Physiology Lecture #6 [Neuronal Signaling and Synaptic Transmission]

Dendrites

Are fine extensions from the cell body of a neuron

Soma

The cell body where all protein synthesis takes place in a neuron

Axon hillock

The first part of the axon

Axon

is a long extension of the soma

Axon terminals

The end part of a neuron

VGNaC

The axon hillock is rich in ______ and integrates received information

terminal field

Axon conducts action potentials to the

other cells

Axon terminals send information to

Excitatory Post Synaptic Potential (EPSP)

If an input to a neuron causes a depolarization it is called an

- Make it easier to excite neurons

- Influx of cations (or Efflux of anions)

EPSP function (general)

Inhibitory Post Synaptic Potential (IPSP)

If an input to a neuron causes a hyperpolarization it is called an

- Make it harder to excite neurons

- Influx of anions (Efflux of cations)

IPSP function (general)

depolarization (often due to opening of cation selective ligand gated channels eg. nAChR, Glutamate)

EPSP's can add up to give you a larger

hyperpolarization (often due to opening of anion selective gated channels eg. GABA and Glycine)

IPSP's can add up to give you a larger

Threshold is reached

All inputs to a neuron that make it to the axon hillock are summed and determine if

VGNaC, action potential

If threshold is reached then sufficient numbers of _______ will open and generate an _____

Axon hillock

All inputs add up along the path to the

an action potential is generated

If inputs depolarize the axon hillock sufficiently then

EPSPs and IPSPs

The response of postsynaptic cells is derived from the sum of the _____ and _____ from all of its synapses

action potential, postsynaptic cell

When the sum of these events causes a depolarization beyond the threshold potential a(n) _______ is generated in the ________

depolarize

When the action potential reaches the terminals it will ____ the terminals

whatever cell they are connected to

The depolarized axon terminals will then pass the signal on to

- Directly electrically (electrical synapses)

- By releases of a neurotransmitter (chemical synapses)

The signal can be passed on to the next cells by one of two ways:

transmit information

Electrical synapses are very fast to

fidelity (accuracy)

- A stimulatory signal is stimulatory on second cell

- An inhibitory signal is inhibitory on second cell

The electrical synapses has high

Bidirectional

- information transfer can occur in both directions

Electrical synapses are

Voltage gated Ca channels to open.

When a depolarization signal reaches the end it causes

leads to an influx of Ca ions into the cytoplasm

The opening of Ca channels...

Conformational changes into the proteins (SNARE) coating vesicles causing the vesicles (filled with NT) to fuse with the membrane in the post synaptic space

The influx of Ca ions in the cytoplasm ends up triggering

to enter the post synaptic cleft and activate a ligand gated channel in the post synaptic neuron

The fusion of the Vesicles with the post synaptic membrane allows for the NT

slower

Because of the lengthy process of the chemical synapses this makes them much ___ than electrical synapses

synapse

Neurotransmitters (NT) need to be cleared from the _____ to terminate the signal from 1 neuron to the other

After opening, they inactivate in the sustained presence of stimulus

- NT clearance helps them "reset" for the next signal relay steps

Ligand gated ion channels mediating synaptic transmission desensitize i.e....

- Passive diffusion (float away)

- Enzymatic removal (AchE)

- Secondary active transport

3 ways neurotransmitters are cleared from the synapse

SSRIs inhibit serotonin transporter (SERT) which typically brings serotonin back into the presynaptic membrane to be repackaged and reused. By keeping it in the synaptic junction, serotonin will have extended effects since it is not being taken back up by secondary transporter (SERT)

How do SSRIs (antidepressants) work in the clearance of serotonin?

Glutamate in the synapse is transported into glial cells by Glutamine synthetase, where it will be converted to Glutamine, then released back into the synapse. Then Glutamine can be brought back into the presynaptic terminal

Glutamate clearance mechanism

Glial cells pick up and break down GABA via GABA transporter

Presynaptic terminal can also bring GABA back into the cell and break it down (coupled with Na flow into the presynaptic vesicle)

GABA and Glycine clearance mechanism

Neurotransmitter

Secondary active transporters in synaptic vesicles mediate ______ loading

vesicular ATPases

Proton gradient in vesicles is established via

Na

Neurotransmitter transporters are usually ___ coupled

Cl+/Cl- antiporters

ATPases

CIC channels

vesicular transport is driven by ____ or membrane potential gradients established by vesicular _____ or ____ _____

Multi-step

The process of fusion of synaptic vesicles to membrane is a ____ process