The function of the brain in animal
The brain is the central organ of the nervous system of all vertebrates and most invertebrates. It is located on the head, usually as close to the sense organs of the senses as vision. It is the most complex organ in vertebrates. In humans, the cerebral cortex contains approximately 1.4-16 billion neurons. The number of neurons in the cerebellum is estimated to be 5.5-70 billion. The neurons are connected to thousands of other neurons through the synapses. These neurons usually communicate with each other through long fibers (called axons), which are trained by signal pulses (called action potentials) to distant parts of the brain or body, targeting specific receptor cells.
Physiologically, the brain exerts central control over other organs in the body. They work elsewhere in the body, producing patterns of muscle activity and stimulating the release of chemicals called hormones. This centralized control allows for quick and coordinated responses to environmental changes. Some basic types of interaction (eg, reflexes) can be mediated by the spinal cord or peripheral ganglia, but complex and purposeful behavioral controls based on complex sensory inputs require the brain to have the ability to integrate information.
The best way to derive information about the anatomy of the brain is by visual inspection, but many more sophisticated techniques have been developed. The brain tissue in its natural state is too soft to function, but it can be strengthened by soaking it in alcohol or other adhesives and then cutting it from the inside for inspection. Visually, the brain is composed of darker regions called gray matter, separated by lighter white matter regions. More information can be obtained by staining slices of brain tissue with various chemicals, which can reveal areas where certain types of molecules are present in high concentrations. You can also use a microscope to examine the microstructure of brain tissue and track the communication patterns from one brain area to another.
Axons take up most of the space in the brain, which is usually connected to each other in so-called bundles of nerve fibers. Myelinated axons are surrounded by a greasy insulating sheath of the myelin sheath, which greatly increases the rate of signal amplification. (There are also non-empty axes.) The myelin sheath is white, making the part of the brain that is completely filled with nerve fibers look like light white matter, while dark gray matter indicates areas with high density of neurons.
The brains of all vertebrates have a common basic shape, which is most obvious in the early stages of embryonic development. In the first image, the brain appears as three protrusions in front of the neural tube; these swellings eventually become forebrain, midbrain, and hindbrain (respectively forebrain, midbrain, and hindbrain). In the early stages of brain development, these three regions are roughly equal in size. In many types of vertebrates, such as fish and amphibians, these three parts remain the same in adults, but in mammals, the forebrain becomes much larger than the other parts, while the midbrain becomes very small.
The vertebrate brain is made of very soft tissue. Living brain tissue is pink on the outside, predominantly white on the inside, with slight color changes. The vertebral brain is surrounded by a connective tissue membrane system called the meninges, which separates the skull from the brain. Blood vessels enter the central nervous system through holes in the meningeal layer. The vascular wall cells are closely related to form the blood-brain barrier, which prevents the passage of many toxins and pathogens (although antibodies and some drugs prevent the treatment of brain diseases at the same time).