M6 L1 : Nerve structure Flashcards
Describe the 3 main parts of a vertebrae neuron
Soma (cell body) and two processes: dendrites to the cell body and axon coming out of it.
What are synaptic inputs vs action potentials and where are they received
Synaptic inputs are inputs from other neurons and are received on the dendritic tree and soma. Whereas Action potentials are conducted away from the soma to the tips of axons: synaptic boutons (axon terminals) communicate with other neurons
What are the two ways by which neurons communicate and where on the neuron does it take place
Electrical signals (dendrite, axon, cell body) and Chemical signals (synapses)
Is communication a chain of events that have conversion between electrical to chemical to electrical
yes
RMP varies between cells but what is the general value and what
between -50 and -70. Usually -65mV
2 ways RMP of neurons measured in real life
using intracellular glass microelectrodes filled with electrolytes placed in the soma, measuring electrical signal
Or with patch- clamp technique using larger tip glass pipettes to measure current in ion channels
What is the problem with patch clamp technique
It dialyses the cell and changes the ionic/ chemical composition
What is the difference of neurons and muscle fibres compared to all cells with respect to RMP
Almost all cells in the body have a negative resting membrane potential. Only neurons and muscle fibres can suddenly respond with a transient change of this potential( ie action potential) in response to stimulus = excitable
What are the 3 causes of the RMP
- The unequal concentrations of Na+ and K+ inside and outside the cell, resulting in electrochemical gradient.
- The unequal permeability (P) of the cell membrane to these ions.
- Electrogenic action o the Na/K pump ( only small)
At rest, describe the separation of charges across the cell membrane and its effect
There are more negative charges inside the cell in comparison to the extracellular fluid. Therefore there is an electrical potential difference.
What is the potential outside the cell referred to
0
What is the contribution of the Na+/K pump to the RMP
It maintains the conc gradient for these ions. It pushes out 3 Na+ but only drags in 2 K+ so a net charge of -1 is built inside the cell.
What are the approximate concentrations of K+ and Na+ ions inside and outside neurons.
K+ is 5mM outside and 100mM inside
Na+ is 150 mM outside and 15 mM inside
What affects the permeability of the cell membrane to Na+ and K+
Selectively permeable: Non-gated ion channels (leak) that are open at rest and Gated ion channels (voltage or ligand) that are usually closed at rest.
What is the ratio of K+ leak channels (K+ permeability) (PK) to Na+ leak channels (Na+ permeability) (PNa) at rest
PK:PNa = 40:1. Therefore there is more passive (positive charges leaving (K+)) than (positive charges entering (Na))
How does the unequal concentration AND unequal cell membrane permeability to Na+ and K+ result in a negative RMP
It sets up an equilibrium potential for each ion which balances out to get a negative RMP
What is the equilibrium potential and why does it happen
The intracellular potential at which the net flow of ions is zero inspite of conc gradient and permeability. This is because ions moving through passive diffusion are actually moving against their electrochemical gradient. When these are balanced, the same amount of ions leaving for diffusion are coming back for electrostatic force.
What does the Nernst equation calculate and what is the equation
equilibrium potential for each ion that contributes to RMP.
Eion= 61.5mV * log [ion]outside / [ion] inside
What is equilibrium potential for an ion proportional to and inversely proportional to
Eion is proportional to Temperature and inversely proportional to charge of ion.
What are the limitations of the Nernst equation
applies only to a situation where a cell membrane is permeable only to one ion
What is the RMP of glia cells
-80mV because they only have leak channels for K+
What does the Goldman equation calculate
Calculating the RMP accounting for both K+ and Na+ equilibrium potentials
If the cell has a higher permeability to one ion how does this affect the RMP of neurons
This ion will have a greater ability to shift the RMP towards its equilibrium. at rest, there is higher permeability to K+ than Na+ so RMP is closer to equilibrium potential for K+. The contribution of Na+ leak channels makes it slightly more positive than -80mV though
What is the ENa and EK+
ENa = +60 mV
EK=-80 mV
What is the goldman equation
Vm= Pk[K+]outside + Pk[Na+]outside divided by
/ Pk[K+]inside + Pk[Na+] inside
