Exam I Flashcards
List basic differences between intracellular and extracellular fluid compartments.
Intracellular (in the cell): more K+, Mg+2, protein, and PO4- and other organic anions.
Extracellular (outside of the cell): more Cl-, Na+, Ca+2 (not too much), and HCO3-
Compare negative vs positive feedback loops.
Negative feedback loop senses a change in a parameter and and responds in order to get back within the optimum parameters. It is stabilizing and diminishes the change.
Positive feedback is a change in a parameter that causes a response that continues to change in the same direction as before. Can be dangerous and can lead to runaway effects.
Give an example of a negative feedback loop.
Regulation of arteriole blood pressure: baroreceptors sense increase in blood pressure -> send inhibitory signals to vasomotor in medulla -> heart pumping decreases and blood vessels dilate -> bp decreases
Give an example of a positive feedback loop.
Stretch of the cervix sends signals that increase the force of uterine contractions that increases stretch on the cervix -> natural end to process, so not dangerous
Explain gain and know how to calculate.
Gain is the degree of effectiveness with which a control system maintains constant conditions.
Calculate difference of uncontrolled and controlled system.
Correction(Uncon-con diff.)/error(difference of controlled from initial amount)
List and describe the major organelles of a eukaryotic cell.
nucleus- protects DNA, replication, transcription
endoplasmic reticulum- produces proteins, lipids, carbs, etc for transport within and out of the cell.
Golgi apparatus- receives, packages, and sends cellular products to correct area within cell
mitochondria- provides a majority of the ATP within the cell
lysosome- breaks down unwanted materials within the cell
peroxisomes- involved in metabolism
endosome- involved in sorting and transport of substances
Describe the universal structure of the cell membrane and explain how structure allows for passage of materials through the membrane.
The membrane is composed of a phospholipid bilayer, cholesterol (rigidity and fluidity in different conditions), proteins (integral and peripheral). Passive vs active transport
Define homeostasis and explain it’s significance in understanding physiological processes.
Homeostasis- the maintenance of nearly constant conditions in the internal environment.
These mechanisms allow the internal environment of the body to remain within liveable limits through adaptive responses. Maintains optimum conc. of ions, water, gases, and nutrients. optimum temp and pressure for healthy cells to live
The sodium-potassium pump is an example of which of the following kinds of transport?
primary active transport -> ATP is directly involved in the process
Glucose transporters (GLUT) involve what type of transport system?
facilitated diffusion
Sodium-calcium pump os an example of what type of transport?
secondary active transport
The sodium-glucose pump is an example of which kind of transport?
secondary active transport
Define kinetic and thermal energy and relate it to molecular movement.
Kinetic energy is the energy an object possesses due to motion.
Thermal energy is the energy that comes from heat and determines how fast the molecule is moving.
Define diffusion and osmosis. How do these relate to semipermeable membranes?
Diffusion is the random movement through spaces. This can be through a semipermeable membrane from high to low levels.
Osmosis is the diffusion of solution (water in the human body) through a membrane from high conc to low conc.
Explain how osmotic pressure is generated.
Osmotic pressure is generated rushes to one side of the membrane. Water will eventually create a pressure on one side of the membrane, usually the one with more ions.
What is the equation for osmotic pressure?
pi = gCRT
pi= osmotic pressure g= # of particles in solution C= conc (mol/L) R= gas constant T= temp
What equation refers to the ease in which a solute permeates a membrane?
effective osmotic pressure (multiplied) reflection coefficient
1= impermeable 0= permeable
What are the energy independent mechanisms of transport?
Diffusion, osmosis, and facilitated diffusion
What requires channels (gated vs non gated)?
Gated: ligand and voltage gated
Non-gated: aquaporins and ion channels
What are the differences in mechanisms between the active transport processes?
Primary- ATPase is utilized directly with the channel.
Secondary- requires multiporters (complexes that transport multiple substances across) and don’t use ATP directly
symporter
2+ molecules are transported into the same direction
antiporter
2+ molecules are transported to opposite side of the pump
Factors that affect the rate of diffusion
- pressure difference
- membrane electric potential
- proportional to conc difference across membrane
What is the diffusion equation?
J=-PA(C1-C2)
J= flow/flux
P=permeability
A= area
C1 and C2= concentration
Describe the mechanism of facilitated diffusion and what uses it.
