The Human neural system is sub categorised into two parts:

1. The Central Neural System (CNS)
2. The Peripheral Neural System (PNS)
   
   

The Central Neural System (CNS) includes the brain and the spinal cord. It is the location of information processing and control. Whereas the Peripheral Neural System (PNS) comprises all the nerves of the body associated with CNS, i.e., brain and spinal cord. The nerve fibres of PNS are of two kinds:

1. afferent fibres
2. efferent fibres
   
   

The afferent nerve fibres transmit impulses from tissues/organs to the CNS, and the afferent fibres transmit regulatory impulses from the CNS to the concerned peripheral (outermost) tissues/organs.

The PNS is sub categorised into two divisions called somatic neural system and autonomic neural system. The somatic neural system communicates impulses from the CNS to skeletal muscles while the autonomic neural system communicates impulses from the CNS to the involuntary organs and smooth muscles of the body. The autonomic neural system can be further classified into the sympathetic neural system and parasympathetic neural system.

The neuron is a microscopic structure consisting of three major parts: the cell body, dendrites, and axon. The cell body consists of cytoplasm with typical cell nucleole/organelles and certain granular bodies known as Nissl’s granules. Dendrites are attachments that are functioned to receive transmissions from other cells. They look like a tree-like structure, forming projections that become stimulated by other neurons and conduct the electrochemical charge to the cell body. 

These fibres transmit stimulus towards the cell body. The axon is a long fibre called nerve fibre, a portion of a nerve cell (neuron) that carries nerve impulses away from the cell body. Established on the number of axons and dendrites, the neurons are categorised into three types:

1. Multipolar - with one axon and two or more dendrites. It is found in the cerebral cortex or CNS and autonomic ganglia.
2. Bipolar - It contains one axon and one dendrite. It is found in the retina of the eye.
3. Unipolar- Unipolar is a cell body with one axon only. It is found usually in the embryonic stage.
   
   

There are two types of axons, namely:

1. Myelinated- surrounded by a myelin sheath, composed of Schwann cells. It found in spinal and cranial nerves
2. Non- myelinated- A neuron in which there is no myelin sheath surrounding the axon. It is found in autonomous and somatic neural systems.

The brain is the main command and control system of our body. It is the central processing organ of the human body. It controls voluntary movements as well as involuntary movements such as lungs, heart, kidneys, etc. It also controls the coordination and balance of the body, thermoregulation, hunger, and thrust, activities of several glands, processing of vision, speech, human behaviours, memory, intelligence, emotions, thoughts, etc.

A human brain is well protected by the skull. The brain is covered by cranial meninges, consisting of the outer layer named dura mater, the very thin middle layer being arachnoid and the innermost layer being the pia mater. The brain can be subdivided into three major parts:

1. Forebrain - The forebrain administers body temperature, reproductive functions, eating, sleeping, and displaying emotions, feelings, and affection.
2. Midbrain - The midbrain is the topmost part of the brainstem, the connection central between the brain and the spinal cord. It is responsible for eye and eyelid movement.
3. Hindbrain - The hindbrain is one of the three major regions of our brains, located at the lower back part of the brain. It includes the majority of the brainstem and a dense coral-shaped structure called the cerebellum. The majority of the 12 cranial nerves are found in the hindbrain.

You must have experienced a certain withdrawal from your body while touching something hot or cold. You might have also experienced fear or movement when you saw a dangerous or poisonous animal, Infront of you. The entire process of response that occurs involuntarily is without conscious effort, or thought requires the involvement of a part of the central nervous system called reflex action. 

The reflex pathway consists of at least one afferent neuron also known as receptor, and one efferent, also known as effector or excitor neuron, organised in a series. A sensory neuron sends electrical impulses to a relay neuron, which is in the spinal cord of the CNS. Relay neurons attach sensory neurons to motor neurons. The motor neuron sends an electrical stimulus to an effector. Effector produces a response that causes reflex action.

Have you ever thought about how you feel when there is a sudden climate change, how you see objects and their colour, and how you hear a sound? The sensory organs regulate all kinds of changes in the environment. It also sends appropriate signals to the CNS, where all the inputs are processed and analysed. Signals are then sent to various parts of the brain. This is how you can sense changes in the environment. Now we will further discuss the functioning of eyes and ears.

Eye- The retina of the eyes is a light-sensitive layer. It contains photoreceptor cells and blood vessels. The retina converts the images formed by the lens into electrical impulses. The electrical impulses are transmitted to the brain with the help of optic nerves. The brain processes the signal and decides what you see.

Ear- Ear performs two sensory functions one is hearing, and another is body balancing. The ear is divided into three parts, outer ear, middle ear, and inner ear. The outer ear collects all the vibration in-ear, which produces sound. The fluid-filled inner ear called the labyrinth is responsible for maintaining body balance.

Q1. List out the topics covered in Chapter 21 Neural Control and Coordination Class 11 Biology NCERT Solutions

Ans.

• Neural system
• Human Neural system
• Neuron as Structural and Functional Unit of Neural System
• Central Neural System
• Reflex Action and Reflex Arc
• Sensory Reception and Processing

Q2. What is Neural Coordination?

Ans. Coordination is the process through which two or more organs interact and complement the functions of one another. The neural system provides an ordered network of point-to-point connections for rapid coordination.

Q3. What is control & coordination?

Ans. Control is defined as the ability to prevent and regulate a process that can be initiated, synchronised at a pace to speed up or slow down or stop completely. Coordination can be defined as the working of the different systems together to produce an appropriate reaction to stimuli.