Nervous System of Human Body

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Nervous System of Human Body
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Nervous System Unit is Neuron.

Minimum power of regeneration is found in Nervous System. Largest cell of our body is Neuron only.

Nervous System is of following types :

  • Central Nervous System : Brain + Spinal Chord
  • Peripheral Nervous System : Nerves
  • Autonomic Nervous System : Sympathetic + Parasympathetic Nervous System.

A. Central Nervous System : Consists of Brain and Spinal Cord.

Brain : Brain is convered by 3 layers (Meninges)

  • Duramater (Toughest)
  • Arachnoid Mater
  • Piamater

Cerebrospinal Fluid is filled between the Meninges. Increased cerebrospinal fluid may result in meningitis.

Brain has the following parts :

(a) Cerebrum

2 distinct Parts : Outer Grey Matter or Cerebral Cortex and Inner White Matter.

Grey Matter Controls Activities such as Speech, Taste, Smell, Hearing (Conscious Activities).

It is the seat of Intelligence, Reasoning, Learning, will pleasure, Pain, Fear, etc. Beneath the Grey Matter is White Matter.

If cerebrum is removed, the person will become a simple reflex animal.

(b) Cerebellum

Concerned with equilibrium of the body and brings about co – ordination and control of muscular activities of the body.

(c) Medulla Oblongata :

Lowest Part of the brain and is connected to the Spinal Cord.

Controls the involuntary actions (Respiration, Heart Beat, Flow of Blood in Blood Vessels, Secretion of Glands, etc).

Nerves : It is of 2 Types :

Efferent : The fibres which carry impulses from the CNS. Many of them pass through the muscles making them to contract, and are therefore called Motor Nerve Fibres.

Afferent : Those which carry impulses to the CNS. The information which they transmit from the skin and deeper tissues often evokes subjective sensation within the nervous system and are therefore called Sensory Nerve Fibres.

Reflex Action :

First discovered by Marshal Hall can be defined as the spontaneous response to the external stimuli.

Coordinated by spinal cord. In this, the stimulus received by the receptor organ is conveyed to the spinal cord by the sensory or afferent nerve fibres.

The order is transmitted to the effectors organs like muscles by motor or efferent nerve fibres.

Conditional Reflex :

First shown by Pavlov on dog.

When the reflex action becomes the regular feature of an animal or the animal becomes habitual of it, such a reflex action is known as the conditional reflex.

It is controlled by the cerebrum.

B. Peripheral Nervous System : Composed of Cranial Nerves and Spinal Nerves. Cranial arise from Brain While Spinal from Spinal Cord.
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Cranial are 12 pairs while spinal are 31 pairs. The following are the Cranial Nerves in man.

They can broadly be divided into Sensory, Motor and mixed Nerves.

  • Olfactory : Sensory
  • Optic : Sensory
  • Occulomotor : Motor
  • Trochlear : Motor
  • Trigeminal : Mixed
  • Abducens : Motor (smallest)
  • Facial : Mixed
  • Auditory : Sensory
  • Glosso pharyngeal : Mixed
  • Vagus : Mixed (largest)
  • Spinal Accessory : Motor
  • Hypoglossal : Motor

Summary of the Human Cranial Nerves

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Amity Career Institute,
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National Educational Trust,
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Karaikudi - 630 003,
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Baby Foundation Charitable Trust,
Uchippillayar Kovil,
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Behind BSC Bata India Ltd.,
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Church Complex, Convent Road,
Opp. Indian Bank,
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Vallal Pandidurai Complex,
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E - nit Academy,
34, I Floor, LIC Colony,
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18, Sathyamoorthy Street,
Sivagangai - 630 561,
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43, Madurai Road,
Near Aravindh Restaurant,
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1, NAPR Complex,
Madurai Road,
Theni - 627 001
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Periyar Maligai,
Four Roads, Puthur,
Thiruchirappalli - 620 017,
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182, E4 / 34, Swami Nelliapar High Road,
Thirunelveli - 627 001,
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Ves Computer Data Processing Centre,
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Thoothukudi - 628 002,
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Madurai Road,
Tirumangalam - 625 706,
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Avinashi Road Corner,
Tirupur - 641 602,
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C. Autonomous Nervous System : Not under voluntary control. Controlled by Central Nervous System.

Controls, Digestion, Excretion, Secretion of Sweat and Digestive Juices, etc. Divided into two :

1. Sympathetic Nervous System :

  • Increases the defence of body against adverse conditions.
  • It is active in stress condition, pain, fear and anger.
  • Speeds up heartbeat, BR etc.
  • Expenditure of energy takes place.
  • Acetyl – choline and sympathetin are released.

2. Parasympathetic Nervous System :

  • Provides relaxation, comfort and pleasure at the time of rest.
  • Lowers heartbeat, thus lowering the BP.
  • Restoration and conservation of energy takes place.
  • Only acetyl – choline is released.

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