Week 1 - Neuron Communication Flashcards
1
Q
What are the driving forces for movement of dissolved particles?
A
- Permeable membrane: Difference in concentration - particles will move in direction of least concentration (greater the difference, greater the drive)
- Semi-permeable membrane: Difference in net charge - if electrical drive equals the chemical drive (concentration), then net movement of ion stops as driving force = 0
2
Q
What sets up resting membrane potential?
A
- Large anions inside cell that cannot get out - make inside of cell negative
- Sodium potassium pump removes 3 Na+ charges out but only brings in 2 K+ charge in - makes inside cell negative
- Potassium leak channel - K+ is driven out by net electrochemical drive - makes inside cell negative
3
Q
What are the main features that determine neuron resting potential? Diagram 1
A
- Leak channels
- Sodium-potassium pump
- Potassium-Chloride Symporter
- Sodium-Calcium Antiporter
- Voltage-Gated Channels
4
Q
What is the voltage inside cell, and intracellular and extracellular ion concentrations of neuron at rest?
A
- Voltage ~ -70 mV
- Concentration:
a) K+ greater inside than outside - electrochemical drive leading out
b) Na+ greater outside than inside - electrochemical drive leading in
c) Ca2+ greater outside than inside - electrochemical drive leading in
d) Cl- greater outside than inside
e) AO- greater inside than outside
5
Q
What are the structures of a neuron? Diagram 2
A
- Dendrites
- Cell body (soma)
- Axon
- Myelin sheath
- Synaptic terminals
6
Q
How do dendrites change membrane potential?
A
- Excitatory input - Na+ channels at dendrites open
a) When summation of inputs reaches threshold (-50 mV) then threshold voltage reaches trigger zone to start change in membrane channel
7
Q
How are action potentials formed? Diagram 3
A
- Once -50 mV threshold is met, voltage gated Na+ gates open and Na+ pours in
- K+ voltage gates open and K+ pours out
- At +40 mV, Na+ gates close and Na+ stops entering but K+ continues to flood out, so inside cell starts to become negative quickly
- At -90 mV, K+ voltage gates close and K+ stops flooding out
- Sodium-potassium pump kicks in and slowly returns to resting membrane potential
8
Q
What are the features of action potentials?
A
- Lasts a few milliseconds
- “All or none” response - it always hits when threshold is reached
- Refractory period:
a) Absolute: neuron cannot fire again
b) Relative: neuron can fire but only with much larger input
9
Q
How does an action potential spread along axon?
A
- Action potential causes adjacent membrane to reach threshold which causes action potential that causes adjacent membrane to reach threshold and so on…
- Works like a wave of depolarisation-repolarising along axon
- Signal can travel 1 m/s
10
Q
How does action potential along axon get sped up? Diagram 4
A
- Diameter of axon - thicker diameter fibre means faster conduction
- Myelin sheaths - allow AP to skip segments of axon to speed up wave along axon (saltatory conduction can be up to 120 m/s)
11
Q
How is information encoded on a neuron?
A
- Information is encoded on neuron via frequency patterning (timing) of spikes (A/Ps) - called pulse modulation
12
Q
What are the different ways neurons can connect? Diagram 5
A
- Convergent pathway - multiple neurons inputting into one final output
- Divergent pathway - one input which gets fed into multiple different outputs
- Oscillating circuit - feedback loop where input leads to output which inputs back into the same system
13
Q
What are some different types of synaptic connection? Diagram 5
A
- Axodendritic - synapses on dendrite
- Axosomatic - synapses on soma of cell
- Axoaxonic - axon synapses with axon of another input (two inputs into one axon)
- Neuromuscular - synapses into muscle
- Neuroendocrine - synapses with endocrine system
14
Q
What are the steps in the chemical synapse of neurons? Diagram 6
A
- AP arrives at axon terminal to voltage gated Ca2+ channels
- Ca2+ channel opens and Ca2+ floods in
- Ca2+ allows vesicles containing neurotransmitters to bind to presynaptic membrane and release neurotransmitters into presynaptic cleft (exocytosis)
- Neurotransmitters bind to ligand gated channel - three possible options
a) Excitatory - Na+ ligand gated channel is bound by neurotransmitter and allow influx of Na+ ions crossing postsynaptic membrane and starts to depolarise it - bringing it closer to threshold
b) Inhibitory - K+ ligand gated channel is bound by neurotransmitter and allow K+ to escape out the postsynaptic membrane and hyperpolarise it - taking it further away from threshold
c) A ligand binding results in release of some other molecule (2nd messenger) which produces another chain of events which affects membrane potential - Neurotransmitter either diffuses away, is broken down by enzymes, is removed by astrocytes, or is pumped back in through presynaptic membrane
15
Q
What are some types of neurotransmitters?
A
- Amino acids:
a) Glutamate - Excitatory neurotransmitter of nervous system
b) GABA - Inhibitory neurotransmitter of nervous system (brain)
c) Glycine - Inhibitory neurotransmitter of nervous system (spine) - Monoamines: Function on attention, cognition, and emotion in brain
a) Serotonin
b) Histamine
c) Dopamine (Catecholamine)
d) Epinephrine (Catecholamine)
e) Norepinephrin (Catecholamine) - Peptides: Perception of pain
a) Endorphin (Opioids) - Other:
a) Acetylcholine - Released by most neurons in ANS and motor neurons that act on skeletal muscle
