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