Lecture 8 Neurons and AP Flashcards
What are Neurons
specialized nerve cells that transmit messages
what is the structure of neurons
- cell body (soma)
2. processes
what does the cell body contain
Nucleus
What is the cell body the site of
site of metabolism
what are processes
fibers taht extend from the soma
what are the types of processes
dendrites: receive info
axons: sends info
Functional properties of Neurons
Irritability
conductiity
What is irritability
ability to respond to a stimulus
what is conductivity
ability to transmit an impulse
what is a Resting Neuron
Plasma Membrane is polariezd
High concentration of Na+ outside the cell
High concentration of K+ inside the cell
fewer + ions vs. outside –> Resting membrane potential (RMP= _ 70mV)
How is the RMP maintained
- Na+/K+ pump
2. Leak channels
Na+/ K+ pump does what?
generate concentration gradient
3 Na+ out
2 K+ in
cost 1 ATP
What are Leak Channels
Small Na+ leak at rest
why:
High force (large gradient) low permwability (Less Channels)
small K+ leak at rest
Why:
Low force (less gradient) high permeability (more channels)
Types of Channels on Neurons
- Leak Channels
- ligand- gated channel
- voltage gated channels
what are Leak Channels
always open
location throughout th neuron
what are Ligand gated channels
open or close when ligand binds to receptors on the membrane
location: usually dendrites and soma
what are voltage gated channels
opens or closes when membrane potential changes
what is Action potential
Rapid large depolarization for communication
What are the stages of Action Potential
- Depolarization
- Repolarization
- hyperpolarization
What is depolarization
Na+ gates causes Na+ to rush in
RMP: increase from -70mV –> +30 mV
upward movement = depolarization
What is Repolarization?
K+ gate to open –> K+ to rush out
Na+ gate is clsoed
RMP= drops -30mV–> -70mV
What is hyperpolarization?
K+ clsoing after RMP
RMP: drops below –> -70mV
What is Action potential time?
Time: 1-2 ms
What is Action Potential properties?
- All or nothing
2. undirectional propagation
What is the all or nothing princple?
Threshold: get to or above threshold , minimum depolarization necessary to open Na+ channels–> AP
- if stimulus is at or above the threshold –> Ap of same magnitude (100mV)
All or nothing Terminology
subthreshold depolarization–> no AP
Threshold depolarization –> AP
Suprathreshold depolarization –> AP
what is unidirectional propagation
- Ap moves down axon toward the terminal
- deoolarization in one patch –> depolarization n adjacent patch
what are Voltage gated Na+ channels
2 gates
- Activation gate
- Inactivation gate
What is activation gate
- Voltage dependent
- opened threshold and depolarization
what is inactivation gate
- voltage and time dependent
- opened in 1st part of depolarization
- closed: second part of depolarization
3 stages of voltage gated channels (Inactivation/activation gate)
- Activation: cosed and inactivation gate closed
- during resting state
- activation gate capable of opening with stimulus
- Activation opened - Inactivation closed
- during depolarization
- allows sodium to rush into the cell - Activation opened –> Inactivation closed
- During 1 ms follwoing depolarization
- will not open untill returned to resting state
what are the 2 types of Refactory period
- absolute
2. relative
what is absolute refractory period ?
second AP can not be generated
Na+ gates are inactivated
Time: a;; of depolarization and part of repolarization
what is relative refractory period ?
second AP can be generated but with a stronger stimulus
Na+ gates closed some inactive
Time: end of polarization and hyperpolarization
What are the consequences of Refractory period ?
- All or nothing
- unidirectional propagation
- frequency coding
what is Frequency Coding
Intensity of the stimulus is coded in AP frequency
Higher intensity = Higher frequncy
lower Intensity = lower frequency
