PHYS20008 Lecture 3: PHYS20008 Lecture 3
10 May 2018
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Lecture 3
- Dendrites: receptors, receive signals
- Axon terminals: release chemical (neurotransmitters) to signal next neuron or gland
- Hundred billion neurons in human brain, 10 quadrillion synapses in brain
- Negative charge in cell: potassium stays inside despite concentration gradient
- If we have perfect negative charge inside the cell that equally opposes that drive
(concentration gradient) to move out of cell (particular number for that concentration
gradient) → we have a balance of concentration gradient (wanting potassium to move
out) and charge (wanting potassium to stay inside)
- Charge required to hold an ion in its currently balance (in its current concentration
gradient) → equilibrium potential (no net movement of ion)
- If inside cell -70mV → not enough negative charge to keep potassium inside cell, it’s
going to leak out of cell, taking positive charge with it → charge inside cell gets more
negative → until reaches -90mV (balances out again)
- Ions are going to move across membrane to drive the charge inside the cell towards
their own equilibrium potentials
- Not positive enough to hold sodium out → leak in and bring positive charge into the
cell → until positive inside cell (+60mV)
- So much potassium inside cell, and extracellular space is an infinite environment
filled with sodium → sodium moving into tiny space isn’t going to change the overall
concentration gradient noticeably → but has massive effect on charge inside cell
- Does not change overall concentration of ions inside or outside cell → massive effect
on charge inside cell
- Cations more concentrated in extracellular fluid → calcium and sodium
- Ions inside cell and outside cell that want to move → cannot have charge inside cell
to be both -90mV and +60mV → need to compromise → desire to move across
membrane gives control → ions can only move when we allow them to (ability to
control whether ions can or cannot move) by whether or not we have channels in the
membrane to let them through or channels that we can spontaneously open or close
→ gives potential
- Difference in charge across membrane, ions that may be allowed to move across
membrane and create an electrical current (ions moving and charge is changing in
cell → electricity) → potential
- Charge across membrane = membrane potential (charge difference)
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- All cells resting membrane potential = -70mV (membrane potential of non-excitable
cells and excitable cells at rest) → potassium slowly leaks out, sodium wants to
enter
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- Charge difference, concentration difference, ions that want to move
find more resources at oneclass.com
find more resources at oneclass.com
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- Negative charge inside cell mostly established by large anions (big proteins, proteins
generally negatively charged)
- Continue to drive membrane potential towards equilibrium potential
- Control charge inside cell by controlling number of channels for each ion
- A lot of channels for potassium and very few channels for sodium → potassium can
move out of cell more quickly than sodium can move in → charge inside cell is going
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Axon terminals: release chemical (neurotransmitters) to signal next neuron or gland. Hundred billion neurons in human brain, 10 quadrillion synapses in brain. Negative charge in cell: potassium stays inside despite concentration gradient. Charge required to hold an ion in its currently balance (in its current concentration gradient) equilibrium potential (no net movement of ion) Ions are going to move across membrane to drive the charge inside the cell towards their own equilibrium potentials. Not positive enough to hold sodium out leak in and bring positive charge into the cell until positive inside cell (+60mv) Does not change overall concentration of ions inside or outside cell massive effect on charge inside cell. Cations more concentrated in extracellular fluid calcium and sodium. Difference in charge across membrane, ions that may be allowed to move across membrane and create an electrical current (ions moving and charge is changing in cell electricity) potential. Charge across membrane = membrane potential (charge difference)
