Introduction to the neurone L3 Flashcards
why is a graded response important>
if only gNa and gk are present
the cell either does not fire or fires very rapidly…
2 extremes - not good. need more gradual
in a neurone cel body is there a graded AP response to injected current
yep
what does the A current do in APs
the A current serves to space out the action potentials in the spike train.
when does bursting occur
depolarisation activates low threshold calcium cahnnels
can yo upicture cortical pyramidal cell bursting and thlamic relay bursting?
different calcium cahnnels i nneurones
what mediates repolarisation of the membrane after Ca2+ mediated burst firing
Action potential firing is also modulated by Ca2+-activated K+ channels. These open when Ca2+ enters through voltage-gated Ca2+ channels, and contribute an outward K+ current which opposes the depolarization and hyperpolarizes the cell.
describe spike frequency adaptation
irnore hand writing
howdo olfactory receptors cope with prolongued stimulation
describe divergence
Each IA afferent will synapse with a number of motor neurons: a process known as divergence.
descibe convergence
is it necessary inthe reflex?
Similarly, each motor neuron will receive synaptic inputs from a number of IA afferents: a process known as convergence.
describe supralinear response summation
describe response occusion
Inhibitory interneurons can be deployed within the spinal cord in two functionally distinct ways.
what are they
feedforward and feedback inhibition
describe feedforward inhibition
In feedforward inhibition, the pathway to the antagonist is inhibited when the agonist pathway is stimulated. This inhibits extensor muscles when flexors are stimulated.
descibe feedback inhibiton
In feedback inhibition the excited cell contacts an inhibitory interneuron via recurrent axon collaterals to inhibit its own firing and that of its synergists. An example is provided by the Renshaw cell of the spinal cord, which stabilises motor neuron firing.
repeated stimulaion of a synapse - what happens?
vescile depletion
synaptic depression ensues, representing a depletion of the readily-releasable vesicle pool.
After the cessation of tetanic stimulation, once the synapse has recovered from depression, the post-synaptic response is transiently _______, reflecting the actions of Ca2+ on vesicle priming. This post-tetanic potentiation can persist for some minutes after repeated stimulation.
After the cessation of tetanic stimulation, once the synapse has recovered from depression, the post-synaptic response is transiently enhanced, reflecting the actions of Ca2+ on vesicle priming. This post-tetanic potentiation can persist for some minutes after repeated stimulation.
describe long term potentiation
However, if both weak and strong inputs are tetanically stimulated together, then the EPSPs evoked by both inputs persistently increase, corresponding to associative long-term potentiation.
label LTP diagram
whats hebbs law:
This potentiation (LTP) obeys Hebb’s law, which states that an input is strengthened when it plays a role in firing the target cell: exactly what is required for learning.
for LTP - t or F
Only when the postsynaptic cell is allowed to depolarise during presynaptic stimulation does long term potentiation take place.
T
hebbian behaviour arises from the rpoperties of which receptor?
the NMDA receptor
NMDA ca2+ admittance when depolarised
LTP may underlie learning
memory
In many central neurons, excitatory inputs are often located ….where?……., which are believed to isolate the postsynaptic machinery both electrically and chemically from events elsewhere within the cell. The high neck resistance of many spines will, however, somewhat attenuate the excitatory current which flows into the dendrite.
In many central neurons, excitatory inputs are often located on dendritic spines, which are believed to isolate the postsynaptic machinery both electrically and chemically from events elsewhere within the cell. The high neck resistance of many spines will, however, somewhat attenuate the excitatory current which flows into the dendrite.
the necks of dendrites have a high or low resistance?
high resistance
how might spine morphological changes underlie memory and LTP?
Changes in the spine shape and biochemistry may underlie learning and memory. Immature small spines undergo cytoskeletal changes upon potentiation which lead to rapid spine enlargement followed by enlargement of the post-synaptic density upon consolidation.
altering resistance to flow - ect
spines may get bigger too!
can potentiation also occur presynapticaly?
yes!
in area CA3 of the hippocampus, LTP does not appear to require the special properties of the NMDA receptor. Instead, potentiation is believed to take place presynaptically, and involve the activation of adenylyl cyclase and protein kinase A subsequent to calcium entry via R-type calcium channels.
describe LTD
long term depression
If, instead, pyramidal cells in CA1 are stimulated at low frequencies which fail to make the target cells fire, a long-term depression of synaptic strength can result.
The first directly antagonises LTP by activation of protein phosphatases following entry of calcium through NMDA receptor channels more modest than that required to evoke LTP. NMDA receptor-dependent LTD appears to be a widespread feature of synapses within the neocortex. The second is initiated by metabotropic glutamate receptors acting via protein kinase C; it does not directly reverse LTP, but many of the details are still poorly understood; mGluR-dependent LTD may be especially important for motor learning in the cerebellum.
fat
mamba
