locomotor system Flashcards
what activates voltage gated sodium channels
when the threshold is reached
what causes action potential
rapid activation and fluxes of ion currents
what causes depolarisation
upstroke of action potential
which ion triggers the contraction of myofilaments
calcium
what introduces calcium into the sarcoplasmic reticulum
sarcoplasmic reticululm calcium ATPase (SERCA)
what removes calcium from the cell
plasma membrane sodium calcium exchanger and the calcium ATPase
what binds to troponin C
cytoplasmic calcium ions
when is an action potential generated
if the depolarising ion, sodium, current of the plasma membrane is large enough
what does the action potential activate
voltage regulated l type calcium channel
describe contraction in smooth muscle
both voltage and receptor mediated influx of calcium may induce contraction
- calcium binds to calmoduin, and this activates myosin light chain kinase that phosphorylates myosin which leads to myosin binding to actin with subsequent induction of the power stroke
what is the difference between the contraction mechanisms of smooth and skeletal muscle
smooth - myosin light chain kinase
skeletal - troponin/tropomyosin complex
what removes calcium from the cell to stimulate relaxation
SERCA
NCX
PMCA
what is the resting membrane potential
-90mV
location of action potential generation in the heart
sino atrial node propagation
location of action potential generation in the voluntary skeletal muscle
motor unit, acetylcholine
location of action potential generation in smooth muscle
neurotransmitters from enruon varicosities
what is the change in calcium concentration inside the cell in contraction
less than 0.1 to 1uM
what do smooth muscle cells rely on for contraction
action potential
agonists
what is myosin
a hexamer, 2 myosin heavy chains and 4 myosin light chains. the myosin head retains all the motor functions of myosin, ie the ability to produce movement and force
myosin is a molecular motor
how large is the displacement from a power stroke
5-10 nanometers
describe the process of excitation contraction coupling
- calcium concentration in cytoplasm
- calcium binds to troponin
- conformational change in troponin
- tropomyosin moves away from binding sites on actin filaments
- myosin head groups bind to actin
- cross bridge cycle begins
describe excitation coupling in smooth muscle
- increase in calcium concentration in the cytoplasm
- calcium binds to calmodulin
- calcium calmodulin complex activates myosin kinase
- activated myosin kinase phosphorylates myosin head groups
- phosphorylates myosin head groups bind to actin
- cross bridge cycle begins
describe the power stroke
- myosin head cocks back in high energy form
- binds to actin
- inorganic phosphate released
- power stroke
- actin pulled toward middle of sarcomere
- ADP released
- rigor is when myosin is in low energy form
- new ATP binds to myosin head
- unbinding of myosin and actin
what is RyR
ryanodine receptor - skeletal muscle calcium release channel
what does an abnormality in RyR lead to
calcium sparks, abnormal acitivty of calcium release events from a single RyR cluster leading to loss of sarcoplasmic reticulum calcium
what is the consequence of abnormal RyR function
intracellular calcium and contraction is reduced leading to heart failure
what is the main reason for reduced contractility in heart failure
reduced intracellular calcium amplitude
what causes muscular dystrophy
reduced calcium and contraction due to mutations in the dystrophin-glycoprotein macromolecular complex coupled to excitation countrating coupling leads to RyR abnormalities, this loss of stability then leads to RyR leak.
what does reduced RyR stability lead to
muscle weakness with loss of skeletal muscle function and control
what is the prognosis of duchenne muscular dystrophy
muscle degeneration
loss of skeletal muscle function
loss of movement
paralysis including muscles for life support
impact of muscular dystrophy on oral health
- masticatory pattern is distorted but the muscle wasting is less than on other skeletal muscles
- patients need more time for mastication due to reduced function
- malocclusion
- poor muscle control leads to difficulty with oral hygiene
what may counteract deficiency in RyR
therapeutically increased SERCA
what are pain receptors
nociceptors
what are the types of nociceptors
a-delta and c fibres
what are the nociceptors that produce sharp and localised pain
alpha delta fibres
what are the nociceptors that produce dull, burning or throbbing pain
c fibres
