Neurons Flashcards
(18 cards)
Neurotransmitters
Neurotransmitter is a chemical substance produced by a neuron that carries a message to other neurons or cells in muscles, organs or other tissue.
Binds to specific receptor sites of postsynaptic neurons that are specialised to receive that specific neurotransmitter.
Neurotransmitters that do not bind to receptors in the postsynaptic neuron is absorbed back into the terminal buttons by the presynaptic neuron in a process called reuptake.
Synaptic Gap
When neurons communicate with one another, most do so by sending neurotransmitter across the tiny space between the terminal buttons of one neuron, which release the neurotransmitter, and the dendrites of another, which receive the neurotransmitter.
This tiny space is called the synaptic gap (or synaptic cleft).
The neural synapse (or neural junction) is the site where communication typically occurs between adjacent neurons. The other two components are the terminal buttons of the presynaptic (‘sending’) neuron and the dendrites of the postsynaptic (‘receiving’) neuron.
Excitatory Effects
Some neurotransmitters have an excitatory effect and consequently stimulate or activate postsynaptic neurons to perform their functions.
Inhibitory Effects
Other neurotransmitters have an inhibitory effect and block or prevent postsynaptic neurons from firing.
Effects of Neurotransmitters
The effects of neurotransmitters are not solely dependent on the chemical itself - also due to the receptor to which it binds to
-whether a neurotransmitter is excitatory or inhibitory depends on the properties of the receptor at the synapse where it is released
Some neurons only produce one type of neurotransmitter, whereas others can create two or more and therefore contain more than one type of neurotransmitter at their axon terminals
Glutamate
-Excitatory neurotransmitter
-Enhances information transmission by making postsynaptic neurons more likely to fire
-involved in most aspects of normal brain function, including learning, memory, perception, thinking and movement
-Its excitatory effects promote the growth and strengthening of synaptic connections between neurons within a neural pathway that subsequently represents what’s been learned
Gamma-aminobutyric acid (GABA)
- Inhibitory neurotransmitter
- Works throughout the brain to make postsynaptic neurons less likely to fire (i.e. it ‘inhibits’ firing).
-One of its roles is to fine-tune neurotransmission in the brain and maintain neurotransmission at an optimal levels.
Neuromodulators
- Some neurotransmitters may influence the effects of other neurotransmitters and are therefore called neuromodulators.
For example, if a neurotransmitter has modulatory effects, it can change the reactivity of receptors to another type of neurotransmitter to enhance their excitatory or inhibitory responses.
Dopamine
Known to play a role in:
voluntary movements
the experience of pleasure
motivation
appetite
reward-based learning and memory
Parkinson’s disease
addiction
Schizophrenia
Although primarily an excitatory neurotransmitter, dopamine can have either an excitatory effect at one location or an inhibitory effect at another, depending on the type of receptors that are present.
Dopamine Pathways
Two other dopamine pathways (mesolimbic and mesocortical) associated with rewarding behaviour through the experience of pleasure. These pathways form what is commonly called the dopamine reward system.
- Behaviours that may be perceived as rewarding due to the release of dopamine include both:
healthy behaviours (such as eating when hungry and drinking when thirsty) and - harmful behaviours that involve a loss of impulse control and have become addictive (such as gambling and video gaming).
Seratonin
serotonin is a modulating neurotransmitter that has a wide range of functions, depending on where in the brain it acts.
For example, it has important roles in mood, emotional processing, sleep onset, appetite and pain perception.
Synaptic Plasticity
Refers to the ability of the synapse to change in response to experience.
Synaptic plasticity enables change involving the strengthening or weakening of connections between the neurons at a synapse.
- Strengthening may occur through continual use of synaptic connections or through the growth of new, additional connections
- Weakening may occur through disuse of synaptic connections resulting in the decay or elimination of a synapse.
Sprouting
Sprouting is the creation of new extensions on a neuron to allow it to make new connections with other neurons.
This occurs through the growth of nerve endings (‘sprouts’) on axons or dendrites, thereby enabling new links to be made, including rerouting of existing connections.
Rerouting
Rerouting occurs when new connections are made between neurons to create alternate neural pathways.
These alternate ‘routes’ may be entirely new neural pathways or connections to other pathways in the brain. The rerouting may involve the existing synaptic connections and/or new connections from the sprouts.
Pruning
Pruning is the elimination of weak, ineffective or unused synapses (and therefore connections to other neurons).
Experience determines which synapses will be retained and strengthened and which will be pruned. The synapses that are frequently used are retained and those that are not decay and disappear.
The entire process occurs as if the rule ‘use it or lose it’ is being followed.
Long-term potentiation
Long-term potentiation (LTP) refers to the long-lasting strengthening of synaptic connections, resulting in enhanced or more effective synaptic transmission.
-LTP strengthens synaptic connections in a way that enables postsynaptic neurons to be more easily activated. The postsynaptic neurons become more and more responsive to the presynaptic neurons as a consequence of repeated stimulation by neurotransmitters.
-The more that the connection is activated, the more the connection is strengthened.
-increasing the efficiency in transferring information along the pathway and decreasing the likelihood that what has been learned will be forgotten (and thereby enhancing memory storage of the information).
Changes due to LTP
- Chemical (i.e. increase in neurotransmitter production)
- Structural (i.e. synapses strengthened by an increase in synaptic vesicles – where neurotransmitters are stored at the end of the axon terminal – and dendritic sprouting which then increases the number of receptor sites)
- Functional (i.e. post-synaptic neurons become more responsive to presynaptic neurons)
Long Term Depression
long-lasting decrease in the strength of synaptic transmission (which is the opposite of LTP). This results from low levels of stimulation of pre- and postsynaptic neurons or prolonged low level stimulation.
- postsynaptic neuron becomes less responsive to the neurotransmitter released by a presynaptic neuron and the effect is to weaken the synaptic connection and therefore weaken or even silence communication at the synapse.
