Lecture 17/Neuro III

1 2 3 4 5 6 7 8

2. Receptor in postsynaptic membrane
The neurotransmitter diffuses across the synaptic cleft and binds to a receptor in the membrane of the postsynaptic cell.

3. Fast vs slow
In fast chemicalsynapses, the neurotransmitter receptor is directly coupled to an ion channel. When the neurotransmitter binds, the channel opens. In slow chemicalsynapses, the binding of the neurotransmitter to its receptor triggers a signal transduction cascade, which eventually opens the ion channel.

4. Excitatory vs inhibitory
Synapses with skeletal muscles are always excitatory. Synapses with neurons can be either excitatory or inhibitory. Like hormones, the same neurotransmitter can cause different effects depending on the receptor.

Some are coupled to Na+ion channels and cause excitatory postsynaptic potentials(EPSP).
Others are coupled to K+ or Cl-ion channels and cause inhibitory post synaptic potentials(IPSP).

Na+ channel
K+ or Cl- channel

EPSP EPSP

5. Summation48.11, 48.12 A single neuron is connected to many others and receives both excitatory and inhibitory signals. Unlike electrical synapses, simply receiving a signal does not mean that the postsynaptic cell will generate an action potential. In the CNS, a single EPSPmay cause a change in membrane potential of only 0.5 mV and a 15 mV change is necessary to reach the threshold. Several EPSPs (from one or more neurons) can add together to cause sufficient Na+ ion channels to open, if they are received at close to the same time. If the neuron receives IPSPs at the same time, the hyperpolarization will tend to counteract the EPSPs, making it less likely that the neuron will fire.

Inhibitory neurons can synapse directly with their target neuron or with the synaptic bulb of the presynaptic excitatory neuron (blocking the release of neurotransmitters by the presynaptic cell). This strategy is used by interneurons that suppress the transmission of pain signals from sensory neurons.


		2. Receptor in postsynaptic membrane The neurotransmitter diffuses across the synaptic cleft and binds to a receptor in the membrane of the postsynaptic cell. 3. Fast vs slow In fast chemicalsynapses, the neurotransmitter receptor is directly coupled to an ion channel. When the neurotransmitter binds, the channel opens. In slow chemicalsynapses, the binding of the neurotransmitter to its receptor triggers a signal transduction cascade, which eventually opens the ion channel. 4. Excitatory vs inhibitory Synapses with skeletal muscles are always excitatory. Synapses with neurons can be either excitatory or inhibitory. Like hormones, the same neurotransmitter can cause different effects depending on the receptor. Some are coupled to Na+ion channels and cause excitatory postsynaptic potentials(EPSP). Others are coupled to K+ or Cl-ion channels and cause inhibitory post synaptic potentials(IPSP).
		Na+ channel K+ or Cl- channel		EPSP EPSP
		5. Summation48.11, 48.12 A single neuron is connected to many others and receives both excitatory and inhibitory signals. Unlike electrical synapses, simply receiving a signal does not mean that the postsynaptic cell will generate an action potential. In the CNS, a single EPSPmay cause a change in membrane potential of only 0.5 mV and a 15 mV change is necessary to reach the threshold. Several EPSPs (from one or more neurons) can add together to cause sufficient Na+ ion channels to open, if they are received at close to the same time. If the neuron receives IPSPs at the same time, the hyperpolarization will tend to counteract the EPSPs, making it less likely that the neuron will fire. Inhibitory neurons can synapse directly with their target neuron or with the synaptic bulb of the presynaptic excitatory neuron (blocking the release of neurotransmitters by the presynaptic cell). This strategy is used by interneurons that suppress the transmission of pain signals from sensory neurons.