Human Nervous System

The UPSC mains GS-3 paper syllabus has various subjects like Economics, Science and Technology. Science and technology in UPSC is mostly concerned with current Affairs. but it is necessary to understand the basics of science. Human Body consists of some of the most complex systems. Nervous systems is an important part of Human body which helps in sensing the surroundings

TOPICS

What is Nervous system
Parts of Nervous system
Central Nervous system
Periferal Nervous system
Neurons

WHAT IS NERVOUS SYSTEM

The nervous system is the part of an animal's body that coordinates the voluntary and involuntary actions of the animal and transmits signals between different parts of its body. Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago. Nervous systems are found in most multicellular animals, but vary greatly in complexity.The only multicellular animals that have no nervous system at all are sponges, placozoans and mesozoans, which have very simple body plans. The nervous systems of ctenophores (comb jellies) and cnidarians (e.g., anemones, hydras, corals and jellyfishes) consist of a diffuse nerve net. All other types of animals, with the exception of a few types of worms, have a nervous system containing a brain, a central cord (or two cords running in parallel), and nerves radiating from the brain and central cord. The size of the nervous system ranges from a few hundred cells in the simplest worms, to on the order of 100 billion cells in humans

PARTS OF NERVOUS SYSTEM

The nervous system is made up of the central nervous system and the peripheral nervous system:

The brain and the spinal cord are the central nervous system.
The nerves that go through the whole body make up the peripheral nervous system.

The human brain is incredibly compact, weighing just 3 pounds. It has many folds and grooves, though. These give it the added surface area needed for storing the body's important information.

The spinal cord is a long bundle of nerve tissue about 18 inches long and 1/2-inch thick. It extends from the lower part of the brain down through spine. Along the way, nerves branch out to the entire body.

Both the brain and the spinal cord are protected by bone: the brain by the bones of the skull, and the spinal cord by a set of ring-shaped bones called vertebrae. They're both cushioned by layers of membranes called meninges and a special fluid called cerebrospinal fluid. This fluid helps protect the nerve tissue, keep it healthy, and remove waste products.

CENTRAL NERVOUS SYSTEM

Brain

The brain controls what we think and feel, how we learn and remember, and the way we move and talk. But it also controls things we're less aware of — like the beating of our hearts and the digestion of our food.

Think of the brain as a central computer that controls all the body's functions. The rest of the nervous system is like a network that relays messages back and forth from the brain to different parts of the body. It does this via the spinal cord, which runs from the brain down through the back. It contains threadlike nerves that branch out to every organ and body part.

When a message comes into the brain from anywhere in the body, the brain tells the body how to react. For example, if you touch a hot stove, the nerves in your skin shoot a message of pain to your brain. The brain then sends a message back telling the muscles in your hand to pull away. Luckily, this neurological relay race happens in an instant.

Parts of the Nervous System

The nervous system is made up of the central nervous system and the peripheral nervous system:

The brain and the spinal cord are the central nervous system.
The nerves that go through the whole body make up the peripheral nervous system.

The human brain is incredibly compact, weighing just 3 pounds. It has many folds and grooves, though. These give it the added surface area needed for storing the body's important information.

Parts of the Brain

The brain is made up of three main sections: the forebrain, the midbrain, and the hindbrain.

The Forebrain

The forebrain is the largest and most complex part of the brain. It consists of the cerebrum — the area with all the folds and grooves typically seen in pictures of the brain — as well as some other structures under it.

The cerebrum contains the information that essentially makes us who we are: our intelligence, memory, personality, emotion, speech, and ability to feel and move. Specific areas of the cerebrum are in charge of processing these different types of information. These are called lobes, and there are four of them: the frontal, parietal, temporal, and occipital lobes.

The cerebrum has right and left halves, called hemispheres. They're connected in the middle by a band of nerve fibers (the corpus callosum) that lets them communicate. These halves may look like mirror images of each other, but many scientists believe they have different functions:

The left side is considered the logical, analytical, objective side.
The right side is thought to be more intuitive, creative, and subjective.

