BRS - Cell Physiology Flashcards

Terms Definitions
What are the components of cell membranes?
Phospholipids and proteins
What is the structure of a phospholipid?
Two hydrophobic fatty acid tails esterified to a hydrophilic glycerol backbone
What sorts of substances can dissolve across cell membranes?
Lipid soluble substances (small, uncharged things) such as O2, CO2, and steroid hormones, because can dissolve in the hydrophobic bilayer
What sorts of substances cannot dissolve across cell membranes?
Water soluble substances (large or charged things) such as Na+, Cl-, glucose, and H2O because they cannot dissolve in the lipid interior
How are lipid-insoluble substances transported across cell membranes?
Water-filled channels, pores, protein transporters
What are integral membrane proteins?
Anchored to and embedded in the cell membrane via hydrophobic interactions. They may span the cell membrane
What are peripheral membrane proteins?
Loosely attached to the cell membrane via electrostatic interactions
What are the two major types of intercellular junctions?
Tight junctions (zonula occludens)
Gap junctions
Describe the major features of tight junctions
Often found between epithelial cells
May serve as an intercellular pathway for solutes
May be tight (impermeable) or leaky (permeable)
Describe the major features of gap junctions
Exist between cells that require intercellular communication
Permit solute flow and electrical coupling between myocardial cells
What is simple diffusion?
Only form of transport that is not carrier-mediated
Occurs down an electrochemical gradient
Does not require energy
What is the formula for flux/diffusion?
J = -PA(C1 - C2)
J = flux
P = permeability
A = area
C = concentration
What is "permeability?"
It describes the ease with which a solute diffuses through a membrane. It depends upon the characteristics of the solute and the membrane
What are some factors that increase permeability of a solute in a membrane?
A high oil/water partition coefficient (increases lipid solubility)
Low radius of the solute (increases speed of diffusion)
Low membrane thickness (decreases the diffusion distance)
What types of molecules have the highest permeabilities in lipid membranes?
Small, hydrophobic solutes
How does facilitated diffusion differ from simple diffusion?
Requires a carrier protein, and is therefore more rapid
What does it mean for a membrane carrier protein to exhibit stereospecificity?
It distinguishes between D- and L- enantiomers
What does it mean for a membrane carrier protein to exhibit saturation?
The transport rate increases as solute concentration increases, until the carriers are saturated (ie when you reach the transport maximum Tm)
What does it mean for a membrane carrier protein to exhibit competition?
Structurally related solutes may compete for transport sites (ie galactose is a competitive inhibitor of glucose transport in the small intestine)
What sort of transport is used to transport glucose into muscle and adipose tissue?
Facilitated diffusion
What happens to glucose uptake in diabetes mellitus?
Glucose uptake by muscle and adipose tissue is inhibited because the carriers require insulin
What are the features of primary active transport?
Occurs against an electrochemical gradient
Requires direct energy input (ATP)
Carrier-mediated
What type of transport does the Na-K pump use?
Primary active transport
What does the Na-K pump do?
Transports 3 Na into the cell and 2 K out of the cell. Both ions are transported against their gradients.
What drugs inhibit the Na-K pump?
Ouabain
Digitalis
What type of transport does the Ca pump use?
Primary active transport
What does the Ca ATPase do?
Transports Ca in the sarcoplasmic reticulum or cell membrane. Note that in the SR, this pump is known as SERCA
What type of transport does the H-K ATPase use?
Primary active transport
What does the H-K ATPase do?
Allows the gastric parietal cells to transport H into the stomach lumen
What drug inhibits the H-K ATPase?
Omeprazole
What are the features of secondary active transport?
The transport of at least two solutes is coupled
One solute is transported downhill and provides energy for the uphill transport of the other solute (the energy comes from the concentration gradient, not ATP)
What are the two types of secondary active transport?
Cotransport/symport -- the solutes move in the same direction across the cell membrane
Countertransport/antiport -- the solutes move in opposite directions
What type of transport is used by the Na-glucose cotransporter in the small intestine?
Symport
What type of transport is used by the Na-K-2Cl cotransporter in the renal thick ascending limb?
Symport
What type of transport is used by the Na-Ca transporter?
Antiport
What type of transporter is used by the Na-H transporter?