-requires uniporter carriers (stereospecific, occurs down electrochemical gradient), Vmax, glucose and amino acids use this method
What is the function of the selectivity filter and how does it function?
The selectivity filter determines which ions are allowed through the channel by recognizing ions. This occurs when an ion enters the filter and binds to the carbonyl oxygens. These dehydrate allowing the ion to pass. The channel is typically only big enough for the one specific ion, but others sometimes manage to pass.
Difference between primary and secondary active transport.
Primary active transport requires ATPase and directly utilizes ATP to transport substances across the membrane. Secondary active transport utilizes multiporters and energy is generated by secondarily from concentration differences created by primary transport.
What is the mechanism for secondary transport?
At least one of the solutes (typically Na+) moves down its electrochemical gradient (creating energy) and another goes with the gradient. ATP is required to set up the conc gradient. Requires energy for the initial primary active transport of Na+ across the membrane (inside cell against gradient).
Describe the basic structure of a neuron.
3 basic parts:
cell body- contains nucleus and other organelles, characterized by local potentials, no voltage gated channels.
dendrites- cellular extensions, few to many, characterized with ligand gated channels, conduct local potentials
axon- typically located on the opposite side of the dendrites, covered by axolemma (membrane), contains voltage gated channels and has the ability to conduct action potential, distal end contains membrane bound vesicles that contain neurotransmitters.
Describe the environment inside and outside of the axolemma at resting potential.
The internal environment has more K+ ions and is more negative, resting at approximately -90mV. The external environment has more Na+ and Cl+ ions and will be more positive.
Nernst potential
diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through a membrane. Measure potential for ONE ion at a time. If more use the Goldman equation.
E= z(61.5)log(Cout/Cin)
What is the electrical dipole layer?
The distribution of positive and negative ions on either side of the membrane resulting in a voltage change.
What are the assumptions when using the Nernst equation?
- equation can only be used for one ion at a time
- membrane must be completely permeable to that ion
- ion must be at equilibrium
Describe what will happen to the concentrations and voltage differences as equilibrium is reached when a membrane is permeable to both Na+ and Cl-?
When at equilibrium the voltage will be 0 and the concentrations on both sides will be equal. As equilibrium is reached Na+ ions will move to the right side dragging water molecules with it, so Cl- is more mobile. The left side will be more negative until conc equilibrium is reached.
Principle of Electrical Neutrality
under biological conditions the sum of the conc of the anions and the conc of the cations must be equal on both sides. The electrical gradient must cancel each other out on one side.
Why is this model not like a real animal cell (refer to slide 29, lecture on cell membrane potential)?
- Proteins actually have a charge
- Potassium is found in extracellular fluid
- The membrane is permeable to both K+ and Cl-
Donnan Equilibrium (don’t need to know equation)
if equilibrium is to be reached the electrical potential must equal the conc gradient for both ions. Deals with two ions that can cross the membrane at the same time.
How is the resting membrane potential maintained?
- diffusion of Na+ out of cell
- diffusion of K+ into cell
- sodium-potassium pump
What are the characteristics of a action potential?
- all or none potentials- either it will occur or it won’t
- self propagating: each region of depolarization serves to generate action potentials
- non-decremental: does not decrease in strength
Describe the two voltage gated sodium channels. When do they open/close? ***check textbook regarding potentials for open/close
activation gate: opens between -70mV to -50mV and stays open until +35mV
Potassium gated channels
- have a single gate
- gate is closed at -90mV
- slowly opens at +35mV to -90mV
- these channels are also leaky
Describe the complete cycle of an action potential of a cell.
Resting: -90mV
Depolarization: membrane becomes permeable to sodium and may overshoot the threshold
Repolarization: sodium channels close after reaching +35mV and potassium channels open allowing K+ out of the cell
What are the two methods one can increase the speed at which an action potential travels? How do each of these work?
- increase the diameter of the axon: utilized in invertebrates, offer larger cross sectional area to conduct the internal flow of the current, current has many alternative paths to follow reducing resistance
- increasing the membrane resistance of the axon: wrap with insulation (myelin sheaths) creating a capacitor effect. In myelinated cells current can only flow across the points of least resistance(between Schwann cells). This causes the potential to jump from node to node (saltatory conduction. Uses 100x less ions.
