3.6.2.1 Nerve impulses Flashcards
describe resting potential
inside of an axon has a negative charge relative to outside. (more positive ions outside)
explain how a resting potential is established across the axon membrane in a neurone
Na+/K+ pump actively transports 3Na+ out of axon and 2 K+ into axon
creating an electrochemical gradient
higher K+ conc inside and higher Na+ conc outside
differential membrane permeability
more permeable to K+ , moves out via facilitated diffusion
less permeable to Na+
explain how a stimulus can lead to depolarisation of an axon.
Na+ channels open, membrane permeability to Na + increases.
Na + diffuse down electrochemical gradient
explain how changes in membrane permeability leads to depolarisation and generation of an action potential.
1.stimulus
2. depolarisation
3. repolarisation
4. hyperpolarisation
5. resting potential
- Stimulus - Na+ channels open, membrane more permeable to Na+
Na diffuses into axon down electrochemical gradient
2.) Depolarisation- if threshold potential reached, an action potential is generated
as more voltage gated Na channels open
so more Na diffuse in rapidly
3.) Repolarisation - voltage gated Na channels close, Voltage gated K channels open, K diffuses out of axon
4.) Hyperpolarisation K channels slow to close therefore there is a slight overshoot too many K diffuses out
5.) Resting potential - restored by Na/K pump
describe the all or nothing principle
for an action potential to be produced, depolarisation must exceed threshold potential
action potential produced are always the same magnitude
bigger stimuli increases frequency of action potentials
explain how an action potential travels across a non myelinated neurone
action potential passes as a wave of depolarisation
Influx of Na+ in one region increases permeability of adjoining region to Na+ by causing voltage gated Na+ channels to open so adjoining region depolarises
explain how an action potential travels across a myelinated neurone
myelination provides electrical insulation
depolarisation of axon only occurs at nodes of ranvier
results in saltatory conduction
so no need for depolarisation across whole length of axon
suggest how damage to the myelin sheath can lead to slow responses or jerky movement
no saltatory conduction so depolarisation occurs whole length of axon. nerve impulses take longer to reach neuromuscular junction, delays muscle contraction
ions may leak to other neurons causing wrong muscle fibres to contract
describe the refractory period
time taken to restore axon to resting potential when no further action potential can be generated
as na channels are closed
why is the refractory period important?
ensures discrete impulses are produced so action potentials dont overlap
limits frequency of impulse transmission at a certain intensity so no overreaction to stimulus
ensures action potentials travel in one direction, cant be propagated in a refractory region
describe the factors that affect speed of conduction
myelination -saltatory conduction as depolarisation only needs to occur at nodes of ranvier, not whole length of axon
axon diameter -less resistance to flow of ions
temperature - increase rate of dissusion of Na+ and K+ as more kinetic energy
but proteins / enzymes could denature
