Week 3 Flashcards
MP
difference in electrical charge between the inside and outside of a cell
neuron resting potential
Potential inside the resting neuron is about 70mV less than that outside the neuron
Neuron’s resting potential is -70mV, and is polarised
there is pressure for Na+ to enter the neuron
Electrostatic pressure from RMP, the -70mV inside attract the Na+ outside
Random motion of Na+ down conc gradient
generation and conduction of PSPs
When neurotransmitters bind to postsynaptic receptors they may:
Depolarisations AKA EPSPs: increase likelihood that neuron will fire
Hyperpolarisations AKA IPSPs: decrease likelihood that neuron will fire
Both are graded: amplitudes of EPSPs and IPSPs proportional to intensity of the signals that elicit them
Transmission of postsynaptic potentials is rapid and decremental (decrease in amplitude as they travel along neuron)
integration of PSPs and APs
Whether a neuron fires depends on the balance between the excitatory and inhibitory signals reaching its axon
APs generated at axon initial segment
EPSPs and IPSPs are conducted to axon initial segment, if the depolarisations and hyperpolarisations are sufficient to depolarise the membrane to a level of threshold of excitation (-65mV), an AP is generated
AP is a massive but momentary reversal of MP from -70 to +50mV
AP are not graded, rather all-or-none
spatial summation
how local EPSPs and IPSPs produced simultaneously affect each other
temporal summation
sum of the postsynaptic potentials produced in rapid succession at the same synapse to form a greater signal
ionic basis of APs
When the MP of the axon is depolarised to the threshold of excitation by EPSP, voltage activated Na+ channels in axon membrane open and Na+ rush in, driving MP from -70mV to 50mV
Influx of Na+ triggers opening of voltage activated K+ channels
K+ driven out first by high concentration gradient and then when AP is near peak, by positive internal charge
After about 1milisecond, Na+ channels close- marking the end of the rising phase and beginning the repolarisation by continued efflux of K+
Once repolarisation has been achieved, K+ channels close
Because they close too gradually, too many K+ leave and neuron is left hyper polarised for brief time
AP involves only ions close to membrane, so AP has little effect on most ions in and outside the neuron
absolute rp
1-2ms after initiation of an AP where it is impossible to elicit a second one
relative rp
possible to fire neuron again but only by applying higher-than-normal levels of stimulation
AP conduction
One AP is activated, travels passively to Na+ channels which opens them, then conducted passively to next Na+ channels, where another AP is triggered and repeated
Wave of excitation triggered by generation of an AP near the axon hillock always spreads passively back through cell body and dendrites
antidromic conduction
if electrical stimulation of sufficient intensity is applied to the terminal end of an axon, an AP will be generated and will travel along the axon back to cell body
orthodromic conduction
axonal conduction in natural direction
axonal conduction in myelinated neurons
In myelinated axons, ions can pass through axonal membrane only at nodes of Ranvier
When an AP is generated, signal is conducted passively (instantly and decremental) along first myelin segment to next node of Ranvier
Signal is diminished but still strong enough to open the voltage activated sodium channels at the node and generate another full blown AP
Then repeated along
Called saltatory conduction
Faster than in unmyelinated
the hodgkin-huxley model in perspective
Based on study of squid motor neurons- difficult to apply to mammalian brain
Used because they are very large
Motor neurons used rather than cerebral neurons
Cerebral neurons fire continually even when no input
Axons can actively conduct both graded signals and APs
APs of different classes of cerebral neurons vary greatly in duration, aptitude and frequency
Many do not display Ads
Dendrites of some cerebral neurons can actively conduct APs
axodendritic synapse
synapses of axon terminal buttons on dendrites
axosomatic synapse
synapses of axon terminal buttons on somas
dendrodendritic synapse
capable of bidirectional transmission
axoaxonic synapse
mediate presynaptic facilitation and inhibition
directed synapse
synapses at which the site of neurotransmitter release and site of neurotransmitter reception are in close proximity
non directed synapse
synapses at which site of release is at some distance from site of reception
Neurotransmitters released from varicosities and dispersed to surrounding target (string of beads synapses)
