16.23
Integration synaptischer Ereignisse
Die Integration synaptischer Ereignisse umfasst hauptsächlich die Summierung von graduierten Potentialen. Graduierte Potentiale, unabhängig von ihrem…
Die Integration synaptischer Ereignisse beinhaltet die Summierung mehrerer abgestufter Potentiale, wie z.B. exzitatorische und inhibitorische postsynaptische Potentiale, am Axonhügel der postsynaptischen Zelle.
Dieser Prozess kann entweder durch räumliche oder zeitliche Summierung erfolgen.
Wenn sich Reize von mehreren Synapsen addieren, spricht man von räumlicher Summation.
Bei der zeitlichen Summierung können sich die Reize, die in schneller Folge an einer einzigen Synapse auftreten, summieren, um die Schwelle zu erreichen.
Ein typisches EPSP erzeugt eine Änderung des Membranpotentials um etwa 0,5 mV, die kein Aktionspotential auslösen kann.
Einzelne EPSPs können das Neuron jedoch bis zur Schwelle summieren und depolarisieren. Drogen wie Nikotin und Koffein erhöhen die EPSP-Summierung, so dass das Neuron die Schwelle schnell erreichen kann.
In ähnlicher Weise können auch einzelne IPSPs summieren, was die Chancen auf das Erreichen der Schwelle verringert und dazu führt, dass Aktionspotentiale seltener ausgelöst werden. Beruhigungsmittel wie Benzodiazepine bewirken eine sofortige Hyperpolarisation, um eine hemmende Wirkung zu erzeugen.
Wenn sich EPSPs und IPSPs summieren, kann die Membran je nach ihrer Stärke hyperpolarisieren, depolarisieren oder auf dem Ruheniveau verbleiben.
View the full transcript and gain access to JoVE Core videos
Q1: What is spatial summation and how does it differ from temporal summation?
Spatial summation occurs when inputs from multiple presynaptic neurons fire simultaneously, causing the postsynaptic neuron to reach threshold. Temporal summation happens when a single presynaptic neuron fires rapidly in succession, allowing stimuli to sum at one synapse. Both processes depend on the summation of graded potentials, but spatial summation depends on physical location of signals while temporal summation depends on timing of incoming signals.
Q2: Why can't a single EPSP trigger an action potential on its own?
A typical EPSP produces only about 0.5 mV change in membrane potential, which is insufficient to depolarize the neuron to its threshold. Individual EPSPs must summate and combine to generate enough depolarization to reach threshold and initiate an action potential. This summation process allows neurons to integrate multiple weak signals into a strong enough stimulus.
Q3: How do drugs like nicotine and caffeine affect synaptic integration?
Nicotine and caffeine increase EPSP summation, allowing neurons to reach threshold more quickly and fire action potentials more readily. These stimulants enhance the neuron's ability to integrate excitatory signals, making it easier for postsynaptic neurons to generate action potentials in response to incoming stimuli.
Q4: What role do inhibitory postsynaptic potentials play in synaptic integration?
Individual IPSPs summate to hyperpolarize the membrane, reducing the likelihood of reaching threshold and resulting in less frequent action potential firing. When EPSPs and IPSPs summate together, the neuron's membrane can hyperpolarize, depolarize, or remain at resting level depending on their relative strength. This balance allows neurons to make decisions about whether to fire.
Q5: How does dendritic integration contribute to synaptic processing?
Dendritic integration refers to the combination of inputs arriving at different parts of the dendrite. Dendrites possess active properties that can amplify or attenuate incoming signals, making this form of integration complex. This process allows neurons to process information locally within dendritic branches before signals reach the axon hillock.
Q6: Why is synaptic integration essential for neural computation and brain function?
Synaptic integration enables neurons to sum excitatory and inhibitory inputs, allowing them to make decisions about firing action potentials. This process facilitates information transfer and processing between neurons, enabling intercommunication among brain regions for learning, memory formation, and decision-making. It also allows the brain to detect environmental changes and respond appropriately.
Q7: How do depressants like benzodiazepines affect neural activity through synaptic integration?
Benzodiazepines cause instant hyperpolarization by enhancing inhibitory effects at synapses. This hyperpolarization makes it more difficult for neurons to reach threshold, reducing the frequency of action potential firing. By increasing inhibitory postsynaptic potential effects, depressants suppress overall neural activity and excitability.