| What are the key features of a typical neuron? | Dendrites.
Soma (cell body).
Axon (inside myelin sheath).
Terminal buttons.
Messages travel from soma/dendrites to terminal buttons via axon. |
| How do neurons in a network connect to one another? | Terminal buttons on one neuron connect to another neuron's synapses on the soma or dendrites. |
| What is an action potential? | When a neuron fires.
"Action potential" refers to the rapid change in the membrane potential of the neuron caused by a movement of ions. |
| What is an action potential caused by? | Changes in flow of charged molecules (ions) across the neuron's cell membrane. |
| Describe the process of action potentials occurring. | Stimulus occurs.
Membrane potential reaches -50mV and action potential is triggered.
Depolarisation:
Na+ channels open, Na+ begins to enter cell.
K+ channels open, K+ begins to leave cell.
Na+ channels become refractory, no more Na+ enters cell.
Repolarisation:
K+ continues to leave cell, causes membrane potential to return to resting level.
K+ channels close, Na+ channels reset.
Hyperpolarisation:
Extra K+ outside become more -ve diffuse away. |
| What are the voltage levels which occur in action potentials in order? | -70mV - resting potential (membrane potential is polarised).
-50mV - potential at which action potential occurs.
+40mV - potential at which the peak of the action potential occurs. |
| Why are action potentials able to occur fast? | As ions are only able to flow in and out across the neuron membrane in the gaps between the myelin. |
| What is the rate law of action potentials? | Neuron firing is "all or none" so frequency of firing determines the strength of the neural signal.
Strong stimulus > leads to faster threshold for activation > more frequent action potentials |
| How many synapses are there in the brain? | 1,000,000 billion. |
| What do synapses do? | Enable communications between neurons. |
| What are the key structural details of synapses? | Terminal button.
Synaptic cleft.
Pre & post synaptic membrane.
Synaptic vesicles.
Microtubles. |
| What are neurotransmitters? | Chemicals that are synthesised within the brains/neurons.
Often referred to as "chemical messengers".
(The action potential stops at the end of an axon so the presynaptic neuron can only influence the post-synaptic neuron through the release of neurotransmitters across the synapse.) |
| What is the process of neurotransmitters crossing the synapse? | 1. An action potential in the pre-synaptic cell triggers synaptic vesicles to move towards the cell membrane.
2. This is followed by a fusion of the two membranes.
3. Neurotransmitter molecules are then released.
4. Neurotransmitter then flows into the synaptic cleft where it is available to bind to receptors on the post-synaptic membrane. |
| Describe neurotransmitter release. | When a synaptic vesicle merges with the presynaptic membrane, the contents are released into the synaptic cleft.
Referred to as "kiss & run". |
| Describe neurotransmitter reuptake. | The synapse has the capacity to recycle and reuse neurotransmitter molecules after they have been released.
This is a process of reabsorption into the synapse - endocytosis. |
| What do exictatory postsynaptic potentials (EPSPs) do? | Depolarise the postsynaptic cell membrane. |
| What do EPSPs increase the likelihood of? | Increase the likelihood that an action potential will be triggered in the postsynaptic neuron. |
| What is the primary exictatory neurotransmitter called? | Glutamate. |
| What do inhibitory postsynaptic potentials (IPSPs) do? | Hyperpolarise the postsynaptic cell membrane. |
| What do IPSPs decrease the likelihood of? | Decrease the likelihood that an action potential will be triggered. |
| What is the primary inhibitory neurotransmitter called? | Gamma aminobutyric acid (GABA). |
| What is the combined effect of EPSPs and IPSPs called? | Neural integration.
A neuron will only fire if the sum of the excitatory inputs is sufficiently greater than the inhibitory inputs to cause the membrane potential to pass the threshold of activation. |
| What are some of the key neuromodulators? | Dopamine.
Noradrenaline.
Histamine.
Serotonin. |
| How is the chemical message received on a post-synaptic neuron? | To cause an effect on the post-synaptic neuron, the chemical message must be "received" by attaching to the binding site of a receptor sensitive to that neurotransmitter.
E.g. opening an ion channel. |
| Why are receptors thought to be very selective? | Lock and key theory.
Each receptor can generally only be activated by one neurotransmitter (or a drug that is designed to mimic that neurotransmitter).
Each receptor also has a very specific function/action.
When a neurotransmitter binds to the receptor, this will trigger the same event every time. |
| What is the action of drugs at receptors? | Drugs work by mimicking the chemical structure of the natural compound (perfectly or partially).
Can act as agonists activating the receptor like the natural compound.
Or can act as an antagonist blocking the receptor and preventing the natural compound from activating it. |
| What are agonistic drug effects? | Drug increases the synthesis of neurotransmitter molecules.
Drug increases the release of neurotransmitter molecules from terminal buttons.
Drug binds to postsynaptic receptors and either activates them or increases the effect of neurotransmitter molecules. |
| What are antagonistic drug effects? | Drug blocks the synthesis of neurotransmitter molecules.
Drug blocks the release of neurotransmitter molecules from terminal buttons.
Drug binds to postsynaptic receptors and blocks the effect of neurotransmitter molecules. |
| Why do drugs impact psychological processes? | Drugs impact psychological processes ONLY because they mimic/trigger the same biological responses triggered nby naturally occurring substances (neurotransmitters, hormones, etc). |
