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The Nervous System: Introduction Transmission of signals for communication and for coordination of body systems 1 Nervous System Functions Sensory input The nervous system has three overlapping functions Gathering of sensory input Integration or interpretation of sensory input Causation of a response or motor output 2 Introduction Sensory input The nervous system has millions of sensory receptors to monitor both internal and external change Integration It processes and interprets the sensory input and makes decisions about what should be done at each moment Motor output Causes a response by activating effector organs (muscles and glands) 3 NERVOUS SYSTEM CNS Brain PNS Spinal Cord Nerves -Cranial nerves - Spinal nerves Ganglia MOTOR Efferent - From CNS Somatic-Motor ANS Parasympathetic SENSORY Afferent - To CNS Visceral Somatic-Sensory Sympathetic 4 Nervous System Two types of cells in nervous system: Neurons – motor, sensory, association Neuroglia – 6 types CNS (Central Nervous System): Brain – cerebrum, diencephalon, brain stem, cerebellum Spinal Cord – horns, columns; ascending and descending tracts PNS (Peripheral Nervous System): Cranial nerves – 12 pairs Spinal nerves – 31 pairs 5 Neurons Functional unit of nervous system Have capacity to produce action potentials electrical excitability/electrical impulses 6 Neuron: Parts and Functions of Ranvier 7 Classification of Neurons Neurons can be classified functionally or structurally Functional classification is usually used to describe how the neurons work within us – see Table 8-1, p156 Structural classification is based on the number of processes that extend from the cell body. 8 1. 2. 3. 9 Structural Classification of Neurons Based on number of processes found on cell body multipolar = several dendrites & one axon most common cell type bipolar neurons = one main dendrite & one axon found in retina, inner ear & olfactory unipolar neurons = one process only(develops from a bipolar) are always sensory neurons 10 Blood-Brain Barrier The blood-brain barrier is selective and incomplete, not an absolute barrier Nutrients, such as glucose, essential amino acids, and some electrolytes, move passively by facilitated diffusion through the endothelial cell membranes Bloodborne metabolic wastes, such as urea and creatinine as well as proteins, certain toxins, and most drugs, are prevented from entering brain tissue 11 The Nervous System: Nerve Impulses Action potentials = AP Neuronal electrical activity 12 Electrical Activity of Axons Functional characteristics of neurons: Excitability/irritability: Ability to respond to stimuli by producing electrical impulses. Conductivity: Ability to transmit electrical impulses 13 Ion Channels Proteins within the membrane can open and close, thus allowing ions to travel in or out. K+ channels allow outward flow Na+, inward 14 The Nervous System: The Synapse Neurotransmitters TRANSMISSION across a Synapse 15 Transmission of Nerve Impulses Between Neurons Synapse: junction between neurons, muscles, glands Signal is carried by neurotransmittors that diffuse across the synaptic cleft. 16 Fig. 12.14 17 Transmission of Nerve Impulses Between Neurons Neurotransmitters can be: Stimulatory: initiates action potential eg. Acetylcholine Inhibitory: prevents action potential eg. GABA, Dopamine 18 Neurotransmitters by function Excitatory – generally cause increase excitability (depolarization) ACH = Acetylcholine NE = Norepinephrine EPI = Epinephrine DA = Dopamine Inhibitory – generally cause decrease excitability (hyperpolarization) GABA = Gamma-aminobutyric acid 5-HT = Serotonin Endorphins, enkephalins, dynorphins 19 Nervous System and Aging: Page 178 20 Clinical Terms: Neurology Rabies Guillain-Barre 21