Inhibitory or excitatory synapses

Excitatory function*:* When a neurotransmitter increases the likelihood that the neuron will fire an action potential.  This depends on the receptor site.  Many neurotransmitters are excitatory when they act on some receptor sites, and inhibitory when they act on others. For example, serotonin is an excitatory neurotransmitter that regulates sleep and wakefulness and is found in neurons in the pons and upper brain stem -  but it is inhibitory in mood and emotion.

Inhibitory function*:* When a neurotransmitter decreases the likelihood that the neuron will fire an action potential.  This depends on the receptor site.  Many neurotransmitters are inhibitory when they act on some receptor sites, and excitatory when they act on others. For example, serotonin is an inhibitory neurotransmitter when it is involved in emotion and mood, but excitatory in sleep and wakefulness.

Neurotransmitters play an important role in human behaviour.  Neurotransmitters are released from the terminal buttons of a neuron and then travel across a synapse where they attach to receptor sites on the postsynaptic membrane. Some neurotransmitters are seen as more inhibitory - that is, they make the target neuron less likely to "fire" an action potential. A neurotransmitter can sometimes have either an excitatory or an inhibitory effect, depending on the receptor sites that it binds to.

One example of how a neurotransmitter binds to inhibitory receptor sites is the role of Acetylcholine in memory formation.

Antonova

Aim: To determine how blocking the acetylcholine receptors with scopolamine affects spatial memory

Procedure: 20 healthy male adults. double-blind. 2 conditions. Injected with either scopolamine or a placebo 70-90 min before the experimental task. participants were put into fMRI scan while playing "Arena task". Participants were first trained in game so they knew the rules. After training, the participants' brain activity was measured for 6 trials. Participants returned 3-4 weeks later and redid the test with opposite treatment to original study. (Arena task: complex virtual reality game, goal is to navigate around an "arena" with goal of reaching a pole. After learning where pole is, screen goes blank for 30 s. during time participants were asked to rehearse how to get to the pole in the arena. When the arena reappeared, the participant was at a new starting point. Had to use spatial memory to determine how to get to the location of the pole.)

Findings: The researchers found that when participants were injected with sopolamine, they demonstrated a significant reduction in the activation of the hippocampus compared to when they received a placebo. This suggests that scopolamine impairs memorization of new information by decreasing spiking activity within the hippocampus.bg