Inhibitory and Excitatory Signals

1. Inhibitory and Excitatory Signals

2. Excitatory Potentials • Excitatory postsynaptic potential (EPSP) occurs when membrane potential goes toward threshold (becomes more depolarized). • ACh and Glutamate gated ion channels are excitatory. • Typically, these neurotransmitter-gated channels are permeable to sodium (Na+) and potassium (K+).

3. Inhibitory Potentials • Inhibitory postsynaptic potential (IPSP) occurs when membrane potential goes toward threshold (becomes more depolarized). • GABA and Glycine gated ion channels are inhibitory. • Typically, an inhibitory neurotransmitter-gated channel is permeable to an anion such as chloride (Cl-).

4. Synaptic Integration • An individual synapse, by itself, cannot generate an action potential in a receiving neuron. • Many EPSP’s add together to produce enough depolarization to cross the threshold and generate an action potential • Two kinds of summation: • Spatial • Temporal

5. Shunting Inhibition • Dendritic length constant determines how far along the dendrite an excitatory current will travel. • Inhibitory synapses located at the soma can prevent an EPSP from reaching the axon hillock. • Inhibitory input occurs only when the inhibitory neuron has an action potential and releases neurotransmitter to inhibitory ion channels.

6. Kinds of Receptors • All neurotransmitters bind and act at more than one kind of receptor. • Two main kinds of receptors: • Ion channel receptors • G-protein-coupled receptors

7. G-Protein-Coupled Receptors • Change the excitability of the neuron in two ways: • Change calcium ion levels (releasing neurotransmitter). • Activate intra-cellular second messengers: • Signal amplification • Signaling at a distance • Cascades of activation • Long-lasting chemical changes in neuron

8. Phosphorylation • Addition of a phosphate group to the protein of an ion channel can change its functioning making it more or less likely to open. • This process is called phosphorylation. • Removal of the phosphate group by a protein phosphatase is called dephosphorylation. • This process results in modulation of the excitability of neurons.

9. Importance of Calcium • Voltage-gated calcium (Ca2) channels permit CA to enter the cell. • As Ca2 rises, it binds with the neuron, preventing additional calcium from entering. • Increased calcium concentrations can cause dephosphorylation or permanent inactivation of a channel. • Calcium signals neurotransmitter release.