Brain,Mass of nerve tissue at the front end of the organism. The brain integrates sensory information and directs motor responses; In the upper vertebrates it is also the learning center. The human brain weighs about 1.4 kg (3 pounds) and consists of billions of cells called neurons. Connections between neurons, known as neuronal synapses, allow the transmission of electrical and chemical messages from one neuron to another in the brain, a process that supports the basic sensory functions that are necessary for learning, memory, thought formation and Other cognitive activities.
In the lower vertebrates, the brain is tubular and resembles the early stage of brain development in the upper vertebrates. It consists of three distinct regions: the midbrain, the midbrain and the forebrain. Although the vertebrate brain of the upper vertebrates undergoes major modifications during embryonic development, these three regions are still visible.
The posterior brain consists of a rectangular medulla and a bonus. The medulla transmits signals between the spinal cord and the upper parts of the brain; It also controls independent functions such as heartbeat and breathing. These parts consist partly of regions that join the spinal cord to higher levels of the brain, and also contain cell groups that carry information from the brain to the cerebellum.
The middle brain, whose upper part has evolved from the visual lobes, is the main center of sensory integration in fish and amphibians. It is also involved with the fusion of reptiles and birds. In mammals, the middle brain is greatly reduced, acting primarily as a link between the posterior brain and the anterior brain.
Connected to the brain, bones, the middle brain by large bundles of fibers is the cerebellum. This relatively large “small brain” in humans controls balance and coordination by producing smooth and coordinated movements of muscle groups.
The anterior brain includes both cerebral hemispheres, and below it, the brain stem, which contains the thalamus and the lower region. The hypothalamus is the main center of migration between the medulla and the brain. The hypothalamus is an important center of control of sexual desire, pleasure, pain, hunger, thirst, blood pressure, body temperature and other visceral functions. The hypothalamus produces hormones that control the secretions of the anterior pituitary gland, and also produces the hormone oxytocin and an anti-urine, which is stored and released in the posterior pituitary gland.
The brain, which originally functions as part of the olfactory lobes, is involved in more complex functions in the human brain. In humans and other advanced vertebrates, the brain has grown over the rest of the brain, forming a moderate layer of gray matter. The degree of torsion depends in part on body size. Small mammals (for example, less anteaters, marmosites) are generally soft brains, and large mammals (such as whales, elephants and dolphins) are generally very twisted.
The cerebral hemispheres are separated by a deep groove, cleft longitudinal fissure. At the base of this fissure is a thick bundle of nerve fibers, called the calcium body, which provides a connection link between the two hemispheres. The left hemisphere controls the right hemisphere, and vice versa, due to the intersection of nerve fibers in the spinal cord or spinal cord, it is less common. Although the left and right hemispheres are identical to each other in many ways, there are important functional differences. In most people, for example, the regions that control speech are in the left hemisphere, while the regions that control spatial perceptions are in the right hemisphere.
Two main indentations: central groove and lateral groove, divide each hemisphere into four sections: frontal, parietal, temporal and occipital lobe. The central groove, also known as the Rolando fissure, also separates the cortical motor region (which is provided by the fissure) from the cortical sensory region (which is behind the fissure). Starting in the upper part of the hemisphere, the upper areas of the engine and the sensory regions control the lower parts of the body, while the lower areas of the engine and the sensory areas control the upper parts of the body. Other functional areas of the cerebral hemispheres have been identified, including the visual cortex in the occipital lobe and the auditory cortex in the temporal lobe. However, much of the primitive cortex is dedicated to any specific motor or sensory function; This supposed cortex is clearly associated with higher mental activities. (For more information about the human brain, see Human Nervous System).