So when you're balancing your checkbook, you're using the left side. When you're listening to music, you're using the right side. It's believed that some people are more "right-brained" or "left-brained" while others are more "whole-brained," meaning they use both halves of their brain to the same degree.

The outer layer of the cerebrum is called the cortex (also known as "gray matter"). Information collected by the five senses comes into the brain to the cortex. This information is then directed to other parts of the nervous system for further processing. For example, when you touch the hot stove, not only does a message go out to move your hand but one also goes to another part of the brain to help you remember not to do that again.

In the inner part of the forebrain sits the thalamus, hypothalamus, and pituitary gland :

The thalamus carries messages from the sensory organs like the eyes, ears, nose, and fingers to the cortex.
The hypothalamus controls the pulse, thirst, appetite, sleep patterns, and other processes in our bodies that happen automatically.
The hypothalamus also controls the pituitary gland, which makes the hormones that control growth, metabolism, water and mineral balance, sexual maturity, and response to stress.

The Midbrain

The midbrain, underneath the middle of the forebrain, acts as a master coordinator for all the messages going in and out of the brain to the spinal cord.

The midbrain and the hindbrain together make up the brainstem. The midbrain is the portion of the brainstem that connects the hindbrain and the forebrain. This region of the brain is involved in auditory and visual responses as well as motor function.

The Hindbrain

The hindbrain sits underneath the back end of the cerebrum. It consists of the cerebellum, pons, and medulla. The cerebellum — also called the "little brain" because it looks like a small version of the cerebrum — is responsible for balance, movement, and coordination.

The pons and the medulla, along with the midbrain, are often called the brainstem. The brainstem takes in, sends out, and coordinates the brain's messages. It also controls many of the body's automatic functions, like breathing, heart rate, blood pressure, swallowing, digestion, and blinking.

Gray matter

Gray matter consists primarily of neuronal cell bodies, or soma. This a spherical structure that houses the neuron’s nucleus.

Function of Gray matter

Gray matter-heavy brain regions include those that control muscular and sensory activity.

Cerebral cortex - The outer layer of the brain, the cerebral cortex, consists of columns of gray matter neurons, with white matter located underneath. This area is essential to many facets of higher learning, including attention, memory, and thought.
Cerebellum - The cerebellum is essential for motor control, coordination, and precision.

White matter

White matter areas of the brain mainly consist of myelinated axons, which are long relays that extend out from the soma, and which are whiteish in color due to the relatively high lipid fat content of the myelin protein that sheathes them, These form connections between brain cells, and white matter is typically distributed into bundles called tracts.

Function of white matter

Neuron-rich brain regions wouldn’t count for much without the rich veins of axonal connections contained within white matter to join them up.

Cerebral Cortex Lobes

The frontal lobe is located at the front of the brain and is associated with reasoning, motor skills, higher level cognition, and expressive language. At the back of the frontal lobe, near the central sulcus, lies the motor cortex. This area of the brain receives information from various lobes of the brain and utilizes this information to carry out body movements. Damage to the frontal lobe can lead to changes in sexual habits, socialization, and attention as well as increased risk-taking.
The parietal lobe is located in the middle section of the brain and is associated with processing tactile sensory information such as pressure, touch, and pain. A portion of the brain known as the somatosensory cortex is located in this lobe and is essential to the processing of the body's senses. Damage to the parietal lobe can result in problems with verbal memory, an impaired ability to control eye gaze and problems with language.
The temporal lobe is located on the bottom section of the brain. This lobe is also the location of the primary auditory cortex, which is important for interpreting sounds and the language we hear. The hippocampus is also located in the temporal lobe, which is why this portion of the brain is also heavily associated with the formation of memories. Damage to the temporal lobe can lead to problems with memory, speech perception, and language skills.
The occipital lobe is located at the back portion of the brain and is associated with interpreting visual stimuli and information. The primary visual cortex, which receives and interprets information from the retinas of the eyes, is located in the occipital lobe. Damage to this lobe can cause visual problems such as difficulty recognizing objects, an inability to identify colors, and trouble recognizing words.

