Connective Tissue of MSK Flashcards
What is hypertrophy?
Hypertrophy
- Increase in size of cells
- Muscle cells respond to increased load levels or activity by increasing the number of myofibrils within each fiber or the number of sarcomeres
What is hyperplasia?
Hyperplasia
- Increase in number of cells
- Possible through satellite cells, but limited capacity in adults
What are the 3 different muscle types? How are they different?
Muscle Types
Smooth: lining of the gut and glands, innervated by the ANS
Cardiac: striated, limited to the heart
Striated (skeletal): active control of the body, mutlinucleated
Describe the cross-bridge cycle that takes place during muscle contraction.
Cross-Bridge Cycle
- Myosin (thick filament) cross bridge attaches to the actin myofilament (thin filament)
- Power stroke: the myosin head pivots and bends as it pulls on the actin filament, sliding it toward the M line; this occurs with the release of ADP + P
- As new ATP attaches to the myosin head, the cross bridge detaches. IMPORTANT: ATP breaks apart the myosin-actin structure, therefore it causes muscle release, NOT contraction. This is why rigor mortis (stiffness) occurs at death. At death there is no more ATP to release the myosin head.
- As ATP is split into ADP and phosphate, the cocking of the myosin head occurs and is ready for another contraction.
Describe the muscle fiber layers: Epimysium, Perimysium, Endomysium, and Sarcolemma.
Muscle Fiber Layers (Connective Tissue)
- Epimysium wraps the entire muscle
- Perimysium wraps muscle fibers into bundles
- Endomysium is connective tissue that wraps individual muscle fiber cells (between fibers)
- Sarcolemma is the cell membrane around the muscle cell
How is calcium absorbed and released and what is its importance for MSK?
Calcium
- All muscles require calcium for contraction
- Thyroid releases calcitonin which causes calcium to be absorbed into bone from blood
- Parathyroid hormone causes release of calcium from bone to blood
What is a motor unit?
A motor unit is a motor nueron and all the muscle fibers that it supplies. The number of muscle fibers per unit varies throughout the body. Muscles that control fine movement such as the fingers have small motor units. The number of muscle fibers per motor unit can vary from four to several hundred.
Describe the neuromuscular junction.
The neuromuscular junction is formed from:
- Axonal endings, which have small membranous sacs (synaptic vesicles) that contain the neurotransmitter acetylcholine (ACh)
- The motor end plate of a muscle, which is a specific part of the sarcolemma that contains ACh receptors and helps form the neuromuscular junction
- Though exceedingly close, axonal ends and muscle fibers are always separated by a space called the synaptic cleft
Describe the action potential at the neuromuscular junction.
Action Potential at the Neuromuscular Junction
- Action potential reaches the neuromuscular junction
- The action potential opens calcium gaits in the axon terminus that causes the release of ACh into the synaptic cleft
- ACh binds with receptors on the sarcolemma of the motor end plate which initiating depolarization.
- ACh is broken down by acetylcholinesterase into acetic acid and choline.
What are the differences between Type I and Type II muscle fibers.
Type I Muscle Fibers
- Slow twitch, oxidative fibers contract slowly, have slow acting myosin ATPases, and are fatigue resistant
- Fast twitch oxidative fibers, contract quickly, have fast mosin ATPases and have moderate resistance to fatigue
Type II
- Fast glycolytic fibers contract quickly, have fast myosin ATPases and are easily fatigued ex. used in sprinting, can have lactic acid build up
What are the characteristics of connective tissue? What are the types of connective tissue?
Connective Tissues have:
- Mesnecyme as their common tissue of origin
- Varying degrees of vascularity
- Extracellular matrix
Types:
- Connective tissue proper (ex. loose tissue such as adipose)
- Cartilage (ex. hyaline, fibrocartilage, elastic cartilage)
- Bone (osseous, compact or spongy)
- Blood
What type of connetive tissue is this? Describe it.
Connective Tissue Proper: Loose
Areolar Connective Tissue
- Gel-like matrix with all three connective tissue fibers (collagen, elastin, reticular)
- Fibroblasts, macrophages, mast cells, and some WBCs
- Wraps and cushions organs
- Widely distributed throughout the body
What type of connective tissue is this? Describe it.
Connective Tissue Proper: Loose
Adipose Connective Tissue
- Matrix similar to areolar connective tissue with closely packed adpocytes
- Reserves for food stores, insulated against heat loss, and supports and protects
- Found under skin, around kidneys, within abdomen, and in breasts
- Local fat deposits serve nutrient needs of highly active organs, reputed to have endocrine function, involved in inflammatory response
What type of connective tissue is this? Describe it.
Connective Tissue Proper: Loose
Reticular Connective Tissue
- Loose ground substance with reticular fibers (ground substance - interstitial goo)
- Reticular cells lie in a fiber network
- Forms a soft internal skeleton, or stroma, that supports other cell types
- Found in lymph nodes, bone marrow and the spleen (spleen is made from reticular tissue)
What type of connective tissue is this? Describe it.
Connective Tissue Proper: Dense Regular
- Parallel collagen fibers with a few elastic fibers
- Major cell type is fibroblasts
- Attaches muscles to bone or to other muscles, and bone to bone
- Found in tendons, ligaments, and aponeuroses (connective tissue sheets)
What type of connective tissue is this? Describe it.
Connective Tissue Proper: Dense Irregular
- Irregularly arranged collagen fibers with some elastic fibers
- Major cell type is fibroblasts
- Withstands tension in many directions providing structural strength
- Found in the dermis, submucosa of the digestive tract, and fibrous organ capsules including joint capsules
Describe the diaphysis vs. epiphyses.
Diaphysis - tubular shaft that forms the axis and is composed of compact bone that surrounds the medullary cavity (which contains the marrow). It is the portion that ossifies from a primary ossificiation centre.
Epiphyses - expanded ends of long bones that ossify from secondary ossification centres. The exterior is compact bone and the interior is spongy bone. The joint surface is covered with hyaline cartilage for articulation and an epiphyseal line separates the diaphysis from the epiphyses.
Describe the microscopic structure of bone (Haversian system or osteon).
Haversian system, or osteon - the structural unit of compact bone
- Lamella: weight bearing, sheet-like composites of collagen fibers with mineralization
- Haversian or central canal: central channel containing blood vessels and nerves
- Volkmann’s canals: channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the haversian canal
