Nerve Cells - Neurons and Glia PDF

The Anatomy of the nervous system Science Explains What Happens To Your Soul After Death A few things fit the bill of fascinating, thought-provoking, and frightening. Death is one such thing. “What happens after we die?” When you stop and think it, you quickly realize t...

The Anatomy of the nervous system Science Explains What Happens To Your Soul After Death A few things fit the bill of fascinating, thought-provoking, and frightening. Death is one such thing. “What happens after we die?” When you stop and think it, you quickly realize there are only two possible answers: something or nothing.  Of course, religion adds some nuance to the abovementioned question, but that’s pretty much it. Either something happens, or nothing happens. Either we are matter to be disposed of and recycled – or we aren’t. “I believe that consciousness, or its immediate precursor proto-consciousness, has been in the universe all along, perhaps from the big bang.” ~ Dr. Stuart Hameroff, MD What is consciousness? The word ‘consciousness’ is defined by the Oxford English Dictionary as: a state of being awake and aware of one’s surroundings. the awareness of perception of something by a person. the fact of awareness by the mind of itself and the world.  Predictably, consciousness – like death – is heavily debated. Some believe that consciousness is the direct result of brain activity. Others think that outside forces, e.g., the ‘Universe,’ ‘God’ – and internal elements, e.g., the ‘Spirit,’ ‘Lifeforce,’ ‘Mind,’ etc., contributes to our state of being.  Death is not the end; it is, in fact, the beginning. We do not stop learning or evolving even after death. And after some time spent in the spirit world, we return to earth in a new body, to continue our journey of learning and growing spiritually. - BY JAIME T. LICAUCO JULY 12, 2016  In order to understand what the brain does, it is first necessary to understand what it is—to know the names and locations of its major parts and how they are connected to one another. No human life is truly independent People talk about growing into adulthood and becoming independent. How often do you hunt your own meat and cook it on a fire you made from scratch? Do you grow your own vegetables?  No doubt you think of yourself as an individual. You don’t think of your mental experience as being composed of pieces... but it is. Your experiences depend on the activity of a huge number of separate but interconnected cells. To understand the nervous system, the place to begin is to examine the cells that compose it  The nervous system and the endocrine system control the functions of the body. The nervous system is composed basically of specialized cells, whose function is to receive sensory stimuli and to transmit them to effector organs,whether muscular or glandular.  The sensory stimuli that arise either outside or inside the body are correlated within the nervous system, and the efferent impulses are coordinated so that the effector organs work harmoniously together for the well-being of the individual. In addition, the nervous system of higher species can store sensory information received during past experiences. This information, when appropriate,is integrated with other nervous impulses and channeled into the common efferent pathway. The central nervous system (CNS) is the division of the nervous system located within the skull and spine, and the peripheral nervous system (PNS) is the division located outside the skull and spine. Nervous system Central Nervous System (CNS) Brain and Spinal Cord The central nervous system is composed of two divisions: the brain and the spinal cord. The brain is the part of the CNS located in the skull; the spinal cord is the part located in the spine.  Both the brain and spinal cord are covered with a system of membranes, called meninges, and are suspended in the cerebrospinal fluid; they are further protected by the bones of the skull and the vertebral column.  The central nervous system is composed of large numbers of excitable nerve cells and their processes, called neurons, which are supported by specialized tissue called neuroglia. The long processes of a nerve cell are called axons or nerve fibers. The central nervous system is the body’s processing centre. The brain controls most of the functions of the body, including awareness, movement, thinking, speech, and the 5 senses of seeing, hearing, feeling, tasting and smelling. The spinal cord is an extension of the brain. It carries messages to and from the brain via the network of peripheral nerves connected to it. Nerves also connect the spinal cord to a part of the brain called the brainstem.  In the peripheral nervous system, the cranial and spinal nerves, which consist of bundles of nerve fibers or axons, conduct information to and from the central nervous system. Although the nerves are surrounded by fibrous sheaths as they run to different parts of the body, they a relatively unprotected and are commonly damaged by trauma.  Peripheral Nervous System (PNS) Connects brain and spinal cord to the rest of the body (cranial, spinal, and autonomic nerves) Somatic Nervous System - is the part of the PNS that interacts with the external environment. (It is composed of afferent nerves that carry sensory signals from the skin, skeletal muscles, joints, eyes, ears, and so on, to the central nervous system and efferent nerves that carry motor signals from the central nervous system to the skeletal muscles.)  Autonomic Nervous System - is the part of the peripheral nervous system that regulates the body’s internal environment. The autonomic nervous system controls specific body processes, such as blood circulation, digestion, breathing, urination, heartbeat, etc. The autonomic nervous system is named so because it works autonomously, i.e., without a person’s conscious effort. The primary function of the autonomic nervous system is homeostasis. Apart from maintaining the body’s internal environment, it is also involved in controlling and maintaining body functions like:  Digestion Metabolism Urination Defecation Blood pressure Sexual response Body temperature Heartbeat Breathing rate Fluid balance  The autonomic nervous system has two kinds of efferent nerves: sympathetic nerves and parasympathetic nerves. The sympathetic nerves are autonomic motor nerves that project from the CNS in the lumbar (small of the back) and thoracic (chest area) regions of the spinal cord. The parasympathetic nerves are those autonomic motor nerves that project from the brain and sacral (lower back) region of the spinal cord  Parasympathetic Autonomic Nervous System: It is located in between the spinal cord and the medulla. It primarily stimulates the body’s “rest and digest” and “feed and breed” responses. The parasympathetic nervous system inhibits the body from overworking and restores the body to a calm and composed state.  