Neurotransmission Flashcards
What is the resting membrane potential?
- -70mV*
- Inside of neuron has net negative change relative to outside
- More potassium leak channels than sodium: membrane more permeable to K+ than Na+
What is the potential difference?
When positive and negative electrical changes are held apart.
What is the potential difference across plasma membrane called?
Membrane potential.
How is the resting membrane potential maintained?
Through sodium potassium exchange pump.
Describe the function of the Sodium Potassium Exchange Pump
Grabs 3 sodium ions and forces it outside of neutron against concentration gradient.
Grabs 2 potassium ions to inside of neutron.
Requires ATP (energy)
What types of ion channels are in plasma membrane of neuron?
- Passive (leak) channels
- Active (gated) channels
How do the passive (leak) channels work?
“Doors” in plasma membrane that is always open (i.e. passive sodium and potassium channels which maintain resting membrane potential).
How do the active (gated) channels work?
- Shut at rest
- Requires a key/stimulus to unlock the channel.
- Ions to move in and out of neuron.
- Change membrane potential making it more or less negative
What are the 3 types of active gated channels?
- Chemically gated channel
- Voltage gated channel
- Mechanically gated channel
What stimulus is required to open chemically gated channels?
Specific chemical.
What stimulus is required to open voltage gated channels?
Change in voltage.
What stimulus is required to open mechanically gated channels
-Mechanical Stimulus (plasma membrane physically distorted- pull, push, stretch).
What is a graded potential?
Local and temporary change in the membrane potential.
What happens if several stimuli arrive on neuron at same time?
Net effect on membrane potential is sum of all graded potentials.
What happens when the membrane potential is less than -55mV or -60mV at axon hillock.
Neuron will discharge an action potential.
This travels from axon hillock –> axon terminal.
What is an action potential?
- Brief reversal of the membrane potential
- Starts at axon hillock, the propagates down axon to axon terminal in 1 direction
- All or none event
What are the four key steps involved in generating an action potential?
1) Stimulus that initiates action potential is a graded depolarization- large enough to open voltage-gated sodium channels.
Opening of channels occur at the threshold (-60mV).
2) Voltage-gated sodium channels open and sodium ions move into the cell. Membrane potential rises to +30mV. Inside contains more positive ions than negative ones.
3) Sodium channels close, voltage-gated potassium channels open. Potassium ions move out of cell.
4) Potassium channels close, both sodium and potassium channels return to their normal states. Voltage-gated potassium channels close as membrane reaches resting potential (-70mV) via sodium-potassium exchange pump.
How does the brief reversal of the membrane potential move
- A fuse: myelin increases speed of propagation of action potentials as it wraps around axon.
- AP jumps segments without myelin (nodes of Ranvier)
- Faster with larger diameter
What is an important key point to remember for neurotransmission?
Sodium rushes in at beginning of action potential
What are the two kinds of neurotransmitters present in chemical synapse?
- Peptide neurotransmitters
- Amine and Amino Acid Neurotransmitters
How are peptide neurotransmitters stored in the axon terminal?
In the secretory granules.
How are amine and amino acid neurotransmitters stored in axon terminal.
In the synaptic vesicles.
What are the four key steps involved in the release of an amine or amino acid neurotransmitter from the axon terminal?
- Arrival of action potential at axon terminal.
- Voltage-gated calcium (Ca2+) channels open and Ca2+ enters presynaptic neuron.
- Synaptic vesicle fuses to plasma membrane.
- Neurotransmitter released into synaptic cleft via exocytosis.
What effect does neurotransmitter have on the postsynaptic neuron?
- Binds to receptor on membrane of post-synaptic neuron.
- Positively charged sodium ions flow into postsynaptic neuron, changes membrane potential to less negative
- Binds to receptor then activates G protein to open ion channels and activates enzymes in postsynaptic neuron.
What processes decrease the amount of neurotransmitter that is present in the synaptic cleft?
1) Re-uptake: recycling neurotransmitter back inside presynaptic neuron.
2) Enzymatic Degradation: enzyme breaks neurotransmitter into smaller parts.
3) Drifts away from synapse, no longer exerts effect.
