SM36 Flashcards
Pre
A highly positive equilibrium potential (for ex. sodium) means what?
Sodium is high outside cells but low inside
The ________ _________ for a particular ion is the membrane potential at which there will be no movement of that ion across the membrane
Equilibrium Potential
The Na/K-ATPase pump pushes ___ out of the cell and ___ into the cell. How many ions for each cycle?
3 Na+ ions moved out of cell and 2 K+ ions moved into cell
Nernst Equation
Used to calculate equilibrium potential
In these tissues, Cl conductance is important for stabilizing the resting membrane potential
Skeletal Muscle
Goldman-Hodgkin-Katz Equation
Ionophores
Chemical pores formed in membranes that promote K+ leakage and lead to cell death
graded potentials
Transient changes in membrane potential. Amplitude and direction of graded potential is dependent on stimulus
Acetylcholine receptors at the neuromuscular junction; glutamate receptors at neuronal synapses
examples of receptors permeable to Na2+ or Ca2+ whose activation causes EPSP
Glycine receptors and GABA receptors
examples of receptors permeable to Cl- whose activation causes IPSP
Disorder that results from loss of “safety factor” for motor neurons at neuromuscular junction. What is the mechanism of loss of the safety factor? How can it be treated?
Myasthenia Gravis – loss of acetylcholine receptors. Can be treated by inhibiting degradation of acetylcholine (inhibiting acetylcholinesterase)
The term ‘safety factor’ refers to the ability of neuromuscular transmission to remain effective under various physiological conditions and stresses. This is a result of the amount of transmitter released per nerve impulse being greater than that required to trigger an action potential in the muscle fibre. The safety factor is a measure of this excess of released transmitter.
______ cells exhibit longer action potentials (hundreds of milliseconds) than _____ cells ( a few milliseconds)
heart muscle cell has longer AP than nerve and skeletal muscle cells
-80 mV
approximate resting membrane potentials of neuronal membranes
What is the electrochemical potential that is favorable towards repolarization
High intracellular K+ concentration (chemical) and depolarized membrane / positive cell interior (electrical)
______ channel inactivation is a major reason for nerve cells having a refractory period (absolute and relative)
Sodium
Phase 0 depolarization of cardiac muscle
Influx of Na via voltage gated sodium channels causes transiet depolarization
Phase 1 of cardiac muscle action potential
Transient repolarization due to fast gating voltage-gated potassium channels accompanied with rapid inactivation of sodium channels. Voltage gated (L-type) calcium channels begin to activate.
Phase 2 of cardiac muscle action potential
plateau phase - delicate balance between inward current (L-type calcium channels + residual Na channels) and outward current (two types of potassium channels - not the same type as in phase 1)
Phase 3 of cardiac muscle action potential
Inward rectiyfing potassium current finish repolarization (Ik1). Occurs following inactivation of calcium channel, tipping the balance in favor of outward current.
Long QT syndrome: causes and pathology
Causes: drugs that impair potassium currents, genetic mutations in genes encoding proteins responsible for ion currents
Pathology: prolonged cardiac porential due to diminished repolarizing potassium current or enhanced depolarizing Ca/Na currents. Predisposition to chaotic electrical impulses (aka ventricular fibrillation)
Inward Current
The influx of positive charge (via influx of positive ions or efflux of negative ions)
Outward Current
Efflux of positive charge (when positive ions exit cell or negative ions enter cell)
