unit 2 excitatory and inhibitory synapses

week 3

failed initiations/sub threshold depolarizations are also called

excitatory post synaptic potentials (EPSPs)

what are the propertries of EPSPs

• dont produce AP

• localized - depolarization is confined to one area of plasma membrane

• magnitude of depolarization =magnitude of stimulus- meaning they are graded (higher the stimulus, larger depolarization)

• they can be summed(stacked up on top of each other producing larger depolarization) multiple epsps are required to produce an AP

• bring neuron closer to an AP

• decay as they propagate across membrane from point of stimulus - further they are from depolarization, the smaller they become

• are produced by neurotransmitters that open na+ and k+ channels

hyperpolarizing potentials are called

inhibitory post synaptic potentials

what are the properties of ipso

• localized- hyperpolarization confined to 1 area of plasma membrane

• magnitude of hyperpolarization = magnitude of stimulus - meaning they are graded (higher stimulus, larger hyperpolarization)

• they can be summed (stacked up on top of each other to produce larger hyperpolarization

• brings neuron further away from AP

• decay as they propagate across membrane from point of stimulus - further from depolarization, smaller they become

• are produced by neurotransmitters that open k+ (moving it out of the cell) or cl- channels (moving cl- into cell)

axon hillock

wether an action potential is generated depends on sum of ipsps and epsps as they reach the trigger zone called the axon hillock

produced by the opening of ligand gated ion channels

graded potential

produced by opening of voltage gated ion channels

action potential

do dendrites and soma have voltage gated channels?

they do not

what are the two ways strength of EPSPs can be increased

temporal summation and spatial summation

why do epsps have to be strong

in order to cause a sufficient depolarization to open voltage gated na+ channels at the axon hillock, positive current of the epsp must be strong enough to spread all the way from the synapse where it originated from to the axon hillock

what is temporal summation

additive effect produced by many epsp generated at the same synapse by a series of high frequency ap on the presynaptic neuron. One neuron fires repeatedly.

spatial summation

additive effect produced by many EPSPs that have been generated at many diff synapases on the same post synaptic neuron at the same time. many neurons fire at the same time to produce EPSPs in the post synaptic neuron.

IPSPs produce ___ thru spatial and temporal summation

larger hyperpolarizations

what is happening (2 steps)

1. both IPSPs and EPSPs decay as they move towards axon hillock

2. IPSPs and EPSPs summed at axon hillock and since threshold is not met at hillock, no ap generated

After being released, the neurotransmitter diffuses across the synaptic cleft, binds to receptors on the post-synaptic membrane and produces a response in the post-synaptic neuron. Depending on the type of neurotransmitter, this response may be excitatory, leading to 1.____ of the 2._____ in the form of 3.____.

If the 4.____ is strong enough, it may fire an 5. _____.

1. depolarization,

2. membrane

3. EPSPs

4. depolarization

5. action potential

On the other hand, the neurotransmitter could produce an 1.___ response leading to 2. _____ of the 3.____________ in the form of 4.____. This makes it 5._____ to generate an action potential. 

1. inhibitory 

2. hyperpolarization

3. post-synaptic membrane

4. IPSPs

5. harder