Neurophysiology: Neural Signals and Transmission Flashcards
Is the electrical potential negative or positive in cells?
Negative
What is the resting membrane potential?
Within excitable cells there is the capacity to change and become more and less negative
What is concentration gradient?
Difference in concentration of a dissolved substance in a solution between a region of high density and one of lower density
What is the resting membrane potential in most neurones?
-70mV
What generates an electrical current?
The difference in the electric potential
What happens when the neurone is inhibited?
Hyperpolarisation, the inside of the membrane is more negative than typically
What is depolarisation?
When the neurone is stimulated and moves closer towards 0
What are the phases during action potential?
Resting potential, rising phase, overshoot (depolarisation), the falling phase, the undershoot (hyperpolarisation), repolarisation
What is passive diffusion
Movement of particles in a fluid from regions of high conc to low until equilibrium is reached
What happens when the molecules are evenly distributed across a fluid?
No net diffusion
What causes the resting membrane potential?
The movement of potassium ions out of the cell
What is the reversal potential?
The point at which direction the net current flow reverses which is the same as the membrane potential
What is the driving force
The rate of net current flow for a particular ion being proportional to the difference between the membrane potential and the equilibrium potential
What is the graded potential?
The local depolarisation of the cell membrane in response to a stimulus
What causes the action potential?
The movement of sodium ions into the cell
What creates an electrostatic gradient?
Charged particles that generate electrostatic forced due to oppositely charged ions being attracted to each other
What is the ratio of the sodium gradient?
10:1, sodium is higher outside the cell
What is the ratio of the potassium gradient?
40:1, potassium is higher inside the cell
What does the sodium-potassium pump do?
Maintains the sodium and potassium gradients of the cell, 3 NA out of the cell and 2 K into the cell
How much energy does the sodium potassium pump consume?
A single ATP molecule
What ion is the neuronal membrane mainly permeable to?
Potassium
What occurs when the potassium diffuses out of the cell?
The inside of the cell builds up a slight excess of negative charge
What occurs at equilibrium in the resting membrane potential?
No net flow of potassium
What will occur if sodium enters the cell?
The inside of the membrane will build up a slight excess of positive charge
What is the action potential dependent on?
Voltage-gated ion channels
What are the two gated channels?
Ligand-gated and voltage-gated ion
What is a ligand-gated channel
A channel that opens in the presence of a signalling molecule that acts as a binding site on the extracellular area of the channel
What is a voltage gated ion channel?
Channels that open and close in response to changes in the membrane potential
What is the structure of the voltage gated ion channel?
Integal membrane proteins, pore loops for a selective filter and a charged domain as a voltage sensor
What is the structure of the VG sodium channel?
Single large protein with 4 repeating motifs
What is the structure of the VG potassium channel?
4 subunits and a characteristic motif
What happens to VG ion channels at rest compared to depolarisation?
Rest= closed. Depolarisation= open
Why do the VG ion channels ion in depolarisation?
Due to the voltage sensors (S4)
What happens to the voltage gated sodium and potassium channels in depolarisation?
NA= open very quickly
K= open after a delay of 1 millisecond
How is an action potential triggered?
By the neuronal cell body being depolarised by 15mV to reach the threshold value of -55mV
What occurs at the threshold depolarisation?
A positive feedback loop so NA+ flows into the neuron so more VG NA channels open so NA+ can enter the cell
When will the action potential be propagated?
During depolarisation to the threshold, in a series of action potentials
What does the inactivation gate on the VG NA channels do?
Closes at the peak of action potential and will not re-open until repolarisation
What is the refractory period?
When an action potential cannot be triggered until the sodium channel inactivation gate has reopened during repolarisation
What is an electrotonic wave?
When the action potential is triggered in a certain part of the axon so a localised current of sodium is generated
How does the electrotonic wave spread?
Along the axon in both directions and then decays when the positive charge goes across the neuronal membrane
What occurs to the electrotonic wave in an unmyelinated axon?
Action potentials are close together as the electrotonic wave reaches a short diatance to trigger the next action potential
How does bigger axon diameters effect nerve impulses?
Speed them up as there is less electrical resistance to the current flow so the electrotonic wave moves further as action potentials are not close together
What does myelin sheath do?
Insulates axons and prevents current leakage
What is myelin sheath made of?
300 layers of lipid rich cell membrane
What are nodes of Ranvier?
Gaps between myelinated segments on an axon
