Synapse Flashcards
What are the 2 fundamentally different functions of the neurons?
In dendrites towards the cell body and in axons away from the cell body.
What is the stem of the axon from the cell body called?
The axon hillock.
What is the potential on the inside of a neuron?
Negative 70. The resting membrane potential.
What instrument measures the potential of a neuron?
Measured using a glass electrode.
What are the properties of an action potential?
Self propagates and travels in one direction.
How are action potentials graded?
By frequency.
What is the apex of the neuron?
The axon.
Where does secretion of chemicals occur in a neuron?
At the axon terminal.
What is the base of a neuron?
The dendrites.
What are synapses?
Specilised regions of close approach between axon and another cell.
What is the axon end bulb?
The site of chemical neurotransmitter release.
What are the microtubules in the pre-synaptic membrane for?
Vesicle transport.
What is the synaptic cleft?
The gap which is after the presynaptic cell and before the postsynaptic cell.
What is a bouton?
The terminal of the presynaptic cell forms a swelling called a bouton.
How big is the synaptic gap?
20nm
How do dendrites increase surface area?
Through dendrite trees and dendritic spines.
How does the vesicles and presynaptic membrane recognise each other?
V-snare on vesicle complexes with t-snare at presynaptic membrane
What happens when the v-snare and t-snare binds?
The complex folds strongly and draws the membranes close.
What causes exocytosis of the vesicle?
Calcium induces synaptotagmin to displace complexin and exocytosis proceeds.
Where are peptide neurotransmitters made?
In the RER and packaged into vesicles in the Golgi.
Where are small molecular neurotransmitters found?
Made locally then imported into the vesicle.
What are the 2 types of receptors for NTs on the postsynaptic membrane?
Ionotropic receptors and metabotropic.
What do ionotropic receptors allow?
Fast signals.
What are metabotropic receptors?
Slow signals.
What happens when a NT binds to an ionotropic receptor?
A conformational change is induced.
Which NTs can bind to ionotropic receptors?
Ach, GABA and glutamate.
What was the opening of pores visualised by?
Cryo-electron microscopy.
What is the function of the G protein complex?
To bind GTP and hydrolyse it to GDP.
How fast is a metabotropic receptor?
100ms to minutes.
What is the initial step in the metabotropic receptor?
The receptor bind the G-protein and GTP replaces GDP.
What is the second step in the metabotropic receptor?
Active G-protein leaves and binds to the target enzyme.
What is the third step in the metabotropic receptor?
Enzyme generates the messenger and the messenger binds to the channel to open it.
What is the fourth step in the metabotropic receptor?
GDP-ase removes Pi from GTP and inactivates the G protein.
What is the penultimate step in the metabotropic receptor?
G protein leaves the enzyme and inactivates it.
What is the final step in the metabotropic receptor?
G protein is free and ready to bind to the receptor again.
What can detect the release of single vesicles?
Electrophysiology.
What have electrophysiological experiments shown?
That the release of neurotransmitters is quantal (in packets).
What does quanta relate to?
The release of contents of single vesicles at the presynaptic membrane.
What does the strength of signal correlate to?
The more vesicles released, the stronger the signal at the postsynaptic membrane.
What are postsynaptic potentials caused by?
The passage of ions through ion channels which have opened following receptor interactions.
Why would a response be called excitatory?
A net flow of positive ions into the cell depolarises the membrane and is thus called excitatory.
What is the amplitude of the signal related to?
For both inhibitory and excitatory PSPs the amplitude of the signal decreases with distance as well as time.
What are the different types of summation?
Spatial and temporal.
What is spatial summation?
Multiple neurons stimulating the same postsynaptic membrane.
What is temporal summation?
Same neuron with multiple action potentials.
What does EPSP stand for?
Excitatory postsynaptic potential.
What does IPSP stand for?
Inhibitory postsynaptic potential.
Do EPSPs propagate?
They do not actively propagate along the axon.
What can cause EPSPs?
