Inhibitory and Excitatory Signals

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+).

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-).

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

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.

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

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

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.

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.