Cellular and molecular neuroscience
Brain measurements:
Spatial: measure brain at it’s different levels
Temporal: time frame of activity measurement
Electrophysiology: measurements by EEG , patch clamp
Cell types:
Neurons:
Unipolar cell
Bipolar cell
Pseudo-unipolar cell
Multipolar cell: motorneuron , pyramidal cell , Purkinje cell
Neuron common structure: cell body , axon , (dendrite)
Glial cells:
Oligodendrocyte: production of myelinisation + allow fast signal propagation in CNS
Schwann cell: production of myelinisation + allow fast signal propagation in PNS
Astrocyte: involved in blood-brain barrier + provide neuron with metabolites
Electrical signaling:
Neuronal membrane: phosopholipid bilayer separating intra- and extracellular
Impermeable to ions + organic molecules
Different ionic composition intra- and extracellular
Membrane potentials:
Resting membrane potential: difference across membrane when neuron is at rest
≈ -65mV due to unequal ion distribution
High intracellular K+ concentration
High extracellular Na+ concentration
Action potential: voltage change initiated close to neuronal cell body propagating through neuronal axons
Equilibrium potential: membrane voltage at which a specific ion is balanced (no movement across membrane)
Determined by concentration gradient + voltage gradient
Obtained when ion-channel is permanently open
When ion-channel opens it moves potential towards it’s equilibrium potential
Membrane proteins:
Ionic pumps:
Pumps: energy used to keep ion concentrations away from their equilibrium potentials
Bv Na+/K+ ATPase , Ca2+/Mg2+ ATPase , Na+/Ca2+ exchanger , KCC2co-transporter
Voltage-gated channels:
Voltage gated channels: small changes in membrane potential surpassing threshold activates all
voltage-gated channels Bv voltage-gated Na+ channel
Large flux of ions AP generation
,Pharmacological targets:
Membrane protein study: by using channel/pump/transporter- specific blockers
TTX: Na+ channel blocker
TEA: K+ channel blocker
Ouabain: Na+/K+ ATPase blocker
Myelinisation:
Increases speed
Decreases energy expenditure: ion flux only happened at nodes of Ranvier
(high Na+ channel concentration along the axon)
Chemical signaling:
Paracrine signalling: transmission to a larger volume of neurons at a distance
By ACh , dopamine , norepinephrine
Can determine the state (awake/sleep) of the brain
Endocrine signalling: signalling by blood between body and brain
Synapses:
Typical neuron recieves 100-1000 synaptic inputs
Computational power: 1015 synapses * 10 impulses/second = 1016 synapses/second
Assumes release probability of 1 (every synaps releases neurotransmitter when AP present)
Synaptic transmission probability: not every AP gets converted into a secretory signal (only 10-20%)
Intra- / extracellular signals can enhance/ diminish chance of neurotransmitter release
Synaps complexity:
Neurotransmitter diversity
Receptor diversity
Effector signal polarity: signal can be excitatory (↑ membrane potential) and induce an AP
or inhibitory (↓ membrane potential) and inhibit AP formation
Variable temporal signals: channel opening time can vary , …
Signal amplification / diminution by cellular cascades bv GPCR
Molecular frequency filtering: allow certain frequencies of AP to have more effect
Plasticity: short-term or long term changes in synapses
Synaps vesicles:
1. Neurotransmitter loading in vesicle
2. Vesicles stacked in active site at the axonal end
3. Docking to plasma-membrane
4. Priming for fusion with SNAREs
5. Ca2+-triggered vesicle fusion by binding to synaptotagmin
6. Clathrin mediated budding + formation of new synaptic vesicle
7. Clathrin uncoating
8. Reuptake of neurotransmitters
SNAREs: v-SNARE (synaptobrevin) , t-SNARE (syntaxin) , SNAP-25
,Neurotransmitters:
Acetylcholine
Amino acids: glutamate (excitatory) , GABA (inhibitory) , glycine (corelease)
Biogenic amines: dopamine , noradrenaline , adrenaline , serotonin , histamine , ATP
Receptors:
Ionotropic receptor: compound binding opens ion channel (specific for certain ion) bv NMDA-
receptor
Has rapid desensitization for compound
Specific peak conductance (max ion flow when open)
Metabotropic receptor: compound binding activates intracellular second messenger system that
activates further cellular cascades bv GPCR
How many ions moved to create a potential difference:
Very small amount of charge needs to shift for electrical signalling
