Unit 5 Study Guide Flashcards
Fascicles
- muscle fibers organized into bundles
- are bundled within the whole skeletal system
Epimysium
layer of dense irregular connective tissue that surrounds the whole skeletal muscle
Perimysium
- surrounds the fascicles
- contains extensive arrays of blood vessels and nerves that branch to supply muscle fibers within each fascicle
Endomysium
- innermost connective tissue layer
- surrounds and electrically insulates each muscle fiber
- Contains reticular protein fibers that help bind together neighboring muscle fibers and to support capillaries near this fiber
What is the purpose of the three layers of connective tissue?
- provides protection
- sites for distribution of blood vessels and nerves
- site for attachment to skeleton
What is the purpose of the skeletal muscle’s being vascularized?
- the extensive network of blood vessels deliver both oxygen and nutrients to the muscle fibers
- also remove waste products
neuromuscular junction
the junction(gap) between an axon and muscle fiber
Sarcoplasm
the cytoplasm in the skeletal muscles
satellite cells
- the myoblasts that do not fuse with the muscle fibers during development
- remain in adult skeletal muscle
- can be stimulated to differentiate and fuse with a damaged skeletal muscle to assist in repair and regeneration to a limited extent
Sarcolemma
- The plasma membrane of the skeletal muscle fiber
- connected to the SR by T-tubules
T-Tubules
- deep invaginations of the sarcolemma
- extend into the skeletal muscle fiber as a network of narrow membranous tubules to the sarcoplasmic reticulum
What type of channel(s) are located in the sarcolemma and T-tubules
-Na+ and K+ Voltage gates channels
Myofibrils
- compose the muscle fiber
- extends the length of the muscle fiber
- composed of bundles of myofilaments enclosed within segments of the SR
Sarcoplasmic Reticulum
- reservoir for Ca2+ ions
- contains Ca2+ pumps and Ca2+ voltage-gated channels
Terminal Cisternae
- blind sacs at either end of individual sections of the SR
- serve as reservoirs for calcium ions
- immediately adjacent to each T-Tubule
Triad
-formed by two terminal cisternae and a centrally located t-Tubule that function during muscle contraction
Thick Filaments
- assembled from myosin protein molecules
- the head contains a binding site for actin of the thin filaments
- contains a catalytic site where ATP attaches
- myosin molecules are oriented so that their long tails point toward the center of the thick filaments and the heads point toward the ends of the thick filaments
Thin Filaments
- composed of two strands of actin protein that are twisted around each other to form a helical shape
- Each actin contains a myosin binding site
- the myosin head attaches to the myosin binding site of actin during muscle contraction
Tropomyosin
- regulatory protein associated with thin filaments
- covers the myosin binding sites in a non contracting muscle
Troponin
- regulatory protein associated with thin filaments
- attached to tropomyosin
- contains the binding site for Ca2+
Connectin
- protein that extends from the Z disks to the M line through the core of the thick filament
- stabilizes the position of the thick filament
- maintains thick filament alignment within a sarcromere
- contributes to muscle elasticity
Dysotrophin
- anchors myofibrils that are adjacent to the sarcolemma to proteins within the sarcolemma
- links internal myofilament proteins to a muscle fiber to external proteins
Myoglobin
-binds oxygen when the muscle is at rest and releases it for use during muscular contraction
List the steps that occur at the neuromuscular junction
- a nerve signal is propagated down a motor axon and triggers the opening of voltage-gated Ca2+ channels, releasing it into the synaptic knob
- Ca2+ binds to proteins in synaptic vesicle membrane
- calcium binding triggers synaptic vesicles to merge with the synaptic knob plasma membrane and ACh is exocytosed into the synaptic cleft
- ACh diffuses across the fluid-filled synaptic cleft in the motor end plate to bind with ACh receptors-causes excitation of a skeletal muscle fiber
What is the structure and function of the motor end plate?
- specialized region of the sarcolemma of a muscle fiber.
- Numerous folds and junctions fold to increase the surface area covered by synaptic cleft.
- has vast numbers of ACh receptors, which upon ACh binding, allows Na+ to flow into the muscle fiber and K+ to exit
What is the end plate potential?
- the minimum voltage change in the motor end plate that can trigger opening of voltage-gated channels in the sarcolemma to initiate an action potential.
- Goes from -90mV to -65mV.
- The EPP initiates an action potential to be propagated along the sarcolemma and T-Tubules
Describe the steps in excitation-contraction coupling?
1) ACh binding causes chemically-gated ion channels to open and Na+ to rapidly enter the skeletal muscle fiber and K+ to slowly exit, which results in the development of an end-plate potential at the motor end plate.
