Presentation Transcript
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