Human Nervous System

The nervous system connects the brain to all parts of the body through a network of nerves. Nerves carry messages between the brain and different parts of the body. The brain sends instructions to the body, and the body sends information back to the brain. The brain and the network of nerves are together called the nervous system. The nervous system helps us coordinate all our body functions, like moving, feeling, and reacting to things.

The nervous system in humans can be divided into three main parts
1. Central Nervous System: The central nervous system comprises the brain and the spinal cord. The brain controls all the functions in the human body. The spinal cord is the relay channel for signals between the brain and the peripheral nervous system.

2. Peripheral Nervous System: The peripheral nervous system comprises the cranial and spinal nerves. There are 12 pairs of cranial nerves, which come out of the brain and go to the organs in the head region. There are 31 pairs of spinal nerves, which come out of the spinal cord and go to the organs below the head region.

3. Autonomous Nervous System: The autonomous nervous system comprises a chain of nerve ganglions that run along the spinal cord. It controls all the involuntary actions in the human body. The autonomic nervous system can be divided into two parts :

• Sympathetic Nervous System: It is a part of the autonomic nervous system that prepares the body for action by increasing the activity of certain organs. For example, during exercise like running, it increases the heart rate and breathing rate to supply more oxygen to the body, helping meet the increased demand. It activates the "fight or flight" response during stressful or active situations.
• Parasympathetic Nervous System: It is a part of the autonomic nervous system that helps the body relax and conserve energy by slowing down organ activity. For example, during sleep, it reduces the heart rate and breathing rate, promoting rest and recovery. It is often called the "rest and digest" system, as it supports relaxation and energy conservation.
   

Human nervous system

The neuron is a highly specialised cell that is responsible for the transmission of nerve impulses. The neuron consists of the following parts:
1. Cyton or cell body: The cell body, or cyton, is somewhat star-shaped, with many hair-like structures protruding out of the margin. These hair-like structures are called dendrites. Dendrites receive the nerve impulses.

2. Axon: This is the tail of the neuron. It ends in several hair-like structures called axon terminals. The axon terminals relay nerve impulses.

3. Myelin sheath: There is an insulator cover around the axon. This is called a myelin sheath. The myelin sheath insulates the axon against nerve impulses from the surroundings.

4. Synapse: A synapse is the point of contact between the terminal branches of the axon of one neuron and the dendrite of another neuron.

5. Neuromuscular Junction: It is the point where a muscle fibre comes in contact with a motor neuron carrying nerve impulses from the control nervous system.

6. Transmission of the nerve impulse: Nerve impulses travel in the following manner from one neuron to the next: Dendrites → cell body → axon → nerve endings at the tip of the axon → synapse → dendrite of the next neuron. Chemicals released from the axon tip of one neuron cross the synapse or neuromuscular junction to reach the next cell.

7. Receptors: Receptors are the specialised tips of the nerve fibres that collect the information to be conducted by the nerves.
Receptors are in the sense organs of the animals.
These are classified as follows :

• Phonoreceptors: These are present in the inner ear. Functions: The main functions are hearing and balance of the body.
• Photoreceptors: These are present in the eye.
  Function: These are responsible for visual stimulus.
• Thermoreceptors: These are present in the skin.
  Functions: These receptors are responsible for pain, touch and heat stimuli. These receptors are also known as thermoreceptors.
• Olfactory receptors: These are present in the nose. Functions: These receptors receive smell.
• Gustatory receptors: These are present in the tongue. Functions: These help in taste detection.

Types of Neuron:

1. Sensory neuron: These neurons receive signals from a sense organ.
2. Motor neuron: These neurons send signals to a muscle or a gland.
3. Association or relay neuron: These neurons relay the signals between sensory neuron and motor neuron.

1. The nervous system's basic function is to send signals between cells or different parts of the body.
2. Signals can be sent through hormones (chemical signals) or through neurons (specific point-to-point connections).
3. Neurons send signals much faster and with greater precision compared to hormones, with some nerve signals travelling over 100 meters per second.
4. The nervous system controls the body by gathering information from the environment through sensory receptors, processing it in the central nervous system, and sending signals to muscles or glands for appropriate responses.
5. This system enables advanced abilities like vision, quick organ coordination, and integrated signal processing in animals.
6. In humans, it supports complex functions like language, abstract thinking, social interactions, cultural development, and advanced perception, made possible by the highly evolved brain.