Week 4 Flashcards
What are the two most important types of ionotropic glutamate receptors? What are the key differences in their properties (inc. time length of current)?
AMPA
- K+ and Na+ permeable
- 5pS
- 1ms
NMDA
- is voltage dependent, because Mg2+ is likely to block the channel at lower voltages.
- Permeable to Ca2+ as well.
- 50pS
- 100ms
How does glutamate move around in a synaptic cleft?
It is expelled out at 1mM for about 1ms. It may bind with and open ionotropic glutamatergic receptors
Explain why EPSPs decay slower than EPSCs
Because of time constant of cell membrane due to membrane capacitance. EPSPs will decay over ~20ms.
Why does the time-course of an EPSP differ in dendrites compared to the soma?
Due to cable properties. Dendrites have a higher resistance and low capacitance. EPSPs are LARGE and FAST in the dendrites. But it will grow smaller and slower on its way to soma due to cable properties.
What is the calyx of held?
When dendrite fully surrounds a bouton, such that NT release at the bouton will almost definitely lead to AP.
Otherwise, the actual proportion of EPSPs which lead to APs is low because a unitary EPSP ~= 2-5mV and so is unlikely to push the -70mV resting potential above the necessary activation threshold.
What is a barrel in the neocortex?
Corresponds to a 1mm thick column from top to bottom of neocortex. Composed of layers L1-L6, pyramidal cells.
What is the pathway from whisker sensation to cognition?
Whisker -> Mechano-gated ion channels -> trigeminal nerve -> brain stem -> thalamus -> neocortex (primary somatosensory cortex)
What is LTP?
- Unlike short-term, long-term potentiation can also occur in the POST-synaptic density
- ## Instigated by pairing of AP firing with EPSP input, required by unblocking NMDA, increasing Ca2+, etc… eg. high frequency stimulation of many axons, or depolarising current injection. It all leads to conductance of the AMPAR at the synapse and/or in the insertion of more AMPAR at the synapse.
How do glutamate receptors get to the synapse?
AMPA receptor (AMPAR) insertion happens via the membrane fusion
between vesicles and cell membrane (exocytosis). Once inserted,
AMPARs diffuse in the membrane around the synapse. Some AMPARs
are tightly bound by the postsynaptic density (PSD) where they are more
likely to bind glutamate when it is released.
What is LTD?
- Long-term depression.
- Unlike short-term, long-term potentiation occurs in the POST-synaptic density
- Caused by repetitive low frequency (1Hz) stimulation of many axons, or injecting weak depolarising current
- these must activate NMDAR and protein phosphatases which removes proteins, as opposed to kinase which adds
- one protein phosphatase is CALCINEURIN, which dephosphorylates and ultimately removes AMPA receptors
What is STDP?
Spike Timing-Dependent Plasticity
- If EPSPs regularly occur right before APs, then future EPSPs which are not succeeded by APs will have an increased amplitude. Conversely true for EPSPs right AFTER APs.
What are the measurements of a dendritic spine?
~1um
The connection to the dendrite is 100-200nm
What purposes might dendritic spines serve?
Huge resistance at base of spine meaning biochemical reactions can occur in isolation (eg calcium concentrations can occur in isolation).
The spine neck also offers a very high electrical resistance allowing larger and longer-lasting EPSPs
Actin filament is what forms and can relocate spines is associated with the phenomenon of learning.
What is a typical amplitude and duration of an EPSP measured at the soma and evoked by a single action potential in a single presynaptic neuron?
1mV; 10ms
What are the reversal potentials of AMPA, NMDA?
Both 0mV
