Neurons Flashcards
What is Hyperpolarisation
Where the inside of the neuron becomes more negative
Define Depolarisation
Where the inside of the neuron becomes more positive
What types of cells are excitable and what does it mean
Neurons and muscle cells are excitable, this means they can respond with a transient change in membrane potential
What influences membrane potential
1-The amount of ion channels present in the membrane influences the permeability of the P.M to the ions
2-The concentration gradients of these ions between the inside and outside of the excitable cell
3-Electrogenic action of Na-K pump (small contributor)
How is the resting membrane potential changed
Change the concentration of ions inside and outside these excitable cells. Change in the number of ion channels in the membrane
Changes to the electrogenic action of the Na-K pump
What is the typical resting membrane potential
-50 to -70 mv
What is a neuron
A principle building block and the instument of communication within the brain
What is the diameter of the soma and typical length of a dendrite projection
soma- 20um and dendrite- 1mm
Where are synaptic potentials formed
They form from the dendritic region and travel towards the cell body
What is the function of the soma
Acts as a computing region, that determines whether a response is carried out to the stimuli
Where are action potentials transmitted
across the axon
Nervous communication is made of what two components
Electrical signals (dendrites, cell body and axon) and chemical signals (synapse)
Why is the membrane potential negative?
The difference in the concentrations of ions between the inside and the outside of the neurone, resulting in more negative charges inside the cell compared to outside
How can you measure RMP
Place one electrode into the intracellular spaces and a reference electrode to extracellular space.
How does the resting membrane potential of glial cells compare to a typical neuron
glial cells have a more negative resting membrane potential (-90mv) compared to a neuron (-60-70mv)
How can you measure the RMP or intracellular potential
Using the patch clamp technique or microelectrode recording technique
Describe the Microelectrode recording technique
A Glass capillary with a thin tip less than 1 micron wide is open and filled with an electrolyte solution. This solution is used to conduct a current and will be connected to an amplifier in order to measure the p.d between the inside and outside of the cell.
The capillary penetrates the cell and a reference or 2nd pole is in the extra cellular space
Describe the patch clamp technique
A series of patch pipettes are used inorder to create a seal between the two ends of the lipid bilayer ( imagine it acting as a bridge which conducts ) lā-l
What is the adv of patch clamp technique
Can measure the pd and current flows for a particular channel you want to look at
Disadv of patch clamp technique
Need to fill the patch pipette with a electrolyte to allow for current to flow, however this has the consequence of causing the dialysis of the cell- a change in the composition of inside hence making an artificial situatuion
What is the respective concentrations of Na+ inside and outside the neuron
150mM outside
15mM inside
What is the concentration of K+ outside the neuron
outside 5mM
Inside 100mM
How are conc gradients for K+ and Na+ maintained?
The action of the Na+ K+ pump. It is also reliant on the fact the membrane is not fully permeable to these ions otherwise the conc gradient would dissapear due to diffusion. NOTE the membrane is partially permeable to Na+ such that Na+ will gradually enter into the cell causing dissapation of the gradient. 3 Na+ out and 2K+ in, using energy from hydrolysis of ATP
Explain the difference in permeability to different ions (Na+ and k+)
There are leaks channels (non gated) and Gated channels ( voltage, ligand, mechanically). Differences in the number of these channels in the membrane will affect the permeability . Note that there are many K+ leak channels and few Na+ leak channels resulting in a greater permeability to K+. K+ diffueses out as the conc inside the cell is much greater than outside the cell. Ratio of perm is 40:1 (K+ to Na+)
What type of channel determines the rmp
leak channels
What can act on the gated channels causing them to open
Mechanical, electrical and chemical can interact with these gated channels causing them to open
Describe equilibrium potential
This is the intracellular potential at which there is no net flow of ions , despite the presence of a conc gradient. Two forces act on the cell at a time 1- Diffusion
2- Electrostatic forces .
E.g- conc gradients drive the movement of k+ ions out of the cell via passive diffusion, this leaves a negative charge into the cell as this occurs and this attracts the ions back into the cell at a point the force due to conc grad and electrical force balance hence no net flow.
What is the E(Na+) and E(K+)
E(Na+)= +60mv E(K+)= -80mv
How can you inteprate the Equil potent for na and k
If the permeability of the cell to K+ was greater than the permeability to na+ then the potential of membrane shifts closer to k+
Nernst equation is used for what and state rmp for glial cells
calculating the ep of ions
glial cells have rmp of -80mv as they only havee leak channels for k+
WHy is the RMP not exactly the ep for the ions in neurons
this is because both k+ and na+ leak channels affect rmp. Higher permeability to a particular ion means better ability of ion to shift rmp to eq value.
Why do Neurons have lower RMP than glial cells
small number of leak Na+ channels that shift the rmp to wards the Ena+ slightly hence rmp is -65mv approx.
Goldman equatin is for what
allows calc of rmp while taking into account the relative permeability to ions and conc
