EVOLUTIONARY TRENDS IN THE STRUCTURE OF BRAIN- SHARK,
FROG, PIGEON AND RABBIT
The nervous system is a complex network of nerves and cells that carry messages to and from
the brain and spinal cord to various parts of the body.
Nervous system
The Autonomic nervous system is a control system that acts largely unconsciously and
regulates bodily functions such as the heart rate, digestion, respiratory rate, urination and sexual
arousal. The Peripheral nervous system consists of nerves and ganglia outside
the brain and spinal cord. The central nervous system (CNS) is the part of the nervous
system consisting of the brain and spinal cord. The central nervous system is so named because
it integrates information it receives from, and coordinates and influences the activity of, all parts
of the bodies of bilaterally symmetric animals.
In vertebrates, the brain is protected by the skull. The brain and spinal cord are both
enclosed in the meninges. The meninges are three layers of protective tissue called the dura
mater, arachnoid mater, and pia mater.
The central nervous system is divided in outer white and inner gray matter. Grey matter is a
major component of the central nervous system, consisting of neuronal cell bodies,
dendrites and myelinated&unmyelinated axons), glialcells, synapses, and capillaries. Grey matter
contains numerous cell bodies and relatively few myelinated axons, while white matter contains
Central NS
Peripheral NS
Autonomic NS
relatively few cell bodies and many myelinated axon tracts. The colour difference arises mainly
from the whiteness of myelin
Every vertebrate's brain is built in accordance with a single architectural plan. The brain
exhibits varying degrees of differentiation and segregation of the sense organs in the head region.
It is in the form of a swollen anterior end of the neural tube and is known as 'encephalon'. The
brain of all vertebrates has the same basic structure, it has the following parts.
1. Forebrain or Prosencephalon: subdivided into Telencephalon (comprises of the cerebral
hemispheres) and Diencephalon (comprises of epithalamus, thalamus and hypothalamus)
2. Midbrain or Mesencephalon: comprises of tectum,tegminum and optic lobes
3. Hind Brain or Rhombencephalon: subdivided into Metencephalon and Myelencephalon,
which has medulla oblongata and cerebellum.
A serous fluid the cerebrospinal fluid fills all the ventricles of the brain. It is secreted by the
choroid plexus. It is also present in the spaces between the meninges.
FUNCTIONS OF THE BRAIN
1. Olfactory lobes - Sense of smell
2. Cerebral hemispheres-Seat intelligence and memory.
3. Diencephalon - Controls the general metabolic functions of the body
4. Optic lobes - Sense of vision.
5. Cerebellum - Co-ordinates the movements of voluntary muscles.
6. Medulla oblongata - Controls the involuntary functions of the body
features Fish Frog Bird Rabbit
SIZE, SHAPE OF BRAIN Bilaterally symmetrical
and white.
Elongated & larger than
frog
Bilaterally
symmetrical and
white
Elongated and smaller
Bilaterally symmetrical and
white
Large but short and
rounded
Bilaterally symmetrical
and white
Large
DIVISIONS OF BRAIN Forebrain, midbrain and
hind brain
Forebrain, midbrain
and hind brain
Forebrain, midbrain and
hind brain
Forebrain, midbrain and
hind brain
MENINGES no meninges 2 Layered meninges
inner pia mater
&outer dura mater
2 Layered meninges inner
pia mater & outer dura
mater
3 Layered meninges inner
pia mater, middle
arachnoid &outer dura
mater
FORE
BRAIN Olfactory Lobe
Olfactory tract/peduncle
end in Olfactory lobe
(OL).
elongated OL
seperated by a
longitudnal groove
OL small & poorly
developed
OL club shaped, arised
from cerebrum and
olfactory bulb
Size, shape and
position of OL
Short &fully covered by
cerebellum
Behind CH Hardly can be seen from CH Narrow & triangular
FORE
BRAIN
Ant. Choroid
plexus
Thin roof of D forms Ant.
choroid plexus
Roof of D forms Ant.
choroid plexus
Thin&highly vasularised roof
forms Ant. choroid plexus
Thin&highly vasularised
roof forms Ant. choroid
plexus
Pineal body Dorsal Dorsal Dorsal Dorsal& hangs from a
pineal stalk
Pitutary & its
intermediary lobe
Ventral
-
Ventral
-
Ventral, intermediary
lobe lacking
Ventral & has a post
swelling-corpus
albicans
Optic chiasma Infront of
infundibulum
Infront of
infundibulum
Ant. to infundibulum &
ventral
Ant to infundibulum &
ventral
Optic thalamus The floor of D is
hypothalamus
Lateral walls of D
forms
hypothalamus
Lateral walls of D forms
OT
MID BRAIN
features Fish Frog Bird Rabbit
Optic lobes 2 2 large, The condition:
Corpora bigemina
2 , Corpora bigemina 4, Corpora Quadri gemina. Ant
pair of lobes are larger
Crura cerebri no Present &connecting
diencephalon with
medulla oblongata
A pair of band of thick nerve
fibres connecting
diencephalon with medulla
oblongatas
A pair of band of thick nerve
fibres connecting diencephalon
with medulla oblongatas
HINDBRAIN cerebellum
Well developed
Rhomboidal in
shape, divided in to
Rt &left by median
longitudinal groove
Narrow band behind
optic lobes on dorsal
surface
Well developed
divided in large median lobe
(vermis) &2 small conical
lobes (Floculli)
Well developed
divided in large median lobe
(vermis) &2 small conical lobes
(Floculli)
2 thick bands of nerve fibres
(Pons varoli) connecting 2 sides
of cerebellum
Medulla
oblongata
Broad ant and tapers
post
Broad ant and tapers post Broad ant and tapers post
HINDBRAIN
Thin roof forms
Post. choroid plexus
Thin roof forms Post.
choroid plexus
Post. choroid plexus on
dorsal surface
Post. choroid plexus on dorsal
surface
It continues as
spinal chord
It continues as spinal
chord
It continues as spinal chord It continues as spinal chord
Ant. Gives off two
hollow corpora
restiformis
Floor of fourth ventricle
is thick
Median ventral fissure
continues into SC
Median ventral fissure
continues into SC
VENTRICLES All the ventricles
are present
All the ventricles are
present
All the ventricles are present All the ventricles are present
Other
Comments
Metacoel continues
as central canal of
SC
Metacoel continues as
central canal of SC
Metacoel continues as
central canal of SC
Metacoel continues as central
canal of SC
Sense of smell
Well developed, OL
well developed
poorly developed, OL
poorly developed
poorly developed, OL small
& poorly developed
OL well developed
Comp. To fish, frog & bird
Cerebrum
Not well developed
CH Well developed
CH Well developed with
large corpora striata (!!!)
CH Well developed-frontal,
parietal & temporal
Cerebellum
Well developed for
Equilibrium &
coordination for
swimming
Not Well developed
Well developed for
Equilibrium & coordination
for flight
Well developed for Equilibrium
& coordination of voluntary
muscles
Others
- Crura cerebri
Faster transmission of
impulses
Instinctive behav.
More intelligent...
BRAIN OF FISH
Dorsal view Ventral view
BRAIN OF MAMMAL
Dorsal view Ventral view