Theory:

Compared to the other animals, the nervous system of humans is a well developed one. It is composed of neurons or nerve cells. The nerve system is an important component of the human body as it is involved with the conduction and coordination along with the endocrine system.
The organs of the nervous system:
I_M2_36.jpg
Human Nervous System
 
Brain:
  
The brain is a prominent organ of the nervous system as it is the organ that controls and regulates all of the activities throughout the body. It is a complex organ that is made up of neurons or nerve cells and is placed inside the cranium or skull.
 
It is enclosed by three membrane layers known as meninges. The brain can be divided into three regions: the forebrain, midbrain and the hindbrain. It is an organ that conducts the signals to and from the brain. Hence it is also known as the controlling centre of the body.
 
148.jpg
Structure of human brain
 
Spinal cord:
  
It is a bundle of nerves that extends from the medulla oblongata (brain stem) of the hind brain. The vertebral column protects it. It is the organ that connects the brain to the different parts of the body through the nerves.
 
20068091.jpg
Structure of spinal cord
 
Peripheral nerves:
  
These are a network of nerves and ganglions that carry signals to and from the central nervous system. They comprise of the intercostal nerves, radial nerves and the femoral nerve.
The functions of the nervous system:
1280px-Afferent_and_efferent_neurons_en.svg.png
Sensory and motor nerves
  
Sensory or afferent input:
It involves the conduction of signals from the sensory receptors.
 
Integration:
It is the interpretation of the sensory signals and the formulation of responses.
 
Motor or efferent output:
It is the conduction of signals from the brain and spinal cord to the effectors organs such as the muscle and gland cells.
Reference:
https://www.freepik.com/free-vector/colored-labeled-human-brain-diagram_1311040.htm#page=1&query=brain%20structure&position=3
https://www.freepik.com/free-vector/anatomy-spine-spinal-curves-infographic_11252113.htm#page=1&query=spinal%20cord&position=1
https://oli.cmu.edu/repository/webcontent/42d831d580020ca60119754e87e0e10c/_u1_motivation_introduction/_u1_m2_intro_systems_00/webcontent/I_M2_36.jpg
https://en.wikipedia.org/wiki/Afferent_nerve_fiber#/media/File:Afferent_and_efferent_neurons_en.svg