Lecture 13 Flashcards
(16 cards)
Properties of action potential?
Change in voltage across membrane
Depends on ionic gradients and membrane permeability
Only occurs if threshold reached
Propagated without loss of amplitude
All or nothing
Where is an AP intiated?
At the axon hillock of a neuron. Depolarisation travels to axon hillock where it may trigger an AP
What ion is responsible for AP
Sodium, if low extracellular sodium less likely to get AP
Why after AP does membrane potential dip below resting potential?
Sodium channels open to cause upstroke. Potassium channels then open to try hyperpolarisation the membrane again. These remain open for a bit longer and cause potential to dip below the resting value temporarily.
How does threshold lead to AP
Sodium channels engage in positive feedback mechanism where depolarisation causes them to open and them opening causes further depolarisation which causes more to open etc until K+ channels also open
What do ARP and RRP stand for?
Absolute refractory period and relative refractory period. During relative can get AP but quite difficult
Why do sodium channels open with depolarisation?
Change in membrane potential causes them to go through a conformational change. Na channels have one subunit as opposed to 4 for K+ channels
How do local anaesthetics like lidocaine work?
Block sodium channels and so stop action potentials.
What is the length constant?
Distance for potential to fall to 37% of its original value. Longer length constant means faster conductance
How well App will spread depends on capacitance and resistance of membrane.
High capacitance means the membrane can store charge well
High resistance means a lower number of ion channels are open.
Low capacitance= voltage moves fast
High resistance= moves further
Why is a refractory period important?
Ensures AP only travels in one direction
What cells form the myelin sheath?
Oligodendrocytes in the CNS and schwann cells in the PNS
What is the advantage of myelination?
It increases the length constant through increasing resistance and decreasing capacitance.
Leads to faster conduction velocity
Disease of CNS affecting conduction of AP’s?
MS a demyelination disease is the most common demyelination get disease
What is a node of ranvier?
Gap between myelin sheaths where you get high concentration of Na+ channels to generate action potential
What is Saltatory conduction?
Term to describe the way action potential jumps from node to node in myelinated axons
