Neurons and Action Potentials Flashcards
Neurons (what they are and structure)
-specialized nerve cells that transmit messages
Structure
- soma (cell body)
- processes
Cell body (soma)
- contains nucleus
- site of metabolism
Processes (what they are and types)
-fibers that extend from the soma
Types:
- dendrites: receives information
- axons: sends information
Function properties
- irritability: ability to respond to a stimulus
- conductivity: ability to transmit an impulse
Resting Neurons
- plasma membrane polarized
- high concentration of sodium outside
- high concentration of potassium inside
- fewer + ions inside vs outside –> resting membrane potential
- RMP= -70mV
How is RMP maintained?
- Na+/K+ pumps
- leak channels
Na+/K+ pumps
- generate concentration gradient
- 3 Na+ out, 2 K+ in
- Cost: 1 ATP
Leak channels (types, why)
- small Na+ leak at rest
- WHy? high force (large gradient), low permeability (less channels)
- small K+ leak at rest
- Why? Low force (less gradient), high permeability (more channels)
Channels on neurons
- leak channels
- voltage-gated channels
- ligand-gated channels
Leak channels (when they are open and location)
-always open
Location: throughout neuron
Ligand- gated channels (when they are opened or closed and location)
- open or closed when ligand binds to receptors on the membrane
- location: usually dendrites and soma
Voltage gated channels (when they are opened/closed and location)
- open or closed when membrane potential changes
- location: mostly on axon but throughout
Action potential (what it is, stages, time, properties)
-rapid, large depolarization used for communication
stages:
- depolarization
- repolarization
- hyperpolarization
Time: 1-2 ms
Properties:
- all-or-nothing principle
- unidirectional propagation
Depolarization, depolarization, hyperpolarization (what happens in each event and the RMP)
Depolarization:
- Na+ gates open –> Na+ rushes in
- RMP: -70mV –> 30mV
Repolarization:
- K+ gates open –> K+ rushes out
- Na+ gates close
- RMP: 30mV –> -70mV
Hyperpolarization
- K+ gates close after RMP
- RMP drops below -70mV
All-or-nothing principle (threshold, what happens if stimulus is at or above threshold, terminology)
Threshold: -55mV
- minimum depolarization necessary to open Na+ channels –> AP
- if stimulus is at or above threshold –> AP of some magnitude (100mV)
Terminology
- subthreshold depolarization –> no AP
- threshold depolarization –> AP
- suprathreshold depolarization –> AP
Unidirectional propagation
- AP moves down axon toward axon terminal
- depolarization in one patch –> depolarization in adjacent patch
Voltage gated Na+ channels (how many and types)
-2 gates
- activation gate
- inactivation gate
activation gate (dependent on what, when it is opened)
- voltage dependent
- opened: threshold and depolarization
inactivation gate (dependent on what, when it is opened, when it is closed)
- voltage and time dependent
- opened: first part of depolarization
- closed: second part of depolarization
3 stages of gates of activation and inactivation gates
- activation closed- inactivation opened
- during resting state
- activation gate capable of opening with stimulus - activation opened- inactivation opened
- during depolarization
- allows Na+ to rush into cell - activation opened- inactivation closed
- during 1 msec following depolarization
- will not open until it returns to resting state
refectory period (how many types, types)
-2 types
- absolute
- relative
Absolute refractory period
- second AP cannot be generated
- Na+ gates are inactivated
- time: all of depolarization and part of depolarization
relative refractory period
- second Ap can be generated but with stronger stimuli
- Na+ gates: closed, some inactive
- Time: end of repolarization, and hyperpolarization
consequences of relative refractory period
- all-or-nothing principle
- unidirectional propagation
- frequency coding
