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MEDICAL-SURGICAL NURSING By: Anthony T. Villegas R.N. Overview of structures and functions: NERVOUS SYSTEM The functional unit of the nervous system is the nerve cells or neurons The nervous system is composed of the ff: Central Nervous System Brain Spinal Cord – serves as a connecting link between the brain & the periphery. Peripheral Nervous System Cranial Nerves –12 pairs; carry impulses to & from the brain. Spinal Nerves – 31 pairs; carry impulses to & from spinal cord. Autonomic Nervous System subdivision of the PNS that automatically controls body function such as breathing & heart beat. Special senses of vision and hearing are also covered in this section Sympathetic nervous system – generally accelerate some body functions in response to stress. Parasympathetic nervous system – controls normal body functioning. CELLS A. NEURONS Primary component of nervous system Composed of cell body (gray matter) , axon, and dendrites Basic cells for nerve impulse and conduction. Axon Elongated process or fiber extending from the cell body Transmits impulses (messages) away from the cell body to dendrites or directly to the cell bodies of other neurons Neurons usually has only one axon Dendrites Short, blanching fibers that receives impulses and conducts them toward the nerve cell body. Neurons may have many dendrites. Synapse Junction between neurons where an impulse is transmitted Neurotransmitter Chemical agent (ex. Acetylcholine, norepinephrine) involved in the transmission of impulse across synapse. Myelin Sheath A wrapping of myelin (whitish, fatty material) that protects and insulates nerve fibers and enhances the speed of impulse conduction. o Both axons and dendrites may or may not have a myelin sheath (myelinated/unmyelinated) o Most axons leaving the CNS are heavily myelinated by schwann cells Functional Classification 1. Afferent (sensory) neurons Transmit impulses from peripheral receptors to the CNS 2. Efferent (motor) neurons Conduct impulses from CNS to muscle and glands 3. Internuncial neurons (interneurons) Connecting links between afferent and efferent neurons Properties 1. Excitability – ability of neuron to be affected by changes in external environment. 2. Conductility – ability of neuron to transmit a wave of excitetation from one cell to another. 3. Permanent Cell – once destroyed not capable of regeneration. TYPES OF CELLS BASED ON REGENERATIVE CAPACITY 1. Labile Capable of regeneration. Epidermal cells, GIT cells, GUT cells, cells of lungs. 2. Stable Capable of regeneration with limited time, survival period. Kidney cells, Liver cells, Salivary cells, pancreas. 3. Permanent Not capable of regeneration.
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