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Term Paper on Nervous System
Term Paper # 1.
Meaning and Parts of Nervous System:
The nervous system is chief controlling and coordinating system of the body. It controls and regulates all activities weather voluntary or involuntary and adjusts the individual to the given surroundings. It is based on special properties of sensitivity, conductivity and responsiveness.
Parts of Nervous System:
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1. Central Nervous System:
It has two parts- Brain and spinal cord.
2. Peripheral Nervous System:
Peripheral nervous system has two parts:
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(a) Cerebrospinal Part (Somatic):
This comprises of 12 pairs of cranial nerves and 31 pairs of spinal nerves and Exteroceptors.
(b) Autonomic Nervous System (Visceral):
This has two constituents:
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i. Sympathetic nervous system.
ii. Parasympathetic nervous system.
Nervous Tissue:
Develops from neuro-ectoderm and mesoderm.
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Term Paper # 2.
Units of Nervous System:
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1. Neuron:
It is the main structural and functional unit of nervous system (ectodermal in origin).
This consists of:
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(a) Soma or cell body – having a central nucleus and nissl’s granules in its cytoplasm.
(b) Neuritis or Processes:
i. Long – Axons
ii. Short – Dendrites
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Cell bodies of the neurons form grey matter and nuclei in the CNS, and ganglia in PNS.
Cell processes (axons) form tracts in CNS and nerves in PNS.
Types of Neurons:
I. According to number of their processes these are called:
i. Unipolar, e.g., Mesencephalic nucleus.
ii. Bipolar, e.g., Spiral and vestibular ganglia.
iii. Pseudo-unipolar, e.g., Sensory ganglia.
iv. Multipolar, e.g., Most common type.
II. According to Length of Axon:
i. Golgi type I – neurons with a long axon.
ii. Golgi type II – neurons (microneurons) with a short or no axon.
Dynamic Polarity:
i. It is present in the processes of neurons. It impulse flows towards soma in the Dendrites and away in the axons. In microneurons, which has no neurons; the impulse can flow in either direction through their dendrites.
2. Synapse:
Neurons form long chains along which impulses are conducted in different directions. Junction between neurons is called synapse. They contact by contiguity and not by continuity. Impulse is transmitted by specific neurotransmitters like – acetylcholine, catecholamine (nor-adrenaline and dopavarine), serotonin, histamine, glycine, and certain polypeptides).
Types of Synapse:
i. Axo-dendritic
ii. Somato-dendritic
iii. Somato-somatic
iv. Axo-axonic
v. Somato-axonic
vi. Dendro-dendritic.
The synapse may be inhibitory or excitatory.
3. Neuroglia:
Neuroglia is non-excitable supporting cells in nervous system.
These are:
(a) Neuroglial Cells:
These are found in parenchyma of brain and spinal cord.
(b) Ependymal Cells:
These line the internal cavities.
(c) Capsular or Satellite Cells:
These surround nerves of sensory and autonomic ganglia.
(d) Schwann Cells:
From sheaths for axons of peripheral nerves.
(e) Supporting Cells:
Several types and these ensheath motor and sensory nerve terminals.
Nuroglial Cells:
They are of two types:
(a) Macroglia:
These are ectodermal in origin and are star shaped astrocytes, (fewer in number) oligodendrocytes and glioblasts (stem cells).
(b) Microglia:
Mesodermal in origin and are much smaller but more numerous than neurons. These are phagocytic in nature and are derived from circulating monocytes.
Functions of Glial and Ependymal Cells:
i. Provide mechanical support to nervous tissue.
ii. Act as insulator between nerves and prevents spreading of impulses in unwanted directions.
iii. Phagocytosis – remove cell debris and foreign body.
iv. Can repair damaged areas of nervous tissue.
v. Stores neurotransmitters.
vi. Maintains a suitable metabolic and ionic environment for neurons.
vii. Oligodendrocytes – These are myelinated tracts.
viii. Ependymal cells – Help in exchange of materials between brain and C.S.F.
ix. Glial cells provide nutrition to nerve cells.
