Ch 4: Action Potentials

Slide 1: 

How Neurons Send and Receive Signals Chapter 4 Neural Conduction and Synaptic Transmission

Generation and Conduction of Postsynaptic Potentials (PSPs) : 

Generation and Conduction of Postsynaptic Potentials (PSPs) Neurotransmitters bind at postsynaptic receptors These chemical messengers bind and cause electrical changes Depolarizations (making the membrane potential less negative) Hyperpolarizations (making the membrane potential more negative)

Slide 3: 

Postsynaptic depolarizations = an Excitatory PSP (EPSP) Postsynaptic hyper-polarizations = an Inhibitory PSP (IPSP) EPSPs make it more likely a neuron will fire; IPSPs make it less likely PSPs are graded potentials – their size varies

EPSPs and IPSPs : 

EPSPs and IPSPs Travel passively from their site of origination Decremental – they get smaller as they travel Graded—stronger stimuli produce bigger EPSPs and IPSPs

Integration of PSPs and Generation of Action Potentials (APs) : 

Integration of PSPs and Generation of Action Potentials (APs) One EPSP typically will not suffice to cause a neuron to “fire” and release neurotransmitter – summation is needed In order to generate an AP (or “fire”), the threshold of activation must be reached near the axon hillock Integration of IPSPs and EPSPs must result in a potential of about -65mV in order to generate an AP

Integration : 

Integration Adding or combining a number of individual signals into one overall signal Temporal summation – integration of events happening at different times Spatial summation – integration of events happening at different places

Slide 7: 

Spatial summation Temporal summation

The Action Potential : 

The Action Potential All-or-none – when threshold is reached the neuron “fires” and the action potential either occurs or it does not When threshold is reached, voltage-activated ion channels are opened

The Action Potential (continued) : 

The Action Potential (continued) The opening and closing of voltage-activated sodium and potassium channels during the three phases of the action potential

Refractory Periods : 

Refractory Periods Absolute – impossible to initiate another action potential Relative – harder to initiate another action potential Prevent the backwards movement of APs and limit the rate of firing

PSPs vs. Action Potentials (APs) : 

PSPs vs. Action Potentials (APs) EPSPs/IPSPs Decremental Fast Passive (energy is not used) Action Potentials Nondecremental Conducted more slowly than PSPs Passive and active

Conduction in Myelinated Axons: Saltatory Conduction : 

Conduction in Myelinated Axons: Saltatory Conduction Passive conduction (instant and decremental) along each myelin segment to next node of Ranvier New action potential generated at each node Instant conduction along myelin segments results in faster conduction than in unmyelinated axons