University:
University of Phoenix
Course:
BIO 101T | Principles of Biology 3
Academic year:

2021
Views:

720

Pages:

7
Author:

Arnav Newman

Comparative Account of Brain in Vertebrates Introduction: Brains of all vertebrates follow a basic architectural plan, but their form differs based on the habits and behavior of the animals. Cephalochordata: In Amphioxus, the brain consists of an anterior prosencephalon, with two cerebral vesicles and a single enlarged ventricle. The midbrain and hindbrain are absent, and in some cases, even the forebrain is missing. Cyclostomes: The brain is primitive, with non-permanent subdivisions. In some cases, the olfactory lobes are well developed. The cerebral hemispheres are rudimentary, and the optic lobes are not well developed. The medulla oblongata is developed. Fishes: Elasmobranchs: Olfactory lobes are large and attached to the cerebrum via olfactory tracts (also called peduncles). Optic lobes are moderately sized. The brain cavity is large, and the optic lobes and pituitary apparatus are well developed. Osteichthyes: More specialized than elasmobranchs, osteichthyes have larger cerebral hemispheres and optic lobes, with a larger cerebellum. Some bony fishes have a large diencephalon, and in catfishes, the vagal lobes are large. Amphibians: Amphibians have smaller olfactory lobes and larger optic lobes. The cerebrum shows greater development, known as the corpus striatum. Two cerebral hemispheres show more complex development for better locomotion and feeding activities. Reptiles: The reptilian brain is more advanced in size and proportion than amphibians, mainly due to their terrestrial life mode. The midbrain is the center of brain activity. The optic lobes are large, and the cerebellum is more developed. Birds: Birds have proportionally larger brains than reptiles. Olfactory lobes are small and degenerate, as birds rely less on smell. Cerebral hemispheres are large, and the cerebellum is larger and shows a branching pattern (arbor vitae) for flight coordination. Mammals: Mammalian brains show the highest development, with enlarged cerebral hemispheres divided into lobes. The cerebrum is larger and convoluted, with the presence of the corpus callosum in higher mammals. Olfactory lobes are reduced and covered by the hemispheres. The cerebellum is large and involved in motor coordination, and the medulla oblongata controls digestion, respiration, and circulation. Spinal Cord: The spinal cord extends from the neural axis behind the brain and is a continuation of the medulla oblongata. It extends the full length of the vertebral column in amphibians, reptiles, birds, and mammals. In some species like cyclostomes and limbless amphibians, the spinal cord has uniform diameter, but in others, it shows enlargements called cervical and lumbar enlargements.