Effects of Excitatory and Inhibitory Potentials on Action Potentials Amelia Lindgren

Overview of A Neuron Found in brain, spinal cord and nervous system Found in brain, spinal cord and nervous system Electrically excitable Electrically excitable Communicate via electrical and chemical synapses Communicate via electrical and chemical synapses Made up of a soma (cell body), dendritic tree and an axon Made up of a soma (cell body), dendritic tree and an axon

Axon Properties Where action potential is propagated Where action potential is propagated Contains voltage gated sodium and potassium channels Contains voltage gated sodium and potassium channels Contains leak channels (Cl - channels and passive K + channels) Contains leak channels (Cl - channels and passive K + channels) Resting membrane potential: ~ -67 mV Resting membrane potential: ~ -67 mV

Action Potential Occurs when membrane potential exceeds the threshold potential Occurs when membrane potential exceeds the threshold potential Occurs when Na+ channels are activated (influx of Na + ) Occurs when Na+ channels are activated (influx of Na + ) Causes positive slope of action potential Causes positive slope of action potential K+ channels open slightly later (efflux of K +) K+ channels open slightly later (efflux of K +) Causes downward slope of action potential Causes downward slope of action potential

Action Potential Cont. To achieve an action potential To achieve an action potential Pre-synaptic cell action potential releases Ca 2+ in the axon terminal Pre-synaptic cell action potential releases Ca 2+ in the axon terminal Axon terminal releases vesicles filled with neurotransmitters Axon terminal releases vesicles filled with neurotransmitters Inhibit or help create an action potential Inhibit or help create an action potential Excitatory Neurotransmitters: Excitatory Neurotransmitters: Acetylcholine Acetylcholine glutamate glutamate Inhibitory Neurotransmitters: Inhibitory Neurotransmitters: GABA GABA glycine glycine

Post Synaptic Potentials Excitatory Post Synaptic Potentials (EPSP) Excitatory Post Synaptic Potentials (EPSP) Creates positive synaptic potential Creates positive synaptic potential Positive charged ions flow in Positive charged ions flow in Allows Na + into cell Allows Na + into cell Easier for Action Potential to fire Easier for Action Potential to fire Inhibitory Post Synaptic Potentials (IPSP) Inhibitory Post Synaptic Potentials (IPSP) Decreases the potential of the membrane Increases permeability of K + K + flows out of cell Decreases the chances of an action potential

Ways to Achieve Action Potential Temporal Summation Temporal Summation One neuron acting on another One neuron acting on another Potential starts before the previous one ends Potential starts before the previous one ends Amplitudes of potentials summate to create larger potential Amplitudes of potentials summate to create larger potential Spatial Summation Spatial Summation Multiple cells provide input Input is received in different areas Input is summated to create a larger potential

Hodgkin-Huxley Model of Action Potential + I app

Parameters of Neuron α m =0.1(25-v)/ (e (25-v)/10 -1) α m =0.1(25-v)/ (e (25-v)/10 -1) α h = 0.07e -v/20 α h = 0.07e -v/20 α n = 0.01(10-v)/(e (10-v)/10 -1) α n = 0.01(10-v)/(e (10-v)/10 -1) β m = 4e -v/18 β m = 4e -v/18 β h =1/(e (30-v)/10 +1) β h =1/(e (30-v)/10 +1) β n =0.125e -v/80 β n =0.125e -v/80 g Na =120 g Na =120 g K =36 g K =36 g L =0.3 g L =0.3 v Na =115 v Na =115 v K =-12 v K =-12 v L =10.6 v L =10.6

Stimulation of 9 μA Key: ▀ = membrane potential (mV) ▀ = stimulus current ( μA) ▀ =m(v) ▀ = n(v) ▀ =h(v)

Stimulation of 5 μA Key: ▀ = membrane potential (mV) ▀ = stimulus current (μA) ▀ =m(v) ▀ = n(v) ▀ =h(v)

Stimulation of 3.7 μA Key: ▀ = membrane potential (mV) ▀ = stimulus current (μA) ▀ =m(v) ▀ = n(v) ▀ =h(v)

Stimulation of 3.6 μA Key: ▀ = membrane potential (mV) ▀ = stimulus current (μA) ▀ =m(v) ▀ = n(v) ▀ =h(v)

Threshold potential At 3.7 μA an action potential occurs At 3.7 μA an action potential occurs at 3.6 μA one does not at 3.6 μA one does not threshold value is in between threshold value is in between Threshold potential is typically around - 55mV Threshold potential is typically around - 55mV

Successive Stimulations of 6 μA at t=0 ms and t=10 Key: ▀ = membrane potential (mV) ▀ = stimulus current (μA) ▀ =m(v) ▀ = n(v) ▀ =h(v)

Sequential Stimulation of 6 μA at t=5 ms and 7 μA at t=10 ms Key: ▀ = membrane potential (mV) ▀ = stimulus current (μA) ▀ =m(v) ▀ = n(v) ▀ =h(v)

Temporal Summation Stimulation of 2.5 μA at t=0 ms and 2.5 μA at t=.6ms Key: ▀ = membrane potential (mV) ▀ = stimulus current (μA) ▀ =m(v) ▀ = n(v) ▀ =h(v)

Temporal Stimulation of 2 μA and 1 μA Key: ▀ = membrane potential (mV) ▀ = stimulus current (μA) ▀ =m(v) ▀ = n(v) ▀ =h(v)

Spatial Summation Stimulation of 8 μA and -3 μA Key: ▀ = membrane potential (mV) ▀ = stimulus current (μA) ▀ =m(v) ▀ = n(v) ▀ =h(v)

Spatial Summation of Stimulation of 5 μA and -4 μA Key: ▀ = membrane potential (mV) ▀ = stimulus current (μA) ▀ =m(v) ▀ = n(v) ▀ =h(v)

Observations Increasing the intensity does not increase the size of the action potential Increasing the intensity does not increase the size of the action potential Action potential is “all or none” response Action potential is “all or none” response Potentials can summate to elicit or inhibit and action potential Potentials can summate to elicit or inhibit and action potential Must reach a specific threshold potential to create and action potential that will be propagated Must reach a specific threshold potential to create and action potential that will be propagated

Conclusion Many different ways to elicit an action potential or to inhibit one Many different ways to elicit an action potential or to inhibit one Temporal and Spatial Summation allow for greater complexity in neural networks Temporal and Spatial Summation allow for greater complexity in neural networks This allows for greater complexity in organisms This allows for greater complexity in organisms neuron can communicate with multiple neurons > greater efficiency. neuron can communicate with multiple neurons > greater efficiency.