Cell membrane = capacitor: insulator between 2 conductive salt solutions can store charge
Capacitance: how much charge a lipid bilayer can store at a particular voltage
Ohm’s law: V = I*R
I = V/R = g*V
Quantity Unit Symbo Equivalent
l
Current (I) Ampere A C/s
Charge (Q) Coulomb C A*s
Potential (V) Volt V J/C
Resistance (R) Ohm Ω V/A
Conductance (g) Siemens S 1/Ω
Capacitance (C) Farad F C/V
Energy Joule J V*C , W*s
Fundamental constants
Avogadro’s number (NA) 6,022*1023 particles/ mol
Elementary charge (e) 1,602*10-19C
Faraday’s constant (F) 96480 C/mol
Absolute temperature (T) T(Kelvin) = 273,16 + T(Celsius)
Boltzmann’s constant (k) 1,381*10-23 V*C/K
Gas constant (R) 8,315 J/K*mol
Biological membrane as electronic circuit:
Capacitance: ability of a system to store electric charge = lipid bilayer
1
Conductance: how easy ions can flow over the membrane G= = ion channels
R
Open ion channels high conductance
Stored energy discharges when channels open
Electromotive force: driving force increases when potential is further away from the ions equilibrium potential
, 1
Membrane time constant τ : time it takes to reach of the original voltage
3
Current = conductance * driving force I x =g x ( E , t )∗(E−E x )
Charge: Q=C∗V
I -V curves:
I =g∗V
I =g∗(V −Er )
Higher current when voltage is further away from equilibrium potential (higher Er )
Assumes conductance is all or nothing (switch from open to close)
Non-linear relationship
I x =g x ( E , t )∗(E−E x )
Ions across membrane:
Nernst equation:
RT [ X ]o RT [ X ]o
Nersnt equation: E x = ∗ln =2,3 ∗log
zF [ X ]i zF [ X ]i
[ X ]o
At physiological conditions: E x =60∗log
[ X ]i
60mV change in membrane potential for 10x fold change
Equilibrium potentials:
Ion Exctracellular Intracellular Equilibrium
concentration concentration potential
+
Na 145mM 12mM +67mV
K+ 4mM 155mM -98mV
2+
Ca 1,5mM 100nM +129mV
Cl- 123mM 4,2mM -90mV
Goldman-Hodgkin-Katz equation:
Based on Nernst equation
Takes Cl- into consideration to explain AP better
GHK assumptions:
Ions move independently
Membrane is homogeneous (not true bcs proteins not equally distributed over membrane)
Diffusion constants invariant
Only univalent ions (Na+ , K+ , Cl-)
Linear voltage drop over lipid bilayer (constant field)
Brain measurements:
Spatial: measure brain at it’s different levels
Temporal: time frame of activity measurement
Electrophysiology: measurements by EEG , patch clamp
Cell types:
Neurons:
Unipolar cell
Bipolar cell
Pseudo-unipolar cell
Multipolar cell: motorneuron , pyramidal cell , Purkinje cell
Neuron common structure: cell body , axon , (dendrite)
Glial cells:
Oligodendrocyte: production of myelinisation + allow fast signal propagation in CNS
Schwann cell: production of myelinisation + allow fast signal propagation in PNS
Astrocyte: involved in blood-brain barrier + provide neuron with metabolites
Electrical signaling:
Neuronal membrane: phosopholipid bilayer separating intra- and extracellular
Impermeable to ions + organic molecules
Different ionic composition intra- and extracellular
Membrane potentials:
Resting membrane potential: difference across membrane when neuron is at rest
≈ -65mV due to unequal ion distribution
High intracellular K+ concentration
High extracellular Na+ concentration
Action potential: voltage change initiated close to neuronal cell body propagating through neuronal axons
Equilibrium potential: membrane voltage at which a specific ion is balanced (no movement across membrane)
Determined by concentration gradient + voltage gradient
Obtained when ion-channel is permanently open
When ion-channel opens it moves potential towards it’s equilibrium potential
Membrane proteins:
Ionic pumps:
Pumps: energy used to keep ion concentrations away from their equilibrium potentials
Bv Na+/K+ ATPase , Ca2+/Mg2+ ATPase , Na+/Ca2+ exchanger , KCC2co-transporter
Voltage-gated channels:
Voltage gated channels: small changes in membrane potential surpassing threshold activates all
voltage-gated channels Bv voltage-gated Na+ channel
Large flux of ions AP generation
,Pharmacological targets:
Membrane protein study: by using channel/pump/transporter- specific blockers
TTX: Na+ channel blocker
TEA: K+ channel blocker
Ouabain: Na+/K+ ATPase blocker
Myelinisation:
Increases speed
Decreases energy expenditure: ion flux only happened at nodes of Ranvier
(high Na+ channel concentration along the axon)
Chemical signaling:
