MMED2931 Lecture Notes - Lecture 2: Relative Permeability, Depolarization, Nernst Equation
4 Jun 2018
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Nervous system lectures:
- Lecture 1: membrane potential & action potential
- Lecture 2: central nervous system, neurons and sensation
- Lecture 3: control of movement: simple reflexes
- Lecture 4: control of visceral organs: autonomic nervous system ANS
Membrane Potential and Action Potential: learning objectives
1. Resting membrane potential (RMP)
2. Action potential (AP)
3. Major types of ionic channels
4. Synaptic transmission and integration
The Nervous System, neurons and neural circuits:
- Neurons: handles info processing within brain (sense changes in environment,
communicate these changes to other neurons, command body response)
- Dendrites: receive connections (info) from other neurons
- Axon: the output (transmit info away) from the cell. Usually only one axon that
leaves the cell body, but may branch
- 100 billion neurons in the CNS, 100 trillion connections with other neurons
- Neurons communicate with each other/other cells using electrical/chemical signals
The nerve cell membrane:
- All electrical activity of nerve cells is caused by the movement of ions (which are
eletrially harged) aross the euro’s erae
- Na+, K+, Cl-, or Ca2+ ions can move across the membrane only via ion channels (not
thru bilayer), transporters or pumps. And only if the ion channels are open
-
The concentration gradients for K+ and Na+ ions:
- Unequal distribution of ions across a cell membrane: e.g. much more K+ inside than
outside. Opp for Na+ and Cl- (Cl goes with Na), Ca2+ VERY little inside (important ion).
Concentration gradients for K+ & Na+ maintained by Na+/K+ ATPase pump. 2K+ and
3Na+ in opp directions, use ATP
find more resources at oneclass.com
find more resources at oneclass.com
The flux of K+ ions across a cell membrane: equilibrium potential for K+
- First consider that cell membrane has K+ leak channel and no other channels. K+ will
leak out down concentration gradient taking 1+ charge, until diffusional and
electrical forces are in equilibrium – no net movement of K+
-
Equilibrium potential: the Nernst equation
- NOTE: T in Kelvin
- EK = equilibrium potential for K+ ions: when concentration gradient (leave cell)
counterbalanced by electrical gradient (pulled back in)
- At rest cell, membrane is predominantly permeable for K+ ions, that is why
membrane potential (MP, Em or Vm. When at rest, Vm is called RMP resting
membrane potential) is close to the value of EK
Equilibrium potentials and resting membrane potential:
- At resting state, only leak ion channels are open in a neuron
- Neurons at rest are somewhat permeable to K+, Cl-, Na+
- Permeability is a measure of how easily an ion can cross the membrane
- Relative permeability (p) at rest is high for K+, very low to Na+ and low to Cl-
▪
Changes in MP (membrane potential): depolarisation and hyperpolarisation
- The opening of an ion channel and the movement of ions thru the channel
causes changes in MP
- Cells use changes in their MP as communication signals
- Depolarisation: change of MP in (+) direction: excitability of neuron
- Hyperpolarisation: change of MP in (-) direction: excitability of neuron
Sequential opening of Na+ and K+ channels generates the action potential: threshold=-55
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lecture 2: central nervous system, neurons and sensation. Lecture 4: control of visceral organs: autonomic nervous system ans. Membrane potential and action potential: learning objectives: resting membrane potential (rmp, action potential (ap, major types of ionic channels, synaptic transmission and integration. Neurons: handles info processing within brain (sense changes in environment, communicate these changes to other neurons, command body response) Dendrites: receive connections (info) from other neurons. Axon: the output (transmit info away) from the cell. Usually only one axon that leaves the cell body, but may branch. 100 billion neurons in the cns, 100 trillion connections with other neurons. Neurons communicate with each other/other cells using electrical/chemical signals. All electrical activity of nerve cells is caused by the movement of ions (which are ele(cid:272)tri(cid:272)ally (cid:272)harged) a(cid:272)ross the (cid:374)euro(cid:374)"s (cid:373)e(cid:373)(cid:271)ra(cid:374)e. Na+, k+, cl-, or ca2+ ions can move across the membrane only via ion channels (not thru bilayer), transporters or pumps. And only if the ion channels are open.
