Question

In a neuron with a complex morphology such as a cortical pyramidal cell, explain how features such as dendritic spines, dendritic shape and non ligand-dependent ion channels in the membrane affect spatial and temporal summation of post synaptic potentials.

Answer 1

In a neuron with a complex morphology such as a cortical pyramidal cell. Dendritic spines, dendritic shape and non ligand-dependent ion channels affect spatial and temporal summation of post synaptic potentials in the membrane. Postsynaptic potentials develop in the membrane of postsynaptic cell, when neurotransmitter binds to receptors and leads to the opening of ion channels.

There are two different ways local potentials can sum to excite the postsynaptic cell to have an action potential. EPSPs and IPSPs are local potentials.

EPSP: Opening of sodium- or calcium channels, which lead to depolarization of the membrane. If there is enough depolarization, the threshold potential is reached and an action potential is produced in the postsynaptic membrane. If, the membrane becomes hyperpolarized when the ions move, an inhibitory postsynaptic potential (IPSP) produces.

IPSP: Opening of potassium- or chloride channels, that leads to hyperpolarization of the membrane. The current is outward for potassium ions and inward for chloride ions. When, these two channels will opens then, they cause the postsynaptic membrane to hyperpolarize.

Temporal summation occurs when successive EPSPs at a single synapse occur in quick succession. The successive potentials occur before the before ones die out, which produces an increasing depolarization of membrane. Temporal summation occurs when one synapse stimulates the postsynaptic cell very quickly and the EPSPs produced in the postsynaptic cell piggyback on each other, it causes an increasing level of depolarization.

Summation can also occur when the multiple presynaptic neurons stimulate the postsynaptic neuron at the same time known as spatial summation. Each individual synapse allows in a limited number of ions and modify the membrane potential in a little. The collective effect of all the synapses permits in enough ions to reach the threshold potential and an action potential is activated.

The structure and branching of a neuron's dendrites and the availability and variation of voltage-gated ion conductance influence how the neuron combines the input from other neurons. This integration is both temporal summation of stimuli in rapid succession and spatial summation, which entails the aggregation of excitatory and inhibitory inputs from separate branches.

Dendrites communicate electrical stimulation passively. This passive transmission changes the voltage measured at the cell body. It is the result of activation of distal synapses, which propagate the electric signal towards the cell body without the aid of voltage-gated ion channels. Passive cable theory explains the changes voltage at a particular location on a dendrite. It transmits this electrical signal by the system of converging dendrite segments of different diameters, lengths, and electrical properties. Dendrite architectures affects the overall output characteristics of the neuron. The characteristic of dendrites, endowed by their active voltage gated conductance. It is their ability to send action potentials back into the dendritic arbor. These signals depolarize the dendritic arbor and provide a important element toward synapse modulation and long-term potentiation. It is produced at the soma and induce a calcium action potential (dendritic spike) at the dendritic initiation area in certain types of neurons.