Nervous System | Lucent for GK - UPSC PDF Download

Introduction

• Unit is Neuron.
• Largest cell of our body is Neuron .

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 has the following parts :

(a) Cerebrum

 (b) Cerebellum

(c) Medulla Oblongata :

(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.

B. Peripheral Nervous System : 

• Composed of Cranial Nerves and Spinal Nerves.
• Cranial arise from Brain While Spinal from Spinal Cord.
• 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

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
  • 2. Parasympathetic Nervous System :

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 etc.
• Expenditure of energy takes place.

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.