Topic 9 Control and Coordination
Introduction:
- Plants and animals both show a control and coordination mechanism.
- In plants this done by sending chemical signals and bringing about various types of movements.
- Animals, show a gradual increase in the complexity of their control and coordination by giving both electrical and chemical singles.
- The nervous system and endocrine control system are two coordinating systems in them.
- In this chapter you will study about development of nervous system in different animal groups and details of the system in humans.
Nervous system in different animal groups
Nervous System in Hydra : Phylum : Cnidaria
- Hydra, a cnidarian shows the diffused nervous system in the form of nerve net.
- It is the most primitive nervous system.
- There are two nerve nets in the mesoglea one connected towards the epidermis and second towards the gastro-dermis.
- Hydra lacks sensory organs, but the .sensory cells scattered in the body wall.
- The nerve impulse shows no polarity or direction.
- As all neurons are interconnected the response is seen throughout the body.
Nervous System in Planaria (flatworm) :
Phylum :Platyhelminthes
- Planaria is a flatworm and belongs to the phylum Platyhelminthes.
- It is the most primitive animal with a Central Nervous System (CNS) located on the ventral side of body
- Nervous system consists of a mass of cerebral or cephalic ganglion appearing like an inverted U-shaped brain.
- Ventrally from below the ganglia arise a pair of Ventral Nerve Cords (VNC) or long nerve cords. These are interconnected to each other by transfer nerve or
- commissure in a ladder like manner.
- The PNS include sensory cells arranged in lateral cords in the body.
Sponges : Phylum : Porifera
- Nervous System : Lack nervous system
Earthworm : Phylum : Annelida
- Nervous System :Ganglionated
- Position :Ventral, solid
- Composition: CNS, PNS, Sympathetic NS
Cockroach : Phylum : Arthropoda
- Nervous System : Ganglionated
- Position :Ventral, solid
- Composition : CNS, PNS, and ANS
Human : Phylum : Chordata
- Nervous System : Non-ganglionated
- Position : Dorsal, hollow
- Composition : CNS, PNS, and ANS
Neural tissue:
- Two types of cells in neural tissue — the neurons and the neuroglia or glial cells.
- Nerve is bundle of axons. Outside the CNS, it is called nerve while inside it is called tract.
Types of nerves :
- Sensory (with sensory fibres),
- Motor (with motor fibres) and
- Mixed type (with both sensory and motor fibres).
Neurons/Nerve cells :
- Neuron is structural and functional unit of the nervous system.
- Each multipolar neuron has three parts — cyton or cell body, dendron and axon.
Grey matter and white matter :
- Grey matter is darker part of CNS due to presence of cytons.
- White matter is lighter part of CNS. This is due to presence of myelin sheath axons.
- In PNS however, the accumulation of cyton causes a swelling on the nerve.
- Such a swelling is called ganglion. [cytons within CNS form nuclei while those in PNS form ganglia]
Connective tissue layers in a nerve are :
- Endoneurium : covers each nerve fibre
- Perineurium : covers each nerve bundle having a number of neurons
- Epineurium : covers many nerve bundles to form a peripheral nerve
Neuroglial cells :
- More in number than the neurons.
- They are supporting cells of the Central Nervous System (CNS) and Peripheral Nervous System (PNS).
- Neurilemma is the plasma membrane of Schwann cell.
Types of Neuroglial cells
a. Ependymal cell b. Oligodendrocytes
c. Satellite cells d. Astrocytes
e. Microglia f. Schwann cells
Neuroglial cells at CNS (Central Nervous
System)
A. Oligodendrocytes
- These cells have few branches and mainly form the myelin sheath around the central axons, which form the white matter of CNS.
- Myelin an insulating sheath is made up of protein and fatty substances. It allows quick transmission of electrical impulses.
B.Microglia or brain macrophages
- Small sized cells with few branches.
- These are derived from monocytes and act as macrophages.
- They go to the site of injury, dead neurons and cell debris in the CNS.
- They mediate immune response in the CNS.
C.Astrocytes
- Star shaped cells and the most abundant glial cells of CNS.
- They have varied roles in the brain, secretion and absorption of neural transmitter and miniatous of blood-brain barrier BBB.
- Regulate the transmission of electrical impulses with the brain.
D.Ependymal cells
- Form single layer of squamous or columnar, often ciliated epithelial cells lining the ventricles or brain cavities and central canal of spinal cord.
- Mainly responsible for production and probably also for circulation of CSF in brain ventricles and central canal.
Neuroglial cells at PNS (Peripheral Nervous System)
E. Schwann Cells
- These are the most abundant glial cells of PNS.
- They produce myelin sheath around medullated nerves of PNS.
F. Satellite cells
- They support the functions of neurons.
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