Neurons and synapses
Content
Action potentials.................................................................................................................................3
Types of neurons ................................................................................................................................6
Classification of inhibitory neurons .................................................................................................7
l. Morphology classification .........................................................................................................7
II. Electrophysiology classification: ..............................................................................................8
III. Molecular classification ..........................................................................................................9
Four examples of inhibitory neurons: ..............................................................................................9
Chemical synapse part I .................................................................................................................... 10
Structure of the synapse ............................................................................................................... 10
Two types of synapses .................................................................................................................. 11
Dendritic spines ............................................................................................................................ 12
Axonal Boutons ............................................................................................................................. 12
Neurotransmitters ........................................................................................................................ 13
Neuromuscular junction ............................................................................................................ 13
Central nervous system ............................................................................................................. 13
Autonomic nervous system ....................................................................................................... 14
Receptors...................................................................................................................................... 14
Neurotransmitter receptors ...................................................................................................... 14
Subtypes of neurotransmitter receptors.................................................................................... 15
Neuromodulators and metabotropic receptors ......................................................................... 15
Neurotransmitter analogues ..................................................................................................... 16
Glutamate receptors ................................................................................................................. 16
GABA receptors......................................................................................................................... 17
Chemical synapse part ll.................................................................................................................... 17
EPP: Neuromuscular junction ........................................................................................................ 18
EPSP.............................................................................................................................................. 19
IPSP .............................................................................................................................................. 19
Electrical synapse.............................................................................................................................. 20
Parkinson’s Disease........................................................................................................................... 21
Synaptic plasticity part l .................................................................................................................... 24
Long term potentiation (LTP) ........................................................................................................ 25
Long-term depression (LTD) .......................................................................................................... 26
Spike-timing dependent plasticity (STDP) ...................................................................................... 27
, LTP in inhibitory synapse ............................................................................................................... 27
Homeostatic plasticity ................................................................................................................... 27
Morphological changes by plasticity .............................................................................................. 28
Synaptic plasticity part ll ................................................................................................................... 29
Short term plasticity ......................................................................................................................... 30
Neural Circuit & Signal integration .................................................................................................... 31
Summations .................................................................................................................................. 31
Layer-specific connections in neocortex ........................................................................................ 33
Molecular dynamics at the synapse .................................................................................................. 34
Delivery of proteins to synapses .................................................................................................... 35
Sushi belt model........................................................................................................................ 36
Surface diffusion for transmembrane proteins .......................................................................... 36
Local mRNA translation/protein synthesis ................................................................................. 38
Neural recording methods ................................................................................................................ 38
Pros and cons of recording techniques .......................................................................................... 39
Network properties of neuronal tissue .............................................................................................. 41
Memory in dissociated cortical networks ...................................................................................... 43
Extra notes after re-watching all the lectures: ................................................................................... 44
,Action potentials
After touching the receptor of, for example, a finger, the membrane potential gets depolarized. So
the membrane potential gets less negative. This depolarization is transient (=only lasts for a short
period of time) and the membrane potential will go back to its resting state.
From the resting membrane potential, if the stimulus is high enough and goes up (above the
threshold), action potential takes place. This is depolarization. If the membrane potential gets more
negative, hyperpolarization takes place.
Action potentials are:
• Short (about 1 ms)
• All-or-none
• Standard shape and amplitude
• Frequency encodes strength
To understand the action potential, you first have to understand the membrane
potential in rest. The changes in membrane potential is to achieve equilibrium.
Membrane potential is influenced by two underlying mechanisms:
• Chemical gradient: difference in intra and extra-cellular ion concentrations.
• Electrical gradient
If the K+-channels are open, K+ moves towards the negative side until equilibrium
is reached. ~-58 for K+(potassium) and ~58 for Na+ outside the cell. Only a small
amount of ions have to pass through the channels for equilibrium so the concentration in- and
outside the membrane stays more or less the same.
Nernst-equation is used to calculate the rest potential and is influenced by with absolute
temperature (T), ion charge (z) the gas- (R) and Faraday (F) constants as well as the equilibrium
potentials of the ions in the solution.
During action potential more Na+ channels open up, allowing Na+ ions to enter the cell and
depolarizes the cell. After depolarization, resting potential settles at a new level where the influx of
Na+ is balanced by the efflux of K +.
In a neuron several ions play a role , as well as the relative permeability (P) of the membrane (as
determined by how open the ion-channels are). This is calculated by the Goldman-equation.
In rest the permeability for K+ is higher (negative potential). During the action potential the
membrane will be more permeable for Na+ (positive potential).
The Na-K+ pump (and other pumps and transporters) regulate the
Chemical concentration gradients, but are not directly involved in the
action potential generation. It is the conductance of the ion channels
that change.
, The opening and closing can be regulated by different types of stimuli:
Ligand gating, Protein phosphorylation, Voltage gating, Stretch or pressure.
During action potential it is the voltage dependent gating that changes. See figure below: Sequential
opening of voltage-gated Na+ and K+ channels generating the action potential.
Sodium (Na+) channels: Permissive and non-permissive states. (activation gate opens
fast at depolarization, inactivation gate slowly closes at depolarization) An ion channel is open when
all gates are in the permissive state. If any of the gates is non-permissive, ions cannot flow.
