Nervous System: Human Nervous System

Imagine having a fractured bone and not feel a thing. Or having burnt your finger, but without the sensation of pain. Sure, it sounds very ideal and quite the superpower, but from a survival standpoint, it could be disastrous.

Pain is the body’s way of letting us know that something is not right. It can prevent further injuries or push us to seek medical attention. And all of this is possible because humans can respond and react to stimuli due to control and coordination among the various organs and organ systems.

Coordination is the effective outcome of two systems, namely, the nervous system and the endocrine system. Neural system together with the endocrine system regulates the body homeostasis. Endocrine glands constitute the endocrine system which coordinates and control the body metabolism by their secretions called hormones. Let us learn about the human neural system and how it coordinates various functions in our body.

What is the Nervous System?

The nervous system or the neural system is a complex network of neurons specialized to carry messages. The complexity of the nervous system increases as we move towards higher animals. For instance, cnidarians such as jellyfish have relatively simple nerve nets that are spread throughout their body. Crabs have more complicated nervous system in the form of 2 nerve centres called dorsal ganglion and ventral ganglion. As we move further up the ladder, higher organisms such as vertebrates have developed the brain. And it is one of the most complicated structures in the animal kingdom, containing billions of neurons, all intricately connected with each other.

In the human body, the neural system integrates the activities of organs based on the stimuli, which the neurons detect and transmit. They transmit messages in the form of electrical impulses and convey messages to and from the sense organs. Thus, the nervous coordination involves the participation of the sense organs, nerves, spinal cord, and brain.

Human Nervous System

One of the most complex organ system to ever evolve, the nervous system consists of two parts, namely:

  1. Central nervous system (CNS)
  2. Peripheral nervous system (PNS)

CNS consists of the brain and the spinal cord, PNS consists of nerves that connect the CNS to every part of the body.

Nervous System

Diagram of Nervous System

PNS includes two types of nerve fibers:

  1. Afferent nerve fibers – These are responsible for transmitting messages from tissues and organs to the CNS.
  2. Efferent nerve fibers – These are responsible for conveying messages from CNS to the corresponding peripheral organ.

Classification of peripheral nervous system:

  1. Somatic neural system: It is the neural system that controls the voluntary actions in the body by transmitting impulses from CNS to skeletal muscle cells. It consists of the somatic nerves.
  1. Autonomic neural system: Theautonomic neural system is involved in the involuntary actions like regulation of physiological functions (digestion, respiration, salivation, etc.). It is a self-regulating system which conveys the impulses from the CNS to the smooth muscles and involuntary organs (heart, bladder, pupil, etc.). ANS is further divided into:
    1. Sympathetic nervous system
    2. Parasympathetic nervous system


Nerves are thread-like structures that emerge from the brain and spinal cord. It is responsible for carrying messages to all the parts of the body. There are three types of nerves. Some of these neurons can fire signals at speeds of over 119 m/s or over 428 km/h.

  1. Sensory nerves send messages from all the senses to the brain.
  2. Motor nerves carry messages from the brain to all the muscles.
  3. Mixed nerves carry both sensory and motor nerves.

Cranial nerves begin from the brain as these nerves carry impulses to start from the central nervous system. Certain cranial nerves belong to the group of mixed nerves while certain ones fall under sensory nerves. Spinal nerves originate from the spinal cord. All the spinal nerves carry impulses to and from the central nervous system and these are part of mixed nerves.

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Further Reading

Practise This Question

The following questions consist of two statement each : assertion (A) and reason (R).

Mark the correct alternative as described below :
A : Insulin and glucagon have the antagonistic effects on the blood-glucose level.
R : Insulin lowers the blood-glucose level by causing its storage in the liver and consumption in the tissues. Glucagon raises the blood-glucose level by converting liver glycogen into blood-glucose and changing amino acids and fats into glucose.