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

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.

• Receptors present in sense organs detect changes in the environment and send signals to the brain through neurons.
• A neuron has three parts — dendrites (receive signals), cell body (processes signals), and axon (transmits signals) — which work together to carry electrical impulses.
• The electrical impulse always travels in one fixed direction: dendrite → cell body → axon → axon terminal, ensuring a controlled flow of information.
• At the synapse, special chemicals called neurotransmitters are released to pass the impulse from one neuron to the next, or to a muscle or gland.
• The neuromuscular junction is where a nerve meets a muscle fibre; when the impulse reaches this point, it causes the muscle to contract and produce a response.