Neurotransmission (1) Flashcards
What are the names of the researchers who decided “animal electricity” was present in the nerve? And in what year?
Lucia and Luigi Galvani
1781
What is the name (and year) of the researcher who found electricity makes criminals’ corpses twitch
Giovanni Aldini (Galavani’s nephew)
1802
Electrical currents are…
Flows of charged particles
____ charges repel, ____ charges attract
Like, Opposite
Currents only flow through…
Materials that conduct electricity
Voltage is a measure of how much p____ there is for c____ to m____
How much potential there is for charge to move - how much stored electrical energy
Conductance is a measure of what?
How well charge can flow
The amount of current that flows depends on what two things?
- How much potential there is
- How easy it is for the current to flow through the circuit
What is Ohm’s Law?
Current (charge per second or amps) = Potential (volts) x Conductance
OR
Current = Potential / Resistance
What is meant by resistance?
How much a material resists current flow
Around how many times slower is nerve conductance than electricity flows down a wire?
1 million
Currents flow down nerves as a wave of charge movement. This wave of current down an axon is known as what?
The action potential
How do cells signal electrically?
Movement of ions
Electrically charged particle (e.g. sodium chloride = Na+ and Cl-)
Different sizes
Why do cells have a baseline voltage difference across the membrane?
1. W____ is slightly p____ - it has n____ bits and p____ bits, which means the c____ stuff can b____ to it and therefore things like i____ are s____ in water - also the heads of p____ molecules
2. T____ aren’t c____ so they don’t b____ to water and s____ together forming this layer inside the membrane, so water s____ things can’t get through.
- Water is slightly polarised - it has negative bits (the oxygen) and positive bits (the hydrogens) which means the charged stuff can bind to it and therefore things like ions are soluble in water – also the heads of these phospholipid molecules
- Tails aren’t charged so they don’t bind to water and stick together forming this layer inside the membrane, So water soluble things can’t get through
What ions are on the inside and outside of cells?
Outside:
. Na+
. Cl-
. Bit of Ca2+
Inside:
. Proteins (-ve)
. K+
What do ion channels do?
Let ions of the specific channel pass through the membrane
Which way does the potassium concentration gradient go?
How does the create an electrical gradient?
High conc of K+ inside the cell, low conc of K+ outside the cell
Now the inside is negative relative to the outside. This stops more potassium leaving the cell.
An electrochemical gradient is created
Briefly describe the concept of equilibrium potentials, and discuss how negative and positive potentials affect what ions move through the cell membrane
Which direction an ion f____ is dictated by c____ d____ across the m____ and the ion c____ - when both are b____ theres no n____ flow, the membrane potential at which this happens is called the e____ p____.
Which direction an ion flows is dictated by concentration difference across the membrane and the ion charge – when both are balanced there’s no net flow – the membrane potential (voltage) at which this happens is called the equilibrium potential
Lots of K inside cell so will tend to leave, and membrane potential has to get pretty negative to stop the K+ from leaving the cell – so negative equilibrium potential
Lots of sodium outside cell, so tends to go into cell, and will do that very readily when the inside is negative relative to outside – but if membrane becomes really positive, ions will stop entering
Lots of chloride outside so concentration gradient is driving chloride entry to the cell but negative potential inside the cell repels chloride entry
Define equilibrium potential (E)
What are the two things that dictate E?
Potential across membrane at which there is no net flow of an ion
E dictated by concentration difference and ion charge
What does the Nernst equation calculate?
Equilibrium potential for an ion
Says that the equilibrium potential for an ion depends on the temperature, the charge on an ion and the concentration gradient across the membrane of an ion
What is the membrane potential set by?
E____ g____ and p____ of membrane to different i____
Electrochemical gradient and permeability of membrane to different ions
Why is the resting membrane potential of neurons near to the equilibrium potential for potassium?
At rest the membrane is more permeable to potassium than any other ion
What will happen to the membrane potential if the permeability of the membrane to an ion increases?
The membrane potential will move towards the equilibrium potential for that ion
Ion gradients are maintained via s____-p____ p____
Via sodium-potassium pumps
Intracellular transmission is ____
Intercellular transmission is ____
Intra = electrical
Inter = Chemical
What can electrical signals be measured with?
A voltmeter
Resting membrane potential is ____
Negative
Define action potential
Wave of t____ d____ that travels d____ the a____
Wave of transient depolarisation that travels down the axon
What is the resting membrane potential in millivolts?
~-70mV
What happens to the membrane potential when only
1. K+ channels
2. Na+ channels
are open?
- , K+ leaves the cell, until the membrane potential reaches about -80mV
- Na+ enters the cell, making the membrane potential more positive, until the membrane potential is about +60mV
At what voltage are voltage-gated sodium channels and voltage-gated potassium channels activated at?
Sodium = -55mV
Potassium = +30mV
What are some properties of action potentials?
Wave of transient depolarisation of the cell’s membrane
Conveys a fast signal from one place to another in the body
Generated by changes in membrane permeability due to opening and closing of voltage ion channels
Self-regenerating electrical wave
Is a transient change (~1ms) in membrane potential
occurs only if a threshold membrane potential is achieved in the axon initial segment (axon hillock), which transiently opens voltage gated sodium channels
What are the five action potential events?
1. T____ p____ reached
2. D____ due to opening of s____ channels
3. D____ due to i____ of s____ channels and opening of v____-gated p____ channels
4. H____ as v____-gated p____ channels are still o____
5. S____ channels released from i____
- Threshold potential reached
- Depolarisation due to opening of sodium channels
- Depolarisation due to inactivation of sodium channels and opening of voltage-gated potassium channels
- Hyperpolarisation as voltage-gated potassium channels are still open
- Sodium channels released from inactivation (can fire AP again)
What is the scientific word for when all sodium channels are inactivated?
Absolute refractory period
What is the term for when some sodium channels are inactivated?
R____ r____ p____
Relative refractory period
Some sodium gates are inactivated, potassium open and the neuron is repolarising
Action potentials are ____ or ______
All or nothing
(Must reach a threshold point)
