Nervous system

The nervous system is a network of fibers and neurons controlling the actions and reactions of the body. Nervous system is mainly a network of a special type of cells which transmit nerve impulses. It process information and causes reaction of various parts of our body. In fact nervous system is responsible for each and every response of our body towards various situations and conduction with object.

Nervous system is basically consists of two types of cells:

        i.            Neuron

      ii.            Glial cells

Neuron: Within nervous system information is basically processed and transmitted through an electrically responsive cell called neuron. Neurons are the central part of the brain, peripheral nerves, the vertebrate spinal cord and invertebrate ventral nerve cord. A variety of neuron exists within a nervous system. Sensory neurons are responsive to the light, sound, heat, touch and numerous other stimuli effecting sensory organs and send signals towards the spinal cord and brain, motor neurons receive signals from the brain and spinal cord and result muscle contractions and affect glands.

Glial Cells: Glial cells are non-neuronal cells. It provides support and nutrition and participates in the transportation of signal. The number of glia is same as neuron in the human brain. Glial cells provide support and protection for neurons. Glial cells perform four main functions; surround neurons and hold them in place, supply nutrients and oxygen to neurons, destroy pathogens and remove dead neurons and insulate one neuron from another.

Human body consists of 30 types of nerves. They are:

1.      Brain

2.      Cerebellum

3.      Radial nerve

4.      Median nerve

5.      Ulnar nerve

6.      Brachial plexus

7.      Lateral pectoral nerve

8.      Spinal cord

9.      Intercostals nerve

10.  Subcostal nerve

11.  Iliohypogastric nerve

12.  Ilioinguinal nerve

13.  Femoral nerve

14.  Sciatic nerve

15.  Common peroneal nerve

16.  Deep peroneal nerve

17.  Superficial peroneal nerve

18.  Medial dorsal cutaneous nerve

19.  Dorsal digital nerve

20.  Medial plantar nerve

21.  Lateral plantar nerve

22.  Saphenous nerve

23.  Interosseous nerve

24.  Dorsal cutaneous nerve

25.  Tibial nerve

26.  Spinal ganglion

27.  Phrenic nerve

28.  Vagus nerve

29.  Facial nerve

30.  Optic nerve

Types of nervous system:

There are mainly two types of nervous system:

v  Central Nervous System

v  Peripheral Nervous System

Central Nervous system (CNS): CNS is the largest part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms. In vertebrates, the central nervous system enclosed in the meninges. It contains the major portion of the nervous system. It consist the brain and the spinal cord. Brain is protected by the skull and the spinal cord is protected by the vertebrae. The whole CNS is covered by the meninges, a three layered protective coat.

Peripheral Nervous System (PNS): The PNS is a regional term for the collective nervous structure that does not lie in the CNS, either in the brain or spinal cord. But the longer parts of these cells, known as axons, extend through the limbs and the flesh of the forso. The large majority of the axons which are commonly called nerve are considered to be PNS.

The PNS consists of two parts:

1.      Sensory Neurons

2.      Motor Neurons

The Peripheral Nervous System is sub-divided to two parts:

        i.            Sensory-somatic nervous system

      ii.            Autonomic nervous system

Sensory-somatic nervous system: The sensory-somatic nervous system consists of 12 pairs of cranial nerve and 31 pairs of spinal nerves.

The cranial nerve:

The spinal nerve:

All of the spinal nerves are “mixed”; that is, they obtain both sensory and motor neurons.

Autonomic Nervous System: ANS is part of the PNS that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affect heart rate, digestion, respiration rate, salivation, and perspiration, diameter of the pupils, micturition, and sexual arousal.

ANS is subdivided into two parts:

·         Sympathetic nervous system

·         Parasympathetic nervous system

What Nervous System does:

The main role of the nervous system is to relay electrical signal through the body. The Central Nervous System comprises the brain and the spinal cord, which receive and integrate signals relayed from the sense organs (such as eyes, nose and ears) via the peripheral nervous system. The latter includes the autonomic nervous system, which controls unconscious functions, such as heartbeat and breathing. In response to stimuli, sensory neurons generate and propagate to the CNS which then processes and conducts signals back to the muscles and glands. The neurons of the nervous system of animals are interconnected in complex arrangement and use electrochemical signals and neurotransmitters to transmit impulses from one neuron to another. The interaction of different neurons from neural circuits regulates an organism’s perception of the world and what is going on with its body, thus regulating its behavior.

Reference:

·         en.wikipedia.org

·         users.rcn.com

·         web.jjay.cuny.edu