Unicellular organisms have a simple organisation of their life processes. However, a multicellular organisms
body organs and organ systems requires a control over their life processes as well as a co-ordination between the
various systems to maintain homeostasis of the organism.
Plants and animals both show a control and coordination mechanism.
In plants, control and co-ordination by sending chemical signals and brining about various types of movements
takes place. (e.g. phototropic, chemotactic, thingmotactic (response to stimulus of touch or contact), etc.
In Animals, specially the higher vertebrates show a gradual increase in the complexity of their control and
coordination by giving both electrical and chemical signals.
The porifera (sponges) are the most primitive of the animal phyla. Even though there are different types of
cells in sponges for carrying out different functions, a proper nervous system is absent.
However, to bring about efficient working of the body these multicellular animals show division of labour
among the cells. This leads to specialization of cells for the various activities like digestion, respiration, excretion and
others.
Later in the higher animals, phyla the different cells forms tissues, organs and systems, which must work in
coordination with each other for smooth internal functioning of the body. Also, the organism must be able to respond
and coordinate with respect to various stimuli or changes in the external environment.
In the lower animals like Hydra and Planaria the control and co-ordination is carried out by nervous system, while in
higher more complex animals, it is done by two coordinating systems - the nervous (electrical) system and endocrine
(chemical) control system.
NERVOUS COORDINATION
Nervous System in Hydra:
❖ Hydra, a cnidarian shows primitive nervous system in the form of diffused nervous system.
❖ The cnidarians are the first animal group showing true simple nervous system.
❖ It consists of the sensory cells and the nerve cells or neurons along with their fibers.
❖ The nerve cells are distributed throughout the body and interconnected to each other by synapses
between their fibers to form the nerve net.
❖ There are two nerve nets present in the mesoglea (hydrostatic skeleton)-
a.one connected towards the epidermis
b. second towards the gastro-dermis.
❖ There are sensory cells scattered in the body wall and tentacles, but sense organs are absent.
❖ Neurons have fibers but there are no sensory and motor nerves.
❖ The nerve impulse shows no polarity or direction.
❖ In Hydra, activation of sensory cells produced at any point, and from this point impulse can be carried
throughout the body in any direction, thus bringing movements of the body or tentacles e.g. catching of
prey during feeding.
❖ The diffused type of nervous system is the first important landmark in the nervous system.
❖ It is seen in the phylum Ctenophora as well as in the enteric system or gut wall of higher animals including
man.
1
,Nervous System in Planaria (flatworm):
1. Planaria is a flatworm belonging to the phylum Platyhelminthes.
2. It is the most primitive animal with a central nervous system (CNS) located on the ventral side of
body.
3. It consists of a mass of cerebral or cephalic ganglion appearing like an inverted U-shaped brain.
4. These lie in the anterior or head region and from each ganglion arise nine branches towards the
outer side.
5. Ventrally from cerebral ganglia arise a pair of Ventral Nerve Cords (VNC) which runs posteriorly,
are inter connected to each other by transvers nerve or commissure in a ladder like manner.
6. From the ventral nerve cord arises peripheral nerve plexus.
7. The PNS include sensory cells arranged in lateral cords in the body.
8. A pair of photo sensory structure, the eyes are located on dorsal side of the brain and single sensory
cells scattered in the body.
There is a high level of specialization in the formation of neurons as electrically signaling cells and
also in the entire system, gradually from a diffuse neural system to a centralized nervous system. The
expansion into a properly organized system involving the brain, its gradual expansion in size and functions.
This has led to centralization of various sense organs assisting in coordinating the internal
environment with that of the external environment. There evolution of a complex networking system which
efficiently transmits signals between one part or organ of the body and another.