The Spinal Cord

The spinal cord is a cylindrical shaped bundle of nerve fibers that is connected to the brain at the brain stem. The spinal cord runs down the center of the protective spinal column extending from the neck to the lower back. The brain and spinal cord are the major components of the central nervous system (CNS). The CNS is the processing center for the nervous system, receiving information from and sending information to the peripheral nervous system. Peripheral nervous system cells connect various organs and structures of the body to the CNS through the cranial nerves and spinal nerves. Spinal cord nerves transmit information from body organs and external stimuli to the brain and send information from the brain to other areas of the body.

PERIFERAL NERVOUS SYSTEM

The peripheral nervous system (PNS) is the division of the nervous system containing all the nerves that lie outside of the central nervous system (CNS). The primary role of the PNS is to connect the CNS to the organs, limbs and skin.

These nerves extend from the central nervous system to the outermost areas of the body. The nerves that make up the peripheral nervous system are actually the axons or bundles of axons from neuron cells. In some cases, these nerves are very small but some nerve bundles are so large that they can be easily seen by the human eye. The peripheral nervous system is divided into two parts: the somatic nervous system and the autonomic nervous system

The Somatic Nervous System

The somatic system is the part of the peripheral nervous system responsible for carrying sensory and motor information to and from the central nervous system. The somatic nervous system derives its name from the Greek word soma, which means "body." The somatic system is responsible for transmitting sensory information as well as for voluntary movement. This system contains two major types of neurons: sensory neurons (or afferent neurons) that carry information from the nerves to the central nervous system, and motor neurons (or efferent neurons) that carry information from the brain and spinal cord to muscle fibers throughout the body.

The Autonomic Nervous System

The autonomic system is the part of the peripheral nervous system responsible for regulating involuntary body functions, such as blood flow, heartbeat, digestion and breathing. This system is further divided into two branches: the sympathetic system regulates the flight-or-fight responses, while the parasympathetic system helps maintain normal body functions and conserves physical resources.

The sympathetic nervous system responds to impending danger, and is responsible for the increase of one's heartbeat and blood pressure, among other physiological changes, along with the sense of excitement one feels due to the increase of adrenaline in the system. ("Fight or flight" responses).
The parasympathetic nervous system, on the other hand, is evident when a person is resting and feels relaxed, and is responsible for such things as the constriction of the pupil, the slowing of the heart, the dilation of the blood vessels, and the stimulation of the digestive and genitourinary systems. ("Rest and digest" responses).

NEURON:

A neuron is a nerve cell that is the basic building block of the nervous system. Neurons are similar to other cells in the human body in a number of ways, but there is one key difference between neurons and other cells. Neurons are specialized to transmit information throughout the body. These highly specialized nerve cells are responsible for communicating information in both chemical and electrical forms. There are also several different types of neurons responsible for different tasks in the human body. Sensory neurons carry information from the sensory receptor cells throughout the body to the brain. Motor neurons transmit information from the brain to the muscles of the body. Interneurons are responsible for communicating information between different neurons in the body.

There are three basic parts of a neuron: the dendrites, the cell body and the axon. However, all neurons vary somewhat in size, shape, and characteristics depending on the function and role of the neuron. Some neurons have few dendritic branches, while others are highly branched in order to receive a great deal of information. Some neurons have short axons, while others can be quite long. The longest axon in the human body extends from the bottom of the spine to the big toe and averages a length of approximately three feet!

Structure of neuron

Dendrites are treelike extensions at the beginning of a neuron that help increase the surface area of the cell body. These tiny protrusions receive information from other neurons and transmit electrical stimulation to the soma. Dendrites are also covered with synapses.

Dendrite Characteristics -

Most neurons have many dendrites
However, some neurons may have only one dendrite
Short and highly branched
Transmits information to the cell body
The axon is the elongated fiber that extends from the cell body to the terminal endings and transmits the neural signal. The larger the axon, the faster it transmits information. Some axons are covered with a fatty substance called myelin that acts as an insulator. These myelinated axons transmit information much faster than other neurons.

Axon Characteristics -

Most neurons have only one axon
Transmit information away from the cell body
May or may not have a myelin covering