muscles Flashcards
What is the location of smooth muscle?
internal organs, walls of blood vessels, around hollow organs, around tracts
What is the function of smooth muscle?
move food, urine and reproductive tract secretion, regulate diameter of blood vessels
What are the shape of smooth muscle cells?
spindle-shaped
What is the length and width of smooth muscle cells?
100-300 micrometers, 2.5 micrometres
Is smooth muscle striated or non-striated?
non-striated
What do varicosities do?
increase surface area of smooth muscle, close to effector cells so can communicate more easily
What do hormones/neurotransmitters do in smooth muscle excitation contraction coupling?
open voltage or ligand gated Ca2+ channels in the sarcolemma causing Ca2+ influx or bind to G-protein coupled receptors inducing IP3 generation
What does Ca2+ bind to in the sarcolemma (smooth muscle)?
calmodulin
What activates myosin light chain kinase (MLCK)?
Ca2+-calmodulin
What does MLCK do?
phosphorylates myosin light chains, enabling muscle contraction
What is single unit smooth muscle examples?
GIT, bladder
What is multi unit smooth muscle examples?
iris, airways, vasculature
What is phasic contraction?
relatively quick contraction with short durability
What is tonic contraction?
relatively slow contraction with long durability
Where do calcium ions come from in smooth muscle?
sarcoplasmic reticulum and extracellular fluid
How is the SR in smooth muscle compared to cardiac and skeletal?
less well organised and developed
What is the latch state?
an adaptation of smooth muscle which allows sustained muscle tone with low rate of cross-bridge cycling
What are differences between smooth muscle and cardiac and skeletal muscle?
smooth muscle contraction is thick filament regulated, contractions can be slow and sustained
What is the length and width of cardiac muscle?
10 and 100 um
What are mechanical junctions of cardiac muscle?
fascia adherens and desmosomes
What are electrical junctions of cardiac muscle?
gap junctions
What are the two types of action potentials in cardiac muscle?
slow response (pacemaker cells) and fast response (cardiac action potential)
What cells undergo slow response?
SAN and AVN
What cells undergo fast response?
atrial & ventricular myocytes and purkinje fibres
What is stage 0-4 in fast response cells?
0 = Na+ entry, 1 = K+ efflux, 2 = Ca2+ entry, 3 = K+ efflux, 4 = RMP slightly more negative
What is stage 0, 3 + 4 in slow response cells?
0 = slow inward current of Na+ and Ca2+, 3 = repolarisation due to K+ efflux and Ca2+ channels closing, 4 = RMP less negative - slow depolarisation
What come first: action potential and contraction?
contraction force follows action potential
What channels are in pacemaker cells?
funny channels: inward Na+ current
What does the absolute refractory period allow?
heart to fully relax between beats
What are I bands and A bands ad H zone?
I = light (thin filaments) A = dark (thin and thick filaments) H = thick filaments
What are some important proteins in cardiac muscle?
scaffolding proteins (mermyosin, C protein, nebulin, alpha actin), titin (enables relaxation)
What does Ca2+ bind to in cardiac muscle electrochemical coupling?
troponin which enables filament sliding
What is not conformationally coupled in cardiac muscle?
DHPR and RyR
What does ca2+ bind to which allows more Ca2+ release in cardiac muscle?
ryanodine receptor
What shape channels does calcium come through in cardiac muscle?
L-shaped
Does cardiac or skeletal muscle have a higher resistance to stretch?
cardiac
What is the Frank-starling law?
stretching occurs at times of increased venous return, - Force of contraction is increased by stretch and enhanced by sympathetic stimulation
What is positive chronotropy?
increase rate of contraction
What is positive inotropy?
increase force of contraction
What is positive lusitropy?
increased rate of relaxation
What receptors are conformationally coupled in skeletal muscle?
DHPR and RyR
What activates DHPR ?
propagation of action potential down into T-tubules
What does calcium bind to in skeletal muscle in excitation coupling?
troponin which has a conformational change to tropomyosin
What happens in the sliding filament theory?
1) binding to myosin to actin. Pi released. 2) power stroke - actin gets pulled towards middle of sarcomere. 3) rigor. ADP released 4) new ATP binds to myosin head 5) unbinding of myosin and actin 6) ATP is hydrolysed 7) cocking of myosin head
What is Rigor Mortis caused by?
depletion of ATP
What colour is fast twitch skeletal muscle?
white (lower myoglobin and capillary content)
What colour is slow twitch skeletal muscle?
red (high myoglobin and capillary content
At approximately what sarcomere length do skeletal muscle fibres usually function?
2 um
What is tetanic fusion frequency?
frequency of action potentials that are needed to not see summation and produce a smooth graded contraction as seen in normal muscle contraction
