Details of vertebrate Brain
Vertebrate Brain
has undergone evolution which resulted in the formation of hindbrain, midbrain
and forebrain. Central canal of the spinal cord extends in the brain and
expands into channels called ventricles. The ventricles are filled with
cerebrospinal fluid.
Hindbrain:
It is continuous
with spinal cord and includes medulla oblongata, cerebellum and pons.
Medulla oblongata:
It is enlargement
where the spinal cord enters the brain. It contains reflex centres for
breathing, swallowing, cardio vascular function and gastric secretion. Medulla
oblongata is well developed in all jawed vertebrates reflecting its ability to
control visceral functions and to serve as a screen for information that leaves
or enters the brain.
Cerebellum:
It is an
outgrowth of medulla oblongata. It coordinates motor activity associated with
limb movement maintaining posture, and spatial orientation. Cerebellum in cartilaginous
fishes has distinct anterior and posterior lobes. In Teleosts the cerebellum is
large in active swimmers and small in inactive fishes.
Amphibians often
have rudimentary cerebellum, reflecting their simple locomotor pattern.
In other
Tetrapads cerebellum is laterally expanded. These expanded lateral lobes
provide locomotor control of muscles of the appendages.
The cerebellum
is much larger in Birds and Mammals, a reflection of complex locomotor patterns
and a common evolutionary history of limb development and phylogeny as
terrestrial vertebrates.
Pons:
Pons is a bridge
of transverse nerve tracts from the cerebrum of the forebrain of both sides of
the cerebellum. It also contains tracts that connect the forebrain and spinal
cord in all vertebrates.
Midbrain:
Midbrain was
originally centre for coordinating reflex response to visual input. As the
brain evolved it look on added functions relating to tactile touch and auditory
hearing input but it did not change in size. The roof of midbrain called optic rectum
is thickened region of gray matter that integrates visual and auditory signals.
Forebrain:
Vertebrate
forebrain has changed great deal during vertebrate evolution. Forebrain has two
main parts, diencephalons and telencephalon.
Diencephalon: It
lies just in front of midbrain and contains pineal gland, pituitary gland,
hypothalamus and thalamus. Thalamus relays all sensory information to higher
brain centres. Hypothalamus lies below the thalamus and regulates many
functions such as body temperature, sexual drive, carbohydrate metabolism,
hunger and thirst. Pineal gland controls body rhythms. Pituitary is major
endocrine gland.
In fishes and
amphibians diencephalons possesses sensory information. In reptiles and birds
most important part of brain is corpus striatum which plays a role in their
complex behaviour patterns. As the diencephalons slowly expanded during
evolution and handled more and more sensory functions. The telencephalon (first
part of forebrain) expanded rapidly in both size and complexity.
Cerebrum:
External to
corpus striatum is cerebrum by which large groove divides into right and left
cerebral hemispheres. The parts of brain related to sensory and motor
integration hanged greatly as vertebrates became more agile. Many functions shifted
from optic tectum to the expanding cerebral hemispheres. In mammals outermost
part of cerebrum called cerebral cortex increased in size and complexity. This
layer folds back on itself to remarkable extent, suggesting that the evolution
of mammalian cerebrum output the enlargement of the skull bones housing it.
Different parts of the cerebrum have specific functions. For example cerebral
cortex contains primary sensory areas and primary motor areas. Other areas of
the cortex are involved in the perception of visual or auditory signals from
the environment. In humans this includes the ability to use language both
written and spoken.
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