Prab at 11:55, 1 April 2025

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Prab at 11:19, 6 September 2023

2023-09-06T11:19:45Z

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The '''brain''' is the part of the body which lets animals make sense of things. It gets input from [[sense organs]], and changes [[behaviour]] in response to this information. In humans, the brain also controls our use of [[language]], and is capable of [[wikt:abstract|abstract]] [[thought]].<ref name=Calvin>Calvin, William H. [1996] 1998. ''How brains think: evolving intelligence, then & now''. Phoenix, London. {{ISBN|0-75380-200-7}}</ref> The brain is the main control centre of the whole body.<ref>''Encyclopedia of discovery: science''. Weldon Owen, 2001, 30{{ndash}}31. {{ISBN|1740893298}}</ref> The brain is made up of a special type of [[cell]]s. They are connected with each other and with the [[nerve]]s in our body. In all animals the delicate brain is protected in some way. In ourselves, and all [[vertebrates]], it is protected by the [[bone]]s of the [[skull]].

[[File:Brain-en.png|Brain|thumb]]
== Function ==
The brain does the [[thinking]], learning, and feeling for the body. For humans, it is the source of [[consciousness]].<ref>We do not know whether other mammals have consciousness.</ref> The brain also controls basic [[autonomic]] body actions, like [[breathing]], [[digestion]], [[heartbeat]], that happen automatically. These activities, and much else, are governed by [[unconscious]] functions of the brain and [[nervous system]]. All the information about the world gathered by our [[senses]] is sent through nerves into the brain, allowing us to see, hear, smell, taste and feel things. The brain processes this information, and we experience it as pictures, sounds, and so on. The brain also uses nerves to tell the body what to do, for example by telling muscles to move or our [[heart]] to beat faster.

[[File:Brain-ALZH.png|Brain cross section|thumb]]
This is generally true but some activity is caused by the [[spinal cord]] directly, for example, [[reflex]] actions do not involve the brain. In lower animals, a good deal is done without their brain being involved.

All [[vertebrates]] have brains and, over time, their brains have [[evolved]] to become more complex. Some simple animals, however, like [[sponge]]s, do not have anything like a brain. [[Segmented]] [[invertebrates]] have [[ganglion]]s in each segment, and a ring of nervous tissue around the [[alimentary canal]] at the front. This acts to bring [[sense data]] from the front into play with the movement of the body.

== Parts ==
In [[mammal]]s, the brain is made of three main parts: the [[cerebrum]], the [[cerebellum]] and the [[brainstem]]. The surface of the cerebrum is the [[cerebral cortex]], which all vertebrates have. Mammals also have an extra layer, the [[neocortex]]. This is the key to the behaviour which is typical of mammals, especially humans.

=== Cerebral cortex ===
The cortex has [[Sensory system|sensory]], [[Motor system|motor]], and association areas. The sensory areas are the areas that receive and process information from the senses. The motor areas control voluntary movements, especially fine movements performed by the hand. The right half of the motor area controls the left side of the body, and vice versa. Association areas produce a meaningful experience of the world, and supports abstract thinking and language. This enables us to interact effectively. Most connections are from one area of the cortex to another, rather than to subcortical areas; The figure may be as high as 99%.<ref>Braitenberg V. and Schüz A. 1991. ''Anatomy of the cortex: statistics and geometry''. NY: Springer-Verlag.</ref>

[[File:CT of a normal brain, sagittal 11.png|CT of a normal brain, sagittal|thumb]]
=== Cerebellum ===
The cerebellum coordinates [[muscle]]s so they work together.<ref name=igcse>{{cite book|title=Edexcel IGCSE Biology: Student Book|page=75|date=2009|publisher=Pearson Education|first1=Phil|last1=Bradfield|first2=Steve|last2=Potter|isbn=9780435966881}}</ref> It is also the centre of maintaining position and balance, a vital part of movement helping with simple motor skills.
[[File:Neural signaling-human brain.gif|thumb|Neural signaling in the human brain. Small electrical charges go from one neuron to the next]]
=== Brain stem ===
The [[brain stem]] is at the back of the brain (actually underneath it in humans). It joins the rest of the brain with the [[spinal cord]]. It has lots of different parts that control different jobs in the body: for instance, the brain stem controls breathing, [[heart]]beat, sneezing, [[eye]] blinking, and swallowing. Body temperature and hunger are also controlled by parts of the brain stem.

== Size ==
The [[volume]] of the human brain (relative to the size of the whole body) is very large, compared to that of most other animals. The human brain also has a very large surface (called [[Cerebral cortex|cortex]]) for its size, which is possible because it is very wrinkled. If the human cortex were flattened, it would be close to a square [[metre|meter]] in area. Some other animals also have very wrinkled brains, such as [[dolphin]]s and [[elephant]]s. Here is a [[rule of thumb]]: the larger an animal is, the larger its brain will be.<ref name=Calvin/>p15 Even allowing for that, the human brain, and in particular the neocortex, is very large. We know it increased in size four-fold over the last several million years of [[evolution]].<ref name=Calvin/>p79 There are ideas about why this happened, but no-one is quite sure. Most theories suggest complex social activity and the evolution of [[language]] would make a larger brain advantageous.<ref name=Calvin/>p80<ref>Pinker, Stephen 1994. ''The language instinct''. Morrow. p363</ref> As an additional note, [[Einstein]]'s brain weighed only 1,230 grams, which is less than the average adult male brain (about 1,400 grams).<ref>{{cite web|url=http://faculty.washington.edu/chudler/ein.html|title=Neuroscience For Kids - einstein's brain|website=faculty.washington.edu}}</ref> The detailed organisation of a brain obviously matters, but in ways which are not understood at present.

=== Glial cells ===
A human brain accounts for about 2% of the body's weight, but it uses about 20% of its energy. It has about 50–100 [[billion]] nerve [[cell]]s (also called [[neuron]]s), and roughly the same number of support cells, called ''glia''. The job of neurons is to receive and send [[information]] to and from the rest of the body, while glia provide [[nutrients]] and guide blood flow to the neurons, allowing them to do their job. Each nerve [[cell]] has contact with as many as 10,000 other [[nerve]] cells through connections called [[synapse]]s.

== Related pages ==
*[[Spinal cord]]
*[[Vertebrate brain]]
*[[Human Connectome Project]]
== References ==
{{reflist}}
{{stub}}
{{Nervous system}}
{{Portal bar|Philosophy}}
[[Category:Brain| ]]
[[Category:Organs (anatomy)]]
[[Category:Human anatomy by organ]]
[[Category:Animal anatomy]]
[[Category:Basic English 850 words]]

Brain - Revision history

Prab at 11:55, 1 April 2025

Prab: CSV import

Prab at 11:19, 6 September 2023