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Questions and Answers
What is the approximate duration of the synaptic delay?
What happens when excitatory input exceeds inhibitory input but the membrane is not sufficiently depolarized?
What is the function of neuromodulators?
What is the term for the sum of activities in all pre-synaptic nuclei?
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What happens when there is a balance of activated excitatory and inhibitory inputs?
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Study Notes
Neurons and Action Potential
- Neurons are the basic functional unit of the central nervous system.
- Action potential is composed of four principal phases: polarization, depolarization, hyperpolarization, and repolarization.
- The refractory period ensures unidirectional propagation of the action potential and limits the frequency of action potential.
Refractory Period
- The refractory period consists of two phases: absolute refractory period and relative refractory period.
- During the absolute refractory period, the axonal membrane cannot initiate another action potential, regardless of stimulation.
- During the relative refractory period, a second action potential can be produced only by a stronger-than-usual stimulus.
- The length of the refractory period varies for different types of neurons.
- A longer refractory period results in a greater delay period before a new action potential can be initiated and a lower frequency of response to repeated stimulation.
Action Potential and Synapses
- Action potential occurs in an all-or-none fashion.
- A stronger stimulus triggers a greater number of action potentials per second.
- The junction between two neurons is called the synapse.
- A neurotransmitter carries the signal across a synapse.
- Some synapses excite the post-synaptic neurons, while others inhibit.
- The synaptic delay is approximately 0.5-1 millisecond.
Neurotransmitters and Synaptic Activity
- Neurotransmitters are quickly removed from the synaptic cleft to wipe the post-synaptic slate clean.
- The grand post-synaptic potential depends on the sum of activities in all pre-synaptic neurons.
- There are four possible outcomes of the grand post-synaptic potential:
- Excitation and action potential
- Facilitation and increased likelihood of action potential
- Inhibition and prevention of action potential
- No effect due to balance of excitatory and inhibitory inputs
Neuromodulators
- Neuromodulators are chemical messengers that bind to neuronal receptors at non-synaptic sites.
- They activate second messenger systems that produce long-term intracellular biochemical effects, altering the effectiveness of ongoing synaptic activity.
- Neuromodulators may act at pre-synaptic or post-synaptic sites.
- They can fine-tune synaptic responses by influencing neurotransmitter synthesis or post-synaptic receptor sensitivity.
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Description
Test your knowledge of the phases of an action potential, including polarization, depolarization, hyperpolarization, and repolarization. Learn about the refractory period and its role in neural transmission.