L8-11 Excitable Cells Flashcards
The action potential in a neurone originates at the ? and moves towards the ? ⚡️
Axon hillock, axon terminal
An action potential is a rapid change in the..
Membrane potential
Resting membrane potential (RMP/ Em) is…
-70mV
Resting membrane potential is maintained by the action of (2)…
- Potassium leak channel
* Sodium/Potassium ATPase pump
The Na+/K+ ATPase pump can be described as electrogenic because…
It creates an electrical gradient between the inside and outside of the membrane
The Nerst Equation calculates the point at which the concentration gradient and the electrical gradient balance out, a.k.a….
The equilibrium potential ⚖️
E ion =
( -RT /zF ) * ( ln [ion] in / [ion] out )
An action potential can be divided into 3 distinct phases…
- Depolarisation
- Repolarisation
- Hyperpolarisation
The voltage gated ion channels involved in action potentials are (2)…
- Voltage gated Sodium channel
- Voltage gated Potassium channel
The refractory period can be divided into 2 phases…
- Absolute Refractory period
2. Relative Refractory period
The absolute refractory period is defined as the…
Period in which the membrane cannot generate another action potential, no matter how big the stimulus
The relative refractory period is defined as the…
Period in which the membrane can generate another action potential, but only if the stimulus is bigger than normal
Why is a greater stimulus required during the refractory period in order to generate an action potential?
Because the membrane is hyperpolarised, so the membrane potential is more negative than usual, thus further from the threshold
Action potentials travel down the axon via…
Current loops 🔁
Backwards movement of an action potential is prevented by…
The refractory period
Action potentials are caused by an influx of (A) and an efflux of (B) through voltage-dependent ion channels
(A) = Sodium ions (IN) (B) = Potassium ions (OUT)
During depolarisation, the membrane potential ( increases to 30mV / decreases to -70mV / stays the same )
Increases to 30mv
During depolarisation, the membrane potential decreases, because the voltage gated potassium channels are ( open / closed )
Open
Voltage gated sodium channels open quickly, inactivate quickly and close ( quickly / slowly )
Slowly 🐢
Voltage gated sodium channels are opened when the membrane potential exceeds the threshold voltage (-55mv). Inactivation and closure are ? dependent.
Time 🕐
The voltage gated potassium channel is either open or closed. These phases are ( slow / fast ) and both voltage gated.
Slow 🐌
The three factors affecting action potential velocity (V) are…
- Diameter (D) - more room for current loops
- Membrane resistance (Rm) - less current lost
- Distance between Modes of Ranvier - shorter distance = faster
To increase membrane resistance (Rm), some axons are surrounded by a…
Myelin sheath
The action potential ‘jumps’ from node to node. This is known as…
Saltatory conduction
Myelination has ( no effect / a significant effect / a small effect ) on conduction velocity (V).
A significant effect
NMJ stands for…
NeuroMuscular Junction
The synaptic cleft is only ? across.
50nm
In the NMJ, the post-synaptic membrane is known as the…
Muscle endplate
The muscle endplate features invaginations known as…
Junctional folds
An increase in ? concentration in the axon terminal causes vesicles to migrate and fuse with the pre-synaptic membrane.
Ca2+
The Acetylcholine (Ach) receptors on the muscle endplate also function as…
Ligand-gated sodium channels (the ligand being Ach)
The Ach receptor protein is also permeable to potassium ions, thus potassium ions move out from the (synaptic cleft / muscle endplate) via ion channel mediated facilitated diffusion.
Muscle endplate
The endplate potential (EPP) is ? mV, which is between the equilibrium potentials of sodium and potassium
-15mV
There is no action potential at the muscle endplate because…
There are no voltage gated sodium channels!
Mini endplate potentials (mini EPPs) measure ? mV
0.5mV
An mEPP represents the random fusion of a single ? with the membrane.
Vesicle
One mEPP equates to one vesicle, which is known as…
One ‘quantum’
Although 100 vesicles can generate sufficient change in membrane potential, 200-300 are generated as a…
Safety factor
Acetylcholine is broken down by…
Acetylcholineesterase (Ach-ase)
The EPP triggers an action potential via…
Nearby voltage gated sodium channels in the junction folds
Curare is South American arrow poison, which blocks the Ach receptor. It is administered as a…
Muscle relaxant by anaesthetists
Myasthenia Gravis is an autoimmune disorder which results in the…
Destruction of Ach receptors
Myasthenia Gravis is treated by increasing the availability of Ach by using…
Ach-ase inhibitors (Anti-cholineesterase)
