The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals.
The nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body.
Invertebrates are animals that neither possess nor develop a vertebral column, derived from the notochord.
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Only a few invertebrates such as sponges, jellyfish, adult sea squirts and starfish do not have a brain; diffuse or localised nerve nets are present instead.
Sponges, the members of the phylum Porifera, are the sister of the ParaHoxozoa or Epitheliozoa with which they form a basal animal clade, the Parazoa.
A nerve net consists of interconnected neurons lacking a brain or any form of cephalization.
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The brain is located in the head, usually close to the primary sensory organs for such senses as vision, hearing, balance, taste, and smell.
Hearing, or auditory perception, is the ability to perceive sound by detecting vibrations, changes in the pressure of the surrounding medium through time, through an organ such as the ear.
Taste, gustatory perception, or gustation is one of the five traditional senses that belongs to the gustatory system.
A sense is a physiological capacity of organisms that provides data for perception.
In a typical human, the cerebral cortex is estimated to contain 15–33 billion neurons, each connected by synapses to several thousand other neurons.
The cerebral cortex is the largest region of the mammalian brain and plays a key role in memory, attention, perception, cognition, awareness, thought, language, and consciousness.
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another neuron.
A neuron is an electrically excitable cell that processes and transmits information through electrical and chemical signals.
These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells.
In physiology, an action potential occurs when the membrane potential of a specific axon location rapidly rises and falls: this depolarisation then causes adjacent locations to similarly depolarise.
An axon, is a long, slender projection of a nerve cell, or neuron, that typically conducts electrical impulses away from the neuron's cell body.
Protoplasm is the living content of a cell that is surrounded by a plasma membrane.
Physiologically, the function of the brain is to exert centralized control over the other organs of the body.
The brain acts on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones.
A hormone is any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour.
A gene is a locus of DNA which is made up of nucleotides and is the molecular unit of heredity.
This centralized control allows rapid and coordinated responses to changes in the environment.
The pons is part of the brainstem, and in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum.
Some basic types of responsiveness such as reflexes can be mediated by the spinal cord or peripheral ganglia, but sophisticated purposeful control of behavior based on complex sensory input requires the information integrating capabilities of a centralized brain.
A reflex, or reflex action, is an involuntary and nearly instantaneous movement in response to a stimulus.
The operations of individual brain cells are now understood in considerable detail but the way they cooperate in ensembles of millions is yet to be solved.
Recent models in modern neuroscience treat the brain as a biological computer, very different in mechanism from an electronic computer, but similar in the sense that it acquires information from the surrounding world, stores it, and processes it in a variety of ways, analogous to the central processing unit in a computer.
A central processing unit is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logical, control and inputO circuitry.
A computer is a device that can be instructed to carry out an arbitrary set of arithmetic or logical operations automatically.
This article compares the properties of brains across the entire range of animal species, with the greatest attention to vertebrates.
Attention is the behavioral and cognitive process of selectively concentrating on a discrete aspect of information, whether deemed subjective or objective, while ignoring other perceivable information.
It deals with the human brain insofar as it shares the properties of other brains.
The ways in which the human brain differs from other brains are covered in the human brain article.
Several topics that might be covered here are instead covered there because much more can be said about them in a human context.
The most important is brain disease and the effects of brain damage, covered in the human brain article because the most common diseases of the human brain either do not show up in other species, or else manifest themselves in different ways.
Central nervous system diseases, also known as central nervous system disorders, are a group of neurological disorders that affect the structure or function of the brain or spinal cord, which collectively form the central nervous system.