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Chapter 29

Chapter 29 Neural Control.docx

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BIOL 1001

Chapter 29 Neural Control Neurons • The basic units of communication in nearly all nervous systems • Monitor info in and around body, issue commands for responsive actions • They are excitable cells – undergo a change in charge across the plasma membrane 3 Classes: 1. Sensory Neurons: converting external stimuli from the environment into internal stimuli 2. Interneurons (relay neurons): connects afferent neurons and efferent neurons in neural pathways 3. Motor Neurons: project their axons outside the CNS and directly or indirectly control muscles *Lou Gehrigs Disease (ALS) is a motor neuron disease Two Types: 1. Afferent Neurons: carry nerve impulses from receptors or sense organs to the central nervous system 2. Efferent Neurons: motor or effector neurons, carry nerve impulses away from the central nervous system to muscles or glands Neuroglia (Glial Cells) • Make up more than half the volume of the vertebrate nervous system, half of brain tissue • A variety of cells that metabolically assist, structurally support, and protect the neurons • Cancers of the brain usually involve glial cells Examples of glial cells 1. Astrocytes: - Largest and most numerous of the glial cells in the brain and spinal cord - Contribute to the blood-brain barrier, - Regulate the chemical environment around cells, release regulatory sustances that influence nerve cells - Maintenance of extracellular ion balance - Respond to injury, have a role in the repair and scarring process of the brain and spinal cord - Provide nutrients 2. Microglia: - Macrophages derived from bone marrow - Scavengers, engulfing dead cells and other debris - - In Alzheimer’s, they are found associated with dying nerve cells and B-amyloid plaques 3. Oligodendrocytes: - Wrap axons with myelin sheaths in CNS which improves the speed and reliability of impulse conduction - Main function is the myelination of axons exclusively to the central nervous system, help insulate neurons - Produce substances that inhibit the regeneration of axons in the adult CNS Synapse • The junction across which a nerve impulse passes from an axon terminal to the dendrite of a second neuron, to a muscle cell, or to a gland cell • When a neuron is excited, calcium is released from small vesicles at the axon terminal, and then neurotransmitters are released from vesicles into the synapse • Neurotransmitter release occurs by exocytosis • Acetylcholine and dopamine are neurotransmitters in the CNS Resting Potential (of a neuron) • Charge difference across the plasma membrane of a neuron • Fluid just outside cell is more positive charged than fluid inside • Resting potential of plasma membrane of a neuron is -70 millivolts • This membrane potential is true for all somatic cells in the body Sodium-Potassium Pump • A plasma membrane pump that uses ATP to transport sodium out and potassium in across
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