Brain

! Confusion between the latest definitions (TA2-2019) of brain, cerebrum and telencephalon !

BRAIN

A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals.

It is located in the head, usually close to the sensory organs for senses such as vision.

It is the most complex organ in a vertebrate's body.

In a human, the cerebral cortex contains approximately 14–16 billion neurons, and the estimated number of neurons in the cerebellum is 55–70 billion.

Each neuron is connected by synapses to several thousand other neurons.

These neurons typically communicate with one another by means of long fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells. Physiologically, brains exert centralized control over a body's other organs.

They act on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones.

This centralized control allows rapid and coordinated responses to changes in the environment.

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. 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.