BIOS 252 structural and functional organization of the brain week4 Edapt
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BIOS 252
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BIOS 252
BIOS 252 structural and functional organization of the brain week4 Edapt
BIOS 252 structural and functional organization of the brain week4 Edapt
BIOS 252 structural and functional organization of the brain week4 Edapt
1 Structural and Functional Organization of the Brain The Brain - Introduction: In this section, we’re going to explore quite possibly the most astonishing organ that exists within the human body, the brain. Harbored inside your skull, the brain is a three- pound mass of tissue made up largely of water, fat and protein. If you were to hold this organ in your hands, it would feel as though you’re holding some soft cheese or butter. It has a rather lumpy appearance and appears to be a dull -grayish color. Needless to say, the brain is quite underwhelming structurally. Functionally however, the brain is perhaps the most advanced structure that exists within the known universe. It allows you to facilitate complexities such as decision making, perception, taking action, awareness, and just plain thinking. It integrates every bit of information that you are conscious of and even some information that you have no consciousness of whatsoever. It stores and relays information through vast networks of electrical wiring that are the axons found within the brain. Altogether, one human brain is estimated to hold as much information as “the entire digital content of today ’s world”, according to Nature Neuroscience. This is no ordinary feat especially when you consider all of the movies, music, and pictures that exists within the digital world. Q: Unlike the spinal cord, the outer portion of the brain is made up of matter, while the inner portion is made up of matter. A: Gray; white Q: All ventricles of the brain are paired, except for the fourth ventricle. A: False Brain Development: Let’s take a look at how the human brain comes into being. As an embryo begins to develop, the brain and the head are the two structures that start to take shape first. Human development essentially begins from the top down. 2 The brain begins as a cluster of cells that are dividing as the embryo is growing. A couple of weeks into embryological development, the cells move into a layered formation. One region of the outermost layer ultimately folds to form a tube known as the neural tube. The neural tube is what gives rise to the brain and spinal cord. The tube forms hollow fluid -filled cavities within the brain known as ventricles, as we will discuss later. It is important to recognize that th e brain is developed as these deep ventricle walls gives rise to outgrowths that ultimately form different parts of the brain. Two months into embryological development, these outgrowths or projections result in three primary vesicles 1. Forebrain (Prosenceph alon) 2. Midbrain (Mesencephalon) 3. Hindbrain (Rhombencephalon) As the brain continues to develop, these three primary vesicles give rise to five secondary vesicles which ultimately give rise to the principal parts of the brain. 1. Telencephalon → Cerebrum 2. Diencephalon →Thalamus, hypothalamus, epithalamus 3 3. mesencephalon →Midbrain 4. metencephalon →Pons, Cerebellum 5. Myelencephalon →Medulla Oblongata Q: Which adult structure(s) arises from the diencephalon? A: Thalamus, hypothalamus and retina Q: Which of the following structures is not considered a secondary vesicle? A: Prosencephalon General Anatomy of the Brain: The brain is housed in the cranial cavity and is surrounded by a bony structure known as the cranium. The cranium confers a level of protection to the brain. This is especially important because the brain has a very soft consistency, almost like that of soft cheese or butter. Directly deep to the cranium, the brain is surrounded by layers of connective tissue known as the meninges. The three layers differ in their durability and structural makeup. Listed in order from superficial to deep, the meningeal layers are: 4 1. Dura Mater 2. Arachnoid Mater 3. Pia Mater The dura layer in the brain consists of two separate layers known as the periosteal layer and the meningeal layer. These layers fused together except at points where they separate to create venous sinuses that serve as drainage points for the brain. Additionally, three extensions of the dura mater separate the different pats of the brain when they penetrate deep inside the brain. 1. Falx Cerebri : Separates the two hemispheres of the brain 2. Falx Cerebelli : Separates the two hemispheres of the cerebellum 3. Tentorium Cerebelli : Separates the cerebrum from the cerebellum When we look at the brain itself superficially, we see that it has a lumpy, heavily folded surface. The grooves are known as sulci when they are shallow, and fissures when they are deep. The ridges are known as gyri. Think of sulci and fissures as valleys and a gyri as hi lls on the surface of the brain. This arrangement of this folded pattern is unique in each person. The outer layer of the brain is made of gray matter . It is also referred to as the cortex. Deep to the cortex, the brain is made up of white matter . Recall that the difference between gray and white matter has to do with the presence of myelinated axons. Gray matter consists of axons that are unmyelinated, whereas white matter consists of myelinated axons. Recall that in the CNS, a bundle of axons carrying impulses from one point to another is known as a tract. Principle Parts of the Brain: Now, let us look at the principal parts of the brain. The brain is composed of four major regions:
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