1 Bioelectrical cell biology
Introduction and basic concepts
Cell types
Brain has 1011 neurons lots of different types that mostly differ in the processes:
Unipolar Bipolar Pseudo-unipolar Multipolar
Dendrite and Cell body in Cell body process Dendrite is adjacent to the cell body, can be
axon in same middle of axon that branches basal or apical (further away) or can have a
direction of cell and dendrites into dendrites large amount of branching (Purkinje fiber)
body and axon
The specialisation of the neuron is based on its function sensory neuron has
dendrites in skin cells and synapse of axon to ganglion, motor neurons have
their synapses at muscle level, neuroendocrine cells have their synapses at
capillary level, …
Aside from neurons, the brain also contains glial cells (10-5011)
oligodendrocytes, shwann cells, astrocytes, …
Typing of the neurons is based on the Golgi-stained technique (with AgNO 3)
that was first performed by Golgi and Ramón y Cajal.
Electrical signalling
Here the neuronal membrane plays a crucial role it acts as a barrier that separates the intra- and extra-
cellular space the phospholipids in the membrane act as insulators mosaicism in the membrane
enables transport/flow between the 2 spaces aside from phospholipids, proteins like ion channels are
present ⇒ allow the flow of ions that are the base of electrical signalling.
The ion distribution across the spaces is roughly the same in all animals
causes the resting membrane potential and when the equilibrium is
disturbed we mainly get an action potential.
The action potential
= an electoral potential (voltage) that is initiated close to the cell body
and propagates through the processes.
All neurons have a resting membrane potential = voltage difference
across the membrane in the cell at rest = no AP firing result of the
unequal ion distribution negative inside the cell, positive outside the
cell.
intracellular extracellular
The resting membrane potential (RMP) is determined by the open ion
channels open ion channels encourage the membrane potential to
move towards the equilibrium potential of the ion.
The RMP is closest to the EK K-channels contribute most to the RMP.
The ionic pumps/exchanger use energy to keep ion concentrations away from Ex e.g. Na/K-
ATPase pumps out 3 Na and pumps in 2 K with usage of ATP.
Ion channels are mostly voltage-gated with a certain voltage the channel opens ion flow will be
based on its concentration gradient.
Neurons can be characterized by their frequency of AP’s different ionic currents underlie the pattern of
the AP other current types give different frequencies of AP’s.
,2 Bioelectrical cell biology
How many ions are needed to create a change in voltage
We can see the biological membrane as an electronic circuit contains a capacitance = limiting the flow
speed of ions and a conductance = separation between the different charges.
The capacitance is fixed as it is based on the composition of the lipid bilayer:
Only a very small amount of charge needs to transfer for an efficient electric signal.
Computation
The axons of neurons are myelinated in CNS this is done by oligodendrocytes, in PNS by Schwann cells
myelination is needed for facilitating the propagation of electrical signals:
Unmyelinated Myelinated
Adjacent depolarization causes a slow propagation of the Saltatory conductance between the nodes of Ranvier
signal ion fluxes throughout the whole axon only causes a fast propagation ion fluxes only take place at
change in shape and size can regain speed the node
Synaptic inputs are received by the dendrites typical neurons may make/receive 100-1000 synaptic
inputs.
The brain has 1015 synapses have a computational power of 1016 when there are 10 impulses/second (=
average). Synapses can be close to dendrites (axodendritic), to soma (axosomatic) or to axons (axoaxonic).
With chemical transmission, computational power is added due to:
→ Diversity of neurotransmitters
→ Diversity of receptors
→ Variability in polarity of the effector signal
→ Variability in temporal signals
→ Signal amplification due to intracellular cascades
→ Molecular frequency filtering
→ Short and long term plasticity
Not every AP is converted into a secretory signal 10-20% trigger a release due to modulation by
intracellular messenger, extracellular modulators or previous synapse use (memory).
Chemical signalling
Chemical transmission can happen locally (synaptic or paracrine) or distantly (endocrine). In the synapse
vesicles are present loaded with proteins (neurotransmitters) by a proton gradient AP leads to fusion
of vesicles and therefore release due to SNARE-complex proteins binding and conformational changes
causes membrane fusion:
, 3 Bioelectrical cell biology
Neurotransmitter systems
Neurotransmitters are presynaptically synthesized and stored with an AP the exocytosis is triggered by
increase of Ca2+ trigger the post-synaptic receptors action is terminated by enzyme catabolism =
breakdown or by re-uptake.
4/5 main classes of neurotransmitters
1. Ach (acetylcholine) used for motor neurons and in CNS
2. Amino acids can be excitatory (Glu, Asp) or inhibitory (GABA)
3. Amines catecholamines = dopamine and norepinephrine + indolamines = serotonin +
imidazoleamine = histamine
4. Peptides 3-30 AA long and stored in dense core granule vesicles
5. Purines mostly ATP
Neurotransmitter receptors
Many of the NT receptors are ion channels binding of an NT will cause different scenarios:
→ Influx of Na depolarisation (EPSP = excitatory post synaptic potential = more positive on the
inside)
→ Efflux of K hyperpolarisation (IPSP = inhibitory post synaptic potential = more negative on the
inside)
→ Influx of Cl hyperpolarisation
→ Influx of Ca activation of enzymes
Other NT receptors are metabotropic G-protein coupled receptors will cause ion channels to open or
will cause activation of enzymes and an intracellular cascade.
Co-transmission
NT’s are found to co-transmit adds to the power of the nervous system.
