Membrane Equilbirum + Action Potentials Lectures 3.1-7.2 Flashcards
Communication and control:
Measuring the resting potential;
Membrane potential is the separation of opposite charge across the cell membrane
Intracellular fluid is negative compared to extracellular fluid
What is the concept of potential?
Determination of membrane potential by unequal distribution of positive and negative charges across the membrane
Resting membrane potential (RMP)
A separation of charge exists across the membrane of all cells due to:
*an unequal distribution of key ions between the ICF and ECF (mainly Na+/K+ and also A-) occurs due to:
-the Na+ K+ ATPase pump: pumps 2K+ into the cell for every 3Na+ out of the cell
-selective permeability of the membrane
Equilibrium potential for K+
-K+ moves out of the cell, down conc gradient
-inside becomes increasingly more negative- negative membrane potential= electrical gradient
-K+ attracted to - charged interior, repelled by + charged exterior: K+ moves into the cell
-net movement is out of cell initially however electrical gradient becomes stronger and stronger until both inward and outward forces are equal= dynamic equilibrium
-occurs at a membrane potential= -90mV
-referred to as the equilibrium potential for K+^
Equilibrium potential for Na+
-Na+ moves into of the cell, down conc gradient
-inside becomes increasingly more positive- positive membrane potential= electrical gradient
-Na+ attracted to - charged exterior, repelled by + charged interior: Na+ moves out the cell
-electrical gradient becomes stronger and stronger until both inward and outward forces are equal
-occurs at a membrane potential= +60mV
-referred to as the equilibrium potential for Na+^
Work out equilibrium potential for an ion
Page 6
Goldman-Hodgkin-Katz equation
Work out page 8
Action potential in a single axon
Page 9
Communication + control
What are excitable tissues?
Nerve and muscle are excitable tissues
*they produce rapid changes to their membrane potential by producing electrical signals
-neurons use these signals to receive process, initiate and transmit messages
-muscles respond to electrical signals by contracting
How are electrical signals produced?
*electrical signals are produced by rapid changes in ion movement across the plasma membrane in response to a triggering event
What are the opening of ion channels?
Ion channels are:
*pores in cell membranes
*selective for a particular ion
*passive; no energy is required- ions flow down their electrochemical gradient
*leak channels; open all the time
*may be gated
What is the function of the neuron?
-transports impulses around the body; allowing communication
-contains the same fundamental structures as other cells of the body such as: plasma membrane, nucleus, endoplasmic reticulum, Golgi apparatus and mitochondria
-specialised for its function in 3 ways: axon, dendrites and myelin sheath
What is graded and action potentials?
-two basic forms of electrical signal:
*Graded potentials (GPs); serve as short-distance signals
-generated in the dendrites and cell body in response to incoming signals
-if big enough= can spread to axon hillock
*Action potentials (APs); serve as long-distance signals
-summation occurs if Vm passed a threshold—> action potential occurs
-action potential then propagated to the axon terminals
More about graded potentials:
*short lived, localised changes in RMP occur in varying degrees
*triggering stimuli; neurotransmitters acting at ligand gated in ion channels
*sensory stimuli acting at receptors
*magnitude of GPs varies with the duration of the stimulus
*may be either hyper- or depolarisation
• die out over short distances
Diagrams explained
? Page 15
-Go through majority of the slides (diagrams) on lecture 4.1+ 4.2
More about action potentials:
-brief, rapid and large changes in membrane potential during which the potential actually reverses; becomes positive
-only involves a small portion of the total excitable cell membrane at any one time
-in contrast to GPs- it does not decrease in strength as they move along the membrane- propagated without attenuation
Action potential- rapid reversal of the RMP
Explain diagram? Page 16
What is the all-or-none law of the action potential?
-if the stimulus is too low, there is no action potential (none part)
-if the stimulus is above a threshold then an action potential is generated and is always the same size (all part)
*as the action potential travels along the axon, doesn’t fade but is same size
^then triggers the next section of axon to fire
What is the restoration of the RMP?
-electrical charge across the membrane is restored immediately by the opening and then closing of voltage-gated K+ channels
-conc of the ICF and ECF is restored by the Na/K ATPase pump
*3Na+ = pumped into the ECF
*2K+= pumped into the ICF
Action potential propagation and the refractory period:
What are the 2 types of propagation?
*contigous conduction:
-conduction in unmyelinated fibers
-AP spreads along every portion of the membrane
*saltatory conduciton:
-rapid conduction in myelinated fibres
-impulse jumps over sections of the fibre covered with insulating myelin
Contiguous conduction:
Explain diagram page 4 lecture 4.3
Diagrams
Explain them on lecture 4.3
