Lecture 4- Membrane potential and the Peripheral nervous system Flashcards
(39 cards)
Do action potentials move in more than one direction? why?
no they move in one direction down neuron because behind them repolarisation is happening immediately as sodium channels are inactivated so they cannot move backwards
How are action potentials triggered?
when the stimulus has reached the the threshold for an action potential
If the stimulus is stronger what happens to the number of action potentials?
more action potentials are created- there is no change to the height of the peak
What is an action potential?
the transient depolarisation of a cell
What do you call cells that generate action potentials?
excitable cells
How do action potentials transfer information?
information is coded by the frequency of action potentials passing along a nerve
What kind of events do action potentials initiate?
cellular events such as muscular contraction
What is the threshold of an action potential?
the critical potential necessary to depolarise the cell
Can anything happen when the cell is repolarising?
no
What is hyper-polarisation?
when the membrane potential how become more negative than the resting potential
What is the all or nothing law?
once an action potential has been initiated varying the strength pf the stimulus does not alter the configuration of the action potential
What did experiments by alan hodgkin and huxley show?
depolarisation was due to a transient increase in membrane Na+ permeability but eventually the membrane returns to its resting state
-membrane potential repolarises to the resting potential and the action potential terminates
- repolarisation is aided by an ever greater than normal increase of K+ permeability
What does sodium influx and potassium efflux do?
sodium influx causes depolarisation
potassium efflux causes repolarisation
Describe the process of an action potential
- resting membrane potential exists
- stimulus depolarises membrane potential to the threshold
- voltage gated Na and K channels begin to open
- rapid entry of Na+ depolarises the cell
- Na channels close and slower K channels open
- K+ moves from cell to extracellular fluid
7.K+ ions remain open and additional K ions leave the cell causing hyperpolarization
8.voltage gated K+ channels close and less K ions leak out of the cell - cell returns to resting ion permeability and resting membrane potential
How is an action potential initiated?
the cell must be depolarized from the resting membrane potential to the threshold potential,
- at the threshold potential voltage activated ion channels open and allow cations to enter the cell- this generates the action potential
what does a stimulus do?
- an action potential requires energy to be added to the sytem in the form of a stimulus
- if a cell needs a larger stimulus it is less excitable
- the magnitude of the required stimulus determined excitablility of the cell; if a small stimulus is required the cell is usually more excitable
How can we get from a resting to a threshold potential? What are the different ways to make this happen?
- atrificial application of a current
- neurotransmitters bind to ligand-gated channels on a target cell
-pacemaker cells can bring action potentials spontaniously - sensory cells
What is the trigger zone?
the region of a cell that generates an action potential- represented by the reversal of the membrane potential polarity
what is the local circuit hypothesis?
that a local current precedes the action potential wavefront in the cytoplasm
a local current precede the action potential wavefront in the cytoplasm, What happens if some of this current leaks across the membrane?
what happens is that voltage gated Na+ channels open and Na enters the axon
- this results in a positive charge flowing into the sections adjacent to the movement of the local current flow
;as the current leaks across the membrane it depolarises it
What does local current flow from the active region do?
the local current flow from the active region causes new sections of the membrane to depolarize
What does the refractory period do? How is the membrane repolarised?
the refractory period prevents backwards conduction; in the refractory period potassium is being lost from the cytoplasm in order to repolarise the membrane
What factors affect how rapidly information can be sent from your brain to your body using action potentials?
-cell diameter
CV increases as the fibre diameter increases
-temperature
increasing temperature generally increases conduction velocity
-myelation
myelin increases CV sd the AP jumps from node to node; this is known as saltatory conduction
