Lecture 7: Membrane Potential Flashcards
Neurons
Specialized for communication with other cells in the form of electrical impulses (ion gradiant)
In vertebrates, most neurons are part of the —-
CNS
Dendrites
Receive information
Axons
Conducts outgoing information
Terminal knobs
where impulses are transmitted to the target cell
Myelin Sheath
wraps most vertebrate axons (lipid rich)
Membrane potential/membrane voltage
Difference in charge across a membrane
Resting potential
The membrane potential when a nerve cell is in an unexcited state.
-70mV
Negative voltage
Inside of the cell is negative compared to the outside
What contributes to the difference in charge across the membrane?
- Na+/K+ ATPase pump pumps 3 Na+ ions out per 2K+ ions pumped in
- K+ ions are the charged substance with the most permeability in a resting nerve cell. (Flow out through potassium leak channels, following their concentration gradient)
Equilibrium with K+ in the cell
Balance is reached between the concentration gradient favouring K+ leaving the cell and the electrical gradient favouring K+ staying in the cell. (-70mv)
Action Potential (2)
What it is x2+ includes
- Changes in membrane potential after a stimulus and is the basis for neural communication
- include depolarization and repolarization phases
During resting membrane, ion permeability for Na+ and K+ is
low
During depolarization (4):
- a decrease in the electrical potential difference across a membrane
- A stimulus causes sodium channels to open, sodium diffuses in
- If the stimulus results in depolarization above a threshold value of -50mv, then voltage gated sodium channels open (and sodium goes in inside reverse and be +)
- The increased permeability to Na+ ions results in a membrane potential of about +40mV
During repolarization (4):
- The depolarization (increasing voltage) triggers the opening of voltage-gated potassium channels
- Sodium gated channels close
- Membrane potential goes back to negative (-80mV) Too much K+ leaves
- Large negative membrane potential causes the voltage-gated potassium channels to close
Why is it -80mV not -70mV
Because K+ channels are slow to close
Although the membrane voltage changes during the action potential, the
Na+ and K+ concentration gradients are barely affected. Overall number of ions on either side are barely affected
An action potential is propagated along a neuron by
triggering action potentials in adjacent portions of the membrane
Continous conduction (4)
- occurs in unmeylinated axons
- The flow of current causes the membrane in the region just ahead to become depolarized
- The action potential is propagated without any loss of intensity
- Portion of the membrane that juist experienced the action potential will be in a bried refractory period (Na+ channels cant reopen for a few ms)
Saltatory conduction (5)
- occurs in myelinated axons
- Impulses in myelinated axons are 20X faster than in an unmyelinated axon
- Myelin prevents the passage of ions across the membrane
- Most Na+ and K+ channels are found in or near unmyelinated regions called: Nodes of Ranvier
- Action Potential at node of Ranvier triggers an action potential at the next node
Synapse
The specialized junction of a neuron with its target cell
Presynaptic cell
Conducts the impulse towards a synpase (eg. neuron)
Synaptic vesicles
Storage for neurotransmitters in the terminal knobs of axons
