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Cephalization is an evolutionary trend in animals that, over a sufficient number of generations, concentrates the special sense organs and nerve ganglia towards the front of the body where the mouth is located, often producing an enlarged head. This is associated with the animal's movement direction and bilateral symmetry.
The human brain contains 86 billion neurons, with 16 billion neurons in the cerebral cortex. [ 2 ] [ 1 ] Neuron counts constitute an important source of insight on the topic of neuroscience and intelligence : the question of how the evolution of a set of components and parameters (~10 11 neurons, ~10 14 synapses) of a complex system leads to ...
The fundamental bilateral body form is a tube with a hollow gut cavity running from the mouth to the anus, and a nerve cord with an enlargement (a ganglion) for each body segment, with an especially large ganglion at the front, called the brain. The brain is small and simple in some species, such as nematode worms; in other species, such as ...
The brainstem, resembling a stalk, attaches to and leaves the cerebrum at the start of the midbrain area. The brainstem includes the midbrain, the pons, and the medulla oblongata. Behind the brainstem is the cerebellum (Latin: little brain). [7] The cerebrum, brainstem, cerebellum, and spinal cord are covered by three membranes called meninges.
Typically, each body segment has one ganglion on each side, though some ganglia are fused to form the brain and other large ganglia. The head segment contains the brain, also known as the supraesophageal ganglion. In the insect nervous system, the brain is anatomically divided into the protocerebrum, deutocerebrum, and tritocerebrum.
The brain is small and simple in some species, such as the nematode worm, where the body plan is quite simple: a tube with a hollow gut cavity running from the mouth to the anus, and a nerve cord with an enlargement (a ganglion) for each body segment, with an especially large ganglion at the front, called the brain.
The head contained the brain and carried sensory and feeding appendages. The trunk bore the appendages responsible for locomotion and respiration ( gills in aquatic species). In almost all modern arthropods, the trunk is further divided into a "thorax" and an "abdomen", with the thorax bearing the main locomotory appendages.
A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may not have a head, but many bilaterally symmetric forms do, regardless of size.