Lecture 30 - Neuronal Communication Flashcards
Structure and fundamental task of a neuron
structure: cell body (with nucleus), usually one long axon and several shorter, branching dendrites
function: to receive, integrate, conduct and transmit signals
How did we figure out that neurons are discrete cells?
- a scientist injected ink into neurons and noticed that the ink diffused throughout the cell, but did not diffuse further
Membrane potential
- the difference in the concentrations of ions on opposite sides of the membrane
- cell membranes: -70 to -40 MV
- depolarization: interior voltage becomes less negative
- hyperpolarization: interior voltage becomes more negative
- cells read change in voltage and use it as an intracellular signal
When a neuron is not active, its membrane potential is called _______ ________
resting potential
What channels do excitatory signals open? What about inhibitory signals?
excitatory: NA cation channels open, depolarize membrane
inhibitory: open either Cl- or K+ channels, suppresses firing -> hyperpolarize the membrane
Membrane potentials _______ through the membrane
propagate; depolarization is spread to open channels down the axon => continues to spread depolarization
What type of channel spreads the depolarization through the neuron/ nervous system/
Voltage-gated sodium channels?
How is the membrane repolarized?
- requires delayed opening K+ channels
- these channels open in response to membrane depolarization (i.e., also voltage-gated), but have slower kinetics (i.e., open slower)
- ends the depolarization phase
What 3 things give rise to a traveling action potential?
changes in
1. Na+ channels
2. K+ channels
3. current flows
Explain the process of action potentials
- resting state: all gated Na and K channels closed. resting potential is about -60mV
- depolarizing phase: Na channels open, action potential starts when neuron is depolarized by about 20mV to its threshold potential. potential rapidly becomes positive, reaching a value of +40mV
- repolarizing phase: Na channels inactivated and K channels open. once cell reaches its peak positive potential, it repolarizes, returning to a negative potential
- hyperpolarizing phase: K channels remain open and Na channels close. often membrane potential becomes more negative than the resting potential
At what specialized sites are neuronal signals transmitted?
synapses
Chemical vs electrical synapses
chemical:
- neurotransmitters + receptors
- synaptic cleft
- common
electrical:
- gap junctions
- no neurotransmitters
- faster
What is a neurotransmitter?
- a small signal molecule secreted by the presynaptic nerve cell at a chemical synapse to relay the signal to the postsynaptic cell
- diverse molecule types
What happens when the action potential reaches the presynaptic site?
the depolarization of the membrane opens voltage-gated Ca channels that are clustered in the presynaptic membrane
What happens after Ca channels open?
Ca influx triggers release of small molecules known as neurotransmitters into the cleft
- NTs are stored in membrane-enclosed synaptic vesicles and released by exocytosis
What do the NTs do once they are released?
- they diffuse rapidly across the synaptic cleft and provoke an electrical change in the postsynaptic cell by binding to and opening ligand-gated ion channels
What is commonly used to measure increases in intracellular Ca in neurons? What does this signify?
- fluorescent calcium sensors
- a way of measuring neuronal activity
Neuromuscular junction
- specialized chemical synapse between a motor neuron and a muscle cell
- motor neurons release Ach onto AchR located on muscle cells
AchR
- a ligand-gated ion channel
- opens transiently by acetylcholine released from the motorneuron
Optogenics
- biological technique to control the activity of neurons or other cell types with light
- achieved by expression of light-sensitive ion channels in neurons
- channelrhodopsins are photosensitive ion channels that open in response to light
