Karteikarten
Week 1
Karten in diesem Stapel (15)
- 1What maintains gradients of ions across cell membranes?Ion pumps
They use energy to move ions against the conc. gradient. This leads to cells generating electrical signals. They only recognise changes in conc over longer periods of time (maintain conc over the long-term)
They DO NOT set the resting Em!! - 2What are the different gating mechanisms and what do they control?Non-gated (leak): set the membrane potential (Em) of resting membrane
Voltage: generate action potentials
Ligand (chemical): generate Em changes at synapse - 3What 2 aspects influence the resting membrane potential?1) Factors influencing ion movement across membranes (affected by electrical force as the chemical gradient does not change)
2) The permeability factor of each ion (determined by the number of leak channels for that ion) - 4What happens to the movement of K+/Na+ across a cell membrane?K+
1) The chemical gradient causes K+ efflux. This causes a negative Em (due to a loss of +ve charge)
2) A negative Em causes K+ influx
3) When Em is sufficiently negative, K+ efflux=influx. The chemical and electrical influence are balanced and there is no net movement
Na+
1) Chemical gradient causes Na+ influx
2) This leads to a positive Em which repels other Na+ from entering the cell
3) At a positive Em, the chemical and electrical influences are in balance and there is no net movement. - 5What is the resting membrane potential? How does it occur?-65mV
Both the chemical gradient and the electrical force cause Na+ to move into the cell (net Na+ influx). The electrical force is causing K+ influx, but the chemical gradient is greater and causes net K+ efflux.
Na+ influx must equal K+ efflux. Na+ has a large driving force but a low permeability factor (not many leak channels). However K+ has a small driving force (-65mV is close to Ek of -80mV) but a higher permeability factor (Pk is 40x PNa). - 6What needs to happen to the channels for depolarisation and repolarisation to occur?Depolarisation:
-Higher Na+ influx required, increase PNa
Repolarisation:
-Higher K+ efflux required so Pk increases. PNa has to decrease (close 'extra' Na+ channels) - 7What is conductance of ions equal to? Why do we measure conductance instead?Permeability
Easier to measure - 8What happens during depolarisation?1) Voltage-gated Na+ channels open gradually (increases gNa)
2) As more Na+ ions enter the cell, the cell further depolarises, further increasing gNa
3) Em approaches ENa, but doesn't reach it due to K+ leak channels - 9What happens during repolarisation?1) Na+ channels inactivate which decreases gNa
2) Na+ influx stops
3) V-gated K+ channels open, increasing gK
4) K+ exit the cell so Em approaches Ek - 10What happens during hyperpolarisation/return back to resting Em?1) gK rises after the Em returns to rest. This is because the V-gated K+ channels also respond to depolarisation, but are slow to open and close
2) Em approaches EK
3) The V-gated K+ channels close, reducing gK
4) Em returns to resting value via leak channels - 11What is threshold?The Em value for where Na+ influx (v-gated/leak)> K+ efflux (leak).
The initial stimulus has to bring the Em above threshold for an action potential to occur. - 12What are the 2 types of refractory periods?Absolute: no further action potential by any stimulus. The Na+ channels are inactivated and many K+ channels are still open.
Relative: need a stronger stimulus (a bigger depolarisation) Sufficient Na+ channels are needed to overcome to increased gK (higher threshold). The Na+ channels are still recovering from inactivation and there are a few K+ channels open. - 13How is an AP propagated in an unmyelinated axon?1) There is electronic spread due to local current flow
2) When the AP moves forward, it causes depolarisation and V-gated Na+ channels open. A new AP is generated.
3) When the AP moves backwards, it causes depolarisation, but another AP is not generated. Na+ channels are inactivated (relative refractory period) - 14How is an AP propagated in a myelinated axon?-The glial cells wraps around the axon forming a myelin sheath
-Sheath acts as an electrical insulator
-V-gated channels open at Nodes of Ranvier
-Since the AP is propagated between nodes, it flows further and faster (saltatory conduction) - 15What does the conduction velocity of an action potential depend on?1) Myelination (faster is myelinated)
2) Diameter (faster if a larger diameter)
Informationen
- Beschreibung
- Membrane physiology & Neuronal excitability
- Erstellt von
- Dolu Falowo
- Aufrufe
- 2
- Bewertung