Neural tissue
The neural tissue consists primarily of two types of cells –
a) neurons
b) neuroglia or glial cells.
c) Nerve is a bundle of axons.
d) The bundle of axons outside the CNS is called as ‘nerve’ is while inside the CNS called tract.
e) The nerves may be sensory or motor or mix type.
f) mixed nerve having both the types - sensory and motor fibers.
g) All these along with nervous organs make up the nervous system of the higher animal and bring about
co-ordination and control of various activities of the body.
h) This is done by the receptors which bring in sensory inputs towards the central nervous system.
i) Processing is carried out in the CNS and then by the motor commands, the response is sent to effector
organ.
j) The nerves arising from the cytons of the CNS, travel throughout the body transmitting the nerves
impulses to or from the CNS.
2
,Neurons/Nerve cells:
1. These are the structural and functional units of the nervous system.
2. Each multipolar neuron has three parts –
a. cyton or cell body
b. dendron
c. axon.
a) cyton-
1. The cyton has a distinct central nucleus with a nucleolus and Neuroplasm.
2. A clear film of cytoplasm surrounds the nucleus around which there are neurofibrils, Nissl’s granules
and other cell organelles.
3. Nissl’s granules are riboprotein components. They play an important role in the synthesis of the
enzyme required for formation of the neurotransmitter.
4. Neurofibrils play an important role in transmission of nerve impulse.
b)Dendrons–
1. These are many small conical processes arising from the cyton.
2. These are highly branched into fine dendrites.
3. Nissl’s granules and neurofibrils both can be seen at the base of the dendrons, which transmit
message towards the cyton.
c)Axon:
1. It consists of a bundle of neurofibrils.
2. Nissl’s granules are absent.
3. Terminally, the axon gives out branches called telodendrons.
4. The axons carry the messages away from the cytons.
5. The axons may give out lateral branches called collaterals.
6. The terminal branches attach to a muscle, gland, skin or telodendrites of another neuron.
7. The interconnection between two neurons or neuron with motor organ is called synapse. It is usually
axo-dendronic or may be axo-axonic, axo-somatic or dendro-dendronic.
8. The cytons are generally found inside the brain, spinal cord (CNS) and in the ganglia.
9. Small groups of cell bodies inside the white matter of brain are called basalnuclei.
10. A bundle of axons called nerve may be covered only by neurilemma in the non-medullated nerves
while in the medullated nerves it is covered both by medullary sheath and on the outside by
neurilemma.
11. Conduction of impulse by the medullated nerves is 50 times faster than in the non-medullated nerves.
12. The connective tissue covering around the nerve fascicule is called endoneurium.
13. Few nerve fasciculi with endonurium are surrounded by connective tissue, called perineurium and a
still large bundle of nerves is covered on the outer side by epineurium.
14. Blood is supplied to all the nerves to provide oxygen and nutrients.
15. Itis a single long, usually unbranched process arising from the cyton at the axon hillock.
3
, Neuroglial cells:
1. The neuroglial cells are more in number than the neurons.
2. Most of the supporting cells of the nervous system are derived from the embryonic tissue
layer(ectoderm) that produces neurons.
3. The term neuroglia is the supporting cells of the Central Nervous System (CNS) and Peripheral
Nervous System (PNS).
Types of Neuroglial cells and their functions
Synapse:
a) It is a junction between two nerve cells.
b) In between two nerves a minute gap -synaptic cleft is present which allows transmission of impulse
by a neurotransmitter bridge.
1. Properties of nerve fibers:
a. Excitability/Irritability -
nerve fibers are highly excitable tissue respond to various stimuli and Capable of generating electrical
impulse.
b. Conductivity–
action potential is generated in the nerve fiber, which is propagated along its entire length to the
axon terminal.
c. Stimulus–
It is any detectable, physical, chemical, electrical change in the external or internal environment
which brings about excitation in a nerve/muscle/organ/organism.
Threshold stimuli –
the stimuli by which the axons with low threshold fibers are stimulated and a small potential
change recorded.
