Sensory 2 Flashcards
Types of synaptic potentials
1) Postsynaptic potentials
2) Presynaptic potentials
Types of postsynaptic potentials
1) EPSP
2) IPSP
3) GPSP
Types of presynaptic potentials
1) Presynaptic Inhibition
2) Presynaptic facilitation
What is EPSP?
- A local state of partial depolarization of the postsynaptic membrane.
- Produced as a result of binding of an exitatory neurotransmittrer with its receptors.
Ionic basis of EPSP
- Opening of ligand-gated Na+ (or Ca++) channels.
- Closure of Cl- channels.
EPSP on neuron potential
It makes the inside of the cell membrane less negative, thereby more excitable as it is now nearer to the firing level.
Maximum of EPSP after…
1 - 5 msec.
Types of Summation
1) Time summation
2) Space summatiom
Time Summation
One presynaptic neuron is stimulated repetitively.
Space Summation
Several presynaptic neurons are stimulated simultaneously.
What is IPSP?
- A local state of partial hyperpolarization of the post synaptic membrane.
- Produced as a result of binding of an inhibitory neurotansmitter with its receptors.
Ionic basis of IPSP
- Opening of ligand-gated Cl- channels.
- Closure of Na+ (or Ca++) channels.
IPSP on neuron potential
It makes the inside of the cell membrane more negative, thereby less excitable as it is now away from the firing level.
Maximum of IPSP after…
1 - 2 msec.
What is GPSP ?
It is the summation of all EPSPs & IPSPs occurring at the same time.
Outcomes of GPSP
- A balance of excitatory & inhibitory inputs, so the PSMP remains close to the RMP.
- If Excitatory inputs slightly > Inhibitory inputs, Excitatory state (facilitation).
- If Excitatory inputs much > Inhibitory inputs, threshold is reached an AP will be generated.
- If Inhibitory inputs > Excitatory inputs, Inhibitory state (inhibition).
Postsynaptic Potentails
- Do not obey all or none law.
- Graded.
- No absolute refractory period.
- Summated.
- Not blocked by anesthesia.
- Not propagated.
- 20 msec.
Action Potentials
- Obey all or none law.
- Can not be graded.
- Absolute refractory period.
- Can not be summated.
- Blocked by anesthesia.
- Propagated.
- 1 msec.
Lowest threshold potentail is at…
Axon Hillox
Presynaptic Inhibition
- 3rd Inhibitory neuron.
- Axo-axonic synapse.
- Excitatory Presynaptic neuron.
- Inhibitory Neurotransmitter e.g. GABA.
- Ionic basis: Openning of Cl- or K+ channels.
- Hyperpolarization ==> reduced Ca++ influx ==> reduced release of neurotransmitter ==> reduced transmission.
Presynaptic Facilitation
- 3rd Excitatory neuron.
- Axo-axonic synapse.
- Excitatory Presynaptic neuron.
- Excitatory Neurotransmitter e.g. 5-HT.
- Increases cAMPin presynaptic terminals ==> Closure of K+ channels
- Prolongated Depolarization ==> more Ca++ influx ==> more release of neurotransmitter ==> more transmission.
Characters of Synaptic transmission
1) Unidirectional
2) Synaptic delay
3) Fatigue
4) Synaptic plasticity
Unidirectionality
One way only.
From Presynaptic to Postsynaptic neuron.
Synaptic Delay
The time taken by an impulse to be conducted through the synapse.