Antiport
Describe how Na-glucose cotransport works (give details)
This transporter is in the luminal membrane of the intestinal mucosal and renal proximal tubule cells
Glucose is transported uphill and Na is transported downhill
Energy comes from the downhill Na transport
The Na gradient is maintained by the Na-K pump in the basolateral membrane, so poisoning this pump decreases the Na gradient and its coupled glucose transport
Describe how Na-Ca transport works (give details)
Transports Ca uphill out of the cell and Na downhill into the cell
Energy comes from the downhill movement of Na, which is maintained by the Na-K pump
Therefore, poisoning the Na-K pump would abolish Na-Ca antiport
What is osmolarity?
The concentration of osmotically active particles in a solution
What does it mean for osmolarity to be a colligative property?
Can be measured by freezing point depression
What is the equation for osmolarity?
Osmolarity = # particles in solution x concentration
(# of particles in solution is the number that the compound dissolves into in water, so for NaCl, you would use 2, 1 for glucose, etc)
What is osmosis?
The flow of water across a semipermeable membrane from low solute concentration to high solute concentration.
What is osmotic pressure?
The extent to which a compartment attracts water into it by having a high solute concentration. Note that this osmolarity is for osmotically active particles only.
What is the formula for osmotic pressure?
Osmotic pressure = g x C x RT
g = # osmotically active particles (NaCl = 2, glucose = 1)
C = conc
R = constant (0.82)
T = temp
What does it mean when two solutions are isotonic?
They have the same effective osmotic pressure, so no water would flow across a semipermeable membrane separating them
What does it mean when a solution is hypertonic or hypotonic to another?
The hypertonic solution has a higher osmotic pressure than the hypotonic solution
What is colloid osmotic pressure?
Also known as oncotic pressure
It is the osmotic pressure generated by proteins
What is the reflection coefficient?
A number between 0 and 1 that describes the ease with which a solute permeates a membrane
What does it mean if the reflection coefficient is 1?
The solute is impermeable, and is therefore retained in the original solution, where it creates osmotic pressure and causes water flow. Serum albumin is an example of a substance with a reflection coefficient of 1
What does it mean if the reflection coefficient is 0?
The solute is completely permeable, so it does not exert any osmotic effect and does not cause water flow. Urea has a reflection coefficient close to 0
Formula for the effective osmotic pressure
Effective osmotic pressure = osmotic pressure x reflection coefficient
Are ion channels integral or peripheral membrane proteins?
Integral; when they are open, they permit the passage of certain ions
How do ion channels exhibit selectivity?
They permit the passage of some ions but not others. Selectivity is based on the size of the channel and the distribution of charges lining it
What does it mean for an ion channel to be permeable?
They are either open or closed. The conductance of a channel depends upon the probability that they channel is open. The higher the probability of being open, the higher the conductance or permeability
How is the conductance of an ion channel regulated?
The opening and closing of channels is controlled by gates
What does it mean for an ion channel to be voltage-gated?
The channel is opened or closed by changes in membrane potential
How is the activity of the Na channel in nerves regulated?
This channel is voltage-gated
The activation gate is opened by depolarization; Na passes through
The inactivation gate is closed by depolarization; Na cannot pass
What does it mean for an ion channel to be ligand-gated?
The channel is opened or closed by hormones, second messengers, or neurotransmitters
How is the opening and closing of the nicotinic ACh receptor at the motor end plate regulated?
It is a ligand-gated channel
When ACh binds, it opens and is permeable to Na and K, causing depolarization
What is a diffusion potential?
The potential difference generated across a membrane because of a concentration difference of an ion. This type of potential can only be generated if the membrane is permeable to the ion
What determines the size of a diffusion potential?
The size of the concentration gradient. Note that since diffusion potentials are created by the diffusion of very few ions, there is no real effective change in concentration of the diffusing ions on either side of the membrane
What determines the sign of a diffusion potential?
Whether the diffusing ion is positively or negatively charged
What is an equilibrium potential?
The diffusion potential that exactly balances (opposes) the tendency for diffusion caused by a concentration difference
What is electrochemical equilibrium?
The chemical and electrical driving forces acting upon an ion are equal and opposite, so there is no net diffusion of the ion
What is the Nernst equation used for?
Calculation of the equilibrium potential at a given concentration difference for a permeable ion across a cell membrane. It tells us what potential would balance the tendency for diffusion, or the potential at which the ion would be at electrochemical equilibrium
Formula for the Nernst equation
E = -2.3 (RT/zF)log(Cinside/Coutside)
where 2.3(RT/zF) = 60 mV
What is Ena?
+65 mV
What is Eca?
+120 mV
What is Ek?
