Block 2 Flashcards
Fascia of fibrous connective tissue that surrounds entire muscle
Epimysium
Small bundle or cluster of muscle fibers
Fascicle
Connective tissue extensions from the epimysium that surround each fascicle
Perimysium
Connective tissue extensions from the perimysium that surround the muscle fibers and are attached to the sarcolemma
Endomysium
Composed of linear series of repeating sarcomeres
Myofibril
Responsible for muscle contraction. Composed of thick and thin filaments
Myofilaments
Thin cell membrane, enclosing a skeletal muscle fiber cell
Sarcolemma
What is a special feature of the sarcolemma?
Invaginates into the sarcoplasm of the muscle cell, forming T-tubules
What is a muscle fiber made up of?
Bundle of myofibril, sarcomere and type 1 and 2 fibers
What are the type 1 fibers?
Red
What are the type 2 fibers?
White
What is the basic contractile unit of striated muscle fibers?
Sarcomere
Where are the sarcomere found?
Between the Z lines
What gives muscles the striated pattern?
Sarcomere
What are the components of thin filaments?
Actin, Troponin complex, Tropomyosin
What are the components of thick filaments?
Myosin (multiple molecules of myosin make up the thick filament)
Describe the structure of Myosin
Tail of intertwined helices and 2 globular heads
What is the role of the globular heads of Myosin?
To bind ATP and actin
What functions as an ATPase enzyme?
Myosin
Appx. 500 myosin heads of thick myosin filament form what?
Cross bridges
Myosin heads of thick filament form cross bridges that interact with actin to do what?
Shorten the sarcomere
What are the subunits of Troponin?
TnC, TnI, TnT
What provides myofibrils with large amounts of energy allowing for muscle contraction?
Mitochondria
What fibers have more numbers of mitochondria?
Slow twitch (red)
What organelle is responsible for regulating calcium storage, release and uptake?
Sarcoplasmic Reticulum
What organelle allows for rapid transfer of action potentials to the interior fiber?
T-Tubules
T-tubules play an important role in what?
Regulating cellular calcium concentration
What are the smallest functional units of a muscle?
Sarcomere
What two proteins are found in the sarcomere?
Myosin and actin
What must happen before muscle contraction begins?
Myosin heads bind with ATP
What fibers are found to have higher numbers of mitochondria?
Slow-Twitch (red)
What fibers are found to have larger sarcoplasmic reticulum?
Fast Contracting (White)
What initiates muscle action?
Nerve impulse
When an action potential occurs, what is released?
Stored Calcium ions
What actions allow the myosin head to bind to active sites on the actin filament?
When Calcium binds with troponin, the tropomyosin molecules are lifted off the active sites of the actin filament, allowing the myosin head to bind.
What provides energy for muscle action?
When the myosin head binds to ATP- ATPase on the myosin head splits the ATP into a usable energy source
What happens when myosin binds with actin?
The myosin head tilts and pulls the actin filament so they slide across each other. This results in muscle contraction.
When does muscle action end?
When calcium is pumped out of the sarcoplasm to the SR for storage.
What are type 1 (Red) muscle fibers?
Type 1 fibers have high aerobic endurance and are suited to low-intensity endurance activities
What are type 2 (White) muscle fibers?
Type 2 fibers are better for anaerobic or explosive exercises.
What muscle fibers are found to be rich in mitochondria?
Type 1
A muscle that has slow contractile speed allowing for slow prolonged activity would have what type fibers?
Type 1 (Red)
What fibers are mixed oxidative-glycolytic fibers?
Type IIa
These muscle fibers have moderate aerobic capacity and fatigue resistance
Type IIa
What are the features of Type IIa muscle fibers?
Moderate aerobic/oxidative capacity
Moderate fatigue resistance
Fast contractile speed
Highly developed SR
Mixed oxidative-glycolytic fiber
What fibers are glyolytic fibers?
Type IIb
Which of the following is/are NOT a feature of Type IIb fibers?
High anaerobic/glycolytic capacity
High motor unit strength
Fast contractile speed
Highly developed SR
Slow contractile speed
High Fatigue resistance
Slow contractile speed and high fatigue resistance are NOT features of type II b
What class of muscles are responsible for movement?
Agonists
What prevents overstretching of agonist mucsles?
Antagonist
What assists the agonists and fine tunes direction of movement?
Synergists
What happens in concentric muscle action?
The muscle shortens
What happens in static muscle action?
The muscle length is unchanged
What happens in eccentric muscle action?
The muscle lengthens
What are the “stem cells” located in skeletal muscles?
Satellite cells
What are the cells involved in muscle growth and repair?
