13.4 Nervous Transmission Flashcards
What is resting potential
When in a resting axon the inside of the axon always has a negative electrical potential compared to the outside of the axon
What is the potential difference when there is no impulse
Usually about -70mV
Inside of axon has electrical potential about 70mV lower than outside
There are two factors which contribute to establishing and maintaining the resting potential what are they
- the active transport of sodium ions and potassium ions
- differential membrane permeability
Sodium potassium pumps present in membranes of neurones pump what
Use atp to actively transport 3 sodium ions out of the axon for every 2 potassium ions that they actively transport in
Meaning there is a Greater concentration of positive ions outside the axon than There are inside the axon
The movement of ions via the sodium potassium pump establish what
Establishes an electrochemical gradient
Outline the protein channels on a cell surface membrane of neurones
They allow sodium and potassium ions to move across membrane by facilitated diffusion
They are less permeable to sodium ion than potassium ions
Meaning that potassium os can diffuse back down their concentration gradient out of axon at a faster rate than sodium ions
What is an action potential
Action potential is not a flow of electrons but instead occurs via a brief change in the distribution of electrical charge across the cell surface membrane
What are action potential caused by
Caused by rapid movements a of sodium ion and potassium ions across the membrane of the axon
What do voltage gated channel proteins do
They open and close depending on electrical potential across axon membrane
They are closed when the axon membrane membrane is at resting potential
What things occur during action potential
Stimulus, depolarisation, repolarisation, hyperpolarisation and the return to resting potential
Stage 1 stimulus
- sodium in channels open
- whe large enough stimulus detected by a neurone the resting potential can be converted into an action potential
- potential difference -55mV to trigger depolarisation
Stage 2 depolarisation
inside membrane - high k+ & Na+
Outside membrane - low K+, decreasing na+
- example of positive feedback
- action potential rises form -70 to +30mV
Voltage gate sodium channels open
Voltage gated potassium channels closed but leaking
Stage 3 repolarisation
Inside membrane: decreasing K+, high Na+
Outside membrane: increasing K+, low Na+
Axon membrane potential: decreases from +30 to -70mV
Voltage gated sodium channels: closed
Voltage gated potassium channels: open
Example o negative feedback
Stage 4 hyperpolarisation
Inside membrane: decreasing K+ & Na+
Outside membrane: low K+, Na+ increase
Axon membrane potential: -70 to -80mV
Voltage gated sodium channels: closed
Voltage gated potassium channels: closed
