TLDR: The central nervous system (CNS) is made up of the brain and spinal cord. It controls and coordinates all the activities of the body. The CNS is found in animals with bilateral symmetry, except for sponges and diploblasts. In vertebrates, the CNS is protected by the meninges and bathed in cerebral spinal fluid. It consists of white and gray matter, with different types of cells performing different functions. The CNS also includes the retina, optic nerve, olfactory nerves, and olfactory epithelium. The brain is the major functional unit of the CNS and is divided into different regions, including the brainstem, cerebellum, diencephalon, and cerebrum. The spinal cord relays information between the brain and the rest of the body. The CNS is different from the peripheral nervous system (PNS) in terms of its location and the types of cells involved. The development of the CNS starts with the formation of the neural tube in the embryo. The CNS has evolved differently in different species, with mammals having the most complex neocortex. There are many diseases and conditions that can affect the CNS, including infections, neurological disorders, seizure disorders, headache disorders, neurodegenerative diseases, autoimmune and inflammatory diseases, and genetic disorders.

The central nervous system (CNS) is the part of the nervous system that includes the brain and spinal cord. It is responsible for controlling and coordinating all the activities of the body. The CNS is found in animals with bilateral symmetry, which means they have a left and right side that are mirror images of each other. This includes most multicellular animals, except for sponges and diploblasts.

In vertebrates, which are animals with a backbone, the CNS is protected by a layer of tissue called the meninges. It is also bathed in a fluid called cerebral spinal fluid, which helps cushion and protect it. The CNS is made up of two types of tissue: white matter and gray matter. White matter consists of nerve fibers that transmit signals between different parts of the CNS, while gray matter consists of nerve cells and their connections.

The CNS also includes other structures such as the retina, optic nerve, olfactory nerves, and olfactory epithelium. These structures connect directly to the brain and are involved in processing sensory information. For example, the retina is responsible for detecting light and sending signals to the brain to create visual images.

The brain is the major functional unit of the CNS. It is divided into different regions, including the brainstem, cerebellum, diencephalon, and cerebrum. The brainstem controls basic functions such as breathing and heart rate. The cerebellum is involved in coordinating movements and maintaining balance. The diencephalon includes structures such as the thalamus and hypothalamus, which are involved in processing sensory information and regulating basic bodily functions. The cerebrum is the largest part of the brain and is responsible for higher cognitive functions such as thinking, memory, and perception.

The spinal cord is a long, thin structure that extends from the base of the skull to the lower back. It is housed within the vertebral column, or backbone. The spinal cord relays information between the brain and the rest of the body. It is responsible for transmitting signals that control voluntary and involuntary movements, as well as sensory information such as touch, temperature, and pain.

The CNS is different from the peripheral nervous system (PNS), which includes all the nerves outside of the brain and spinal cord. The PNS connects the CNS to the rest of the body and is responsible for transmitting signals to and from the CNS. It includes nerves that control muscles, as well as nerves that transmit sensory information from the body to the CNS.

The development of the CNS starts with the formation of the neural tube in the embryo. This tube eventually gives rise to both the brain and spinal cord. As the embryo develops, different regions of the neural tube differentiate into specific structures of the CNS. For example, the anterior portion of the neural tube differentiates into three brain vesicles, which eventually become the different regions of the brain.

The evolution of the CNS has been a gradual process, with different species developing different structures and functions. For example, planarians, which are flatworms, have a simple CNS consisting of a brain and nerve cords. Arthropods, such as insects, have a ventral nerve cord and ganglia that make up their CNS. In chordates, which include vertebrates, the CNS is placed dorsally, or on the back side of the body, above the gut and notochord. The CNS of mammals, including humans, is characterized by the presence of a neocortex, which is involved in higher thinking and processing of sensory information.

There are many diseases and conditions that can affect the CNS. These include infections such as encephalitis and poliomyelitis