Receptor And Synaptic Potentials Flashcards
What does the Axon hillock do?
Can convert graded EPSPs to (all or none) action potential
What does the Axon terminals do?
Axon terminals converts electrical signals (e.g., action potentials ) to chemical signals
What do Axons do?
Axon conducts action potentials to axonal terminals. Propagation of action potentials hastened with myelination and increased axonal diameter
What do dendrites do?
Dendrites convert chemical signals into graded summating postsynaptic potentials (i.e., EPSPs, IPSPs)
What is a graded potential?
- Amplitude graded- dependent on stimulus intensity
- Decay over time and distance
- Ligand gated ion channels
- Example ligsnds - neurotransmitters (e.g., acetylcholine )
What dies graded potential vary in amplitude?
- stimulus due to Ligand binding to receptor at synapse (e.g. acetylcholine)
- Occur at dendrites, soma, terminal, neuromuscular junction
- Amplitude relates to stimulus intensity
- Signal amplitude decays with from point of initiation
What is excitatory postsynaptic potentials (EPSPs)?
Input is excitatory —> depolarization of membrane potential (Vm)
What is inhibitory postsynaptic potentials (IPSPs)?
- Input is inhibitory —> no depolarization as membrane potential (Vm) pushed further from threshold
- Hyperpolarization: inhibitory neurotransmitters (e.g., GABA) can cause influx of negative ions (e.g., Cl-)
How are inputs integrated on the some/cell body?
- Summation
- EPSP/IPSP
What is summation?
When multiple signals arriving at the trigger zone are superimposed (summed)
- temporal
- spatial
What is temporal summation?
Change in frequency of stimulation (time)
Explain a temporal summation
- Single presynaptic neuron fires many times in quick succession
- Increased frequency- graded potentials sum together
- If summed graded potentials reach threshold —> generates action potential.
- Depends on passive properties (time constant) of cell membrane
What is spatial summation?
Multiple inputs at different locations on neuron (space)
- PSPs arriving at the trigger zone (axon hillock) at the same time can summate.
- Sufficient spatial summation of EPSPs can trigger action potentials
What are the series of events caused by an EPSPs and spatial summation ?
- Three excitatory neurons fire. Their graded potentials separately are all below threshold.
- Graded potentials arrive at trigger zone together and sum to create a suprathreshold signal.
- An action potential is generated
What is an action potential?
- All-or-none (I.e., present-or-absent), amplitude often less subject to modulation (I.e., largely independent of stimulus size)
- Voltage gated ion channels
List sequentially major synaptic events that move an action potential from the pre- to post-synaptic potentials
Graded potentials > threshold > action potentials
What are the Action potential (AP) features?
- All-or-none: action potentials ONLY occurs if stimulus > threshold, if not then no AP
- Stimulus magnitude: has greater impact on frequency of firing of action potentials
- Amplitude: generally no loss in action potential (AP) amplitude during conduction over the length 9f the axon (but, amplitude can be modulated at the terminal)
In the conversion of graded to action potentials, voltage of summated EPSPs must be above threshold, why?
Voltage of summated EPSPs must be above threshold at which a certain # of voltage gated Na+ channels open and initiate an action potential
What is propagation of the action potential?
AP initiated at axon hillock
(Summation/EPSP/IPSP > action potential)
- but how is that signal then sent down an axon?
1. Depolarization in one area
2. Followed by repolarization in that area with depolarization moving dish (wave of action potential )
3. That area then has a period of resting and repolar8zation cint8nues to move down
What role does the Axon hillock/threshold have in propagation ?
Axon hillock/threshold
- Voltage-gated Na+ channels largely absent on soma and dendrites. Hillock (junction of soma and axon) is heavily populated with voltage-gated Na+ channels
- if graded potentials depolarization > threshold, signal converted to action potential
What events occur during propagation of action potential
- membrane depolarization rapid influx of Na+
- depolarization of one axonal region —> positive charge flows to adjacent regions and propagate depolarization
- Voltage gated Na+ channels open in adjacent region and AP moves down axon
- Action potential propagates without losing amplitude
What happens after an action potential is propagated?
Refractory period of action potential
-in refractory region, voltage gated Na+ channel inactivation gate closed
Summarize the steps of the propagation of the action potential
- A graded potential above threshold reaches the trigger zone
- Voltage-gated Na+ channels open and Na+ enters the axon.
- Positive charge flows into adjacent sections of the axon by local current flow
- Local current flow from the active region causes new sections of the membrane to depolarize p
- The refractory period prevents backward conduction. Loss of K+ from the cytoplasm repolarizes the membrane
How does conduction of action potential along an axon occur?
- passive
- saltatory in myelinated axons
