The human brain is the command center for the human nervous system. It receives input from the sensory organs and sends output to the muscles. The human brain has the same basic structure as other mammal brains, but is more "encephalized" — larger in relation to body size than any other brains.
Facts about the human brain
- The human brain is the largest brain of all vertebrates relative to body size
- It weighs about 3 pounds (1.4 kilograms)
- The brain makes up about 2 percent of a human's body weight
- The cerebrum makes up 85 percent of the brain's weight
- It contains about 100 billion nerve cells (neurons), the "gray matter"
- It contains millions of nerve fibers (axons and dendrites), the "white matter"
Anatomy of the human brain
The largest part of the human brain is the cerebrum, which is divided into two hemispheres. Underneath lies the brainstem, and behind that sits the cerebellum. The outermost layer of the cerebrum is the cerebral cortex, which consists of four lobes: the frontal lobe, the parietal lobe, the temporal lobe and the occipital lobe. [Related: Nervous System: Facts, Functions & Diseases]
Like all vertebrate brains, the human brain develops from three sections known as the forebrain, midbrain and hindbrain. Each of these contains fluid-filled cavities called ventricles. The forebrain develops into the cerebrum and underlying structures; the midbrain becomes part of the brainstem; and the hindbrain gives rise to regions of the brainstem and the cerebellum.
Parts of the human brain
The cerebral cortex is greatly enlarged in human brains, and is considered the seat of complex thought. The frontal lobes are associated with higher-level functions such as self-control, planning, logic and abstract thought. Visual processing takes place in the occipital lobe. The temporal lobe processes sound and language, and includes the hippocampus and amygdala, which play roles in memory and emotion, respectively. The parietal lobe integrates input from different senses and is important for spatial orientation and navigation.
The brainstem connects to the spinal cord and consists of the medulla oblongata, pons and midbrain. The primary functions of the brainstem include: relaying information between the brain and the body; supplying some of the cranial nerves to the face and head; and performing critical functions in controlling the heart, breathing and consciousness.
Between the cerebrum and brainstem lie the thalamus and hypothalamus. The thalamus relays sensory and motor signals to the cortex and is involved in regulating consciousness, sleep and alertness. The hypothalamus connects the nervous system to the endocrine system — where hormones are produced — via the pituitary gland.
The cerebellum lies beneath the cerebrum and has important functions in motor control. It plays a role in coordination and balance, and may also have some cognitive functions.
Weight of the human brain
The adult human brain weighs about 3 pounds (1.4 kilograms). It makes up about 2 percent of a human's body weight (for a 150-pound human). The cerebrum makes up 85 percent of the weight of the brain.
Left brain vs. right brain
The human brain is divided into two hemispheres, the left and right, connected by a structure called the corpus callosum. The hemispheres are strongly, though not entirely, symmetrical. The left brain controls all the muscles on the right-hand side of the body; and the right brain controls the left side. One hemisphere may be slightly dominant, as with left- or right-handedness.
The popular notions about "left brain" and "right brain" qualities are generalizations that are not well-supported by evidence. Still, there are some important differences between these areas. The left brain contains regions involved in speech and language (Broca's area and Wernicke's area). The left brain is also associated with mathematical calculation and fact retrieval. The right brain plays a role in visual and auditory processing, spatial skills and artistic ability, though these functions involve both hemispheres.
Brain mapping project
In April 2013, President Barack Obama announced a new research program known as the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative, which will provide $100 million in funding starting in 2014 to map the structure and function of the human brain.
Sometimes called the Brain Activity Map, the project has been planned for some time. In June 2012, six scientists put forth general proposals for developing sensors and protocols for experimenting on single cells within neural networks. Obama first referenced the project in his 2013 State of the Union address in February, and in March 2013, the project's backers outlined their goals in the journal Science, calling for a sustained effort over several years to create tools to understand how brain networks function.
Supporters of the project argue that it will provide the missing piece in how the brain operates at a level between that of single neurons and the whole brain. Opponents claim the project lacks clear goals and may siphon away funding from other research.
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