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Typical Neuron = EPSP + IPSP (Graded Potential Summation at Axon Hillock) Axon Hillock
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Graded Potentials & Action PotentialsExcitatory Post Synaptic Potential (EPSP)
- it results from the opening of ligand-gated Na+ channels
- some positive Na+ ions come into the cell making the cytosol slightly more positive (depolarized)
- it brings the membrane potential closer to threshold (-55mV)
Inhibitory Post Synaptic Potential (IPSP)
- it results from the opening of ligand-gated Cl- or K+ channels
- Some positive K+ ions leak out or some negative Cl- ions leak in making the cytosol more negative (hyperpolarized)
- it takes the membrane potential further away from threshold (-55mV)
Typical Neuron = EPSP + IPSP (Graded Potential Summation at Axon Hillock)
Axon Hillock
Na+ K+Na+/K+ ATPase
Threshold!
Voltage-Gated Sodium Channel Voltage-Gated Potassium Channel
OPEN OPENING - SLOWLY
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
K+K+
K+ K+
K+
K+
K+
K+
K+ K+
FINALLY ssOPEN
Na+
Na+
Na+
K+
K+
K+
ATPADP + P-
Na+
Na+
Na+
K+ K+
CLOSED
DepolarizationRepolarization
Hyperpolarization
CLOSED
Return to RMP (-70mV)
Outside Neuron - Extracellular Fluid
Inside Neuron - Cytosol
Resting Membrane Potential
Outside of Neuron – Extra Cellular Fluid (ECF)
Inside of Neuron - CytosolProteins (-)
Resting Membrane Potential = The difference in the distribution of charged particles (ions) between the inside and the outside of the cell (mV)
In neurons, the resting membrane potential is normally around -70mV
- this means that the inside of the neuron is more negative relative to the outside of the neuron.
Plasma Membrane
Sodium
Na+
Potassium
K+
ChlorideCl-
Phosphate
P-
What factors contribute to the resting membrane potential?
1. Unequal distribution of ions2. Leakage channels and the inability of most
anions to leave the cell3. Na+/K+ ATPases
Plasma Membrane
1. Unequal distribution of ions:
Outside of Neuron
Inside of Neuron
The Extracellular fluid (ECF) is naturally rich in Na+ and Cl-
The cytosol (inside the cell) is rich in K+ and anions (negatively charged molecules)
Outside of Neuron
Inside of Neuron
Plasma Membrane
Na+
Na+
Na+
Na+
Na+
Na+
Na+ Na+
Na+
Na+Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
K+K+ K+
K+
K+
K+
K+
K+
K+
K+
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
P- P-P-
P-P-P-
Proteins (-)
Proteins (-)Proteins (-)
This unequal distribution of ions and large, negatively charged molecules naturally makes the inside of the neuron more negative relative to the outside
Plasma Membrane
2. Leakage Channels: passive diffusion
Outside of Neuron
Inside of Neuron
K+Na+
Na+ Na+
Na+Na+
K+
K+
K+
K+
K+K+
K+K+
K+
Na+
Na+
Na+
Proteins (-)
Since there are more Potassium (K+) channels leaking positive ions out then there are Sodium (Na+) channels leaking positive ions in, and because the large negatively charged molecules can’t escape, this helps to keep the inside of the neuron more negative relative to the outside.
3. Na+/K+ ATPases
Outside of Neuron
Inside of Neuron
Na+/K+ ATPase
Na+
Na+
Na+ Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+K+
K+
K+
K+K+
K+K+
K+
K+
Na+Na+
Na+
ATPADP +
Na+ Na+
Na+
K+K+
Na+
Na+
Na+
ATPADP + P-
K+K+
P-
These three factors:1. Unequal distribution of ions2. Leakage channels and the inability of
most anions to leave the cell3. Na+/K+ ATPases
combine to maintain the neuron’s resting membrane potential at -70 mV, where the inside is negative relative to the outside.
Chemical Synapse
Calcium Ions (Ca2+)
Action potential arrives at terminal end bulb.
Voltage-gated Calcium channels open and Ca2+
rushes in.
Post synaptic neuron
Sodium Ions (Na+)
Synaptic vesicles migrate and fuse with membrane – releasing ACh into synaptic cleft.
Acetylcholine (Ach)
Synaptic vesicles migrate and fuse with membrane – releasing ACh into synaptic cleft.
Action potential arrives at terminal end bulb.
Voltage-gated Calcium channels open and Ca2+
rushes in.
Post synaptic Neuron
ACh binds to ligand-gated Na+ channels allowing Na+ to enter the post synaptic neuron.
Calcium Ions (Ca2+)
Sodium Ions (Na+)
Acetylcholine (Ach)
Graded Potential
This generates a graded potential, which travels down the dendrite.
![Inward rectifying currents stabilize the membrane ... · distal dendrites [20,21], where I (H) shortens the decay time course of excitatory post-synaptic potentials (EPSP) and af-fects](https://img.pdfslide.net/doc/110x75/608f3d31a48d4839c2485827/inward-rectifying-currents-stabilize-the-membrane-distal-dendrites-2021.jpg)
