Neurotransmitters and Their Effect on Behaviour

Neurotransmitters

Neuron Structure and Function

• Neurons receive information from other neurons through their dendrites.
• They transmit information via electrical impulses across the cell body and along the axon.
• The synapse is the gap between two neurons where communication occurs.

The Nervous System

• The nervous system plays a critical role in human behaviour.
• It's an electro-chemical system affecting both physiology and psychology.
• Understanding the structure of the nervous system is essential.

Neurotransmission

• Biologists propose that most behaviour has an electrochemical origin.
• Information travels through neural networks by stimulating the dendrites of a neuron.
• The neuron is polarized, sending an electrical charge to the terminal buttons.
• Terminal buttons release neurotransmitters across the synapse, known as synaptic transmission.
• Neurotransmitters attach to the dendrites of another neuron, influencing behaviour.

Synaptic Transmission Details

• Once the action potential reaches the end of the neuron, neurotransmitters are released from the terminal buttons.
• Neurotransmitter molecules have specific shapes that fit into receptor sites on dendritic branches, similar to a "lock and key" mechanism.
• After release, the terminal buttons either release enzymes to "clean up" the synapse (e.g., acetylcholinesterase breaking down acetylcholine) or undergo re-uptake, where the neurotransmitter is soaked back up.

Drugs and Neurotransmitters

• Drugs affect neurotransmission, altering neurotransmitter levels in the brain.
• This results in various sensations and behaviour changes.
• Example: Alcohol increases dopamine levels in the nucleus accumbens (reward pathway), leading to feelings of pleasure.

Excitatory and Inhibitory Synapses

• Neurotransmitters or drugs can be excitatory (activating the neuron) or inhibitory (preventing the neuron from firing).

Agonists

• Agonists are chemical messengers that bind to neuron receptor sites and activate them, creating a response.
• Drugs can act as agonists for specific neurotransmitter sites.
• Neurotransmitters like serotonin are endogenous agonists, occurring naturally in the brain.
• Agonists bind to receptor sites and mimic the signal of a neurotransmitter.

Antagonists

• Antagonists bind to receptor sites and prevent neurotransmitters from binding and sending a signal.
• This is similar to a "lock-and-key" mechanism, where the antagonist blocks the neurotransmitter.
• Example: Ketamine is an antagonist of glutamate receptor sites, blocking glutamate and potentially helping to treat depression by reducing glutamate transmission in key brain areas.

Communication Between Neurons

• Communication between neurons is a chemical process.
• Neurons send out neurotransmitters, which are picked up by other neurons, potentially continuing the message.

Key Concepts

• Synaptic Transmission: The process by which neurons communicate via neurotransmitters across the synapse.
• Re-uptake: The process where terminal buttons "soak up" neurotransmitters from the synapse.
• Agonists: Chemicals that enhance the effect of a neurotransmitter.
• Antagonists: Chemicals that reduce the effect of a neurotransmitter.
• Excitatory Synapses: Synapses that activate a neuron.
• Inhibitory Synapses: Synapses that prevent a neuron from firing.

Relevant Studies

Rogers and Kesner (2003)

• Investigated the role of acetylcholine in memory consolidation in the hippocampus of rats.
• Showed that blocking acetylcholine receptors impaired memory formation.
• Limitations: Difficult to generalize to humans due to species differences.
• Reliability: Supported by similar findings in human studies (Antonova, 2011).
• Applications: Understanding acetylcholine's role in memory can aid in developing treatments for Alzheimer's and other memory disorders.
• Validity: High internal validity due to placebo control, but reductionistic approach to memory.

Antonova (2011)

• Investigated the effect of scopolamine (an acetylcholine antagonist) on hippocampal activity during spatial memory creation in humans.
• Participants injected with scopolamine showed reduced activation of the hippocampus while playing a virtual reality game.
• Generalizability: Low, as the sample consisted of young males.
• Reliability: High, due to similar results to Rogers and Kesner (2003) and the use of fMRI.
• Applications: Understanding acetylcholine's role in memory can aid in developing treatments for Alzheimer's and other memory disorders.
• Validity: High internal validity due to placebo control, repeated measures design, and double-blind procedure.
• Ethics: Potential ethical concern due to some participants reporting stress in the fMRI.

Key Terminology

• Presynaptic Neuron: The neuron that sends the signal.
• Postsynaptic Neuron: The neuron that receives the signal.
• Transporter Protein: Proteins involved in the re-uptake of neurotransmitters.
• Receptor Cells: Cells on the postsynaptic neuron that bind to neurotransmitters.
• Synaptic Cleft: The gap between the presynaptic and postsynaptic neurons.
• Action Potential: Electrical impulse that travels down the axon of a neuron.