Functions of the Nervous System

Functions of the Nervous System 1. Sensory Input - gathering information ● To monitor changes within and outside the body (changes=stimuli). 2. Integration - Analyzing and interpreting sensory input to determine if a response is necessary. 3. Motor Output - A response that makes muscles or glands work based on processed stimuli. Structural Classification System Neuroglia vs. Neurons Feature Neuroglia (Glial Cells) Neurons Function Support, nourish, and protect neurons; some help with signal transmission. Send signals for communication in the nervous system. Structure Do not have axons or dendrites; smaller cells overall. Contain a cell body, axon, and dendrites to conduct electrical impulses. Electrical Activity Do not generate electrical impulses or action potentials. Capable of generating action potential for signalling. Regenerative Ability Can regenerate and divide, especially after injury. Limited regenerative ability, especially in the CNS. Number Outnumber neurons (10:1 ratio). Fewer than glial cells Myelination Some glial cells (e.g., oligodendrocyte s, Schwann cells) form the myelin sheath around neurons Axons of neurons are myelinated by glial cells for faster transmission. of the Nervous ● Central Nervous System (CNS) ○ Brain ○ Spinal Cord ● Peripheral Nervous System (PNS) ○ All parts of the nervous system outside the CNS Functional Classification of the Peripheral Nervous System ● Sensory (afferent) Division ○ Nerve fibers that carry information to the central nervous system. ● Motor (efferent) Division ○ Nerve fibers that carry impulses away from the central nervous system ○ TWO SUBDIVISIONS: ■ Somatic Nervous System = voluntary ■ Autonomic Nervous System = involuntary Nervous Tissue: Support Cells (Neuroglia or Glia) ● Astrocytes ○ most abundant and versatile neuroglia, starshaped cells ○ from barrier between capillaries and neurons ○ control the chemical environment of the brain (CNS) ● Microglia (CNS) ○ Spider-like phagocytes ○ Dispose of debris ● Ependymal Cells (CNS) ○ Line cavities of the brain and spinal cord ○ Circulate cerebrospinal fluid ● Oligodendrocytes (CNS) ○ produce myelin sheath around CNS nerve fibers Support Cells of the PNS ● Satellite cells ○ protect neuron cell bodies ● Schwann cells ○ form myelin sheath in the peripheral nervous system Nervous Tissue: Neurons ● Neurons = nerve cells ○ cells specialized to transmit messages ○ Major regions of neurons ■ Cell Body - nucleus and metabolic center of the cell ■ Processes - fibers that extend from the cell body (dendrites and axon Neuron Anatomy How Neurons Function (Physiology) ● Cell Body ○ Nucleus ○ Large Nucleolus ● Extensions outside the Cell Body ○ Dendrites - conduct impulses toward the cell body. ○ Axons - conduct impulses away from the cell body (only1!) