1. Membranes & Nerves
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What is Resting Membrane Potential (RMP)?
A difference in electrical potential across the plasma membrane at rest.
What is Action Potential?
- Stimulation of i.e. a spinal reflex --> action potential in a spial motor neuron.
- Allows the neurons (bad at conducting electrical signals long way) to signal across long distances.
What are the intra-/extracellular consentrations for:
K+, Na+, Cl-, Ca2+
- K+: High concentration intracellular
- Na+, Cl-, Ca2+: High concentration extracellular
What are active/passive transporters?
- Active (ion transporters):
- Activly move ions into or out of cells, against their concentration gradient.
- Passive (ion channels):
- Proteins allow certain kinds of ions to cross the membrane in the direction of their concentration gradient.
Describe the K+/Na+ pump
- Uses 1 ATP
- Moves 3 Na+ & 2 K+ against their concentration gradient
- Active transporter
Describe the passive transport of K+ across the membrane
- K+ moves outside the cell, taking its positive charge with it
- Since the charge will be positive outside the cell, it repells the K+ back against it concentration gradient.
- The equlibrium is an "electrochemical" balance
What is the difference between Nernst and Goldmans equations?
- Nernst only considers the concentration of a given ion (eg. K+)
- Goldman considers K+, Na+ and Cl-
Describe the ionic basis of the A.P.
(the steps of AP)
- AP are conducted along the axon, which contains voltage gated Na+ and K+ channels.
- Phases: Rising (depolarization), Overshoot, Falling (repolarization), Undershoot
- 1. The neuronal membrane becomes temporarily permeable to Na+ during the rising phase and overshoot phase due to opening of more and more Na+ channel that are closed at rest.
- 2. The membrane potential deoplarizes and approaches ENa.
- 3. Decrease in Na+ pemebeality (inactivation of Na+ channels) and delayed increase in K+ permeability cause repolarization of the membrane toward the EK and resting levels.
- 4. During the undershoot phase (afterhyperpolarization) the K+ permability is greater that it is at rest.
- 5. The membrane potential returns to resting levels
Name the 3 general classes of ion channels found in neurons.
- Leaked/Non-gated ion channels
- Voltage gated ion channels
- Ligand gated ion channels
How does a Leaked/Non-gated ion channel work?
- Always open and specific for an ion (i.e K+).
- The ions flow aross the plasma membrane down their concentration gradients, taking their charge with them. This in turn causes the potential!
How does a Voltage-gated ion channel work?
- These channels have a charged voltage sensor that detects a change in the membrane potential and permits voltage dependent gating of ion channels.
- Closed at rest, opens when membrane potential changes.
- Example of Voltage gated ion channels: Na+/Ca2+ channel, K+/Cl- channel
How does a Ligand-gated ion channel work?
- Open when a ligand (e.g a neurotransmitter) binds to it.
- Example of neurotransmiters: acetylcholine, glutamate, GABA, glycine.
- Example of ionotropic receptor: the acetylcholine nicotinic receptor
What are ionotropic, ligand gated channels?
- Not selective
- Allow influx of Ca2+ that leads to hyperpolarization
What are the differances between the K+ and Na+ voltage gated channels?
- The Na+ has 2 gates; Close/Active --> Open --> Close/Inactive --> Close/Active
- The K+ has only 1 gate; Close --> Open --> Close
- The Na+ opens faster, causes shooting phase.
- The K+ is slower and cuases the falling phase.
There are 3 groups of neurotransmittors, which are they?
- 1. Small molecules:
- - Biogenic amines (monoamines)
- ---> Catecholamines: Dopamine, Noradrenaline, Adrenaline
- ---> Indoleamines: Serotonin
- - Acetylcholine
- - Aminoacids
- --- GABA and Glycine (-)
- --- Glut and Asp (+)
- 2. Neuropeptides: Opiopds (endorphin), Somatostatin, Substance P
- 3. Others (non-vesicular release): Neuroactive gases (NO, CO, arachidonic acid etc)
Name the events from neurotransmittor release to postsynaptic excitatinon or inhibition
- 1. Neurotransmittor release
- 2. Receptor binding
- 3. Ion channels, open or close
- 4. Conductor change causes current-flow
- 5. Postsynaptic potential changes
- 6. Postsynaptic cells, excited or inhibited
- 7. Summation determines whether or not an AP occurs
Name one inhibitatory and one excitatory neurotransmittor molecule
- Inhibit: GABA and Glycine
- Excite: Glutamate and Aspartate
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