-85 mV
What is Ecl?
-85 mV
What is the resting membrane potential?
The overall membrane potential that is established by diffusion potentials resulting from concentration gradients of all permeant ions. By convention, it is expressed as the intracellular potential relative to the outside, so -70 mV means 70 mV, cell negative
What determines which ions contribute the most to the resting membrane potential
The ions with the highest permeabilities make the largest contributions
At rest, what ion is the principal determinant of the resting membrane potential of the nerve?
K
How does the Na-K pump contribute to the resting membrane potential?
Only indirectly, by maintaining the Ha and K concentration gradients
What is depolarization?
When the membrane becomes less negative (the cell interior becomes less negative)
What is hyperpolarization?
When the membrane becomes more negative (the cell interior becomes more negative)
What is inward current?
The flow of positive charge INTO the cell, depolarizing the membrane potential
What is outward current?
The flow of positive charge OUT of the cell, hyperpolarizing the membrane potential
What is an action potential?
A property of excitable cells that consists of a rapid depolarization (upstroke) followed by repolarization of the membrane. Action potentials are propagating
Are action potentials graded or all-or-none?
All-or-none
What is an action potential threshold?
The membrane potential at which the action potential is inevitable, and the net inward current becomes greater than the net outward current
What is the resting membrane potential of a nerve?
-70 mV, because of the high resting conductance to K
At rest, what is the state of Na channels and Na conductance in nerves?
The Na channels are closed and Na conductance is low
What happens during the upstroke of an action potential?
The membrane depolarizes to threshold
The activation gates of the Na channels open, increasing Na conductance
Because Na conductance is now higher than K's, the membrane potential is driven toward Ena
Thus, rapid depolarization during upstroke is caused by inward Na current
What is the "overshoot" of an action potential?
The brief portion at the peak of the action potential where the membrane potential becomes positive
What is the mechanism of action of tetrodotoxin (TTX) and lidocaine?
They block the voltage-sensitive Na channels of nerves, thereby abolishing action potentials
What is the sequence of events of an action potential?
Resting membrane potential
Upstroke (depolarization)
Repolarization
Refractory period
What happens during the repolarization of an action potential?
Depolarization closes the inactivation gates of the Na channel, abolishing Na conductance
Depolarization slowly opens K channels and increases K conductance to levels higher than rest
This causes the membrane potential to repolarize
Thus, repolarization is caused by outward K current
What is the "undershoot" of an action potential?
When the K conductance remains higher than at rest, even after Na channel closure. This drives the membrane potential very close to Ek
What is the absolute refractory period?
The period during which another action potential cannot be elicited, no matter how large the stimulus. This is because the inactivation gates on the Na channels are still closed
What is the relative refractory period?
The period during which an action potential can be elicited, but only if it is larger than the usual inward current. This is because the K conductance is higher than at rest, so as Em approaches Ek, it moves farther away from threshold
What is accommodation (in the context of action potential propagation)?
Occurs when a cell membrane is held at a depolarized level such that threshold is passed without firing an action potential
Occurs because depolarization closes the inactivation gates on the Na channels
Accommodation is demonstrated in hyperkalemia, where skeletal muscle is depolarized by high serum K concentrations. This closes the Na channels
How are action potentials propagated?
The spread of local currents to adjacent areas of membrane, which are then depolarized to threshold and generate action potentials
What factors increase the conduction velocity of a nerve?
Increased fiber size (increased diameter decreases internal resistance)
Myelination (myelination acts as an insulator)
How does myelin modulate nerve conduction of action potentials?
It increases conduction velocity by acting as an insulator
Myelinated nerves exhibit saltatory conduction because action potentials can only be generated at the nodes of Ranvier (gaps in the myelin sheath)
What are the general features of a chemical synapse?
An action potential in the presynaptic cell causes it to depolarize
Ca enters the presynaptic terminal and causes neurotransmitters to be released
Neurotransmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane, causing a change in ion permeability and membrane potential
What effect do inhibitory neurotransmitters have upon the postsynaptic membrane potential? Excitatory?
Inhibitory -- hyperpolarize the membrane
Excitatory -- depolarize the membrane
What is the neuromuscular junction?
The synapse between the axons of motor neurons and skeletal muscle. The neurotransmitter, ACh, binds to postsynaptic nicotinic receptors
How is ACh synthesized and stored in the presynaptic terminal?
