Question

Briefly explain why Neuron A that receives similar types and strengths of synaptic input to Neuron B, can have very different action potential shapes (i.e. waveforms) and action potential firing rate versus Neuron B. In your answer be sure to describe: (1) What aspects of the neuron’s composition determine this 'intrinsic excitability', (2) Which of these aspects are the most common components in these responses, and (3) Why a neuron might fire more action potentials if it is forced to become hyperpolarized before becoming depolarized.

Answer 1

Each vesicle packet released from the pre-synaptic neuron contains set of neurotransmitters, which will bind to some receptors on the post-synaptic cell. If the neurotransmitter is excitatory, the influx of positive ions will depolarize (bring closer to zero) the cell body. If the neurotransmitter is inhibitory, it will hyperpolarize the cell body. However, a single vesicle of neurotransmitter isn’t enough to depolarize the cell body.

Intrinsic excitability is the electrical excitability of a particular neuron. It depends on number and distribution of ion channels.

The intrinsic excitability is influenced by the conductance of voltage-gated ion channels generating ionic current carried by Na+ and K+ ions which affects the passive and active membrane properties.A balance of ion channel conductance and expressional composition determines the characteristics of spiking activity as well as the neuronal excitability. Sodium-potassium pumps causes two K+ ions to move into the cell while removing three Na+ ions per ATP used.

A small change in the membrane potential is proportional to the size of the stimulus. A graded potential comes in a wide range of slightly different sizes. If just one or two channels open the gradually increasing potential may be small, while if more channels open (due to a larger stimulus), it may be larger. These graded potentials don’t travel long distances along the neuron’s membrane, but rather, travel just a short distance and diminish as they spread, eventually disappearing. Neurons have more potassium leakage channels than sodium.

For hyperpolarization to occur at the peak action potential, K+ channels open.

The action potentil occurs only after hyperpolriztion , hence if multiple hyperpolarization takes place then the action potential may cause nerve excitation.

An action potential begins when a depolarization increases the membrane voltage so that it crosses a threshold value (usually around-55−55minus.