Muscle Physiology 1 Flashcards
what types of muscle cells are striated?
cardiac and skeletal
where are smooth muscle cells present?
vessels, tracts, bladder, GI, lungs
what is the function of a muscle cell?
to contract and relax in order to create movement
what muscle is under somatic control?
skeletal muscle
what muscle is under autonomic control?
cardiac and smooth muscle
what makes muscle cells contract?
excitation-contraction coupling
what do the difference of electrical charges across the plasma membrane create?
chemical and electrical gradient until equilibrium is reached
what is the resting membrane potential?
-90mv
how is the resting membrane potential calculated?
the voltage in the cytoplasm (inside the cell) minus the voltage in the ECF (outside the cell)
why is the inside of the cell -90mv?
the Na/K ATPase transports 3Na+ out for 2K+ in which causes a net transfer of + charge out of the cell so the inside is negative
what are the different types of active (gated) channels?
chemically regulated channels, voltage-regulated channels and mechanically regulated channels
what do active (gated) channels do?
facilitate the diffusion or even move (ATPase) ions against the electrochemical gradient
what is the mechanism of the voltage-gated channels?
they have activation and inactivation gates
- deactivated (closed)
- activated Na+ channels (open) when the threshold is reached AKA depolarisation
- inactivated Na+ channels (closed) when voltage-sensitive K+ channels open AKA repolarisation
- return to the beginning
what is the action potential?
a rapid change in the membrane potential that is propagated along the length of the cell followed by a return to the resting Em
what is the action potential caused by?
movement of ions against the electrochemical gradient = depolarisation to threshold
what does the action potential do?
elicit synchronous contraction/relaxation in muscle, in neurons it is the basis for communication
when is the refractory period
from time action potential begins until normal resting potential returns (the hyperpolarisation bit in the graph)
where is the action potential in the cardiac cycle generated?
in the SA node
where is the action potential in a skeletal muscle generated?
motor unit through Ach
where is the action potential in smooth muscle generated?
neurotransmitters from neuron varicosities
what is the mechanism of AP and membrane depolarisation in muscle cells?
depolarisation (upstroke of AP) activates plasma membrane voltage-sensitive Ca2+ channels that activate inward Ca2+ current, in smooth muscle also agonist-sensitive Ca2+ channels, this gives a small Ca2+ entry into the cell
what is the 1st step of excitation-contraction coupling?
depolarisation (AP) and/or agonists in smooth muscle
what is the 2nd step of excitation-contraction coupling?
depolarisation activates inward Ca2+ channel current
what is the 3rd step of excitation-contraction coupling?
inward Ca2+ entry activates release of Ca2+ from the sarcoplasmic reticulum. This Ca2+ release is mediated by the SR Ca2+ release channels
what is the 4th step in excitation-contraction coupling?
intracellular Ca2+ contraction increased from ~0.2 to 1 nanometer
what is the 5th step in the excitation-contraction coupling?
Ca2+ triggers myofilament contraction
what is the 6th step in excitation-contraction coupling
Ca2+ re-sequestered into the SR via the SR Ca-pump and removed from the cell by the plasma membrane Na/Ca exchanger and Ca-ATPase
what is the 7th step of excitation-contraction coupling?
Ca2+ is removed from myofilaments causing them to relax
why does cytoplasmic Ca2+ bind to in cardiac and skeletal muscle?
troponin C
what does the binding of cytoplasmic Ca2+ to troponin C induce?
a conformational change in the troponin/tropomyosin complex that exposes the myosin-binding sites on actin filaments to the myosin. Myosin heads can then attach to actin
what induces contraction in smooth muscle cells?
voltage and receptor-mediated influx of Ca2+
what is the role of the action of the ligand Ca2+ channel in skeletal and cardiac muscle?
to stimulate SR Ca2+ release through the RyR
what does the influx of Ca2+ in smooth muscle cells do?
activates RyR and IP3 which stimulates IP3R both of which release SR Ca2+
what are myosin heads charged by?
hydrolyzing ATP to ADP and Pi
what does calcium bind to in smooth muscle cells?
calmodulin
summarise muscle contraction in skeletal and cardiac muscle cells
Ca2+ binds to troponin C - conformational change of troponin-tropomyosin complex which exposes actin binding sites - myosin heads bind to these sites - Pi is released and myosin heads move to induce contraction - ADP released and binds to Pi to form ATP and myosin head then releases from binding site and relaxes
summarise smooth muscle contraction
Ca2+ binds to calmodulin - myosin light chain kinase activated which phosphorylates myosin - myosin binds to actin and then moves to induce contraction (power stroke) - removal of cytoplasmic Ca2+ by SERCA, NCX and PMCA inactivates myosin-actin binding by blocking myosin binding site which causes relaxation