Choline acetyltransferases catalyzes the formation of ACh from CoA and choline in the presynaptic terminal
ACh is stored in synaptic vesicles with ATP and proteoglycan for later use
How does depolarization of a presynaptic membrane cause propagation of a signal through an action potential?
Depolarization opens Ca channels
Ca influx causes Ca influx, which induces exocytosis of presynaptic vesicles
How does the ACh receptor in the muscle end plate work?
The nicotinic ACh receptor is also a Na and K ion channel
Binding of ACh to the receptor causes a conformational change that increases conductance for Na and K
What is the mechanism of action of Botulinum toxin (Botox)?
Blocks the release of ACh from presynaptic terminals and completely blocks the neuromuscular action potential
What is the mechanism of action of curare?
Competes with ACh for receptors on the postsynaptic motor end plate
This decreases the size of the EPP and can produce paralysis of the respiratory muscles and death
What is the mechanism of action of neostigmine?
Inhibits acetylcholinesterase
This prolongs and enhances the action of ACh at the muscle end plate
What is the mechanism of action of hemicholinium?
Blocks reuptake of choline into the preynaptic terminal
This depletes ACh stores from the presynaptic terminal
What is the end plate potential in the postsynaptic membrane?
The contents of one synaptic vesicle (1 quantum) produce a miniature end plate potential (MEPP), the smallest possible depolarization
MEPPs summate to produce a full-fledged EPP, which is NOT an action but simply a depolarization (not to threshold) of the muscle end plate
How is the action potential of the neuromuscular junction related to muscle contraction?
Once the end plate depolarizes, local currents cause depolarization and action potentials in the adjacent muscle tissue
Action potentials in the muscle are followed by contraction
How is ACh degraded?
The EPP is transient because ACh is degraded to acetyl CoA and choline by acetylcholinesterase (AChE) on the muscle end plate
Describe the main features of myasthenia gravis
The patient makes antibodies to the ACh receptor, so there is a reduced number of AChR on the muscle end plate
This causes skeletal muscle weakness
The size of the EPP is reduced, so it is more difficult to depolarize the membrane to threshold to produce action potentials
Treatment with AChE inhibitors prolongs the action of ACh in the synapse
What is a one-to-one synapse?
A action in the presynaptic element (the motor nerve) produces an action in the postsynaptic element (the muscle)
This type of synapse is found at the neuromuscular junction
What is a many-to-one synapse?
An action in a single presynaptic cell cannot produce an action potential in the postsynaptic cell by itself
Many cells synapse on the postsynaptic cell to depolarize it to threshold
Presynaptic input may be excitatory or inhibitory
What types of inputs does the postsynaptic cell receive?
Excitatory and inhibitory. These inputs are integrated and the sum of the inputs brings the membrane potential of the postsynaptic cell to threshold, causing the firing of an action potential
What is an excitatory postsynaptic potential (EPSP)?
These are inputs that depolarize the postsynaptic cell and bring it closer to threshold
They are caused by the opening of channels that are permeable to Na and K, similar to ACh channels
They depolarize to a value about halfway between Ena and Ek
What types of neurotransmitters cause an EPSP?
ACh
Norepinephrine
Epinephrine
Dopamine
Glutamate
Serotonin
What is an inhibitory postsynaptic potential (IPSP)?
These are inputs that hyperpolarize the postsynaptic cell, moving it away from threshold
They are caused by the opening of Cl channels, so the Em approaches Ecl
What is spatial summation of synapses?
Two excitatory inputs arrive at a postsynaptic neuron at the same time, and together they produce greater depolarization
What is temporal summation of synapses?
Two excitatory inputs arrive at a postsynaptic neuron in rapid succession
Because the resulting depolarizations overlap in time, they are added in a stepwise fashion
What is facilitation (in the context of the synapse)?
Also known as augmentation and post-tetanic potentiation
This occurs after tetanic stimulation of the presynaptic neuron
Depolarization of the postsynaptic neuron is greater than expected, because greater-than-normal amounts of neurotransmitter are released due to accumulation of Ca in the presynaptic terminal
Long-term potentiation (memory) involves new protein synthesis
Describe the main features of norepinephrine
Primary neurotransmitter released from postganglionic sympathetic neurons
Synthesized in the nerve terminal and released into the synapse to bind to alpha or beta adrenergic receptors
Removed from the synapse
How is norepinephrine removed from the synapse?