4. Blood Brain Barrier:
Barrier exists at the capillary level between blood and nerve cells and is formed by:
i. Capillary endothelium without fenestration.
ii. Basement membrane of endothelium.
iii. End feet of astrocytes covering the capillary walls.
Barrier permits a selective passage of blood contents to the nervous tissue.
5. Reflex Arc:
Is the basic functional unit of nervous system.
This is made up of:
i. Receptor, e.g., skin.
ii. A sensory or afferent neuron.
iii. A motor or efferent neuron.
iv. An effector, e.g., muscle.
6. Nerves:
Nerves are solid white cords. Nerve fibre is an axon with its covering and are supported and bound together by connective tissue sheaths at different levels. It’s whole trunk is ensheathed by Epineurium and each fasciculus is covered by Perineurium. Each nerve fibre is covered by a delicate Endoneurium and toughness of the nerve is due to its fibrous sheaths.
Spinal Nerves:
These are 31 pairs of spinal nerves.
These are as follows:
i. Cervical – 8
ii. Thoracic – 12
iii. Lumbar – 5
iv. Sacral – 5
v. Coccygeal – 1
Dermatome:
It is the area of skin supplied by a single segment of spinal cord.
Formation, course and branches of a typical spinal nerve.
Blood and Nerve Supply of Peripheral Nerves:
i. Supplied by vessels – called vasa – nervosum.
ii. Supplied by nerves – called nervi nervorum.
Functional Components of a Spinal Nerve:
There are three components namely:
1. Somatic Component:
i. Somatic efferents innervate skeletal muscle.
ii. Somatic afferents – convey impulses to CNS form skin, fascia, muscle and joints etc.
2. Visceral Component:
It constitutes autonomic nervous system.
i. Efferents, sympathetic and parasympathetic.
ii. Afferents, innervate viscera and glands.
3. Meningeal Branch:
It receives grey rami communicants and supplies duramater of spinal cord.
Term Paper # 3.
Types of Nervous System:
I. Autonomic Nervous System (ANS):
A.N.S. is divided into two parts:
A. Sympathetic
B. Parasympathetic
It controls involuntary activities of body like – Sweating, salivation, peristalsis etc.
It differs from CNS in having:
(a) Preganglionic fibres arising from CNS.
(b) Ganglia for relay of preganglionic fibres.
(c) Post-ganglionic fibres arising from ganglia to supply effectors – smooth muscles and glands.
A. Sympathetic Nervous System:
1. Also known as thoracolumbar outflow – it arises from T1 to L2 segments of spinal cord.
2. Preganglionic fibres (white rami communicants) arise from lateral column of spinal cord, emerge through ventral rami and are connected to ganglia of sympathetic chain. Fibres can ascend or descend down.
3. Post-ganglionic fibres (grey rami) run for some distance and supply the organ.
4. These are total of 22-23 sympathetic ganglia in each sympathetic chain. When T1 ganglion does not fuse with lower cervical sympathetic ganglion – there will be 23 sympathetic ganglions. When T1 fuses with lower cervical ganglion it becomes 22 in number. Subsidiary ganglia are also present, e.g., celiac, mesenteric etc.
5. Ganglia lie on sympathetic trunk (mostly).
Structure of Sympathetic Ganglia:
1. Outer connective tissue capsule – contains fibres, fibroblasts, blood capillaries and satellite cells.
2. Ganglion cells – multipolar neurons.
B. Parasympathetic Nervous System (PNS):
Also known as cranio-sacral outflow. Preganglionic fibres are carried by – III, VII, IX, X cranial nerves.
Cranial Part:
Parasympathetic nuclei are present in brain are:
1. Edinger-Westphal nucleus
2. Superior salivatory nucleus
3. Inferior salivatory nucleus
4. Dorsal nucleus of vagus (X).
Cranial out flow passes through four small para sympathetic ganglia:
(i) Ciliary ganglion
(ii) Pterygo palatine ganglion
(iii) Submandibular ganglion
(iv) Otic ganglion.
Sacral Part (Parasympathetic System):
Preganglionic fibres are carried by S2, S3 and S4 spinal nerves. Sacral out flow passes through parasympathetic ganglia present near organs.