Physiology of Neurons: Electrochemical Properties and Communication Flashcards
Membrane potential
voltage (difference in charge (more negative inside membrane, more positive outside) across neuron cell membrane
Membrane potential is the result of
the distribution of ions across the cell membrane and the permeability of the membrane
Deploarisation
membrane potential > resting potential
Hyperpolarisation
membrane potential < resting potential
Equilibrium Potential:
the voltage across the membrane that precisely balances the concentration gradient. If you had only one ion then the equillibrium potential would be the same as the resting membrane potential
Na+ Equilibrium Potential:
+60mV (outside to inside is positive potential)
K+ Equilibrium Potential:
-90mV
Ca2+ Equilibrium Potential:
+123
Cl- Equilibrium Potential:
-40mV
How do Na+ and K+ leak channels allow the generation of the membrane potential?
- each channel is selective and restricted (no free flow of ions)
- hence there is a slow transfer of Na+ into and K+ out of)
- the membrane has more K+ leak protein channels and hence is more permeable
- when K+ crosses the membrane, the cytoplasm becomes more negative
- the positive charge increases on the exterior side of the membrane
- which repels more K+ and the negatively charged interior is more attractive
- net movement of K+ becomes zero as less K+ crosses
Na: tries to establish a positive Ek
K: tries to establish a negative Ek
because more permeable to K+, the final resting potential is negative
Na+/K+ pump:
- 3 Na+ out
- 2K+ in
- against concentration grad
Voltage Gated Ion Channels:
- ion channel responds to the membrane potential/voltage in the neuron
- when the neuron is resting at -70mV, Na+ and K+ channels are closed
Ion Channel Summary:
Action Potential General Overview:
K+/Na+ Permeability graph:
Propogation of the action potential:
- membrane in resting state (outside +, inside -)
- depolarisation and outside becomes more negative
- the outside becomes more negative when threshold is achieved
- channels open, more influx of Na+/efflux of K+
- hence action potential spreads
Saltatory Conduction:
Nodes of Ranvier is where ion exchange occurs
hence when myelinated only depolarisation at those points so impulse seems to jump
hence unidirectional transmission of action potential
Detailed action potential generation (include channels open/responsible):
Saltatory Conduction:
Graded Potentials:
1) action potentials are the direct result of a defined stimulus eg received signal at the dendrite
2) graded potentials are a deviation (usually small) from the resting potential)
3) found mainly in dendrites and somas
Small change due to some neurotransmitter binding but threshold is not achieved
Graded potentials:
Graded potential vs action potential:
- graded potential: small amplitude, long wave
- lasts 10ms vs action potential is 1ms
How can graded potentials result in action potentials?
- amplitude of graded potential is directly proportional to the signal
- the signal will weaken in a process known as decremental conduction
- high amplitude graded potential can accumulate more ion channels open and result in threshold and hence action potential firing
*signal summation
What is shown below?
Graded Potential are the result of
generally ligand/mechanical gated ion channels
Graded Potentials travel to adjacent locations on the membrane passively.
True or False?
True
The amplitude of a graded potential increases with travel.
True or False?
False
reduces with travel
Graded potentials have no refractory period because
the change in potential is small
Graded Potentials can travel long distances.
True or False?
False
short distances
Core Drug: Carbamazepine:
- anticonvulsant for epilepsy
- Inhibits Nav
- binds within the core of Na+ voltage
gated channel in the INACTIVE
formation - raises the threshold required for
action potential, resulting in
dampening of stimuli/signals
*30% develop resistance
Core Drug: Lidocaine:
- local anaesthetic
- binds to and inhibits Na+ voltage
gated ion channels - inhibits generation of local action
potentials - raises the threshold required for an
action potential - blocks signalling from local pain
receptors
Sodium Valproate:
- sodium salt of valproic acid
- converted into valproate ion in blood
- increases the conc of GABA
- via the inhibition of catabolic GABA
enzymes, hence increases the conc
of GABA - hence causes hyperpolarisation, so
inhibitory
May indirectly interact with K+ voltage gated channels
Post-Synaptic Receptors:
ionotropic = fast
open and allow passage of ions upon activation but activated by the binding of a ligand
Ionotropic Receptors:
General Receptor Characteristics (6):
- ion permeability
- ion conductance
- dynamics & conductance
- ligand affinity
- agonist
- antagonist
Most synapses contain receptor types that can be activated by
various neurotransmitters
Fast and Slow Transmission:
Metabotropic Receptors:
- as opposed to direct ion channel
binding, the neurotransmitter binds
to a G-protein coupled receptor - binding to GPCR causes a
conformational change - GPCR forms
- heteromic g protein is released
- initiates a biochemical cascade
Metabotropic Receptors:
GPCR
GPCR:
Second Messengers:
What is the secondary messenger when Gs coupled receptor is activated?
- effectory protein = adenylate cyclase
- second messenger = cyclic AMP
What is the second messenger when Gq coupled protein is activated?
- effector protein = phospholipase C (PLC), which converts PIP2 into IP3 and DAG
- secondary messenger = PIP2
Gs & GI
Gq
G-proteins can be inhibitory (?), stimulatory (Gs) or Gq …..
- inhibitory = Gi
- stimulatory = Gs
- Gq = activated PLC