Capacitor effect and how it relates to cell potential
- consists of two plates and insulating barrier (plates are inter and extracellular fluid) and insulating layer is lipid membrane.
- capacitor’s capacitance is directly proportional to the size of the plates(bigger can store more charge), inversely proportional to the distance between plates
Which of the following types of neurons would transmit an AP the fastest?
large diameter, myelinated
Saltatory conduction is characteristic of which part of a typical neuron?
axon
A selectivity filter with carbonyl oxygens is associated with which of the following kinds of ion channels?
potassium
The resting potential for a typical neuron is best represented by which of the following potentials?
-90mV
What is the fatty component that provides insulation in myelinated nerves?
sphingomyelin
What is saltatory conduction?
Occurs in myelinated neurons where the current jumps between nodes of Ranvier because it is an area of least resistance. This greatly increases the speed of conduction.
What is the threshold for an AP?
-65mV
What is a local potential?
Local potentials happen when ligand channels are opened with neurotransmitters. The neurotransmitter has the ability for the cell body or dendrite to determine whether an AP will occur down the axon.
Orthodromic vs antidromic direction
ortho: direction normally taken (toward distal end of axon)
anti: opposite direction (toward axon hillock/cell body)
What is the difference between the absolute and relative refractory periods?
Absolute: no additional AP can occur at this time at all. The fast gated sodium channels are all either open or inactivated. The energy is derived from the breakdown of ATP. The length of this period is determines the frequency of AP.
Relative: an strong AP may occur during this time, but must be stronger than normal
epimysium
connective tissue surrounding entire muscle
muscle
made up of muscle fasicles
perimysium
connective tissue surrounding individual fascicle
fascicle
a bundle of myofibers
endomysium
delicate connective tissue around each myofibers
sarcolemma/plasmalemma
cell membrane of muscle fiber
myofiber
- muscle fiber
- individual multinucleated muscle cell
myofibril
a chain of sarcomeres within a myofiber
myofilament
actin and myosin filaments that make up a sarcomere
Transverse tubules
- invaginations of sarcolemma
- lie close to cisternae of sarcoplasmic reticulum
- form triads with cisternae
- two/ sarcomere
Draw a sarcomere and label the M line, Z discs, I band, A band, and H band.
refer to lecture material for answer
What is the Z disc? I band? A band? H band? Where are the nuclei and mitochondria located?
Z disc- anchor actin filaments, end of sarcomere
I band- composed entirely of actin, width changes during contraction
A band- composed of actin and myosin, width does not change during contraction
H band- composed of myosin, width does change with contraction
mitochondria and nuclei are located on the periphery of the sarcomere
How does the sliding mechanism occur?
- arrival of AP at terminal end of nerve fiber
- opening of voltage gated channels on nerve fiber ending
- release of neurotransmitter (Ach) from synaptic vesicles into synaptic cleft
- opening of ligand-gated sodium channels of sarcolemma
- generation of AP on sarcolemma
- voltage gated channels on T tubules interact with ryanodine receptors on SR membrane (DHP channels)
- opening the ryanodine-sensitive calcium ion release channels
- increase in Ca ion concentration in cytosol
- activation of sliding filament mechanism
- rreleased Ca ions bind to tryponin
- trypomysoin uncovers myosin binding sites on actin
- ATPase heads of myosin molecules split ATP and bind to actin
- stored energy in myosin head causes deformation such that thick and thin filaments slide past each other
- A second ATP binds to myosin and causes it to release actin
- process is repeated over and over
- contraction stops when ATP-dependent Ca pump sequesters Ca ions back into SR
What is the relationship between the myosin head and ATP?
ATP is released when the myosin head binds to the actin, the myosin head has a powerstroke, ATP attaches to the ATPase site of the head, myosin detaches from the actin and releases heat in the process but not the ATP, the myosin head recocks and the process starts over again
What is the relationship between dihydropyridine receptors and ryanodine receptors?
DHP is voltage sensitive Ca channels arranged in quadruplets that are located on the sarcolemma T-tubules. They cause a conformational change in the ryanodine receptors and allow a small amount of Ca into the cytosol via these channels.
Ryanodine receptors are located on the cisternae of the SR and open in response to the DHP receptors changing conformation. This allows the ca to be pumped into the cytosol for muscle contraction.
How does the Ca equilibrium reestablish itself after “depolarization?”
