1. Nervous system

 These may include light, heat, sound, touch, pressure, smell and pain. When a stimulus is received, the body produces a suitable reaction known as a response.

 

For example, withdrawing the hand from a hot object or closing the eyes in bright light . These responses are necessary for survival. To produce correct responses, different organs must work together in an organized manner. This process is called coordination and it helps maintain internal balance known as homeostasis. The nervous system plays a major role in coordination.

The nervous system is made up of nervous tissue consists of neurons and neuroglia. Nerve fibres are parts of neurons.

 

 

Neurons are the structural and functional units that carry nerve impulses. The impulse passes from one neuron to another through a small gap called a synapse.

 

 

During this transmission, chemical substances called neurotransmitters are released. The most important neurotransmitter is acetylcholine, which helps in the quick flow of messages.

 

The human nervous system is divided into three parts: central nervous system (CNS), peripheral nervous system (PNS) and autonomic nervous system (ANS).

 

 

The CNS includes the brain and spinal cord and acts as the control centre. The PNS consists of nerves that connect the CNS with all parts of the body. The ANS controls involuntary activities and includes sympathetic and parasympathetic systems.

The brain is the controlling centre of all body activities. It is protected by the skull, meninges and cerebrospinal fluid.

 

The brain is divided into three major parts: forebrain, midbrain and hindbrain.

 

The forebrain consists of the cerebrum, thalamus and hypothalamus. The cerebrum is the largest part of the brain and is responsible for thinking, memory, intelligence, imagination and voluntary actions.

 

The thalamus acts as a relay centre for sensory impulses. The hypothalamus controls body temperature, hunger, thirst, emotions and hormone secretion, and connects the nervous system with the endocrine system.

The midbrain is located between the forebrain and hindbrain. It contains structures called corpora quadrigemina which control visual and auditory reflexes.

The hindbrain consists of cerebellum, pons and medulla oblongata. The cerebellum maintains body balance and coordinates voluntary muscle movements.

 

The pons helps in breathing and sleep and connects different parts of the brain. The medulla oblongata controls vital activities such as heartbeat, breathing, blood pressure, vomiting and salivation.

The spinal cord is a long cylindrical structure present inside the vertebral column. It extends from the medulla oblongata to the lower back region. The spinal cord transmits sensory impulses to the brain and motor impulses from the brain to the body. It also controls reflex actions.

 

Cerebrospinal fluid is a clear watery fluid surrounding the brain and spinal cord. It protects the brain from mechanical shock, supplies nutrients, removes wastes and maintains constant pressure inside the skull.

The pathway followed by the nerve impulse during reflex action is called the reflex arc. The stimulus is received by receptors and passed through sensory neurons to the spinal cord. The spinal cord sends the impulse through motor neurons to muscles, producing an immediate response.

 

The peripheral nervous system includes cranial nerves and spinal nerves that connect the CNS to the body. The autonomic nervous system controls involuntary functions like heartbeat, digestion and breathing. The sympathetic system prepares the body for emergency situations, while the parasympathetic system restores the body to normal conditions.

 

 

The nervous system controls and coordinates all activities of the body. It helps organisms respond to stimuli quickly and effectively. The brain, spinal cord, nerves and reflex actions together maintain balance and proper functioning of the body.