Subliminal (weak) stimulus-
will have no effect
supraliminal(strong) stimulus–
will produce the same degree of impulse as the threshold stimulus.
d. Summation effect–
4
body organs and organ systems requires a control over their life processes as well as a co-ordination between the
various systems to maintain homeostasis of the organism.
Plants and animals both show a control and coordination mechanism.
In plants, control and co-ordination by sending chemical signals and brining about various types of movements
takes place. (e.g. phototropic, chemotactic, thingmotactic (response to stimulus of touch or contact), etc.
In Animals, specially the higher vertebrates show a gradual increase in the complexity of their control and
coordination by giving both electrical and chemical signals.
The porifera (sponges) are the most primitive of the animal phyla. Even though there are different types of
cells in sponges for carrying out different functions, a proper nervous system is absent.
However, to bring about efficient working of the body these multicellular animals show division of labour
among the cells. This leads to specialization of cells for the various activities like digestion, respiration, excretion and
others.
Later in the higher animals, phyla the different cells forms tissues, organs and systems, which must work in
coordination with each other for smooth internal functioning of the body. Also, the organism must be able to respond
and coordinate with respect to various stimuli or changes in the external environment.
In the lower animals like Hydra and Planaria the control and co-ordination is carried out by nervous system, while in
higher more complex animals, it is done by two coordinating systems - the nervous (electrical) system and endocrine
(chemical) control system.
NERVOUS COORDINATION
Nervous System in Hydra:
❖ Hydra, a cnidarian shows primitive nervous system in the form of diffused nervous system.
❖ The cnidarians are the first animal group showing true simple nervous system.
❖ It consists of the sensory cells and the nerve cells or neurons along with their fibers.
❖ The nerve cells are distributed throughout the body and interconnected to each other by synapses
between their fibers to form the nerve net.
❖ There are two nerve nets present in the mesoglea (hydrostatic skeleton)-
a.one connected towards the epidermis
b. second towards the gastro-dermis.
❖ There are sensory cells scattered in the body wall and tentacles, but sense organs are absent.
❖ Neurons have fibers but there are no sensory and motor nerves.
❖ The nerve impulse shows no polarity or direction.
❖ In Hydra, activation of sensory cells produced at any point, and from this point impulse can be carried
throughout the body in any direction, thus bringing movements of the body or tentacles e.g. catching of
prey during feeding.
❖ The diffused type of nervous system is the first important landmark in the nervous system.
❖ It is seen in the phylum Ctenophora as well as in the enteric system or gut wall of higher animals including
man.
1
,Nervous System in Planaria (flatworm):
1. Planaria is a flatworm belonging to the phylum Platyhelminthes.
2. It is the most primitive animal with a central nervous system (CNS) located on the ventral side of
body.
3. It consists of a mass of cerebral or cephalic ganglion appearing like an inverted U-shaped brain.
4. These lie in the anterior or head region and from each ganglion arise nine branches towards the
outer side.
5. Ventrally from cerebral ganglia arise a pair of Ventral Nerve Cords (VNC) which runs posteriorly,
are inter connected to each other by transvers nerve or commissure in a ladder like manner.
6. From the ventral nerve cord arises peripheral nerve plexus.
7. The PNS include sensory cells arranged in lateral cords in the body.
8. A pair of photo sensory structure, the eyes are located on dorsal side of the brain and single sensory
cells scattered in the body.
There is a high level of specialization in the formation of neurons as electrically signaling cells and
also in the entire system, gradually from a diffuse neural system to a centralized nervous system. The
expansion into a properly organized system involving the brain, its gradual expansion in size and functions.
This has led to centralization of various sense organs assisting in coordinating the internal
environment with that of the external environment. There evolution of a complex networking system which
efficiently transmits signals between one part or organ of the body and another.
