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Unformatted text preview: KIN 216 Chapter 12 Nervous System THE master control and communications center in the body Communication occurs via electrical signals Three overlapping functions Sensory receptors monitor changes Integration (processing and interpreting) Response (motor output) Basic Divisions of the Nervous System
CNS Brain Spinal Cord Basic Divisions of the Nervous System (2) Sensory (afferent) Carry signals TO brain/spinal cord Motor (efferent) Carry signals FROM brain/spinal cord Somatic Structures external to visceral cavity Visceral Organs 4 combinations: somatic sensory, somatic motor ("voluntary"), visceral sensory, visceral motor ("involuntary" autonomic nervous system) Proprioception is part of the somatic sensory system Nervous Tissue Neurons (cell body, dendrites, axons)
Cell body (aka perikaryon, soma) Contains one nucleus Group of cell bodies in CNS = nucleus Group of cell bodies in PNS = ganglia Metabolic center of neuron (contains organelles) Branched processes that extend from cytoplasm of cell body (also have organelles like soma) Receive stimuli and conduct impulses TO cell body Conduct impulses AWAY from cell body If myelinated or large, have increased electrical conduction speed Lengths vary; have axon terminals at end (bulbs) Is a cytoplasmic extension from cell body Dendrites Axons Nervous Tissue (2) Neurons cont'd. Synapses Junction that controls information transfer from one neuron to the next Presynaptic neuron conducts signal TOWARDS synapse Postsynaptic neuron conducts signal AWAY from synapse Synapse can be excitatoy or inhibitory Nervous Tissue (3) Neurons cont'd. Structural Multipolar Most of body's neurons many dendrites and an axon (motor neurons, most interneurons) Bipolar Processes extend from two sides of body (rare, sensory) Unipolar One process that divides like a "T" (sensory neurons) Functional Sensory (afferent) neurons: carry signal TO CNS Motor (efferent) neurons: carry signal AWAY from CNS Interneurons (association neurons): are between sensory and motor neurons located ONLY in CNS Nervous Tissue (4) Neuroglia (support cells, aka glial cells) Have central cell body and branching processes, are smaller than neurons Outnumber neurons 10-1 in CNS Consist of half of brain's mass Can divide throughout life In general they provide a scaffold of support for neurons and cover non-synaptic parts (to insulate and keep them from interfering with each other) CNS Astrocytes, microglia, ependymal cells, oligodendrocytes PNS Satellite cells and Schwann cells Nervous Tissue (5) Types of neuroglia CNS Astrocytes (Greek aster = star) Most abundant neuroglia Key component of blood brain barrier Regulate passage of molecules from blood to brain Only allow small molecules through to brain Microglia Smallest and least abundant neuroglia Phagocytes, thorny-looking Ependymal cells Form simple epithelial layer that lines central cavity of brain and spinal cord Oligodendrocytes Produce myelin sheath around nerve cell axons Fewer branches than astrocytes Nervous Tissue (6) Types of neuroglia PNS Satellite cells Surround cell bodies in ganglia Schwann cells (neurolemmocytes) Surround all axons in PNS Produce myelin sheath (gaps = nodes of Ranvier) Nerves
Collection (bundle) of neurons outside CNS (in PNS) Naked eye can see a nerve, but not a neuron Composed of many axons Nerves often contain both sensory and motor neurons (mixed nerves) Some are sensory or motor only though (cranial nerves) Neurons are held together by CT Endoneurium = surrounds each axon (loose CT) Perineurium = surrounds bundle of axons (fascicle), Epineurium = surrounds entire nerve (bunch of fascicles) Basic Organization of the Nervous System Reflex arcs Chains of neurons that create reflexes Reflex = rapid, automatic, motor response to a stimulus Unlearned and involuntary Somatic or visceral 5 components:
Receptor: site where stimulus acts Sensory neuron: transmits signal to CNS Integration center: one or more synapses Motor neuron: conducts impulse from integration center Effector: muscle or gland that responds Basic Organization of the Nervous System (2) Reflex arcs cont'd. Monosynaptic One synapse is involved Fastest of all reflexes Classic example is knee jerk Polysynaptic One or more interneurons are part of reflex pathway Most contain one interneuron (are 3-neuron reflexes) Gray and White Matter (CNS) Gray matter = cell bodies Is H-shaped in spinal cord (dorsal half has bodies of interneurons and ventral half has bodies of motor neurons) White matter = axons (often myelinated) Tracts = bundles of axons Disorder of the Nervous System Multiple sclerosis (MS) Most common neural disability in young adults Progressive, destroys patches of myelin Cause is not well understood autoimmune ...
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- Spring '08