The brain is a vital part of the nervous system in organisms, consisting of the mass of nerve tissue located at the anterior end. In higher vertebrates, it serves as the center for learning and coordinating sensory information and motor responses. The human brain weighs approximately 1.4 kg (3 pounds) and is composed of billions of cells referred to as neurons. Synapses between these neurons facilitate the transmission of electrical and chemical messages from one neuron to another, which is responsible for basic sensory functions, learning, memory, thought formation, and other cognitive activities.
Together with the spinal cord, the brain forms the central nervous system in vertebrates, controlling both voluntary and involuntary movements. Examples of voluntary movements include walking and speech, while involuntary movements include breathing and reflex actions. The brain also plays a crucial role in emotions and cognitive processes. For more comprehensive information about the human brain, see the section on the nervous system in general.
In lower vertebrates, the brain is tubular and resembles an early developmental stage of the brain in higher vertebrates. It consists of three distinct regions: the hindbrain, the midbrain, and the forebrain. Although the brain of higher vertebrates undergoes considerable modification during embryonic development, these three regions are still discernible.
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Human Organs
human brain; magnetic resonance imaging (MRI)
An image of the human brain produced using magnetic resonance imaging (MRI).
The hindbrain is composed of the medulla oblongata and the pons. The medulla transmits signals between the spinal cord and higher parts of the brain; it also controls such autonomic functions as heartbeat and respiration. The pons is partly made up of tracts connecting the spinal cord with higher brain levels, and it also contains cell groups that transfer information from the cerebrum to the cerebellum.
The midbrain is an important center for sensory integration in fish and amphibians. It evolved from the optic lobes and is involved with integration in reptiles and birds as well. However, in mammals, the midbrain is greatly reduced and primarily serves as a connecting link between the hindbrain and forebrain.
Connected to the medulla, pons, and midbrain by large bundles of fibers is the cerebellum. In humans, this "little brain" plays a crucial role in balance and coordination by producing smooth, coordinated movements of muscle groups.
The forebrain is divided into two hemispheres, the left and right cerebral hemispheres, which are in turn composed of several smaller structures. Underneath these are the brainstem, which consists of the medulla, Pons, and Midbrain. The thalamus is a complex structure located between the cerebrum and the medulla. It serves as the main relay centre that connects the medulla to the cerebrum.
The hypothalamus is another important structure within the forebrain. This region plays a crucial role in regulating various functions throughout the body. For example, it controls our sex drive, pleasure, pain, hunger, thirst, blood pressure, body temperature, and many other visceral functions. The hypothalamus produces hormones that regulate the secretions of the anterior pituitary gland. Additionally, it produces oxytocin and antidiuretic hormone, both of which are stored in and released by the posterior pituitary gland.
In recent studies, scientists have discovered that the McGurk effect can trick your brain. This refers to how visual cues can have an impact on our perception of speech. In order to better understand this phenomenon, researchers conducted an experiment where they asked participants to watch a video of a person saying "beep" while also showing them an image of a beeping sound. When participants heard the actual beeping sound, they experienced confusion and thought that they were hearing someone saying "woodpecker" instead of "beep" because their brains had been tricked by the visual cues in the video.
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The cerebrum is a component of the brain and originally served as part of the olfactory lobes. It has evolved into more complex functions in human brains and other advanced vertebrates. In humans and other advanced vertebrates, the cerebrum has grown over the rest of the brain, forming a convoluted layer of gray matter. The degree of convolution is partly dependent on body size.
Small mammals such as lesser anteaters and marmosets have generally smooth brains, while large mammals like whales, elephants, and dolphins have highly convoluted ones. This distinction in brain structure has implications for how different types of animals interact with their environments. For example, small mammals rely on their keen sense of smell to navigate and hunt for prey, while larger mammals require complex social structures and communication systems to survive in groups.
The cerebral hemispheres are separated by a deep groove, the longitudinal cerebral fissure. At the base of this fissure lies a thick bundle of nerve fibres, called the corpus callosum, which provides a communication link between the hemispheres. The left hemisphere controls the right half of the body, and vice versa, because of a crossing of the nerve fibres in the medulla or, less commonly, in the spinal cord. Although the right and left hemispheres are mirror images of one another in many ways, there are important functional distinctions. In most people, for example, the areas that control speech are located in the left hemisphere, while areas that control spatial perceptions are located in the right hemisphere.
Uncovering the science behind this separation is key to understanding the nature of brain function and how disorders such as split-brain syndrome can affect it. Split-brain syndrome occurs when the two hemispheres of the brain become divided by a stroke or other trauma. This division can lead to a number of problems with cognitive function and emotional regulation, including difficulty speaking, learning new skills, and processing emotions from both sides of the brain. In some cases, individuals with split-brain syndrome may also experience changes in their perception of time and space, as well as difficulty with tasks that require fine motor coordination.
The corpus callosum is a structure that links the left and right hemispheres of the brain, enabling communication between these two sides. When this structure becomes dysfunctional or is absent, it can result in a condition called split-brain syndrome. In this condition, each hemisphere of the brain operates independently.
Split-brain syndrome can lead to various conditions, including alien-hand syndrome. This syndrome is marked by unintentional and coordinated yet purposeful movements of the hands. It can cause difficulties in performing simple tasks such as writing or gripping objects.
Despite its name, alien-hand syndrome is not caused by extraterrestrial beings. Instead, it is a neurological disorder that affects the way the brain processes information from the body. The exact cause of this condition is still unknown, but research has suggested that it may be related to damage or interruptions in the communication pathways between the brain's two hemispheres.
If you are experiencing symptoms such as involuntary hand movements, it is important to seek medical attention immediately. A neurologist can diagnose your condition and recommend appropriate treatment options. With appropriate care and support, individuals with alien-hand syndrome and other conditions related to split-brain syndrome can lead fulfilling lives.
Each of the cerebral hemispheres is divided into four distinct sections: the frontal, parietal, temporal, and occipital lobes. The division between these lobes occurs along two major furrows: the central sulcus and the lateral sulcus. Additionally, the central sulcus, also known as the fissure of Rolando, serves as a boundary between the cortical motor area (located anterior to the fissure) and the cortical sensory area (located posterior to the fissure).
Functionally, the upper regions of each of these areas control the lower parts of the body, while the lower regions control the upper parts of the body. This principle applies to both the motor and sensory areas of the brain's hemispheres. Furthermore, specific areas of the cerebral cortex have been identified for their unique functions. For example, the occipital lobe contains the visual cortex, while the temporal lobe houses the auditory cortex.
However, a significant amount of the primate cortex is not devoted to any specific motor or sensory function. Instead, this so-called association cortex appears to be involved in higher mental activities. By understanding how different areas of the brain work together, researchers hope to gain insights into complex processes such as perception, attention, and memory.
