Action Potentials & Communication Flashcards
Graded potentials?
Short distance communication
Action potentials?
Long distance communciation
How do neurons communicate?
Most commonly Action potentials
Why do action potentials occur?
Opening & closing of ion channels in response to stimuli
What is the resting membrane potential?
The RMP is the voltage difference across the plasma membrane of excitable cells that enable electrical flow of ions
How does the membrane potential change?
The electrical flow produced by ions change membrane potential
What are leak channels?
Potassium and sodium channels that randomly open and close & located in all cells
What are ligand-gated channels?
Channels that open and close in response to ligand bindings such as hormones, neurotransmitters & located in dendrites
What are voltage-gated channels?
Channels that open and close due to voltage differences & located in axons
Variance of RMP?
-40 to -90 mV
Typical RMP value?
-70 mV inside more negative than outside
Factors affecting RMP?
Unequal distribution of ions across ECF and INCF, stuck anions, Sodium-potassium pump which all decrease RMP
Characteristics of graded potentials?
Mainly occurs in dendrites, and cell bodies, amplitude depends on strength of stimulus, travel short distance & die out quickly, and summate potentials
What is an action potential?
Sequence of events that decrease and then reverse the RMP to resting state
Depolarization?
Decreases RMP from negative to positive
Repolarization?
Resting stage that increases RMP back to normal
When does action potentials occur?
When axon is depolarized to -55 mV threshold opening sodium channels and generating action potential
What does action potentials do?
Generate the sequential opening of sodium and potassium voltage channels
Subthreshold stimulus?
Below threshold
Supratheshold stimulus?
Above threshold
What happens during suprathreshold stimulus in action potentials?
The frequency of potentials increases
What happens during depolarization?
During depolarization the NMP decreases and becomes positive, changing the NMP from -55 to + 30 mV, leading to sodium channel domino effect
What is the relative refractory period?
When a supra-threshold stimulus is required to enact another action potential
What is the absolute refractory period?
No level of stimulus will generate action potential
Characteristics of action potentials?
Travel from the trigger zone, are decremental and propagate and need to be regenerated again and again to reach end of terminal
Continuous conduction?
Step-by-step depolarization and repolarization of membrane along unmyelinated axons
Salutatory conduction?
Action potentials jump along the nodes of ranvier in myelinated axons, faster and more energy efficient
Group A fibers?
largest diameter, speed, myelination and lowest refractory period - skeletal muscle motor neurons
Group B fibers?
Less diameter, speed, myelination, longer refractory period - sensory impulses
Group C fibers?
Smallest diameter and speed, no myelination and high refractory period - autonomic motor fibers
Electrical Synapases?
Conduct directly through plasma membrane through gap injunctions through connexons - faster and synchronized potentials
Chemical synapses?
Neurotransmitters carry stimulus from pre-synaptic neurons across synaptic cleft to post-synaptic receptors
Neurotransmitters?
Can inhibit or excite effectors or neurons
Removal of neurotransmitters?
Diffusion - away from receptors, enzyme degradation and reuptake - returned to pre-synaptic neuron by vesicles