Reuptake
Metabolized by monoamine oxidase (MAO) and catechol-o-methyltransferase (COMT) to DOMA and NMN
What types of neurotransmitters cause an IPSP?
y-aminobutyric acid (GABA)
Glycine
Describe the main features of norepinephrine
Primary neurotransmitter released from postganglionic sympathetic neurons
Synthesized in the nerve terminal and released into the synapse to bind to alpha or beta adrenergic receptors
Removed from the synapse
How is norepinephrine removed from the synapse?
Reuptake
Metabolized by monoamine oxidase (MAO) and catechol-o-methyltransferase (COMT) to DOMA, NMN, MOPEG, and VMA
What metabolite is excreted in the urine when you have a pheochromocytoma?
This tumor of the adrenal medulla secretes catecholamines, and norepinephrine degradation causes VMA to be excreted in the urine
How is epinephrine produced?
Synthesized from norepinephrine by phenyl-ethanolamine-N-methyltransferase
Secreted, along with norepinephrine, from the adrenal medulla
What is the biosynthetic pathway that produces norepinephrine and epinephrine?
Tyrosine
L-dopa
Dopamine
Norepinephrine
Epinephrine
Describe the main features of dopamine
Found in midbrain neurons
Released from the hypothalamus
Inhibits prolactin secretion (known as PIF in this case)
Metabolized by MAO and COMT
What are the actions of the receptors bound to by dopamine?
D1 receptors activate adenylate cyclase via a Gs protein
D2 receptors inhibit AC via a Gi protein
What is the molecular basis of Parkinson's Disease?
Degeneration of dopaminergic neurons that use the D2 receptors
What is the molecular basis of schizophrenia?
Increased levels of D2 receptors
Describe the main features of serotonin
Found in the brain stem
Formed from tryptophan
Converted to melatonin in the pineal gland
Describe the main features of histamine
Formed from histidine
Found in the neurons of the hypothalamus
Describe the main features of glutamate
Most prevalent excitatory neurotransmitter in the brain
Four subtypes of receptor
What are two of the important types of glutamate receptor?
Inotropic receptors (ligand-gated ion channels), including the NDMA receptor
Metabotropic receptors, which are coupled to ion channels via heterotrimeric G proteins
Describe the main features of GABA
Inhibitory neurotransmitter
Two types of receptor
What are the types of GABA receptor?
GABA A receptor -- increases Cl conductance; the site of action of benzodiazepines and barbiturates
GABA B receptor -- increases K conductance
Describe the main features of glycine
Inhibitory neurotransmitter found primarily in the spinal cord and brainstem
Increases Cl conductance
Describe the main features of nitric oxide
Short-acting inhibitory neurotransmitter in the GI tract, blood vessels, and CNS
Synthesized from arginine by NO synthase in the presynaptic nerve terminals
Permeant gas that diffuses to target cells
Also acts to activate guanylyl cyclase in a variety of tissues, including vascular smooth muscle
What is the general structure of a muscle fiber?
Each fiber is multinucleated and acts as a single unit
Contains bundles of myofibrils
Surrounded by sarcoplasmic reticulum
Invaginated by T tubules
Each myofibril has interdigitating thick and thin filaments arranged longitudinally into sarcomeres
What defines a sarcomere?
You count Z line to Z line
What gives skeletal muscle its unique banding pattern?
The presence of sarcomeres
What is the structure of a muscle thick filament?
Made of myosin
Thick filaments are found in the B band at the center of the sarcomere
Each myosin has two heads attached to a single tail. The heads bind ATP and actin, and are involved in cross-bridge formation
What is the structure of myosin?
Six polypeptide chains -- one pair of heavy chains and two pairs of light chains
What is the structure of muscle thin filaments?
Present in the I bands and anchored at the Z lines
Interdigitate with the A band
Contain actin, tropomyosin, and troponin
How does the troponin complex regulate muscle contraction?
Troponin is a regulatory protein that permits cross-bridge formation when it binds to Ca
Troponin T attaches the troponin complex to tropomyosin
Troponin I inhibits the action of actin and myosin
Troponin C binds Ca and permits the interaction of actin and myosin
What are T tubules?
They are an extensive tubular network open to the extracellular space that carry depolarization from the sarcolemma to the cell interior. They are found at the junction of A and I bands, and contain a voltage-sensitive dehydropyridine receptor that undergoes a conformational change upon depolarization
What is the sarcoplasmic reticulum?