1. Resting potential: sodium and potassium channels (relatively) closed.
2. Sodium channels open.
3. Depolarization: Activation gates open (positive feedback).
4. Repolarization: Inactivation gates close, Na+ and K+ channels open.
5. Refractory period: Na+ channels closed, K+ still open. (small undershoot).
Content
Action potentials.................................................................................................................................3
Types of neurons ................................................................................................................................6
Classification of inhibitory neurons .................................................................................................7
l. Morphology classification .........................................................................................................7
II. Electrophysiology classification: ..............................................................................................8
III. Molecular classification ..........................................................................................................9
Four examples of inhibitory neurons: ..............................................................................................9
Chemical synapse part I .................................................................................................................... 10
Structure of the synapse ............................................................................................................... 10
Two types of synapses .................................................................................................................. 11
Dendritic spines ............................................................................................................................ 12
Axonal Boutons ............................................................................................................................. 12
Neurotransmitters ........................................................................................................................ 13
Neuromuscular junction ............................................................................................................ 13
Central nervous system ............................................................................................................. 13
Autonomic nervous system ....................................................................................................... 14
Receptors...................................................................................................................................... 14
Neurotransmitter receptors ...................................................................................................... 14
Subtypes of neurotransmitter receptors.................................................................................... 15
Neuromodulators and metabotropic receptors ......................................................................... 15
Neurotransmitter analogues ..................................................................................................... 16
Glutamate receptors ................................................................................................................. 16
GABA receptors......................................................................................................................... 17
Chemical synapse part ll.................................................................................................................... 17
EPP: Neuromuscular junction ........................................................................................................ 18
EPSP.............................................................................................................................................. 19
IPSP .............................................................................................................................................. 19
Electrical synapse.............................................................................................................................. 20
Parkinson’s Disease........................................................................................................................... 21
Synaptic plasticity part l .................................................................................................................... 24
Long term potentiation (LTP) ........................................................................................................ 25
Long-term depression (LTD) .......................................................................................................... 26
Spike-timing dependent plasticity (STDP) ...................................................................................... 27
, LTP in inhibitory synapse ............................................................................................................... 27
Homeostatic plasticity ................................................................................................................... 27
Morphological changes by plasticity .............................................................................................. 28
Synaptic plasticity part ll ................................................................................................................... 29
Short term plasticity ......................................................................................................................... 30
Neural Circuit & Signal integration .................................................................................................... 31
Summations .................................................................................................................................. 31
Layer-specific connections in neocortex ........................................................................................ 33
Molecular dynamics at the synapse .................................................................................................. 34
Delivery of proteins to synapses .................................................................................................... 35
Sushi belt model........................................................................................................................ 36
Surface diffusion for transmembrane proteins .......................................................................... 36
Local mRNA translation/protein synthesis ................................................................................. 38
Neural recording methods ................................................................................................................ 38
Pros and cons of recording techniques .......................................................................................... 39
Network properties of neuronal tissue .............................................................................................. 41
Memory in dissociated cortical networks ...................................................................................... 43
Extra notes after re-watching all the lectures: ................................................................................... 44
,Action potentials
After touching the receptor of, for example, a finger, the membrane potential gets depolarized. So
the membrane potential gets less negative. This depolarization is transient (=only lasts for a short
period of time) and the membrane potential will go back to its resting state.
From the resting membrane potential, if the stimulus is high enough and goes up (above the
threshold), action potential takes place. This is depolarization. If the membrane potential gets more
negative, hyperpolarization takes place.
Action potentials are:
• Short (about 1 ms)
• All-or-none
• Standard shape and amplitude
• Frequency encodes strength
To understand the action potential, you first have to understand the membrane
potential in rest. The changes in membrane potential is to achieve equilibrium.
Membrane potential is influenced by two underlying mechanisms:
• Chemical gradient: difference in intra and extra-cellular ion concentrations.
• Electrical gradient
If the K+-channels are open, K+ moves towards the negative side until equilibrium
is reached. ~-58 for K+(potassium) and ~58 for Na+ outside the cell. Only a small
amount of ions have to pass through the channels for equilibrium so the concentration in- and
outside the membrane stays more or less the same.
Nernst-equation is used to calculate the rest potential and is influenced by with absolute
temperature (T), ion charge (z) the gas- (R) and Faraday (F) constants as well as the equilibrium
potentials of the ions in the solution.
During action potential more Na+ channels open up, allowing Na+ ions to enter the cell and
depolarizes the cell. After depolarization, resting potential settles at a new level where the influx of
Na+ is balanced by the efflux of K +.
In a neuron several ions play a role , as well as the relative permeability (P) of the membrane (as
determined by how open the ion-channels are). This is calculated by the Goldman-equation.
In rest the permeability for K+ is higher (negative potential). During the action potential the
membrane will be more permeable for Na+ (positive potential).
The Na-K+ pump (and other pumps and transporters) regulate the
Chemical concentration gradients, but are not directly involved in the
action potential generation. It is the conductance of the ion channels
that change.
, The opening and closing can be regulated by different types of stimuli:
Ligand gating, Protein phosphorylation, Voltage gating, Stretch or pressure.
During action potential it is the voltage dependent gating that changes. See figure below: Sequential
opening of voltage-gated Na+ and K+ channels generating the action potential.
Sodium (Na+) channels: Permissive and non-permissive states. (activation gate opens
fast at depolarization, inactivation gate slowly closes at depolarization) An ion channel is open when
all gates are in the permissive state. If any of the gates is non-permissive, ions cannot flow.
1. Resting potential: sodium and potassium channels (relatively) closed.
2. Sodium channels open.
3. Depolarization: Activation gates open (positive feedback).
4. Repolarization: Inactivation gates close, Na+ and K+ channels open.
5. Refractory period: Na+ channels closed, K+ still open. (small undershoot).
