Does it matter which ions flow into the cell?

Sodium (Na+) Calcium (Ca2+) Chloride (Cl-)

Positive Positive Negative

Opening Voltage-Gated Na+ Channels

Inhibitory Postsynaptic potentials (IPSP) caused by entry of negative ions

Threshold – Voltage at which Na+ channels open

Excitatory Postsynaptic potentials (EPSP) caused by entry of positive ions

Excitatory and Inhibitory SynapsesExcitatory Synapse:Neurotransmitters open Na+ channels producing EPSPs.

Inhibitory Synapse:Neurotransmitters open Cl- channels producing IPSPs.

Axon hillock reaches threshold and action potential is fired.

IPSPs encounter EPSPs. Threshold is not reached and no action potential is fired.

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But why would you ever want to prevent an action potential from firing?

Getting Pain to the Brain

First Pain Synapse:Pain Receptors

Second Pain Synapse:Spinal Cord

Third Pain Synapse:Cerebral Cortex

Why do we instinctively apply pressure to something that is painful?

Projection Neuron

Interneuron

Pressure neuron

Pain neuron

Build the Circuit in the Spinal Cord

To the Brain

Interneuron

Projection neuron

To Brain

Build the Circuit in the Spinal Cord

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Pain neuron

Projection neuron

To BrainInterneuron

Add the Pain Neuron

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Pain neuron

Pressure neuron

Projection neuron

To BrainInterneuron

Add the Pressure Neuron

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+ X PainPain

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