What can physiologically produce an action potential?
Synaptic transmission from another cell, spontaneously within the cell, another action potential and peripheral receptors.
Where do action potentials typically begin in an axon?
The axon hillock, its threshold is only about -45mV so any depolarization hits the axon hillock 1st.
What is an EPSP?
Excitatory Postsynaptic Potential. They depolarize the membrane to get it to threshold.
What are IPSPs?
Inhibitor Postsynaptic Potential. They hyper polarize the membrane to inhibit action potential
What are the two types of synapses?
Electrical and chemical
Where are electrical synapses used and why?
Cardiac muscle, smooth muscle and gut. Rapid modification of the muscle is not necessary in these places.
What makes up an electrical synapse?
Gap junctions made up of connexons. Na+ traveling through the channel depolarizes the adjacent cell.
What is the mediating agent of electrical synapse?
Where is chemical synapse used?
CNS where behavior must be flexible depending on the circumstances.
What channels are present at the synaptic cleft?
How are vesicles brought close to fuse with the presynaptic membrane?
Ca VGCs allow Ca to come in and control the amount of neurotransmitter released.
What are the different types of channels?
Ionotropic: directly opens or closes postsynaptic channel. Metabotropic: releases a messenger that may activate enzymes, transcription or secondary membrane channels
What creates and EPSP/IPSP?
Ionic current flowing through the open channels in the synaptic cleft?
What is happening here?
It is a motor endplate. An axon is innervating different muscle fibers. Eventually the myelin will go away and form synaptic clefts
What creates an end plate potential?
ACh is released. Channels open that are permeable to both Na and K. More Na goes in than K goes out and the end plate potential is produced. The more channels that open, the greater the end plate potential.
If ACh opens a channel that allows Na and K to flow through, why does more Na enter?
It has a greater driving force than K because its electrical potential is further from the resting potential.
What do crabs have that humans don't?
Inhibitory end plate potentials. Humans only have excitatory end plate potentials.
When does the end plate potential initiate an action potential?
Once it depolarizes the membrane to threshold (60mV)
How does the presynaptic membrane recover after synapse?
Choline is taken back into the cell via Na+ anti port transport. Choline buds off as a vesicle into the cell and is re-acetylated.
Why does the site of action potential generation need to be close to the end plate potential?
End plate potentials do not propagate.
How do action potentials and EPSP/EPP/IPSPs differ? (Activating mediators, propagation, permeability sequence and summation)
Action potentials are activated by voltage and EPSP/EPP/IPSP are activated by neurotransmitters. APs propagate, EPSPs do not propagate. APs have sequential changes in permeability to Na and K, EPSPs have simultaneous changes. APs are not summative and EPSPs can sum.
How does the CNS utilize ionotropic channels to produce action potentials?
Very similarly to neuromuscular junctions but only about 2mV depolarization. EPSPs must be added together to produce an action potential.
How does the CNS produce IPSPs?
Hyperpolarization via increasing permeability to Cl- or K+
How does action potential initiation take place via temporal summation in the CNS take place?
Before all ACh is degraded at the synaptic cleft transmitter is continually spilled out until the membrane potential reaches threshold.
How does action potential initiation take place via spatial summation in the CNS take place?
Multiple synapses are stimulated at the same time to generate enough neurotransmitter to depolarize the membrane to threshold.
Why does summation not take place at the neuromuscular junction?
A single synapse depolarizes the membrane enough to generate an action potential
How do EPSP and IPSP signals effect action potential generation at the axon hillock?
IPSPs produce a hyperpolarization, which requires greater depolarization by EPSP in order to generate an action potential.
How do electrical and chemical synapses differ in their properties? (Continuity, mediating agent, synaptic delay, directionality, behavior and extracellular space).