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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.
Brain mapping can show how an animal's brain changes throughout its lifetime. As of 2021, scientists mapped and compared the whole brains of eight C. elegans worms across their development on the neuronal level [68] [69] and the complete wiring of a single mammalian muscle from birth to adulthood. [38]
Micrograph showing a von Economo neuron of the cingulate. HE-LFB stain.. Von Economo neurons, also called spindle neurons, are a specific class of mammalian cortical neurons characterized by a large spindle-shaped soma (or body) gradually tapering into a single apical axon (the ramification that transmits signals) in one direction, with only a single dendrite (the ramification that receives ...
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals.It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for special senses such as vision, hearing and olfaction.
Two ganglia at the head (the "nerve ring") end function similar to a simple brain. Photoreceptors on the animal's eyespots provide sensory information on light and dark. [28] The nervous system of one very small roundworm, the nematode Caenorhabditis elegans, has been completely mapped out in a connectome including its synapses.
Pictured here is a cross-section showing the gross anatomy of the human brain. Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defined nervous systems ...
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord.The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all parts of the bodies of bilaterally symmetric and triploblastic animals—that is, all multicellular animals except sponges and diploblasts.
On the organ and tissue scale in mammals and other animals, examples include the circulatory system, the respiratory system, and the nervous system. On the micro to the nanoscopic scale, examples of biological systems are cells, organelles, macromolecular complexes and regulatory pathways.