By direct (ionotropic) or indirect (metabotropic) gating.
Why can EPSPs summate?
EPSPs have no refractory period thus a series of EPSPs can summate.
What can cause an action potential?
What can cause an action potential?
What does the strength of the PSP depend on?
Placement and excitatory or inhibitory nature of the inputs.
What determines the level of excitation?
Dendrite structure and synapse location.
What does dendritic spine morphology influence?
PSP summation.
What does PSP stand for?
Post synaptic potential.
Does dendritic spine length influence EPSP summation?
The longer the spine the lower the EPSP.
What are EPSPs and IPSPs important in?
They are passive electrical activity important for setting the axonal response.
What are the other forms of electrical activity in the dendrites?
Self propagating dendritic spikes.
What does the dendritic spike do?
Boost the depolarization in the dendrites.
When do dendritic cells occur?
Especially when stimulation is intense in space or time.
How can dendritic spikes stimulate an action potential?
They can leak into the cell body to stimulate an AP.
Do dendritic spikes act locally?
They are thought to act locally on postsynaptic membranes to generate LTP.
What is memory due to?
Strengthened synapses and making of new synapses.
What is required to reach the threshold?
Spatial and temporal summation of multiple PSPs/dendritic spikes.
What does stronger synapses result in?
Increased: NT release, sensitivity, number of receptors and size of post synaptic machinery.
What does LTP stand for?
Long term potentiation.
What is LTP associated with?
Making new synapses in vivo.
How are stronger synapses formed?
Upregulation of NT secretion and receptor expression.
How are more synapses made?
Sprouting, branching and dendritic spine formation.
What is Hebb’s learning rule about correlation?
Correlated pre and postsynaptic activities cause synapse to strengthen.
What is Hebb’s learning rule about uncorrelation?
Uncorrelated pre and postsynaptic activities cause synapse weakening.
Why could synaptic change occur?
Because of neuronal activity at critical points within a behavioral brain pathway.
What is a good example of changes in behavioral learning?
Addiction.
What could be these synaptic changes?
Increases and decreases in synaptic strength leading to behavioral plasticity.
How can drugs be addictive?
Drugs can cause massive release of dopamine in the reward centre.
What starts the behavioral changes when introduced to an addictive drug?
Synaptic plasticity in glutaminergic synapses.
What is the reward centre?
The nucleus accumbens.
What are the types of inhibition in multi-neuron networks?
Lateral inhibition, feedforward inhibition, feedback inhibition.
What are the types of excitation in multi-neuron networks?
Feedforward and feedback/recurrent.
What start the knee jerk reflex?
By tapping the tendon connected to the quadricep which stretches the muscle.
Describe pyramidal cell firing.
It is under strict time control to prevent run away excitation.
How are the pyramidal cells inhibited?
Done by feedforward and feedback inhibition.
What do inhibitory microcircuits involve?
Interneurons and short axons.
What are the properties of inhibitory microcircuits?
Fast acting and inhibition is mostly by GABA.
Where are central pattern generators?
In the spinal cord.
What are the central pattern generators used in?
Communication in white matter in spinal cord.
What is an example of central pattern generators?
Alternating rhythms for walking generated in the spinal cord.
What is an example of inhibitory interneurons for pain?
Stimulation of touch can help to block transmission of pain impulses to the brain.
How can touch decrease pain?
Touch fibres stimulate inhibitory interneurons to decrease activity in axons of pain fibres.
What affects the degree of convergence?
The more dendrites a neuron has, the higher the degree of convergence.
What are examples of neuronal convergence in a circuit?
Pyramidal cells and Purkinje fibres.
What are pyramidal cells?
A type of multipolar neuron found in areas of the brain.
Where in the brain are pyramidal cells found?
The cerebral cortex, hippocampus and amygdala.
What is neuronal divergence?
Information from a single neuron is passed to a number of other neurons simultaneously.
How is sensory information diverged?
Sensory information arriving at the somatosensory cortex can be diverged widely through the cortex.
