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braintour - Topic 02: Neuroanatomy WELCOME TO THE PSY91...

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Topic 02: Neuroanatomy WELCOME TO THE PSY91 INTRODUCTORY TOUR OF THE BRAIN Please enjoy the tour Nowhere are the beauty and power of life processes better expressed than in the development of the human nervous system. The adult human brain is believed to consist of at least 100 to 200 billion neurons (nerve cells) and probably five to ten times as many glial cells . (Glia in Greek means glue.) Neurons function to transmit information , while glia have support functions (e.g., deliver raw material from vascular system to neurons, release growth factors, remove debris from injured cells, form myelin sheaths to help neuronal conductance). Together these elements make up a three pound mass of protoplasm which is unique on our world and in our solar system and, so far as we now know, in our galaxy. NEURONS The cell body contains the nucleus . Axons usually convey (outgoing) information from the cell body to other neurons. Dendrites usually convey (incoming) information from other cells to the cell body.
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The white matter in the brain and spinal cord is all axons. (It is white because of the wrapping of myelin , which is composed of glial cells.) The gray matter in the brain and spinal cord is all dendrites and cell bodies . (There is no myelin covering to these neuronal structures.) HOW DOES THE CENTRAL NERVOUS SYSTEM DEVELOP EMBRYOLOGICALLY? THE PRIMITIVE CELL LAYERS The emerging embryo is made up of three different types of tissue. Ectoderm includes all of the packaging elements of the organism i.e. skin, hair, nails and, interestingly enough, the nervous system. Mesoderm makes up the major structural components of the body including the great muscle masses, both the voluntary muscles, which underlie all of our work, actions and behavior, and the involuntary muscles which make up the walls of all of our organs such as heart and blood vessels, respiratory and gastrointestinal systems, and our bones. Finally the endoderm includes all of the cell systems, which line our organs and vessels. EARLY BRAIN DEVELOPMENT The inner cell mass originally differentiates into a layer of primitive (presumptive) ectoderm and an underlying and roughly parallel-lying layer of endoderm. In the area between these two cell layers becomes the primitive mesoderm. Their first task is to come together to form a long cylindrical structure. In doing this, they are recapitulating the earliest event in the transition from invertebrates to vertebrate forms, a transition that occurred at least six hundred million years ago. Our vertebral column is made up of 32 separate vertebrae , piled on each other to form our flexible backbone. Through the release of special chemicals, the overlying ectoderm is induced to divide more rapidly, forming a thickened mass called the neural plate . A crease or fold soon appears in this plate. The crease rapidly deepens and becomes known as the neural groove . The entire embryo is lengthening as this happens. The neural groove continues to deepen until its sides, the neural folds, arch
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braintour - Topic 02: Neuroanatomy WELCOME TO THE PSY91...

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