Introduction and basic concepts
Cell types
Brain has 1011 neurons lots of different types that mostly differ in the processes:
Unipolar Bipolar Pseudo-unipolar Multipolar
Dendrite and Cell body in Cell body process Dendrite is adjacent to the cell body, can be
axon in same middle of axon that branches basal or apical (further away) or can have a
direction of cell and dendrites into dendrites large amount of branching (Purkinje fiber)
body and axon
The specialisation of the neuron is based on its function sensory neuron has
dendrites in skin cells and synapse of axon to ganglion, motor neurons have
their synapses at muscle level, neuroendocrine cells have their synapses at
capillary level, …
Aside from neurons, the brain also contains glial cells (10-5011)
oligodendrocytes, shwann cells, astrocytes, …
Typing of the neurons is based on the Golgi-stained technique (with AgNO 3)
that was first performed by Golgi and Ramón y Cajal.
Electrical signalling
Here the neuronal membrane plays a crucial role it acts as a barrier that separates the intra- and extra-
cellular space the phospholipids in the membrane act as insulators mosaicism in the membrane
enables transport/flow between the 2 spaces aside from phospholipids, proteins like ion channels are
present ⇒ allow the flow of ions that are the base of electrical signalling.
The ion distribution across the spaces is roughly the same in all animals
causes the resting membrane potential and when the equilibrium is
disturbed we mainly get an action potential.
The action potential
= an electoral potential (voltage) that is initiated close to the cell body
and propagates through the processes.
All neurons have a resting membrane potential = voltage difference
across the membrane in the cell at rest = no AP firing result of the
unequal ion distribution negative inside the cell, positive outside the
cell.
intracellular extracellular
The resting membrane potential (RMP) is determined by the open ion
channels open ion channels encourage the membrane potential to
move towards the equilibrium potential of the ion.
The RMP is closest to the EK K-channels contribute most to the RMP.
The ionic pumps/exchanger use energy to keep ion concentrations away from Ex e.g. Na/K-
ATPase pumps out 3 Na and pumps in 2 K with usage of ATP.
Ion channels are mostly voltage-gated with a certain voltage the channel opens ion flow will be
based on its concentration gradient.
Neurons can be characterized by their frequency of AP’s different ionic currents underlie the pattern of
the AP other current types give different frequencies of AP’s.
,2 Bioelectrical cell biology
How many ions are needed to create a change in voltage
We can see the biological membrane as an electronic circuit contains a capacitance = limiting the flow
speed of ions and a conductance = separation between the different charges.
The capacitance is fixed as it is based on the composition of the lipid bilayer:
Only a very small amount of charge needs to transfer for an efficient electric signal.
Computation
The axons of neurons are myelinated in CNS this is done by oligodendrocytes, in PNS by Schwann cells
myelination is needed for facilitating the propagation of electrical signals:
Unmyelinated Myelinated
Adjacent depolarization causes a slow propagation of the Saltatory conductance between the nodes of Ranvier
signal ion fluxes throughout the whole axon only causes a fast propagation ion fluxes only take place at
change in shape and size can regain speed the node
Synaptic inputs are received by the dendrites typical neurons may make/receive 100-1000 synaptic
inputs.
The brain has 1015 synapses have a computational power of 1016 when there are 10 impulses/second (=
average). Synapses can be close to dendrites (axodendritic), to soma (axosomatic) or to axons (axoaxonic).
With chemical transmission, computational power is added due to:
→ Diversity of neurotransmitters
→ Diversity of receptors
→ Variability in polarity of the effector signal
→ Variability in temporal signals
→ Signal amplification due to intracellular cascades
→ Molecular frequency filtering
→ Short and long term plasticity
Not every AP is converted into a secretory signal 10-20% trigger a release due to modulation by
intracellular messenger, extracellular modulators or previous synapse use (memory).
Chemical signalling
Chemical transmission can happen locally (synaptic or paracrine) or distantly (endocrine). In the synapse
vesicles are present loaded with proteins (neurotransmitters) by a proton gradient AP leads to fusion
of vesicles and therefore release due to SNARE-complex proteins binding and conformational changes
causes membrane fusion:
, 3 Bioelectrical cell biology
Neurotransmitter systems
Neurotransmitters are presynaptically synthesized and stored with an AP the exocytosis is triggered by
increase of Ca2+ trigger the post-synaptic receptors action is terminated by enzyme catabolism =
breakdown or by re-uptake.
4/5 main classes of neurotransmitters
1. Ach (acetylcholine) used for motor neurons and in CNS
2. Amino acids can be excitatory (Glu, Asp) or inhibitory (GABA)
3. Amines catecholamines = dopamine and norepinephrine + indolamines = serotonin +
imidazoleamine = histamine
4. Peptides 3-30 AA long and stored in dense core granule vesicles
5. Purines mostly ATP
Neurotransmitter receptors
Many of the NT receptors are ion channels binding of an NT will cause different scenarios:
→ Influx of Na depolarisation (EPSP = excitatory post synaptic potential = more positive on the
inside)
→ Efflux of K hyperpolarisation (IPSP = inhibitory post synaptic potential = more negative on the
inside)
→ Influx of Cl hyperpolarisation
→ Influx of Ca activation of enzymes
Other NT receptors are metabotropic G-protein coupled receptors will cause ion channels to open or
will cause activation of enzymes and an intracellular cascade.
Co-transmission
NT’s are found to co-transmit adds to the power of the nervous system.
