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Chapter 2

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Deltcho Valtchanov

Chapter 2: Structure and Functions of Cells of the Nervous System - Information, in the form of light, sound waves, odours, tastes, or contact with objects is gathered from the environment by sensory neurons - Movements are accomplished by the contraction of muscles, which are controlled by motor neurons - Interneurons: neurons that lie entirely within the central nervous system o Local interneurons: form circuits with nearby neurons and analyze small pieces of information o Relay interneurons: connect circuits of local interneurons in one region of the brain with those in other regions - Central nervous system (CNS): brain and spinal column - Peripheral nervous system (PNS): part of the nervous system outside the brain the spinal cord Cells of the Nervous System Neurons: - Soma: contains the nucleus and much of the machinery that provides for the life processes of the cell - Dendrites: receives information from terminal buttons of other neurons o Synapse is the space between two neurons - Axon: conveys information from one end of cell body to the terminal buttons o Message is a brief electrical/chemical event called action potential - Terminal buttons: the bud at the end of a branch of an axon, forms synapses with another neuron, sends information to that neuron o Secrete a neurotransmitter - Multipolar neuron: a neuron with one axon and many dendrites attached to its soma - Bipolar neuron: a neuron with one axon and one dendrite attached to its soma o Usually sensory - Unipolar neuron: neuron with one axon attached to its soma, the axon divides, with one branch receiving sensory information and the other sending the information into the central nervous system o Transmit sensory information from the environment to the CNS, detect touch, temperature changes, and other sensory events that affect the skin, other detect events in our joints, muscles, and internal organs Internal Structure - Fig 2.5 pg 33 - Membrane: the boundary of the cell, consists of lipid molecules o Various proteins are embedded in the membrane - Nucleus: enclosed by the nuclear membrane, contains nucleolus and chromosomes o Nucleolus: responsible for production of ribosomes (protein synthesis??) o Chromosomes: contain DNA  Genes cause production of messenger ribonucleic acid (mRNA), which leave the nuclear membrane and attached to ribosomes - Enzymes: direct the chemical processes of a cell by controlling chemical reactions - Number of genes isn’t correlated with the complexity of the organism o Only 1.5% of human genome encodes for proteins - Cytoplasm: viscous semiliquid substance contained in the interior of a cell - Mitochondria: extracts energy from nutrients o Makes adenosine triphosphate (ATP) that cells use as their immediate source of energy - Endoplasmic reticulum: storage reservoir and a channel for transporting chemicals through the cytoplasm o Rough endoplasmic reticulum contains ribosomes, transported our of the cell or used in the membrane o Smooth endoplasmic reticulum provides channels for the segregation of molecules involved in various cellular processes - Golgi apparatus: Supporting Cells Glia (glial cells) - The supporting cells of the CNS that glue the CNS together - Surround and hold neurons in place, controls their supply of nutrients, insulate neurons and remove the carcasses of neurons killed by disease or injury - Three most important types of glial cells: - Astrocyte: provide physical support to neurons and clean up debris within brain; regulates chemical composition of fluid surrounding neurons; provide nourishment to neurons o Receive glucose from capillaries and break it down to lactate, and release it into the fluid surrounding neurons, neurons use it for energy o Phagocytosis: when astrocytes find dead neurons, they will push themselves against it and engult and digest it - Oligodendrocytes: provides support to axons and produces myelin sheath o Node of Ranvier: the unmyelinated sections of the axon - Microglia: engulf and break down dead and dying neurons; protect the brain from invading microorganisms Schwann Cells - Perform the same functions in the PNS that oligodendrocytes do in the CNS (myelinate axons) o Only one Schwann cell per segment of the myelin sheath, fig 2.11 pg 39 - If an axon dies, the stump of each severed axon grows sprouts, which spread in all directions; Schwann cells rearrange in a series of cylinders that help the axons re-grow; if these sprouts grow through the cylinder, they could re-establish previous connections with the muscles and sense organs o Doesn’t happen in CNS because astrocytes make scar tissue that axons can’t pass o Astrocytes also produce chemical signal that instructs regenerating axons to stop elongating and start sprouting terminal buttons - Oligodendrocyes and Schwann cells produce myelin protein with different chemical compositions The Blood-Brain Barrier - If blue dye in injected into an animal’s bloodstream, all tissues except the brain and spinal cord
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