Calsequestrin in the SR maintains an optimum Ca conc gradient to facilitate return of Ca to SR. SERCA (SR Ca ATPase) used ATP to pump Ca back into the SR.
How is myosin composed? Actin?
The tail contains two heavy chains intertwined and the heads are composed of light chains. Actin is composed of intertwined f actin filaments and have troponin and tropomyosin molecules covering the active sites.
Draw and understand the length-tension diagram.
The tension is measured by the amount of myosin heads on the actin filament. When the myosin has reached the end of the actin filament the tension goes back to 0 because the sarcomere stops the sliding mechanism, so the muscle will not be damaged.
What is the relation of load amount vs velocity of muscle contraction?
As the load increases, the velocity at which the muscle contracts decreases. Reciprocal relationship.
Where is ATP required for during muscle contraction?
- sliding filament mechanism (myosin head detaching from actin active site)
- pumping Ca ions from sarcoplasm back to SR
- pumping Na and K ions through the sarcolemma to reestablish resting potential
How much ATP is kept in the muscle? What are mechanisms to generate more ATP for more muscular endurance?
-approximately 4mmol (1-2sec of contraction) is kept in the muscle
- phosphocreatine(not storage molecule, regenerates ATP quickly): releases energy quickly by reconstituting ATP. Provides enough energy for 5-8sec contraction
- glycolysis: can sustain contraction for 1 min, but creates lactic acid as a by product
- oxidative phosphorylation: provides 95% of the energy for long-term contraction
Isometric vs isotonic contraction?
-isometric: occurs when there is an increase in tension but not in length
-isotonic: muscle length changes
+eccentric: muscle lengthens
+concentric: muscle shortens
Which of the following terms refers to a chain of sarcomeres?
myofibril
Which of the following sarcomeric bands does not undergo a change in length during contraction of skeletal muscle?
A band
Which of the following sacomeric bands is composed entirely of actin filaments?
I band
DHP channels are part of which of the following structures?
T tubules
Ryanodine sensitive Ca ion release channels are part of which of the following structures?
Sarcoplasmic reticulum
Which of the following events occurs during first during the transmission of a signal from an alpha motor neuron to a skeletal muscle fiber?
Calcium influx into Axon Terminal
Which of the following represents the factor by which the conc of Ca ion increases in the cytosol after release from the SR?
100
Which if the following maintains an optimum Ca conc gradient to facilitate return of Ca to SR?
calsequestrin
Fast twitch fibers have which of the following characteristics?
they are more fatigueable
Which of the following represents an example of an eccentric contraction?
the triceps muscle while lowering the body to the floor during a push up
Which of the following are anchored to the presynaptic membrane and associated with synaptic vesicles to which they are tethered by short filaments?
dense bars
In order for ACh gated ion channels to open, how many ACh molecules are necessary to attach to its alpha subunits?
two
How are fiber types classified? What are the two types of muscle fibers?
- endurance (resistance to fatigue)
- speed of contraction
- white, light(fast twitch)
- dark, red(slow twitch)
What are the characteristics of fast twitch fibers?
- few mitochondria
- contract rapidly, but have less endurance
- primarily use anaerobic respiration resulting in buildup of pyruvic acid and lactic acid
- little myoglobin
- larger concentration of ATPase
What are the characteristics of slow twitch fibers?
- contract slower and have more endurance
- more mitochondria
- aerobic respiration
- more myoglobin
- smaller concentration of ATPase
How are muscles composed with the two different types of fibers?
-# of myofibers cannot be increased, but myofibrils can (increases mass of myofiber and muscle
-lost muscle tissue will be replaced with scar tissue
-muscles have a mix of fiber types, but some muscles can be composed of almost entirely one fiber type
ex. gastrocnemius -> white
soleus -> red
What are motor units?
- a single neuron may innervate from a few to several hundred myofibers (neuron and myofibers it innervates)
- when a neuron fires all the myofibers in the motor unit contract
- all or none contraction
- recruit more motor units for stronger contraction
What is summation?
- when electrical events occur faster than mechanical events
- an additional spike can occur before the previous calcium ions have been returned to the SR
- increases the total amount of calcium ion in the cytosol and increases the rate of cycling between the myosin and actin cross bridges
- increases muscle tension
- each additional spike adds to the effects of the previous spike
What is tetany?
