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BSCI201 Final Exam Study Guide- Dr. Opoku Spring 2014THE NERVOUS SYSTEM-2 divisions of the NS1. Central Nervous System (CNS)- consists of the brain and the spinal cord; located in the dorsal body cavity surrounded by meninges2. Peripheral Nervous System (PNS)- consists of the all neural structures outside of the CNS including the cranial nerves, spinal nerves and sensory receptorsComposition of Nervous Tissue-The NS is composed mainly of nervous tissue; connective tissue and blood vessels are also present-Nervous tissue is composed of 2 types of cells: neurons and supporting cells- Neurons- nerve cells that are conducting cells- Supporting cells- non-conducting cellsStructure of a Neuron-3 regions of a neuron: cell body + 2 types of process1. Cell body= Soma= Perikaryona. Contains the nucleus and all other cytoplasmic organelles EXCEPT CENTRIOLES (neurons are AMITOTIC)b. Contains well-developed rough ER called Nissl Body or Chromatophilic substancec. Contains intermediate filaments called neurofilamentsd. Biosynthetic region of a neuron2. Dendritesa. Tapering processes that act as the receptive regions of a neuronb. Receive and convey electrical signals toward the cell body; generate graded potentials that dissipate over a distance toward the cell bodyc. At least one per neuron3. Axona. A single process extending from the cell body (each neuron can only have one axon)b. Generates and transmits action potentials AWAY from the cell body= conductingregion of a neuron (only region that can generate/transmit action potentials, results in the neurotransmitters)c. Branches at the end into telodendria which end in bulbous ends called axon terminals=synaptic knobs= buttonsClassification of Neurons-2 types: Structural and Functional classification1. Structural classification of neurons: 3 types based on number of processes extending fromcell bodya. Multipolar neuron- has at least 3 processes; one axons and at least 2 dendrites’ most abundant neuron in the human bodyb. Bipolar neuron- has 2 processes; one axon and one dendrite; sensory pathwaysc. Pseudounipolar neuron- has one short process extending from the cell body that bifurcates into a central process and a peripheral process (not considered dendrites or axons); rare in human bodyi. The two processes have a uniform diameter, myelinated, transmission of action potentials toward and away cell body2. Functional classification of neurons: 3 types based on the direction of impulse, traveling axon potentials, transmissionsa. Motor (efferent) neuron- transmits impulses AWAY from the CNS to effector organs= glands, organsb. Sensory (afferent) neuron- transmits impulses from sensory receptors TOWARD the CNSc. Association (interneurons) neurons- located in the CNS between sensory neurons and the motor neurons; most of the neurons (99%) in the body are association neurons; hence, the association neurons are multipolar neuronsDefinitions-Tracts= a bundle of axons in the CNS-Nerve= a bundle of axons in the PNS-Nucleus= a cluster of neuron cell bodies in the CNS-Ganglion= a cluster of neuron cell bodies in the PNSStructure of a Nerve or Tract-The plasma membrane of an axon is called an axolemma-Each axon is wrapped in a delicate connective tissue membrane called endoneurium-A bundle of endoneurium-covered axons is called a fascicle-Each fascicle is covered by the coarse connective tissue membrane called the perineurium-A bundle of perineurium-covered fascicles form the nerve or a tract which is covered in a tough connective tissue membrane called the epineuriumSupporting Cells (6)-Supporting cells= Neuroglia- CNS has 4 types of supporting cellso Astrocytes Most abundant  Numerous extensions that wrap around neurons Involved in forming the blood-brain barrier, a selective barrier that regulate the chemical environment of the brain Regulate brain function; NO direct contact between the blood and the neurons in the braino Microglia Since there is no direct contact between the blood and the neurons in the brain, the immune cells (reside in blood) do not have access to these neurons to engulf and destroy pathogens and cell debris Microglia act as macrophages to engulf/destroy pathogens and cell debriso Ependymal cells Ciliated columnar cells that line the ventricles-cavities in the brain that contain cerebrospinal fluid (CSF), which is filtered and drained continuously Provide nutrients/O2 to neuronso Oligodendrocytes Their extensions myelinate axons of neurons in the CNS; each can myelinate segments of several axons, which means each axon is myelinated by cellular extensions of several oligodendrocytes- PNS has 2 types of supporting cellso Schwann cells= neurolemmocytes Myelinate axons of neurons in the PNS; each Schwann cell wraps around a segment of the axon to form the myelin sheath (whitish, fatty protein) Analogous to oligodendrocytes in the CNSo Satellite cells Surround cell bodies of neurons and control their chemical environmentMyelination of Axons-Myelination of axons in the CNS: Oligodendrocytes- Axons in the CNS are myelinated by extensions from the oligodendrocytes; hence, neurilemma is absent-Myelination of axons in PNS: Schwann cells- Each Schwann cell wraps around a segment of an exon (external to the axolemma)- Schwann cell squeezes around the segment of axon wrapping concentric rings of its plasma membrane called myelin sheath around the axono Function of myelin sheath is: protection, electrical insulation, and increase rate of impulse transmission- The cytoplasm and the nucleus of the Schwann cell squeezed outside the myelin sheath isthe neurilemma- The spaces between adjacent myelin sheaths are called Nodes of RanvierSevered axons in the PNS and CNS-Severed axons in the CNS fail to regenerate because:- The microglia poorly clean up area of damage-debridement is not complete- No neurilemma to form a regeneration tube to guide growth of severed axon- Presence of growth-inhibiting proteins in the CNS inhibit regeneration of severed axon-Severed axons in the PNS can regenerate because:- Cells of the immune system clean up the damaged area of cell debris (debridement), which sets the stage for regeneration- The neurilemma of the Schwann cell forms a regeneration tube that guides regeneration of the severed axonNeurophysiology- Generation of Action PotentialsA. Depolarization: entry of Na+ (sodium influx) into axoplasm (cytoplasm of axon) Makes membrane potential less negative Threshold


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UMD BSCI 201 - Final Exam Study Guide

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