Neural tissue
The neural tissue consists primarily of two types of cells –
a) neurons
b) neuroglia or glial cells.
c) Nerve is a bundle of axons.
d) The bundle of axons outside the CNS is called as ‘nerve’ is while inside the CNS called tract.
e) The nerves may be sensory or motor or mix type.
f) mixed nerve having both the types - sensory and motor fibers.
g) All these along with nervous organs make up the nervous system of the higher animal and bring about
co-ordination and control of various activities of the body.
h) This is done by the receptors which bring in sensory inputs towards the central nervous system.
i) Processing is carried out in the CNS and then by the motor commands, the response is sent to effector
organ.
j) The nerves arising from the cytons of the CNS, travel throughout the body transmitting the nerves
impulses to or from the CNS.
2
,Neurons/Nerve cells:
1. These are the structural and functional units of the nervous system.
2. Each multipolar neuron has three parts –
a. cyton or cell body
b. dendron
c. axon.
a) cyton-
1. The cyton has a distinct central nucleus with a nucleolus and Neuroplasm.
2. A clear film of cytoplasm surrounds the nucleus around which there are neurofibrils, Nissl’s granules
and other cell organelles.
3. Nissl’s granules are riboprotein components. They play an important role in the synthesis of the
enzyme required for formation of the neurotransmitter.
4. Neurofibrils play an important role in transmission of nerve impulse.
b)Dendrons–
1. These are many small conical processes arising from the cyton.
2. These are highly branched into fine dendrites.
3. Nissl’s granules and neurofibrils both can be seen at the base of the dendrons, which transmit
message towards the cyton.
c)Axon:
1. It consists of a bundle of neurofibrils.
2. Nissl’s granules are absent.
3. Terminally, the axon gives out branches called telodendrons.
4. The axons carry the messages away from the cytons.
5. The axons may give out lateral branches called collaterals.
6. The terminal branches attach to a muscle, gland, skin or telodendrites of another neuron.
7. The interconnection between two neurons or neuron with motor organ is called synapse. It is usually
axo-dendronic or may be axo-axonic, axo-somatic or dendro-dendronic.
8. The cytons are generally found inside the brain, spinal cord (CNS) and in the ganglia.
9. Small groups of cell bodies inside the white matter of brain are called basalnuclei.
10. A bundle of axons called nerve may be covered only by neurilemma in the non-medullated nerves
while in the medullated nerves it is covered both by medullary sheath and on the outside by
neurilemma.
11. Conduction of impulse by the medullated nerves is 50 times faster than in the non-medullated nerves.
12. The connective tissue covering around the nerve fascicule is called endoneurium.
13. Few nerve fasciculi with endonurium are surrounded by connective tissue, called perineurium and a
still large bundle of nerves is covered on the outer side by epineurium.
14. Blood is supplied to all the nerves to provide oxygen and nutrients.
15. Itis a single long, usually unbranched process arising from the cyton at the axon hillock.
3
, Neuroglial cells:
1. The neuroglial cells are more in number than the neurons.
2. Most of the supporting cells of the nervous system are derived from the embryonic tissue
layer(ectoderm) that produces neurons.
3. The term neuroglia is the supporting cells of the Central Nervous System (CNS) and Peripheral
Nervous System (PNS).
Types of Neuroglial cells and their functions
Synapse:
a) It is a junction between two nerve cells.
b) In between two nerves a minute gap -synaptic cleft is present which allows transmission of impulse
by a neurotransmitter bridge.
1. Properties of nerve fibers:
a. Excitability/Irritability -
nerve fibers are highly excitable tissue respond to various stimuli and Capable of generating electrical
impulse.
b. Conductivity–
action potential is generated in the nerve fiber, which is propagated along its entire length to the
axon terminal.
c. Stimulus–
It is any detectable, physical, chemical, electrical change in the external or internal environment
which brings about excitation in a nerve/muscle/organ/organism.
Threshold stimuli –
the stimuli by which the axons with low threshold fibers are stimulated and a small potential
change recorded.
Subliminal (weak) stimulus-
will have no effect
supraliminal(strong) stimulus–
will produce the same degree of impulse as the threshold stimulus.
d. Summation effect–
4