- the frequency of spikes is fast enough there is no time for relaxation between spikes
- muscle remains at maximal contraction
How are muscles like levers or machines?
- involve two forces (applied to machine[in force] and derived from machine[out force])
- bone-muscle systems transmit forces by levers (bone rotates around joint or fulcrum)
- distance from the in force(muscle attachment) to the fulcrum is the in lever arm
- distance from the out force to fulcrum is the out lever arm
What are the calculations relating muscles to levers?
There are two calculations because there are two moments(in lever and out lever):
Mi=FiLi (M=moment, F=force, L=lever arm)
Mo=FoLo
How many classes of levers are there and what are their differences?
-First class (fulcrum in the middle):
+in and out forces move in different directions
+ex. raising chin using sternocleidomastoid(fulcrum=atlas/axis complex)
-Second class(resistance is in the middle[out force]):
+both in and out forces are on the same side of the fulcrum
+ex. raising body on the ball of foot (fulcrum=ball of foot)
-Third class(effort[in force] is in the middle):
+both in and out forces are on the same side of the fulcrum, both forces move in the same direction
+ex. lifting a weight in the palm of your hand
What are the characteristics of a single axon terminal?
-many mitochindira
-synaptic vesicles with ACh (300,000)
-dense bars: anchored to the presynaptic membrane and associated with synaptic vesicles to which they are tethered by short filaments, not sure what role they play
-synaptic gutter: groove or furrow in the surface of the sarcolemma where the axon terminal makes contact with the sarcolemma
+subneural cleft: smaller cleft in the bottom of the synaptic trough
-synaptic cleft: 20-30nm, narrow gap between axolemma of axon terminal and the sarcolemma of the innervated muscle fiber
-has ACh gated channels (2 alpha proteins, 1 beta protein, 1 gamma, 1 delta; tubular channel remains closed until two ACh bind)
-acetylcholinesterase: degrades ACh into acetate and choline, choline is recycled
Which of he following represents the first thing that happens after ACh binds to the ligand gated channels on the sarcolemma?
an end plate potential is created on the muscle fiber (not AP)
The vesicles for ACh are transported to the axon terminal from where?
Golgi
Which of the following can be used to inactivate acetylcholinesterase?
neostigmine and physostigmine
Which of the following characteristics would be true of cardiac muscle cells but not skeletal muscle fibers?
cells are mononucleated
The resting potential of -85mV is characteristic of which of the following phases of the cardiac fast action potential?
Stage 4
How is an AP transmitted across the cleft?
-vesicles created by the Golgi are transported via axonal transport to the axon terminal where they are filled with ACh.
+ACh is synthesized in the cytoplasm of the nerve axon terminal
-when AP arrives at terminal, voltage gated Ca channels open and Ca+2 enter the axon terminus (Ca+2 is thought to draw synaptic vesicles closer to neurolemma
-vesicles fuse with membrane and empty ACh into synaptic cleft
-two ACh bind to the ligand gated gated channels of the sarcolemma, allowing K+ and Na+ to pass
-principal effect is for large numbers of Na+ to pass through the sarcolemma creating an end plate potential )50-75mV) which initiates an AP
-AP travels down T tubule and activates voltage gated DHP channels
-conformation change induces ryanodine receptors to open Ca+2 channels. Calcium floods onto the sarcomere and binds to troponin beginning the sliding filament contraction
What factors induce the opening and closing of the ryanodine receptors?
Open:
- DHP conformation change due to AP
- activated by Ca+2 release into the cytosol (kind positive feedback)
Close:
-too much Ca+2 in the cytosol induces the channel to close
How is ACh “reuptaken” after an AP?
- clathrin coated vesicles begin forming a few seconds after the AP at the axon terminal. The vesicles separate from the plasmalemma and are refilled as the new synaptic vesicles
- ACh in the synaptic cleft is broken down by acetylcholinesertase into acetate and choline (choline is reuptaken and acetate diffuses away)
What is meant by excitation-contraction (electro-mechanical) coupling?
AP until calcium reaches the sarcomere and induces actin/myosin binding then it turns into mechanical action (contraction)
What drugs have the same effect as ACh, but can’t be broken down by acetylcholinesterase?
methacholine, carbachol, nicotine
What drugs inactivate acetylcholinesterase?
neostigmine, physostigmine, diisoprpyl fluorophosphates
What drug blocks the action of ACh?
curare
What is myasthenia gravis?