Sympathetic Autonomic Nervous System: It is the part of the autonomic nervous system located near the thoracic and lumbar regions in the spinal cord. Its primary function is to stimulate the body’s fight-or-flight response. It does this by regulating the heart rate, rate of respiration, pupillary response and more. prepares the body for the “fight or flight” response during any potential danger. Two types of nerve cells Neurons Receive information and convey the information to other cells. Glia Enhance and modify the activity of neurons in many ways. Neurons Neurons are separated from each other. There are small gaps between the tips of two neuron fibers. Santiago Ramon y Cajal found out about this in late 1800s by staining cells from infant brains using Golgi’s method (staining nerve cells with silver salts) Snell, R. S. (2010). Clinical Neuroanatomy 7th Edition. LWW. Santiago Ramón y Cajal, a Pioneer of Neuroscience Cajal wanted to become an artist, but his father insisted that he study medicine as a safer way to make a living He managed to combine the two fields, becoming an outstanding anatomical researcher and illustrator. His detailed drawings of the nervous system are still considered definitive today. Cajal’s research demonstrated that nerve cells remain separate instead of merging into one another. In spite of Cajal’s evidence, which had persuaded almost everyone else, Golgi clung to the theory that all nerve cells merge directly into one another.  Philosophically, we see the appeal of the old idea that neurons merge. We describe our experience as undivided, not the sum of separate parts, so it seemed right that all the cells in the brain might be joined together as one unit. How the separate cells combine their influences is a complex and still mysterious process.  Neurons are some of Neurons the longest-lived cells in the body. Cells in the cerebral cortex has the same life span as you currently have. Neurons vary in size, shape, and function. The shape determines its connection to other cells which Snell, R. S. (2010). Clinical Neuroanatomy 7th Edition. LWW. determines its function. Neurons Neurons are irreplaceable. Most neurons are amitotic (cannot divide). Neurons have huge appetite. They need constant and abundant glucose and oxygen. Snell, R. S. (2010). Clinical Neuroanatomy 7th Edition. LWW. The Structures of an Animal Cell Neurons have much in common with the rest of the body’s cells. The surface of a cell is its membrane (or plasma membrane), a structure that separates the inside of the cell from the outside environment.  Except for mammalian red blood cells, all animal cells have a nucleus, the structure that contains the chromosomes. A mitochondrion (plural: mitochondria) is the structure that performs metabolic activities, providing the energy that the cell uses for all activities. Mitochondria have genes separate from those in the nucleus of a cell, and mitochondria differ from one another genetically. People with overactive mitochondria tend to burn their fuel rapidly and overheat, even in a cool environment. People whose mitochondria are less active than normal are predisposed to depression and pains. Mutated mitochondrial genes are a possible cause of autism (Aoki & Cortese, 2016). Parts of neurons Neurons are cells that are specialized for the reception, conduction, and transmission of electrochemical signals. They come in an incredible variety of shapes and sizes. Unlike most other body cells, neurons have long branching extensions. All neurons include a soma (cell body), and most also have dendrites, an axon, and presynaptic terminals. The tiniest neurons lack axons, and some lack well-defined dendrites.  Neuron is the name given to the nerve cell and all its processes. Neurons are excitable cells that are specialized for the reception of stimuli and the conduction of the nerve impulse.  They vary considerably in size and shape, but each possesses a cell body from whose surface project one or more processes called neurites. Those neurites responsible for receiving information and conducting it toward the cell body are called dendrites. The single long tubular neurite that conducts impulses away from the cell body is called the axon. The dendrites and axons are often referred to as nerve fiber projects. Parts of neurons  Parts of neurons Cell Body or Soma Dendrites Axons Neurons are found in the brain and spinal cord and in ganglia. Unlike most other cells in the body, normal neurons in the mature individual do not undergo division and replication. Cell body or soma Metabolic center of neurons Contains the following o Nucleus – contains chromosomes o Ribosomes – synthesize new protein molecules o Mitochondria – performs metabolic activities/energy provider. Contains genes separate from nucleus Axon Hillock – connects soma to axon Range of diameter: 0.005 mm to 0.1 mm Dendrites Receives nerve impulses DRT – dendrite=receive impulse=toward cell body Always naked/not myelinated Shorter, mostly microns and seldom more than a millimeter o Synaptic Receptors – lines the dendrite’s surface, receives information from other neurons o Dendric Spines – increase surface of dendrites. axons Transport impulses towards neurons/organs/muscle ATA – axons=transport impulse=away from cell body Myelinated or with myelin sheath Longer, Microns to meters o Myelin Sheath o Nodes of Ranvier o Presynaptic Terminal axons Myelin Sheath – insulating material Nodes of Ranvier – interruptions between myelin sheaths Presynaptic Terminal / Axon Terminal Bulb / end bulb / bouton – points where axon releases chemicals that cross through the junction from one neuron to another cell. Two types of nerve cells Neurons Receive information and convey the information to other cells. Glia Enhance and modify the activity of neurons in many ways.