1/23 Neurotransmission Flashcards
What prevents ion exchange and is necessary for neuron function?
phospholipid bilayer
What kind of ion channels are found in neurons?
sodium, potassium, chloride
What is the membrane potential?
difference in electrical charge between the inside and outside of the neuron
What changes membrane potential?
movement of ions through the channels
At rest the average neuron has a membrane potential of
-65 mV
What is depolarization?
when the membrane potential becomes more positive (moves toward 0).
What is hyperpolarization?
when the membrane potential becomes more negative
There is a pull on each ion to go through the channels based on?
concentration
electrical imbalances
What is equilibrium potential?
the flow of ions in and out has the same pull
What is the initial equilibrium potential of Na+?
initially drawn in by both electrical and concentration gradients
As the membrane potential reaches zero what happens to the electrical gradient for Na+?
electrical gradient starts pulling Na+ back out of the cell
What is the electrochemical gradient for Na+?
+60 mV
What is the electrochemical gradient for K+?
-85 mV
What is the electrochemical gradient for Cl-?
-65 mV
How is equilibrium for electrochemical gradients calculated?
using the Nernst equation
If the current membrane potential is at -70mV which direction will the Na+ ions go to reach their equilibrium?
enter the cell
the concentration gradient would pull into cell
the electrical gradient would pull into cell (+60mV)
If the current membrane potential is at -70mV which direction will the Cl- ions go to reach their equilibrium?
exit cell
electrical gradient stronger pulling negative ions out
concentration gradient weaker but would pull ions into cell
If the current membrane potential is at -70mV which direction will the K+ ions go to reach their equilibrium?
exit cell
electrochemical gradient would pull ions out of cell (-85mV)
concentration gradient would pull ions out of cell
What is happening to ion channels at rest?
K+ channels are open and ions flowing extracellularly
Half as many Cl- channels open (flow depends on membrane potential)
25x less Na+ channels
continuous flow helps to maintain stable resting membrane potential of -65mV
What happens with the sodium potassium pump?
To move potassium back into the cell and sodium out of the cell it requires energy (ATP activates sodium potassium pump)
3 Na+ are transported out
2 K+ are transported in
keeps resting membrane potential at -65mV
What are the dynamic changes in potential?
EPSP - excitatory postsynaptic potentials
IPSP - inhibitory postsynaptic potentials
Each EPSP adds to the previous one to create a summative change to the membrane potential
What happens with EPSP’s?
Stimulus may cause the sodium channels to open
Na+ will come into the cell causing depolarization
What happens with IPSP’s?
When chloride channels open it makes depolarization less likely
What is the action potential?
When the membrane potential decreases past threshold (≈ - 50mV) it creates a sudden opening of voltage gated sodium channels (Rising phase)
1 msec later sodium channels are deactivated and voltage
gated potassium channels are activated causing a rapid repolarization (Falling phase)
Once this process starts all parts will run until completion – “all or none”
What is the absolute refractory period?
Once the membrane potential has crossed the threshold another action potential cannot begin until it has once again dropped below this level.
The voltage gated sodium channels close after the peak and won’t reopen until below threshold.
What is the relative refractory period?
Once below threshold again the potassium channels remain open for a moment and will undershoot the resting membrane potential
During this time it requires a much stronger stimulus to reach threshold again.
How is the action potential released?
progressively along the axon
What makes the impulse faster?
larger axons
thicker myelin
What are the gaps in myelin? How do signals travel along these?
nodes of Ranvier
saltatory conduction
What happens with chemical synapses?
action potential reaches end of axon = stimulates release of neurotransmitters
neurotransmitters reach receptors on postsynaptic membrane
enough binding of neurotransmitters = action potential
What kinds of effects can neurotransmitters have?
excitatory (EPSP)
inhibitory (IPSP)
neuromodulary
What are neurotransmitters composed of?
molecules or amino acids
Do neurotransmitters have the same effect on different receptors?
no, different effects
How many neurotransmitters can be released in a single synapse?
multiple
What are the excitatory neurotransmitters?
glutamate, histamine
What is glutamate?
The most common excitatory neurotransmitter
Found and acts throughout the CNS
What does histamine do?
neuromodulary function
What are the inhibitory neurotransmitters?
gamma-aminobutyric acid (GABA)
glycine
What is GABA?
The most common inhibitory neurotransmitter
Found and acts throughout the CNS
What does glycine do?
Found in the spinal cord
Acts on the spinal cord and brainstem
What do neuromodulators do?
change how neurons function
firing rate, synaptic efficacy, +/- currents
What are the neurotransmitters that perform neuromodulation?
dopamine, serotonin, histamine, norepinephrine, neuropeptides, acetylcholine
What does dopamine neuromodulate?
Substantia nigra & ventral tegmental area
What does serotonin neuromodulate?
Raphe Nuclei
What does histamine neuromodulate?
Hypothalamus & reticular formation
What does norepinephrine neuromodulate?
Sympathetic (postsynaptic) ganglia & locus ceruleus
What do neuropeptides neuromodulate?
entire CNS
What does acetylcholine neuromodulate?
Preganglionic autonomic synapses
Postganglionic parasympathetic synapses
Neuromodulator effect in small areas of the CNS
(all autonomics except postganglionic sympathetics = norepinephrine)
What is the primary neurotransmitter in neuromuscular junctions?
acetylcholine
