VMED 5163 - Neuronal Cell Physiology and Synaptic Transmission

Negative

The resting membrane potential of a neuron has what charge?

Depolarization

When an action potential increases voltage to positive, this process is known as?

After depolarization of a neuron, its voltage sharply decreases to below its baseline membrane potential

Describe the process of hyperpolarization

From high to low concentrations

In general, ion flow goes in what direction?

Voltage

When there is difference in charge across a membrane, a ___ is created

Sodium and chloride

Which ions are present in higher resting concentrations on the outside of the cell?

Inside of the cell

Potassium and organic anions are present in higher concentrations where?

Negative charge; potassium and sodium attracted inward

The inside of a neuron has what charge? What ions does this attract via voltage force?

Its voltage force; due to the negative charge of the neuron, it is repelled

Because it is present in higher concentrations outside of the cell, chloride wants to flow inward. What other forces opposes its concentration force?

Sodium

Which ion has matching concentration and voltage forces?

Potassium (K+)

The most important ion for resting membrane potential is?

-55 mV; voltage gated sodium channels open and depolarization begins

What is the depolarization threshold, and what occurs once it is reached?

Sodium channels open and sodium flows in very quickly due to their voltage and concentration gradients, then rapidly inactivate

During depolarization, what process is occurring within the neuron?

Re-polarization

During which phase of an action potential do potassium channels open and close?

Failed initiations

Most neurons require multiple signals to create and fire and action potential. Those signals which do not cause activation are known as?

Open

Depolarization causes voltage gated sodium channels to?

Re-activates voltage gated sodium channels to be able to open during depolarization

What does hyperpolarization achieve within the neuron?

Information exchange between neurons, or between neurons and other cells

What occurs at a synapse?

Electrical and chemical

What are the classifications of synapses based on impulse conduction?

Direct

An electrical synapse contains pre- and post-synaptic portions in (direct/indirect) contact

Electrical synapse

Which synapse type allows for impulse movement in both directions?

Unidirectional

A chemical synapse allows what type of directional movement?

Chemical synapse; synaptic cleft

A synapse which has no direct contact between its junctions is a? These synapses communicate via what structure?

Neurotransmitters

Substances transmitted between neurons or from neurons to certain cells are known as?

A large number of mitochondria

Because neurotransmitter release requires high amounts of energy, what is seen within cell bodies of neurons?

Presynaptic terminal

Once an action potential is created, it travels to which area in order to open calcium channels?

An influx of calcium activates docking proteins, which cause synaptic vesicles to fuse with the presynaptic membrane

What effect does calcium have on the neuron in the process of neurotransmitter release?

The synaptic cleft

Neurotransmitters are released into what space?

Via enzymes in the synaptic cleft, diffusion, or reuptake; reuptake is primary

In what ways can neurotransmitters be shut down? Which of these mechanisms happens most often?

Astrocytes

Helper cells within the neuron which provide glucose and assist with re-uptake are known as?

Excitatory and inhibitory synapses

What are the classifications of synapses based on conductance of the postsynaptic membrane?

There is an increase in conductance to sodium, which depolarizes the membrane

Within an excitatory synapse, what change is seen within the postsynaptic membrane? What effect does this have?

Inhibitory synapse

A synapse in which there is an postsynaptic increase in conductance to potassium is known as?

Glutamate

The main neurotransmitter within excitatory synapses is?

Opening of ligand-gated sodium channels

In the excitatory pathway, the attachment of neurotransmitters to the post-synaptic membrane receptors causes what?

Excitatory post-synaptic potential, sodium ions

An EPSP, or ____, occurs when there is an influx of what ions into the neuron?

Decreases

An EPSP (increases/decreases) with time and distance

Multiple signals from different neurons combine at one time to create a larger depolarization in order to reach the threshold

Describe a spatial summation and what it achieves

Temporal summation

Multiple signals from different neurons arriving one after the other and causing an action potential is known as?

GABA

The major inhibitory neurotransmitter is?

Chloride and potassium channels

Which ion channels are activated during an IPSP?

Potassium exits the cell, chloride enters

What directions do Cl- and K+ go within an IPSP?

EPSPs

For a neuron to fire and action potential more ___ signals are required

The neuron has a failed initiation and does not fire

If the number of EPSPs and IPSPs are equal, what occurs?

On distal dendrites

In general excitatory synapses are where in the neuron?

Inhibitory synapses

Which synapses are found on proximal dendrites and in the soma?

Ionotropic and metabotropic

Receptors which receive action potentials at synapses can be of what types?

Ionotropic receptors

Acetylcholine, GABA, and glutamate bind to what receptor types?

A transmitter stimulates metabolic changes in the target cell via second messengers via a G protein

How do metabotropic receptors work?

G-protein coupled receptors (GPCRs)

Metabotropic receptors can also be called?

Slow action, no large conductance changes in the neuron

What are the characteristics of metabotropic action?

Metabotropic receptors

Which receptor type is associated with cAMP or cGMP?

They are the targets of 1/3-1/2 of all drugs

What is the major clinical significance of GPCRs?

Acetylcholine

The first identified neurotransmitter is?

Acetylcholinesterase (AChE)

ACh is broken down by what enzyme?

Neuromuscular junctions, autonomic nervous system, and central nervous system

In which general areas of the body is acetylcholine found?

Monoamines

Hormones such as norepinephrine or epinephrine are what type of transmitters?

NO, CO, and H2S

Which gases can act as neurotransmitters?