Evolution of the Vertebrate Brain
The vertebrate brain evolved from a set of three bulges at the anterior
end of the spinal cord. These bulges became the regions known as the
forebrain, midbrain, and hindbrain, and they are still present in all
vertebrates today.
There are three evident trends in the brain's evolution:
- The relative size of the brain increased in certain
evolutionary lineages as the species became more evolved
- There was increased compartmentalization of function. As this
happened, the divisions between the three sections blurred.
- There was increased sophistication and complexity of the forebrain and
an important region called the cerebrum. In mammals especially,
sophisticated behavior is linked to the relative size of the crebrum and
the number of convolutions that it has. These convolutions increase the
surface area, which is more important than the volume of the cerebral
cortex.
Anatomy
The anatomy of the brain is most easily explained to elementary school
children as school building in the head. Each area is like a grade, in
each grade you do different things (cursive, addition, etc.). Slight
brain damage can be likened to a class going out on a field trip, but
returning. Serious brain damage is like the fifth or six grade class that
graduates, and doesn't come back.
Brain Stem: The brainstem is made up of the midbrain and hindbrain;
the hindbrain, in turn, has three parts.
- The Medulla oblongata controls several autonomic and
homeostatic functions like breathing, heart and blood vessel activity, swallowing,
vomiting, and digestion.
- The Pons takes part in many of the activities above, sharing
responsibility with the Medulla. The most
important functions of the Pons and Medulla, is data transfer of sensory
information and motor impulses (see the Nervous
system).
- The Cerebellum coordinates movement and maintains equilibrium.
Hand-eye coordination originates from this part of the brain.
Forebrain
The diencephalon consists of two parts, the Thalamus and the Hypothalamus.
- Thalamus: a relay station for the sensory information before the Cerebrum. It
sorts information and sends it to the correct higher brain centers. It also receives
information from the cerebrum that regulates emotions.
- Hypothalamus: important in the regulation of homeostasis.
Telencephalon
The telencephalon defines the Cerebrum, which is divided into the
right and left cerebral hemispheres. Each hemisphere consists of an outer
covering of gray matter, the cerebral cortex, internal white matter, and a
cluster of nuclei deep within the white matter.
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