Brain

The center of nervous system in all vertebrate, animal and most invertebrate is brain. In vertebrate, the brainis located in the head, protected by skull and close to the primary sensory apparatus of vision, hearing, balance, taste and smell. Brains have extremely nervous system complex. Human brain contains roughly 100 billion neurons, and linked with up to 10,000 synaptic connections each. Each cubic millimeter of cerebral cortex contains roughly one billion synapses. 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 partsof the brain or body and target them to specific recipient cells.

Brains control behaviors either by activating muscles, or by causing secretion of chemical such as hormones. The spinal cord by it self contains neural circuitry capable of generating reflex responses as well as simple motor patterns such as swimming or walking. Sophisticated control of behavior on the basis of complex sensory input requires the information integrating capabilities of a centralized brain. Brain observated by EEG methods to recording and functional brain imaging. EEG methods have information that brain operations are highly organized. But until now, these methods do not have the resolution to reveal the activity of individual neurons.

Vertebrate Brain Main Structure

Here is a list of some of the most important parts, along with a very brief description of their function as currently understood :

The medulla, along with the spinal cord, contains many small nuclei involved in a wide variety of sensory and motor functions.

• The hypothalamus is a small region at the base of the fore brain, it is composed of numerous small nuclei, each with distinct connentions and distinct neuro chemistry. Hypothalamus is the central control station for sleep/wake cycles, control of eating and drinking, control of hormone release and many other critical biological functions.
• The thalamus is a collection of nuclei with diverse functions. Some of them are involved in relaying information to and from the cerebral hemispheres. Others are involved in motivation. The subthalamic area (zona incerta) seems to contain action-generating systems for several types of "consummatory" behaviors, including eating, drinking, defecation, and copulation.
• The cerebellum modulates the outputs of other brain systems to make them more precise. Removal of the cerebellum does not prevent an animal from doing anything in particular, but it makes actions hesitant and clumsy. This precision is not built-in, but learned by trial and error. Learning how to ride a bicycle is an example of a type of neural plasticity that may take place largely within the cerebellum.
• The tectum, often called "optic tectum", allows actions to be directed toward points in space. In mammals it is called the "superior colliculus", and its best studied function is to direct eye movements. It also directs reaching movements, though. It gets strong visual inputs, but also inputs from other senses that are useful in directing actions, such as auditory input in owls, input from the thermo sensitive pit organs in snakes, etc. In some fishes, it is the largest part of the brain.
• The pallium is a layer of gray matter that lies on the surface of the forebrain. In reptiles and mammals it is called cortex instead. The pallium is involved in multiple functions, including olfaction and spatial memory. In mammals, where it comes to dominate the brain, it subsumes functions from many subcortical areas.
• The hippocampus, strictly speaking, is found only in mammals. However, the area it derives from, the medial pallium, has counter parts in all vertebrates. There is evidence that this part of the brain is involved in spatial memory and navigation in fishes, birds, reptiles, and mammals.
• The basal ganglia are a group of interconnected structures in the forebrain, of which our understanding has increased enormously over the last few years. The primary function of the basal ganglia seems to be action selection. They send inhibitory signals to all parts of the brain that can generate actions, and in the right circumstances can release the inhbition, so that the action-generating systems are able to execute their actions. Rewards and punishments exert their most important neural effects within the basal ganglia.
• The olfactory bulb is a special structure that processes olfactory sensory signals, and sends its output to the olfactory part of the pallium. It is a major brain component in many vertebrates, but much reduced in primates.

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