Brain activity is made possible by the interconnections of neurons that are linked together to reach their targets. [126] A neuron consists of a cell body, axon, and dendrites. Dendrites are often extensive branches that receive information in the form of signals from the axon terminals of other neurons. The signals received may cause the neuron to initiate an action potential (an electrochemical signal or nerve impulse) which is sent along its axon to the axon terminal, to connect with the dendrites or with the cell body of another neuron. An action potential is initiated at the initial segment of an axon, which contains a specialised complex of proteins. [127] When an action potential reaches the axon terminal it triggers the release of a neurotransmitter at a synapse that propagates a signal that acts on the target cell. [128] These chemical neurotransmitters include dopamine, serotonin, GABA, glutamate, and acetylcholine. [129] GABA is the major inhibitory neurotransmitter in the brain, and glutamate is the major excitatory neurotransmitter. [130] Neurons link at synapses to form neural pathways, neural circuits, and large elaborate network systems such as the salience network and the default mode network, and the activity between them is driven by the process of neurotransmission. Other animals, including whales and elephants have larger brains than humans. However, when the brain-to-body mass ratio is taken into account, the human brain is almost twice as large as that of a bottlenose dolphin, and three times as large as that of a chimpanzee. However, a high ratio does not of itself demonstrate intelligence: very small animals have high ratios and the treeshrew has the largest quotient of any mammal. [218] In popular culture [ edit ] Phrenology summarised in an 1883 chart The cerebrum is the largest part of the brain and is divided into nearly symmetrical left and right hemispheres by a deep groove, the longitudinal fissure. [16] Asymmetry between the lobes is noted as a petalia. [17] The hemispheres are connected by five commissures that span the longitudinal fissure, the largest of these is the corpus callosum. [7]

The function of sleep is not fully understood; however, there is evidence that sleep enhances the clearance of metabolic waste products, some of which are potentially neurotoxic, from the brain and may also permit repair. [52] [143] [144] Evidence suggests that the increased clearance of metabolic waste during sleep occurs via increased functioning of the glymphatic system. [52] Sleep may also have an effect on cognitive function by weakening unnecessary connections. [145] Research [ edit ] a b Kolb, B.; Whishaw, I. (2009). Fundamentals of Human Neuropsychology. Macmillan. pp.73–75. ISBN 978-0-7167-9586-5. Thomas Willis is considered a second pioneer in the study of neurology and brain science. He wrote Cerebri Anatome ( Latin: Anatomy of the brain) [c] in 1664, followed by Cerebral Pathology in 1667. In these he described the structure of the cerebellum, the ventricles, the cerebral hemispheres, the brainstem, and the cranial nerves, studied its blood supply; and proposed functions associated with different areas of the brain. [233] The circle of Willis was named after his investigations into the blood supply of the brain, and he was the first to use the word "neurology." [238] Willis removed the brain from the body when examining it, and rejected the commonly held view that the cortex only consisted of blood vessels, and the view of the last two millennia that the cortex was only incidentally important. [233] a b Ribas, G. C. (2010). "The cerebral sulci and gyri". Neurosurgical Focus. 28 (2): 7. doi: 10.3171/2009.11.FOCUS09245. PMID 20121437. Goard, M.; Dan, Y. (October 4, 2009). "Basal forebrain activation enhances cortical coding of natural scenes". Nature Neuroscience. 12 (11): 1444–1449. doi: 10.1038/nn.2402. PMC 3576925. PMID 19801988.Main article: History of neuroscience Early history [ edit ] Hieroglyph for the word "brain" ( c. 1700 BC) Main article: Stroke CT scan of a cerebral hemorrhage, showing an intraparenchymal bleed (bottom arrow) with surrounding edema (top arrow) Pavel, Fiala; Jiří, Valenta (January 1, 2013). Central Nervous System. Karolinum Press. p.79. ISBN 978-80-246-2067-1.

The human brain has many properties that are common to all vertebrate brains. [256] Many of its features are common to all mammalian brains, [257] most notably a six-layered cerebral cortex and a set of associated structures, [258] including the hippocampus and amygdala. [259] The cortex is proportionally larger in humans than in many other mammals. [260] Humans have more association cortex, sensory and motor parts than smaller mammals such as the rat and the cat. [261] When it comes to oxygen, your brain just can’t get enough. Even though it makes up less than 2% of your body weight, the brain consumes a whopping 20% of the oxygen in your bloodstream.

looks at the interaction of brain regions whilst the brain is not performing a specific task. [158] This is also used to show the default mode network. One is obliged to admit that perception and what depends upon it is inexplicable on mechanical principles, that is, by figures and motions. In imagining that there is a machine whose construction would enable it to think, to sense, and to have perception, one could conceive it enlarged while retaining the same proportions, so that one could enter into it, just like into a windmill. Supposing this, one should, when visiting within it, find only parts pushing one another, and never anything by which to explain a perception. Gaillard, F. "Glymphatic pathway". radiopaedia.org. Archived from the original on October 30, 2017. The philosophy of the mind studies such issues as the problem of understanding consciousness and the mind–body problem. The relationship between the brain and the mind is a significant challenge both philosophically and scientifically. This is because of the difficulty in explaining how mental activities, such as thoughts and emotions, can be implemented by physical structures such as neurons and synapses, or by any other type of physical mechanism. This difficulty was expressed by Gottfried Leibniz in the analogy known as Leibniz's Mill: Rather than working with an actual chip, Jonas and Kording used a simulation, albeit one accurate enough to run classic games like Donkey Kong, Space Invaders, and Pitfall. That gave them experimental omniscience and omnipotence—they knew everything and could tweak anything. For example, they could disable each of the chip’s transistors one at a time. And by doing so, they found several that were essential for booting up all three games, and others that were essential for just one.