Paracrine signalling: transmission to a larger volume of neurons at a distance
By ACh , dopamine , norepinephrine
Can determine the state (awake/sleep) of the brain
Endocrine signalling: signalling by blood between body and brain
Synapses:
Typical neuron recieves 100-1000 synaptic inputs
Computational power: 1015 synapses * 10 impulses/second = 1016 synapses/second
Assumes release probability of 1 (every synaps releases neurotransmitter when AP present)
Synaptic transmission probability: not every AP gets converted into a secretory signal (only 10-20%)
Intra- / extracellular signals can enhance/ diminish chance of neurotransmitter release
Synaps complexity:
Neurotransmitter diversity
Receptor diversity
Effector signal polarity: signal can be excitatory (↑ membrane potential) and induce an AP
or inhibitory (↓ membrane potential) and inhibit AP formation
Variable temporal signals: channel opening time can vary , …
Signal amplification / diminution by cellular cascades bv GPCR
Molecular frequency filtering: allow certain frequencies of AP to have more effect
Plasticity: short-term or long term changes in synapses
Synaps vesicles:
1. Neurotransmitter loading in vesicle
2. Vesicles stacked in active site at the axonal end
3. Docking to plasma-membrane
4. Priming for fusion with SNAREs
5. Ca2+-triggered vesicle fusion by binding to synaptotagmin
6. Clathrin mediated budding + formation of new synaptic vesicle
7. Clathrin uncoating
8. Reuptake of neurotransmitters
SNAREs: v-SNARE (synaptobrevin) , t-SNARE (syntaxin) , SNAP-25
,Neurotransmitters:
Acetylcholine
Amino acids: glutamate (excitatory) , GABA (inhibitory) , glycine (corelease)
Biogenic amines: dopamine , noradrenaline , adrenaline , serotonin , histamine , ATP
Receptors:
Ionotropic receptor: compound binding opens ion channel (specific for certain ion) bv NMDA-
receptor
Has rapid desensitization for compound
Specific peak conductance (max ion flow when open)
Metabotropic receptor: compound binding activates intracellular second messenger system that
activates further cellular cascades bv GPCR
How many ions moved to create a potential difference:
Very small amount of charge needs to shift for electrical signalling
Cell membrane = capacitor: insulator between 2 conductive salt solutions can store charge
Capacitance: how much charge a lipid bilayer can store at a particular voltage
Ohm’s law: V = I*R
I = V/R = g*V
Quantity Unit Symbo Equivalent
l
Current (I) Ampere A C/s
Charge (Q) Coulomb C A*s
Potential (V) Volt V J/C
Resistance (R) Ohm Ω V/A
Conductance (g) Siemens S 1/Ω
Capacitance (C) Farad F C/V
Energy Joule J V*C , W*s
Fundamental constants
Avogadro’s number (NA) 6,022*1023 particles/ mol
Elementary charge (e) 1,602*10-19C
Faraday’s constant (F) 96480 C/mol
Absolute temperature (T) T(Kelvin) = 273,16 + T(Celsius)
Boltzmann’s constant (k) 1,381*10-23 V*C/K
Gas constant (R) 8,315 J/K*mol
Biological membrane as electronic circuit:
Capacitance: ability of a system to store electric charge = lipid bilayer
1
Conductance: how easy ions can flow over the membrane G= = ion channels
R
Open ion channels high conductance
Stored energy discharges when channels open
Electromotive force: driving force increases when potential is further away from the ions equilibrium potential
, 1
Membrane time constant τ : time it takes to reach of the original voltage
3
Current = conductance * driving force I x =g x ( E , t )∗(E−E x )
Charge: Q=C∗V
I -V curves:
I =g∗V
I =g∗(V −Er )
Higher current when voltage is further away from equilibrium potential (higher Er )
Assumes conductance is all or nothing (switch from open to close)
Non-linear relationship
I x =g x ( E , t )∗(E−E x )
Ions across membrane:
Nernst equation:
RT [ X ]o RT [ X ]o
Nersnt equation: E x = ∗ln =2,3 ∗log
zF [ X ]i zF [ X ]i
[ X ]o
At physiological conditions: E x =60∗log
[ X ]i
60mV change in membrane potential for 10x fold change
Equilibrium potentials:
Ion Exctracellular Intracellular Equilibrium
concentration concentration potential
+
Na 145mM 12mM +67mV
K+ 4mM 155mM -98mV
2+
Ca 1,5mM 100nM +129mV
Cl- 123mM 4,2mM -90mV
Goldman-Hodgkin-Katz equation:
Based on Nernst equation
Takes Cl- into consideration to explain AP better
GHK assumptions:
Ions move independently
Membrane is homogeneous (not true bcs proteins not equally distributed over membrane)
Diffusion constants invariant
Only univalent ions (Na+ , K+ , Cl-)
Linear voltage drop over lipid bilayer (constant field)