Internal tubular structure that stores and releases Ca for excitation-contraction coupling
Terminal cisternae make contact with the T tubules in a triad
Membrane has a Ca-ATPase that transports Ca into the SR
Contains Ca loosely bound to calsequestrine
Releases Ca into the cell interior through the ryanodine receptor
What are the steps of excitation-contraction coupling?
Action potentials in the muscle cell membrane depolarize the T tubules
The dehydropyridine receptors in the T tubules undergo a conformational change
This opens Ca release channels (ryanodine receptors) in the SR
Ca is released into the cytoplasm from the SR lumen
Intracellular Ca increases and binds to troponin C, initiating the cross-bridge cycle so that the muscle contracts
Ca goes back into the SR through the Ca ATPase and the cross-bridge cycle stops (muscle relaxes)
What are the steps of the cross-bridge cycle?
Ca binds to myosin and the cross-bridge cycle begins:
When myosin is not bound to ATP, it is tightly attached to actin
ATP binds myosin and causes a conformational change such that myosin releases actin
Myosin is displaced toward the plus end of actin. This involves ATP hydrolysis -- ADP remains attached and P dissociates
Myosin attaches to a new site on actin; this is the power stroke
ADP is released and myosin returns to its original rigor state
As long as Ca is bound to troponin C, this cycle repeats
What is the mechanism of muscle relaxation?
Ca is reaccumulated by the SR Ca-ATPase (SERCA)
Intracellular Ca concentration decreases and Ca is released from troponin C
Tropomyosin again blocks the myosin-binding site on actin
What is the mechanism of tetanus?
If a muscle is stimulated repeatedly, more Ca is released from the SR
This causes a cumulative increase in intracellular Ca, extending the time for cross-bridge cycling
The muscle does not relax during this time
What are isometric muscle contractions?
Contractions at a fixed length. The length (preload) is fixed, the muscle is stimulated to contract, and the developed tension is measured. There is no muscle shortening.
What are isotonic muscle contractions?
The load against which the muscle contracts (afterload) is fixed, the muscle is stimulated to contract, and shortening of the muscle is measured.
What is the length-tension relationship of muscle?
Measures tension during isometric contractions when the muscle is set to fixed lengths (preloads)
What is passive muscle tension?
The tension developed by stretching the muscle to different lengths
What is total muscle tension?
The tension developed when the muscle is stimulated to contract at different lengths
What is active muscle tension?
The difference between total and passive tension, representing the active force developed from muscle contraction
Active tension is proportional to the number of cross-bridges formed
How does the degree of muscle stretch affect active tension?
Tension is maximal when there is maximum overlap of thick and thin filaments
When the muscle is greatly stretched, there is less overlap
When the muscle length is decreased, the thin filaments collide and can't generate a good power stroke, so tension is decreased there too
What is the force-velocity relationship of muscle?
Measures the velocity of shortening of isotonic contractions when the muscle is challenged with different afterloads
The velocity of shortening decreases as the afterload increases
How does smooth muscle differ from skeletal muscle?
Thick and thin filaments are not arranged in sarcomeres, so it does not appear striated. Contraction is involuntary. Also, there is no troponin
What are the main features of multi-unit smooth muscle?
Found in the iris, ciliary muscle of the lens, and vas deferens
Behaves as separate motor units
Little or no electrical coupling between cells
Densely innervated; contraction is controlled by neural innervation
What are the main features of urinary smooth muscle?
Most common type of smooth muscle, found in the uterus, GI tract, ureter, and bladder
Spontaneously active (exhibits slow waves) and has pacemaker activity
Pacemaking is modulated by hormones and neurotransmitters
Lots of electrical coupling between cells to allow for coordinated contraction
What are the steps of excitation-contraction coupling in SMOOTH muscle?
Depolarization of the cell membrane opens voltage-gated Ca channels
Ca enters the cell
This causes additional release of Ca from the SR
Hormones and NTs can also cause SR Ca release through IP3-gated Ca channels
Intracellular Ca concentration increases
Ca binds to calmodulin, and the Ca-calmodulin complex binds to/activates myosin light-chain kinase
MLCK phosphorylates myosin and allows it to bind to actin
Contraction occurs
What ion mediates the upstroke of the action potential in smooth and cardiac muscle?
Ca
What types of muscle exhibit a plateau in their action potential?
Atria, ventricles, and purkinje fibers in the cardiac muscle
What type of muscle has the shortest action potential duration? What about the longest duration?
Shortest -- skeletal
Longest -- cardiac
What types of muscle use Ca-troponin C for contraction?
Skeletal and cardiac muscle
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