Satellite cells
What cells become activated when a muscle is injured?
Satellite cells
What is formed when satellite cells are activated after muscle injury?
New muscle fibers or myofibers
What is the primary function of Myostatin?
Regulate muscle growth and development
What is inhibited with myostatin?
It inhibits the proliferation and differentiation of muscle cells
Myostatin is produced and secreted by what cells?
Skeletal muscle cells
Where does smooth muscle receive its nerve signals from?
Autonomic nervous system (sympathetic and parasympathetic)
Smooth muscle can be divided into what two categories?
Single Unit (visceral)
Multi-Unit
Where is Single Unit smooth muscle typically found?
GI tract, bile duct, ureters, uterus, many blood vessels
Where is Multi Unit smooth muscle typically found?
Ciliary and iris muscles of the eye, base of hair follicles, smaller airways to lungs, walls of large blood vessels
In what type of smooth muscle does each fiber contract independently?
Multi-Unit
In what type of smooth muscle do the fibers work together as one unit?
Single Unit
What type of smooth muscle would you find where very small, fine movements are needed?
Multi Unit
Although smooth muscle contains thick and thin filaments, what do they NOT contain?
Myofibrils or sarcomere
What are the actin filaments of smooth muscle attached to?
Dense bodies (analogous to the Z-discs of striated muscle)
What configuration allows myosin to pull actin filament in opposite directions, in smooth muscle?
Side-polar cross-bridges
One side bend in one direction and the other side bends in the opposite (Think Chinese finger trap! When you pull in opposite directions it “flattens out”/pulls tight)
Once smooth muscle is initiated, low energy is needed to keep the tonic contraction, which can last for hours or even days. What is an example of this?
Maintaining blood pressures
What is different about the SR in smooth muscle compared to skeletal?
It is only slightly developed
What is the major source of Ca2+ for smooth muscle contraction?
Extra cellular fluid
What is not present in all smooth muscle fibers, but when it is, is found near the cell membrane?
Sarcoplasmic Reticulum
What feature is believed to excite calcium release from the SR in smooth muscle?
Caveolae
What structure in smooth muscle is similar to that of T-tubes from skeletal muscle?
Caveolae
If the SR is more extensive in smooth muscle, what is the result?
More rapid contractions
What do smooth muscles use Calmodulin for?
As a calcium binding protein to regulate contraction process (rather than troponin as in skeletal muscle)
What is the result of activated calmodulin?
It activates enzyme MLCK which phosphorylates specific regions of Myosin
What happens to phosphorylated myosin?
It binds to actin, forming a cross-bridge allowing muscles to contract
What happens when the ion calcium concentration is reduced?
Myosin phosphatase removes the phosphate from the myosin light chain, causing muscle relaxation
Found in the cytoplasm, Dense bodies serve as what?
Anchoring points for actin filament
The arrangement of actin, myosin and dense bodies allow for what in smooth muscle?
Coordinated contraction and relaxation of the muscle
What cells make up the myocardium?
Cardiomyocytes or cardiocytes
Cardiac muscle contains a less developed….
Sarcoplasmic reticulum
What are the similarities between cardiac and skeletal muscle?
Fibers are striated
Myofibrils are made up of actin and myosin
Similar organization of sarcomere
T-tubes also release calcium
What are some differences in cardiac muscle compared to skeletal?
Cardiac muscles:
Contraction is involuntary
Fibers are shorter and branched
Usually uninucleated
Interconnected by intercalated discs
Generate their own action potential (pacemaker fibers)
Cardiac action potential is NOT initiated by nervous activity, instead, it is generated by what?
Pacemaker cells
Pacemaker cells have what kind of action potential?
Automatic
Where are pacemaker cells found?
Sinoatrial node of right atrium
Cardiac muscle is a function synctium. What does this mean?
It means the cells function together; they are electrically connected to each other through intercalated discs
Cardiac muscle fibers remain separated as distinct cells with their respective sarcolemma. So how are they connected?
Via intercalated discs
What muscle has single multinucleated fibers during embryonic development?
Skeletal muscle (morphological syncytium)
Dark, dense cross-band found in the end of each myocardial disc
Intercalated disc
What structure is continuous with the sarcolemma and contains important cell-cell junctions
Intercalated discs
What cell-cell junction provides mechanical strength and stability?
Desmosome
What are the functions of the gap junction?
Allow diffusion of ions and to allow action potential to travel easily from one cell to the next
What accounts for the striations in cardiac muscle?
Organized arrangement of actin and myosin filaments
Smooth muscles differ from skeletal and cardiac muscles in that they lack what?
Smooth muscle lacks myofibrils
What is the role of tropomyosin in skeletal muscle contraction?
