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Not all animals have neurons; Trichoplax and sponges lack nerve cells altogether. Neurons may be packed to form structures such as the brain of vertebrates or the neural ganglions of insects. The number of neurons and their relative abundance in different parts of the brain is a determinant of neural function and, consequently, of behavior.
The size of the brain is a frequent topic of study within the fields of anatomy, biological anthropology, animal science and evolution.Measuring brain size and cranial capacity is relevant both to humans and other animals, and can be done by weight or volume via MRI scans, by skull volume, or by neuroimaging intelligence testing.
The entire central nervous system forms 6% of the body mass of M. mymaripenne, and the brain makes up 2.9%. Of the wasp's 7,400 neurons, 4,600 are located in the brain. A small insect from other families often deals with the issue of having a large brain in relation to its head size by shifting its brain into its thorax and even abdomen.
Brain size usually increases with body size in animals (i.e. large animals usually have larger brains than smaller animals); [4] the relationship is not, however, linear. Small mammals such as mice may have a brain/body ratio similar to humans, while elephants have a comparatively lower brain/body ratio. [4] [5]
It is possible that the fluid protects the brain should the animal fall from a tree. [23]: 52–53 The koala's small brain may be an adaptation to the energy restrictions imposed by its diet, which is insufficient to sustain a larger brain. [11]: 81 Its small brain limits its ability to perform complex behaviours. For example, it will not eat ...
Some animal phyla have gone through major brain enlargement through evolution (e.g. vertebrates and cephalopods both contain many lineages in which brains have grown through evolution) but most animal groups are composed only of species with extremely small brains.
Scientists discovered a 520-million-year-old fossilized larva with brains and guts intact, ... Some are just impressions of small creatures or animals left in rocks, but most have something in ...
The tardigrade nervous system consists primarily of the brain and four segmental ganglia associated with the four body segments. [10] The brain comprises about 1% of the total body volume. [11] The brain develops in a bilaterally symmetric pattern. [12] Tardigrades have a dorsal brain atop a paired ventral nervous system.