sarcolemma is the cell membrane of a myocyte. It is capable of propagating an action potential and can distribute the action potential to all sarcomeres in a muscle using a system of transverse tubules (T-tubules) that are oriented perpendicularly to the myofibrils. Each myocyte, or muscle cell, contains many myofibrils arranged in parallel and can also be called a muscle fiber. The nuclei, of which there are many, are usually found at the periphery of the cell. Finally, many myocytes in parallel form a muscle.

Function of skeletal muscle

Skeletal muscle is essential for supporting the body and allowing for movement. The contraction of skeletal muscle also compresses venous structures and helps propel blood through the low-pressure venous system toward the heart, as well as lymph through the lymphatic system. Rapid muscle contraction also leads to shivering, which is important in thermoregulation. Storage of calcium. Synthesizes components of blood: hemotopoiesis (WBCs, RBCs, platelets).

Function of smooth and cardiac muscles

Smooth muscle is responsible for involuntary movement, such peristalsis. Smooth muscle also aids in the regulation of blood pressure by constricting and relaxing the vasculature. Cardiac muscle is a special type of muscle that is able to maintain rhythmic contraction of the heart without nervous system input. Both smooth and cardiac muscle exhibit myogenic activity. These muscle cells will respond to nervous input, but do not require external signals to undergo contraction.

smooth muscle characteristics: Structure? Gap junction present? T tubules present? SR present? Source of calcium for contraction? Does calcium bind to troponin? Past pacemaker present? Tetanus possible? Supply of ATP?

Smooth muscle: - The structure is narrower and smaller. - Lacks T-tubules. - Uninucleated, no striation. - No troponin-trypomyois complex. contraction is regulated by calmodulin + myosin light chain kinase. (Calmodulin binds Ca2+ and activates MLCK. MLCK phosphorylates myosin molecules, thus activating enzymatic activity). - Relies on extracellular calcium. - AP varies, depends on location of muscle. - Has fluctuating resting potential. - Innervated by autonomic motor neurons.

Parts of the sarcomere:

The Z disc: - Z-lines define the boundaries of each sarcomere. M line: - The M-line runs down the center of the sarcomere, through the middle of the myosin filaments. A band: - all of the thick filament, whether or not it is overlapping. I band: I is a thin letter (thin filaments only). H zone: H is a thick letter (thick filaments only). During contraction, the H-zone, I-band, the distance between Z-lines, and the distance between M-lines all become smaller, whereas the A-band's size remains constant.

Muscle contraction: Relaxation

The binding of ATP is required for releasing the myosin head from the actin filament. It is the dissociation of ADP and Pi from myosin that is responsible for the powerstroke, not the binding of ATP. Acetylcholine is degraded in the synapse by the enzyme known as acetylcholinesterase. This results in termination of the signal at the neuromuscular junction and allows the sarcolemma to repolarize. As the signal decays, calcium release ceases, and the SR takes up calcium from the sarcoplasm. The SR tightly controls intracellular calcium concentrations so that muscles are contracted only when necessary. ATP binds to the myosin heads, freeing them from actin. Once the myosin and actin disconnect, the sarcomere can return to its original width. Without calcium, the myosin-binding sites will be covered by tropomyosin and contraction will be prevented.

Tetanus disease

The disease tetanus is caused by a bacterium called Clostridium tetani that releases the toxin tetanospasmin. Tetanospasmin blocks the release of GABA from the neurons that inhibit motor neurons, making the motor neurons overexcitable. This leads to constant contraction of muscles, which can be so strong as to fracture bones

Muscle contraction: Shortening of the Sarcomere

The free globular heads of the myosin molecules move toward and bind with the exposed sites on actin. The newly formed actin-myosin cross bridges then allow myosin to pull on actin, which draws the thin filaments toward the M-line, resulting in shortening of the sarcomere. Myosin carrying hydrolyzed ATP (ADP and an inorganic phosphate, Pi) is able to bind with the myosin-binding site. The release of the inorganic phosphate and ADP in rapid succession provides the energy for the powerstroke and results in sliding of the actin filament over the myosin filament. Then, ATP binds to the myosin head, releasing it from actin. This ATP is hydrolyzed to ADP and Pi, which recocks the myosin head so that it is in position to initiate another cross-bridge cycle.

The appendicular skeleton

The portion of the skeletal system that consists of the limbs, the pectoral girdle and the pelvis.

The axial skeleton

The portion of the skeletal system that consists of the skull, vertebral column, the ribcage and the hyoid bone. It provides the basic central framework for the body.

The Sarcomere

The sarcomere is the basic contractile unit of skeletal muscle. Sarcomeres are made of thick and thin filaments. The thick filaments are organized bundles of myosin. The thin filaments are made of actin along with two other proteins: troponin and tropomyosin. These proteins help to regulate the interaction between the actin and myosin filaments.

which filament is associated with troponin and tropomyosin,

actin has a T in it.

Destruction of articular cartilage

arthritis

Myogenic activity

contraction w/out neural input. smooth muscle + cardiac muscle.

fasicle

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

Sarcolemma

muscle cell membrane contains polysaccharides and collagen.

muscle structure size

muscle, > fascicle, > fiber, > myofibril, > sarcomere, > myofilaments

Types of joints

synarthrosis joints, - immovable joints consist of bones that are fused together to form sutures. - found primarily in the head, where they anchor bones of the skull together. amphiarthrosis , - limited mobility. - Filling the gap between the vertebrae is a thick pad of fibrocartilage called an intervertebral disc. - Found in verterbrae joint. diarthrosis joints: - include joints (like the elbow or knee), ball-and-socket joints (like the shoulder or hip). - Movable joints are strengthened by ligaments, and consist of a synovial capsule, which encloses the actual joint cavity (articular cavity).

oxygen debt

the amount of oxygen required after physical exercise to convert accumulated lactic acid to glucose.

Simple Twitch

the response of a single muscle fiber to a brief stimulus at or above the threshold stimulus and consists of a latent period, a contraction period, and a relaxation period. The latent period is the time between reaching threshold and the onset of contraction. It is during this time that the action potential spreads along the muscle and allows for calcium to be released from the sarcoplasmic reticulum.

sliding filament model: changes in sacromere during contraction and relaxation.

theory on the mechanism for muscle contraction