- autoimmune disease where antibodies attack the ACh receptors
- end plate potentials are too weak to initiate the opening of the sodium channels
- neostigmine can be used to inactivate acetylcholinesterase (potentially allowing an end plate potential to build)
What are some characteristics of cardiac muscle tissue?
- mononucleated
- striated in appear due to sarcomeric arrangement
- central nuclei
- syncytium
- cells branch
- intercalated discs
How is a cardiac muscle potential different from a skeletal muscle contraction?
- cardiac plateaus when depolarizing, depolarized for 0.2sec
- sudden repolarization at end of cycle (no hyperpolarization)
- averages 105mV, from -85mV to 20mV
Differences between cardiac and skeletal muscle structure in terms of T tubules and SR.
Cardiac:
- T tubules along Z line
- one T tubule per cisternae, diads with SR
- SR less extensive
- forms a syncytium
Skeletal:
- T tubules found at ends of think filaments
- two T tubules/cisternae, triads with cisternae
- SR is more extensive
- motor unit arrangement(nerve fiber synapses with one or more skeletal muscle fiber)
What are the two cardiac action potentials and what are their characteristics?
Fast:
- found in atria, ventricles, and conduction system
- very rapidly conducting but non-contractile in Purkinje fibers
- rapidly conducting and contractile in atrial adn ventricular fibers
- high amplitude(100mV)
Slow:
- found in SA and AV nodal tissues
- conducts slower
- automatically depolarizes during resting phase(leaky channels)
- low amplitude(60mV)
What are the phases of fast action potentials?
Phase 4- resting potential
Phase 0- rapid depolarization
Phase 1- initial, incomplete repolarization(beginning of plateau)
Phase 2- plateau or slow decline of membrane potential
Phase 3- repolarization
What are the characteristics of a fast action potential?
-changes due to changes in conductance of K, Na, and Ca
-conductance pattern due to voltage dependent gate
-following result in faster conduction:
+greater Ap amplitude
+more rapid rate of rise of phase 0
+larger cell diameter
What are the characteristics of a slow AP?
- no fast sodium gates
- upstroke of AP is due to Ca
- resting potential 4 is close to -60mV rather than -90mV characteristic of fast Ap
- change in potential is less than that for fast AP
- Sa and Av nodal tissue will spontaneously depolarize slowly during phase 4
Fast contractile vs fast noncontractile vs slow noncontractile
FC:
- large diameter
- high amplitude
- rapid onset of AP
FNC:
- very large diameter
- very rapid upstroke-Perkinje
SNC:
- small contractile
- low amplitude
- slow rate of depolarization
What causes the initial spike in fast contractile cardiac muscle?
-sodium channels, followed by Ca channels
Where do sources of Ca+2 come from in the heart?
DHP receptors: open in response to AP (actually secrete Ca from T tubule)
-ryanodine receptor: Ca from the DHP receptor induces this receptor to open and release Ca
The sodium-calcium exchanger in the sarcolemma of the cardiac muscle cell is an example of which of the following mechanisms?
a) primary active involving antiporter
b) primary active involving symporter
c) secondary active involving symporter
d) secondary active involving antiporter
d
Left ventricular isovolumic contraction occurs immediately follwoing which of the following events?
a) closure of aortic valve
b) opening of aortic valve
c) closure of AV valve
d) opening of AV valve
c
Which of the following statements is true for the period of rapid ejection?
a) it occurs when the left ventricle pressure is above 80mm Hg
b) the semilunar valves are closed during this phase
c) it occurs during the last 2/3 of ejection
d) it results in the ejection of about 90% of the total volume of blood
a
Stroke volume output can be increased by which of the following mechanisms?
a) decreasing EDV
b) increasing EDV
c) increasing ESV
d) by decreasing EDV and increasing ESV
b
Describe the automaticity/rhythmicity of the heart.
-some cardiac tissues will gradually depolarize during phase 4, eventually reaching reaching threshold (SA, AV, and purkinje fibers)
+SA node depolarizes first and becomes pacemaker of the heart
-rate of depolarization determines the rhythmicity of the heart
-gradual depolarization during phase 4 due to special Na channels which open following phase 3
Differentiate between skeletal muscle and cardiac excitation-contraction coupling.
