Learning objectives
- Organization of primitive brains
- evolution of “large brains”
- relationship between the brain and energy
- storage of fat and the brain
- our brain is shrinking, but PFC and cerebellum increase
- relationship white matter / grey matter
- features of neuronal ...
Primitive brains exist of a collection of neurons spread over the body. Brains appear in the head
because most sensory input enters here.
Contrary to a popular myth, dinosaurs didn’t have butt brains. They though this because some
dinosaurs had extra-large cavities in their hips.
The human brain has at least 40 billion neurons and 100 billion brain cells. The human brain is also
much larger then we would expect based on our body size.
In mammals, a negative correlation is found between brain size and degree of fat storage. So species
with a large brain have in general a low fat storage. One of the few mammals that combine fat
storage with a large brain, are animals that do not have high energy expenses while moving. NOTE,
THIS CORRELATION DOES NOT HOLD FOR PRIMATES.
Brains are expensive. To evolve a larger brain relative to its ancestor, a species must either increase
their net energy intake, or reduce the allocation of energy to another function.
Consequences of lack of oxygen and glucose due to blood flow
- 8-10 seconds —> fainting
- 30-40 seconds —> lose action potentials
- 3-5 minutes —> glucose levels become to low
- 6-10 minutes —> neurons die
Why can humans generate enough energy for their large brains?
- Walking on two legs saves energy
- Efficient in dealing with food (cooking for example)
- Storage of fat
, Which parts show the largest expansion in humans?
The biggest growth of areas in the human brain are the association cortex;
But at the moment or brain is shrinking, it is also becoming smaller. However, there is an increase in
the size of the prefrontal cortex (PFC).
The main functions of the PFC are:
- Planning complex cognitive behaviour
- Personality expression
- Cognitive decision making
- Moderate social behaviour
Another region that is expending is the cerebellum. It increased even more than the PFC.
Genetic data based on ancient DNA suggest positive selection of several genes important for nervous
system development, brain function, and behavior in our lineage including genes involved in axonal
and dendritic growth or synaptic transmission
Convolutions of the manatee
The manatee has no convolutions and a remarkably little associative cortex. This is possibly due to
the fact that they live in a very stable environment, with almost no predators, so their brains might
not need the convolutions. However, they might be less flexible in adapting when changes occur.
Grey and white matters
If the brain becomes larger, relatively more white matter is needed than grey matter, just to be able
to maintain the connectivity in the brain.
The model says, that if the brain
would continue to increase, by the
size of 10.000 cm3 the brain would
contain 65% white matter.
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