Human Nervous system:
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 spread throughout their body. Crabs have a more complicated nervous system in the form of 2 nerve centers called dorsal ganglion and ventral ganglion.
As we move further up the ladder, higher organisms such as vertebrates have a developed brain. Moreover, it is one of the most complicated structures in the animal kingdom, containing billions of neurons, all intricately connected.
Central Nervous System:
Central Nervous System (CNS) is often called the central processing unit of the body. It consists of the brain and the spinal cord.
BRAIN:
The brain is one of the important, largest and central organ of the human nervous system. It is the control unit of the nervous system, which helps us in discovering new things, remembering and understanding, making decisions, and a lot more. It is enclosed within the skull, which provides frontal, lateral and dorsal protection. The human brain is composed of three major parts:
Forebrain: The anterior part of the brain, consists of Cerebrum, Hypothalamus and Thalamus.
Midbrain: The smaller and central part of the brainstem, consists of Tectum and Tegmentum.
Hindbrain: The central region of the brain, composed of Cerebellum, Medulla and Pons.
Also read: Human Brain
SPINAL CORD:
The spinal cord is a cylindrical bundle of nerve fibers and associated tissues enclosed within the spine and connect all parts of the body to the brain. It begins in continuation with the medulla and extends downwards. It is enclosed in a bony cage called vertebral column and surrounded by membranes called meninges. The spinal cord is concerned with spinal reflex actions and the conduction of nerve impulses to and from the brain.
Peripheral Nervous System:
Peripheral Nervous System (PNS) is the lateral part of the nervous system that develops from the central nervous system which connects different parts of the body with the CNS. We carry out both voluntary and involuntary actions with the help of peripheral nerves.
Also refer: Peripheral Nervous System
PNS includes two types of nerve fibers:
Afferent nerve fibers – These are responsible for transmitting messages from tissues and organs to the CNS.
Efferent nerve-fibers – These are responsible for conveying messages from CNS to the corresponding peripheral organ.
Classification of the peripheral nervous system:
Somatic neural system (SNS): 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.
Autonomic neural system (ANS): The autonomic neural system is involved in 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 and pupil). The autonomic neural system can be further divided into:
Sympathetic nervous system
Parasympathetic nervous system.
What is Neurons?
Neurons (also called neurones or nerve cells) are the fundamental units of the brain and nervous system, the cells responsible for receiving sensory input from the external world, for sending motor commands to our muscles, and for transforming and relaying the electrical signals at every step in between. More than that, their interactions define who we are as people. Having said that, our roughly 100 billion neurons do interact closely with other cell types, broadly classified as glia (these may actually outnumber neurons, although it’s not really known).
Neuron Structure
A neuron varies in shape and size depending on its function and location. All neurons have three different parts – dendrites, cell body and axon.
Parts of Neuron
Following are the different parts of a neuron:
Dendrites
These are branch-like structures that receive messages from other neurons and allow the transmission of messages to the cell body.
Cell Body
Each neuron has a cell body with a nucleus, Golgi body, endoplasmic reticulum, mitochondria and other components.
Axon
Axon is a tube-like structure that carries electrical impulse from the cell body to the axon terminals that pass the impulse to another neuron.
Synapse
It is the chemical junction between the terminal of one neuron and the dendrites of another neuron.
What is a Nerve?
A nerve is a cable-like structure within the body designed to conduct nerve impulses that relay information from one part of the body to another.
A typical nerve is made up of a bundle of fibres which are wrapped around layers of tissue and fat, and they stretch throughout the body. These nerves transmit information along the axons to the respective organs. These are the basic elements that constitute a nerve.
Nerves are a part of the nervous system. They are primarily involved in control and the coordination of all the parts of the body.
The nervous system not only sends and receives messages but also processes them into chemical signals called impulses in the human body. A wide network of nerves is spread throughout our body, which also runs through the brain, the spinal cord and many organs.
The structure of a nerve is explained below:
A group of neurons is organized into bundles inside the nerves. This bundle is known as fascicles.
The perineurium surrounds and holds together each fascicle.
The perineurium is concentrically laminated and composed of flattened cells collagen fibres and basement membranes.
Neurons and blood vessels are held inside the fascicles by a loose connective tissue known as endoneurium. It covers and holds the outer surface of the nerves together.
Arteries and veins are present between the fascicles. These blood vessels supply nutrients and gases to the neurons inside the fascicles.