- initiation and propagation of an action potential along the sarcolemma and T-tubules (depolarization and repolarization)
- action potential triggers release of Ca2+ from the terminal cisternae of the sarcoplasmic reticulum. Diffuses into the sarcoplasm
Sarcomere
- repeating microscopic cylindrical units of myofilaments
- composed of overlapping thick and thin filaments
Z discs
- at the end of each sarcomere
- composed of specialized proteins that are positioned perpendicular to the myofilaments
- serve as anchors for the thin filaments
I band
- extend from both directions of Z disc
- contain only thin filaments
- disappears during contraction
A Band
- central region of sarcomere that contains the entire thick filament
- thin filaments overlap thick filaments on each end
- does not change in length during muscle contraction
H Zone
- most central portion of the A band
- only thick filaments are present
- disappears during contraction
M line
- thin protein meshwork in the center of the H zone
- Attachment site for the thick filaments
- aligns the thick filaments during contraction/relaxation
Steps of Crossbridge Cycling
- Calcium binding
- Crossbridge formation
- Power stroke
- Release of myosin head
- Reset myosin head
Calcium binding
- Ca2+ from SR binds to troponin in muscle thin filaments, causing a conformational change in troponin
- Troponin changes shape and the entire troponin-tropomyosin complex is moved
- tropomyosin no longer covers the myosin binding site on actin
Crossbridge formation
- myosin heads, in a cocked position, bind to exposed myosin binding site on actin forming a cross bridge between the thick and thin filaments (myosin and actin)
Power stroke
- the myosin head swivels toward the center of the sarcomere, pulling along the attached thin filament a small distance past the thick filament - power stroke
- ADP and Pi released
- ATP binding site becomes available again
Release of myosin head
- ATP binds to ATP binding site on myosin head
- causes release of the myosin head from the binding site on actin
Where ATP is used in muscle contraction
- ATP is used during release of the myosin head
- It binds to the binding site on the myosin head,
- causes the release of the myosin head from the actin binding site
- provides energy to reset the myosin head
Phosphagen system
- an additional few seconds of energy generated by transfer of a high-energy phosphate
- Myokinase transfers a phosphate from one ADP to another ADP, yielding ATP and AMP
- Creatine kinase transfers a Pi from creatine phosphate to ADP, yielding ATP and creatine
- proves an additional 10-15 seconds of energy
- during times of rest, as small amounts of ATP accumulate, the pathway is reversed
Aerobic cellular respiration
- Occurs within mitochondria
- nutrient source is pyruvate made in glycolysis
- oxidized to CO2 in Krebs
- results in NADH and FADH2
- Used in ETC to generate ATP through oxidative phosphorylation
Anaerobic cellular respiration
- Goes through glycolysis then fermentation
- used to regenerate NAD+
- Pyruvic acid or organic molecule is final electron acceptor
- Only 2 ATP produced from glycolysis in entire process
Structural characteristics of cardiac muscle
- individual muscle cells arranged in thick bundles in heart wall
- branch and are shorter and thicker than skeletal
- individual cells joined at intercalated junctions
- striated
- controlled by ANS
intercalated junctions
- where individual cardiac muscle cells join to adjacent muscle
Structural characteristics of smooth muscle
- small and widest in middle with tapered ends and centrally located nucleus
- diamater 10X small and lengths 1000X shorter
- endomysium wraps around each smooth muscle cell. Tapered ends overlap
- T-tubules are absent
- Sarcolemmal surface area increased by caveolae
- No Z discs or sarcomeres
Smooth muscle thin filaments
- composed of actin and tropomyosin but do not contain troponin
- instead have Calmodulin
Calmodulin
- binds to Ca2+ and forms Ca2+-calmodulin complex
Myosin Light-chain kinase (MLCK)
- activated by Ca2+-calmodulin complex to phosphorylate smooth muscle myosin head
- activation of ATPase activity
Steps of smooth muscle contraction
- Stimuli triggers opening of voltage-gated Ca2+ channels
- enters sarcoplasm from IF and SR
- binds to Calmodulin, forming Ca2+-calmodulin complex, and activating MLCK
- MLCK phosphorylates myosin head and actives myosin - slow
Activated myosin
- binds to thin filaments to form cross bridges.
- Myosin ATPase hydrolyzes ATP providing energy for power stroke
- Myosin head releases and reattaches to actin repetitively, causing the thin filament to slide past the thick filament.
- the process is repeated
- the force generated is transferred to the anchoring filaments and the smooth muscle shortens
- allow for much stronger contractions.
RyR1 receptor
mediates release of Ca2+ from sarcoplasmic reticulum into the cytoplasm
DHP receptors
- found in T-tubule membrane
- arrival of AP initiates change in receptor (allows Na+ in) which initiates a change in RyR1 receptor
