neurotransmission II Flashcards
what are the key events in an action potential?
Threshold reached → Sodium channels open (depolarization) → Sodium channels inactivate and potassium channels open (repolarization) → Potassium channels stay open briefly (hyperpolarization).
do many ions move during an action potential?
No, very few ions move, barely altering concentration gradients.
what is the absolute refractory period?
All sodium channels are inactivated; no new action potential can be fired.
what is the relative refractory period?
Some sodium channels are still inactivated; a very strong stimulus is needed to fire an action potential.
are action potentials graded?
no they are all-or-nothing events
Where are K+ and Na+ concentrated at rest?
High K+ inside the cell, high Na+ outside the cell.
Why is resting membrane potential about -70 mV?
Because the membrane is mostly permeable to K+, and slightly to Na+.
how do action potentials propagate along the axon?
Depolarization opens nearby sodium channels; propagation continues as a wave.
why can’t the action potential go backward?
sodium channels behind are inactivated
what affects action potential speed?
Membrane leakiness, capacitance, axon diameter
how does axon diameter affect speed?
larger diameter = faster conduction
what is saltatory conduction?
Action potentials “jump” between nodes of Ranvier, speeding up conduction.
how does myelin help?
Insulates the axon, reduces charge loss, increases speed and efficiency.
what are the steps of an action potential?
Threshold → Sodium channels open → Depolarization → Potassium channels open → Repolarization → Return to resting state.
why are action potentials unidirectional?
sodium channel inactivation enforces one-way flow
what happens when an action potential reaches the axon terminal?
Voltage-gated calcium channels open, Ca2+ enters, neurotransmitter vesicles fuse with membrane.
what happens after neurotransmitter release?
Neurotransmitter binds ligand-gated ion channels → Postsynaptic ion flow → Depolarization (EPSP) or hyperpolarization (IPSP).
What neurotransmitter is the main excitatory one?
Glutamate (causes EPSPs by depolarizing the postsynaptic cell).
what neurotransmitter is the main inhibitory one?
GABA (causes IPSPs by hyperpolarising the postsynaptic cell)
What is synaptic integration?
Neurons sum excitatory and inhibitory inputs to decide whether to fire an action potential.
what affects input strength?
Distance from axon hillock, neuron shape, location relative to inhibitory inputs.
how do different neurons compute differently?
By varying how they integrate synaptic inputs, like mini-computers.
how is information coded in neurons?
By changing the timing and frequency of action potentials.
What is an example of feedforward excitation and inhibition?
The knee extension reflex (excite extensor muscle, inhibit flexor muscle).