It covers the binding sites on actin, preventing myosin binding
What is the role of calcium ions in skeletal muscle contraction?
Binding to troponin, allowing actin-myosin interaction
How do T-tubules contribute to the excitation contraction coupling process in skeletal muscle cells?
By transmitting action potentials
Which connective tissue layer surrounds the entire skeletal muscle, enclosing all the muscle fascicles?
Epimysium
Four cell layers that make up the epidermis
- Stratum corneum
- Stratum granulosum
- Stratum spinosum
- Stratum basale
What layer of skin contains layers of keratinocytes and dead cells still connected by desmosomes?
Stratum corneum
What layer of skin has high keratin content and is where flattening of the cells occurs?
Stratum granulosum
In this layer of skin, cells are joined by desmosomes providing mechanical strength.
Stratum spinosum
What layer of skin contains the stem cells?
Stratum basale
In what layer do we find dendritic cells?
Stratum spinosum
In what layer do we find melanocytes?
Stratum basale
Where would we see a thicker, more prominent stratum corneum?
Hairless, thick skin (ie. pawpads)
What are the 4 cells of the epidermis?
- Keratinocytes
- Melanocytes
- Langerhans Cells
- Merkel’s cells
What are the most prominent cells in the epidermis?
Keratinocytes
What are the 3 functions of keratinocytes?
- Produce keratin- major structural protein for epidermis
- Contribute to formation of the epidermal water barrier
- Makes up majority of structure of the skin, hair and nails
In what skin layer does cell division occur?
Basal layer (stratum basale)
What are the intermediate keratin filaments?
Tonofilaments
What layers of skin does tonofilament synthesis occur?
Stratum basale and stratum spinosum
Extended response/Concept
Explain Keratin synthesis and the formation of the epidermal water barrier.
- Cell division occurs in the stratum basale where cells begin to synthesize tonofilaments. (intermediate keratin filaments)
*Cells are then pushed to the stratum spinosum where tonofilament synthesis continues and cells begin to produce keratohyalin granules which help convert granular cells to cornified (keratinization) and lamellar bodies. - Cells are pushed into the stratum granulosum and continue to stratum corneum.
*Lamellar bodies are discharged by exocytosis into spaces between the SG and SC.
*Lamellar bodies and the lipid envelope create an epidermal water barrier.
Where does synthesis of melanocytes begin?
It begins in the premelanosomes from the amino acid Tryosine
What skin type will see faster lysosome degradation?
Light skin
What are the two forms of melanin pigments?
Eumelanin -> brownish black
Pheomelanin -> Reddish yellow
Why does exposure to UV light accelerate the rate of melanin production?
As a way to protect the skin
Where we do find Langerhans cells?
Stratum spinosum
Who are the first line defenders, also playing a role in antigen presentation?
Langerhans Cells
What cells are antigen presenting cells?
Dendritic cells
Where are Merkel’s cells found?
Stratum basale
Where are Merkel’s cells most abundant?
Where sensor perception is acute, such as fingertips
What are the cells of the dermis?
- Fibroblasts (primary cells)
- Macrophages
- Leukocytes
- Mast cells
Strong and flexible connective tissue composed by cells and collagen fibers
Dermis
Tissues derived from the epidermis extend into the dermis and give rise to what?
Sweat glands, sebaceous glands, papillae from hair and feathers
What nerve endings are found only in hairless skin?
Meissner (touch receptors)
What nerve endings have deep pressure receptors for mechanical and vibratory pressure?
Pacini
What nerve endings are only found in haired skin?
Hair follicle sensor (tactile hairs)
What nerve endings respond to mechanical displacement of adjacent collagen fibers?
Ruffini
Cells in what layer would produce new hair follicles in the invent of skin injury?
Stratum basale
Hair follicles are formed by invaginations of what layers?
The epidermis and dermis
What region of the hair bulb produces new daughter cells that are pushed towards the surface?
The matrix
Single layer of dead, scale-like keratinocytes
Cuticle
Several layers of dead keratinocytes containing hard keratin
Cortex
Dead loosely keratinized cells
Medulla
Smooth muscle associated to the hair bulb and anchored to the outer layer of the dermis. (Sympathetic innervated)
Piloerector muscle
Hair follicles have cycles of activity… List them in order and what they are associated with.
Anagen (growth) to Catagen (regression) to Telogen (resting) to Exogen (shedding)
What are the two types of feathers?
Flight
Covert (down)
What is the flat part of the feather?
Vane
What does the vane consist of?
Barbs that are at angles of 45 degrees
Hooklets are present where?
Only on the barbules of one side of the barb on feathers
