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Summary Nutrition and the Brain (HNH31706)
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A summary of the course Nutrition and the Brain HNH31706
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Nutrition and the brainTuesday March 16 - Lecture 1 Basic brain function and anatomy
- Brain tissue:
o Neurons (100 billion), which are supported by glia cells
- Glia cells:
o Astrocytes (Central nervous system (CNS), supporting neurons)
o Oligodendrocytes (CNS, produce myelin, action potential)
o Microglia (CNS, neuroinflammation)
o Ependymal cells (CNS, form outer layer of the brain, inside the ventricles,
cerebrospinal fluid)
o Schwann cells (Peripheral nervous system (PNS), myelin)
o Satellite cells (PNS, support)
Neurons
There are different types of neurons; unipolar, bipolar, pseudo unipolar and multipolar. Most
common one is the multipolar. It consists of a dendrite (where the signal enters), then a cell body;
which accepts the signal and then decides if it wants to proceed sending the signal to another neuron
or making into an action potential, and if the cell body decides to proceed the signals (turn it into an
action potential), then this action potential hops from the node of Ranvier towards your synapse.
Synapses are at the end of the axon.
,Glia cells
Astrocytes are really connected to neurons, it is the multipolar neuron and with end feet; with little
feet they project on this neuron, so they can communicate with this neuron, but also send signals or
for example, sends the glucose levels within these neurons. The oligodendrocytes produce the
myelin. The myelin is along the axons and these oligodendrocytes are sort of in the middle of myelin
structuring fibres. The microglia are small and not really connecting if you compare them with the
oligodendrocytes and astrocytes. They can morphologically change if there is for example a level of
inflammation or stress in the brain. The ependymal cells in the outer layer and in the ventricles. They
produce, along with choroid plexus, the cerebrospinal fluid (CSF). You have approximately 150mL of
CSF floating through your brain and it is refreshed 4 times a day. Then within your peripheral nervous
system, they are sort of the astrocytes, but they call it satellites and the Schwann cells, the Schwann
cells are responsible for the myelin within your spine and the satellite cells are responsible for the
support within your spine.
Neuronal communication
- Synaptic transmission
o Neurotransmitters, pre-post synapses
- Action potential
o Action potential from the cell body, reaches down towards the axons, towards the
synapse, and then at the bottom at the synapse, there are synaptic vesicles filled
with neurotransmitters (dopamine, serotonin). When an action potential reaches the
synapse, these vesicles dock towards the membrane and then release the
neurotransmitters into the synaptic cleft. If it is released into the synaptic cleft, then
it can reach the dendrite of the other neurons and it can decide if it is enough
stimulating to proceed towards the cell body with this signal and eventually
proceeding with the action potential and given through signals.
o Na/K-pumps, membrane potential
,The neurotransmitters you will see the most are dopamine and serotonin. Dopamine, you can think
about Parkinson’s disease and addiction. Serotonin you can think about depression. Most of the
times, you have these neurotransmitters within your body, but they cannot cross the blood brain
barrier. The precursors cross the blood brain barrier and then they are transformed into
neurotransmitters in the brain, which is a safety rule. So, the blood brain barrier is a sort of strict
bouncer for certain compounds.
Neurotransmitters or precursors obtained by diet
For example, a precursor of serotonin is tryptophan. If you eat for example an egg, tryptophan
reaches your body and blood stream and can be transported over the blood brain barrier and then
transformed into serotonin.
Neurotransmitter release
In more detail the neurotransmitter release. An action potential is coming from above, guided
through the axon towards the synapse. Then, if this action potential reaches the synapse, there is the
case of membrane depolarisation and it results in the influx of calcium. That influx of calcium is a
signal to the vesicles. These vesicles store neurotransmitters, for example dopamine and serotonin.
The signal then via certain proteins, leads to docking of the vesicles and then opening of the vesicles
into the synaptic cleft and release of the neurotransmitters. When these neurotransmitters are
released, they can bind on the postsynaptic cell to a receptor. If enough neurotransmitters are bind
to the receptor, then again, a calcium influx and then again, the action potential proceeds towards
the cell body of another neuron. What happened with the neurotransmitters if they are released in
the synaptic cleft? They are degenerated directly, but they are taken up in the pre-synapse again,
that happens with dopamine and serotonin.
For example, for Prozac in depression, it is thought that there are low levels of serotonin in the
synaptic cleft and Prozac blocks the reuptake mechanism, so a higher level of serotonin is left in this
synaptic cleft, increasing the signals proceeding at the post-synapse and can affect your depressive
feelings. Another example, for dopamine is cocaine, that also blocks the reuptake receptors. So,
, cocaine blocks that reuptake receptors and then a high level of dopamine is left in the synaptic cleft
and really stimulating the receptors.
Instant synthesis
Neurotransmitters are stored within these vesicles in the synapse. You have another way of
neurotransmission between neurons and astrocytes for example and those are endocannabinoids. It
can be instantly formed, so when an action potential arrives at the pre-synapse, a neurotransmitter
is released at the post-synapse and if necessary, endocannabinoids can be formed from the cell
membrane and then you can get different kinds of signalling; you can go back to the pre-synapse or
to the astrocytes, so that is a sort of instant cell signalling between neurons and astrocytes, so you
have different types of signalling around these pre-synapse/post-synapses and astrocytes mainly.
Neuronal communication
Of this neuronal communication, most important is to create synaptic plasticity. Synaptic plasticity is
a base of learning and memory processes. If you learn, then you repeat them, so a certain pathway is
stimulated every time. Then, the synapses change a bit because they are stimulated so much. If you
do it repeatedly, you have more synapses, more receptors and it adapts to your system.
- After long term potentiation (LTP), synaptic communication is strengthened
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