- in skeletal, sodium channels close rapidly
- cardiac, sodium channels also close rapidly, but Ca channels open slowly and stay open for longer
- there is also a delay ion the opening of the K channels
- large conc of both Ca+2 and K+ is responsible for plateau
How is a ventricular fiber different from a skeletal muscle fiber in terms of Ca release in the cytosol?
- calcium floods into the sarcoplasm and completes the electromechanical coupling process
- fewer calcium induced calcium release channels in cardiac muscle compared to skeletal
- allows for fine control over sarcoplasmic Ca conc and contractility
- skeletal releases max amount of Ca into sarcoplasmic reticulum
What does electromechanical coupling mean?
It means that an electrical gradient (action potential) has the ability to contract muscle via the pathway outlined from axon terminal to sliding filament mechanism.
What are the two transporters responsible for relaxation?
SERCA: stimulated via phosphorylation via phospholambian(ATP inhibits its ability to inhibit SERCA)
- returns calcium to SR during diastole, allowing for a greater calcium release on the next beat
- fast clearance of calcium from sarcoplasm
sodium-calcium exchanger (sarcolemma): pumps calcium out of the cell
Describe the events of the cardiac cycle.
Atria as primer pumps- 80% of blood from atria flows from atria to ventricles before contraction, contraction can add up to 20%
ventricular systole- AV valves are closed during the systole
end of ventricular systole- AV valves open at the end of systole because of increased pressures in the atria
first third of diastole- rapid filling of ventricles
middle third of diastole(diastasis)- small amount of blood flows into the ventricles representing blood that continues to flow into atria during diastole
last third of diastole- atria contract to push last 20% of blood into the ventricles
isometric/isovolumic contraction- ventricles contract, but semilunar valves do not open for 0.02-0.03 sec
What is the difference between the periods of fast and slow ejection?
rapid/fast
- occurs when left ventricular pressure is above 80mm Hg and right ventricle is above 8mm Hg
- semilunar valves open
- 70% of blood is ejected
- occurs during the first third of ejection
slow
- remaining 30% of blood ejected from ventricles
- last 2/3 of ejection
What is the Frank-Starling law?
the greater the heart muscle is stretched, the greater the force of contraction
-actin and myosin have an optimal degree of overlap for force generation
What is EDV? SV? ESV?
EDV (end diastolic volume)= 110-120mL, can be increased to 150-180mL
SV (stroke volume) = 70mL -> can be increased or decreased
ESV (end systolic volume) = 40-50mL, can be decreased to 10-20mL
How do you calculate the ejection fraction?
stroke volume/end diastolic volume, will be a percentage
How can stroke volume output be increased?
- increase EDV
- decrease ESV
How does the flow and velocity change from the distal and proximal aorta?
Proximal
- mean velocity- 40cm/s
- flow is phasic
- velocity ranges from 120cm/s (systole) to negative value before the aortic valve closes in diastole
Distal
- velocity is greater in systole than diastole
- forward flow is continuous because of elasticity of vessel walls during diastole
What forces can affect the flow of blood?
- blood flow is proportional to tissue need
- active tissues need 20-30x more blood flow than at rest
- cardiac output cannot exceed 4-7x greater than rest
- microvessels monitor tissue needs
- nervous system and hormones also control tissue blood flow
What cranial nerve innervates the SA and AV nodes?
vagus
How is cardiac output affected during parasympathetic and sympathetic stimulation?
both result in changes in heart rate and contractile strength
sympathetic- cardiac output increases
parasympathetic- cardiac output decreases
What is the pathway of conduction in the heart?
sinoatrial node -> internodal pathways -> atrioventricular node -> AV bundle (bundle of His) -> Purkinje cells
Characteristics of the SA node
- pacemaker of the heart
- composed of special cardiac muscle cells
- fibers connect directly to atrial fibers
What is the timing of electrical system of the heart from SA node depolarization to contraction of the ventricle?
-SA node depolarizes
-AV node receives signal from SA node .03 sec after origin
-signal is delayed in the AV node for .09 sec
+due to size of cells, low amplitude of AP, and slow rate of depolarization during excitation
-final delay of .04 sec occurs in the penetrating bundles (bundles of His)
-there is a .16 sec delay from the initial origin of the signal until onset of ventricular contraction
How is the conduction of the heart slowed?
