Neurotransmitters Flashcards
Define neurotransmission
Neurotransmission is the process of neurochemical messaging in the brain in response to external and internal stimuli
Outline the process of neurotransmission
- action potential is started, message travels down axon
- electrical impulse triggers movement of vesicles containing neurotransmitters to move to the membrane (exocytosis)
- Dendrites on post synaptic cleft have receptor sites (proteins), absorbing chemicals, which then stimulate an action potential in post synaptic neuron
- Neurotransmitters are then released from receptors. Some are re-uptaken back into the pre-s neuron through transporter proteins. Some are degraded by enzymes
- process continues down the neural network
Define excitatory and inhibitory neurotransmitters
Excitatory neurotransmitters - increase the likelihood of a neuron firing by depolarising the neuron. (eg. acetylcholine)
Inhibitary neurotransmitters - decrease the likelihood of a neuron firing by hyperpolarising the neuron. (eg. GABA)
Define agonists and antagonists
Agonists are chemicals (either endogenous or exogenous) that stimulate neurotransmission (action potential)
- all neurotransmitters are agonists
Antagonists stop neurotransmission, either blocking receptor sites, or blocking re-uptake process
- Antagonists are always exogenous
Antonova et al
Aim: Determine the role of acetylcholine in the formation of spatial memory
Participants: 20 healthy male adults, with a mean age of 28 years old.
Details:
- double-blind procedure and participants
- randomly allocation
- repeated measures design
Procedure:
- Participants were trained in the “Arena task” to ensure comfort and that rules were understood
- Participants were randomly allocated to one of the conditions - either being injected with either Scopolamine or a placebo 70 - 90 minutes before the experimental task.
- Participants underwent an fMRI scan while they were playing the “Arena task”
- complex virtual reality game (navigating around an arena to reach a pole)
- After the participants reached the pole, the screen would go blank for 30 seconds and participants were asked to rehearse how to get too the pole
- After 30 seconds, participants began in a new starting position and get back to the pole
- Activity measured for 6 trials
- Participants returned 3-4 weeks after initial experiment and exposed to other condition
Results
When participants were injected with scopolamine, there was a significant reduction in the activation of the hippocampus compared to when they received a placebo.
Conclusion
Due to the difference in hippocampal activity, it can be concluded that acetylcholine could play a key role in the encoding of spatial memories in humans.
Evaluation
- observational rather than operational
- low participant and researcher bias
- repeated measures - reduced participant variables
- time gap between 2 conditions reduces testing effect
- virtual reality - lacks ecological validity, may not be generalisable to real world
- participants were only young men, not generalisable to women or people outside age bracket
- ethnocentricity
- repeatable, therefore reliable
- participants stated they were anxious and stressed in fMRI conditions
- correlates with existing research
Rogers and kesner
Aim: Determine the role of acetylcholine in the formation and retrieval of spatial memory
- true lab exp.
Participants: 30 healthy rats
Procedure
- Acclimate (familiarise) 30 rats with a Hebb Williams maze by placing food in one of the corners, ensuring the rats are comfortable in the environment
- Randomly allocate rats to one of the 2 conditions - either injected with a saline solution or injected with scopolamine 10 minutes before running the maze directly into the hippocampus
- scopolamine blocks acetylcholine receptor sites
- Each rat runs the maze, 5 times at the beginning of the first day, 5 times at the end, and then 5 times at the beginning of a second day
- errors between day 1 first and last trials used to assess encoding
- errors between day 1 last trials and day 2 first trials used to assess retrieval
Results
Group injected with scopolamine made more errors and took longer when navigating the maze in the learning process, or day 1 trials. However, there was minimal to no difference between groups on day 2.
Conclusions
acetylcholine plays a role in the formation of new spatial memories within the hippocampus as the rats with active acetylcholine receptors were able to learn and navigate the maze more effectively. However, as there was no difference between results of groups in the retrieval stage of the experiment, it can be deduced that acetylcholine does not have a function in retrieving spatial memory.
Evaluation
- Functions as a model for human behaviour and allows further research to take place
- Can establish causation
- Repeatable, and therefore reliable
