The Nervous System: Action Potential, Axon Conduction-Lecture 10 Exam 2 Flashcards
Ligand-Gated Na+ Channels
Located on dendrites & cell body (soma)
Voltage-Gated Na+ Channels
Located at the axon hillock & along the axon
Voltage-Gated K+ Channels
Located along axon
Leak Channels
Located across the entire neuronal membrane, including the dendrites, cell body (soma), & axon
Action Potential Phase 1: Threshold
Stimulus opens ligand-gated Na+ channels (a small amount of Na+ enters the neuron) which depolarizes the membrane to -55 mV (threshold)
Action Potential Phase 2: Rising Phase
Voltage-gated Na+ channels open (triggered by -55 mV), and more Na+ enters the cell, further depolarizing the membrane to +30 mV
Action Potential Phase 3: Overshoot
Voltage-gated Na+ channels close when membrane potential reaches +30 mV, Na+ stops entering neuron
Action Potential Phase 4: Falling Phase
Voltage-gated K+ channels open at +30 mV and K+ flows out of the cell repolarizing the membrane
Action Potential Phase 5: Undershoot
Voltage-gated K+ channels are slow to close, additional K+ leaves the cell, hyperpolarizing the membrane to -90 mV
Action Potential Phase 6: Refractory Period
Cell membrane returns to resting potential (-70 mV) and another AP cannot be generated immediately
Threshold
-(-55 mV)
-Voltage at which an action potential is triggered
-Voltage that opens voltage-gated Na+ channels
Why is an Action Potential considered All-or-None?
Under constant environmental conditions (e.g. temperature), all effective stimuli produce action potentials of equal amplitude
Describe how voltage-gated Na+ channels conduct/propagate an action potential down an
axon from the axon hillock to the axon terminal
-APs are conducted along the axon in one direction from axon hillock to axon terminal
-Moving depolarizations that travel long distances without weakening
The impact of absolute refractory periods on the excitability of a neuron
-Time required for voltage-gated Na+ channel gates to reset
-No stimulus can trigger another action potential
The impact of relative refractory periods on the excitability of a neuron
-Only some VG-Na+ channel gates have reset
-Only a larger-than-normal stimulus can initiate a new action potential
How does Axon Diameter affect Conduction Velocity?
-Large diameter axon = fast conduction
-Small diameter axon = slow conduction
How does Myelination affect Conduction Velocity?
-Myelinated axons prevent ion leakage & conduct action potentials faster than unmyelinated axons
-Saltatory Conduction
The Role of Myelin in Saltatory Conduction
Prevent ion leakage & conduct action potentials faster than unmyelinated axons
Saltatory Conduction
Action potential “jumps” from one node of Ranvier to the next node of
Ranvier moving APs down the axon quickly