-diminished number of gap junctions, increasing resistance
In a typical EKG, which of the following waves occurs at the beginning of the contraction of the atria?
a) T
b) R
c) S
d) P
e) Q
d
Which of the following events is generally not seen on a typical ECG?
a) atrial depolarization
b) atrial repolarization
c) ventricular depolarization
d) ventricular repolarization
b
Which of the following is the direction of bipolar lead III?
a) 0
b) 60
c) 90
d) 120
d
Of the three bipolar leads, which one is connected to both left and right arms?
a) Lead I
b) Lead II
c) Lead III
d) all leads are connected to only one arm each
a
What are the characteristic of the sinoatrial node?
PACEMAKER OF THE HEART
- resting membrane potential at -55 to -60mV (threshold= -40mV)
- fast sodium channels are inactivated
- slow sodium-calcium channels can open, so AP is slower to develop and repolarization is slower
- slow leak of Na+ back into cells
- sodium-calcium channels are inactivated100-150msec after opening
What is the difference in potentials of the SA node and ventricular fibers?
ventricular fibers:
- resting: -85 to -90mv
- threshold: 20mV
SA
- resting: -55 to -60mV
- threshold: -40mV
Characterize the resting membrane potential of the SA node.
- large numbers of K= channels open at the time the sodium-calcium channels become inactivated
- nodal cells become repolarized
- K channels remain open for a few tenths of a second
What is the name of AP originating in the SA node? What’s an AP not from the SA called?
SA origination -> sinus rhythm
anywhere else -> ectopic focus/pacemaker
Describe how the parasympathetic system effects the heart. What specifically acts on it?
-vagus nerve -> ACh
- muscarinic receptors and acts SA and AV nodes
- reduces rate of rhythm of SA node (negative chonotropic effect)
- decreases excitability of the AV junctional fibers, slowing transmission of the cardiac impulse into the ventricles
- increases permeability of the fiber membranes
- hyperpolarizes to -65 to -70mV rather than -55 to -60mV
How does the sympathetic division affect the heart’s rhythmicity?
- utilizes norepinephrine and the ganglia are distributed to all parts of the hear (heart, primarily ventricles)
- stimulates beta-1 adrenergic receptors
- increases depolarizariion rate (positive chronotropic effect)
- increase permeability of the fiber membranes to sodium and calcium ions
What are the different components of the ECG and what do they represent?
P= atrial depolarization QRS= ventricular depolarization T= repolarization of ventricles
What is an ECG a graphical representation of?
electrical activity of the cardiac muscle tissue produced by regions of depolarization and repolarization, measures EXTRACELLULAR potential.
- deflection from 0 occurs where there is current flow, current of different membrane potentials
- atrial and ventricular musculature is electrically isolated, current flow does not occur when there are different potentials between the atria and ventricles
What are some characteristics of the ECG?
monophasic AP of the ventricular muscle
- includes repolarization and depolarization
- QRS wave appears at the beginning of the potential
- T wave at end of potential
- no potentials are recorded when the ventricle is completely polarized or depolarized (only partial polarization or depolarization)
What are the components of the ECG in relation to heart contraction?
- P wave occurs at beginning of atrial contraction
- QRS complex occurs at the beginning of ventricular contraction
- repolarization of ventricles at end of T wave
- P-Q interval: 0.16sec
- Q-T interval: 0.35sec
Describe the three limb leads utilized to record an ECG.
Typical ECG has 9 leads
Lead I:
- negative terminal connected to right arm
- positive terminal connected to left arm
- look at heart from left to right
Lead II:
- negative terminal connected to right arm
- positive terminal connected to left leg
- look at heart from upper to lower left
Lead III:
- negative terminal connected to left arm
- positive terminal connected to left leg
- look at heart from upper left to lower left
What is Einthoven’s triangle?
The three leads together make the apices of the triangle. If two of the potentials are known, then the third can be calculated.
How does current flow in the heart?
-current flows from negative to positive in the direction from the base to the apex. The electrode nearer the base will be negative and the apex will be positive.
How are the three leads read according to charge of the heart?
Lead I:
-when point where right arm connects to the chest is negative the ECG records positive
Lead II:
-when right arm is negative with regard to left leg, then ECG will be positive
Lead III:
-when left arm is negative with regard to left keg, then ECG will be positive
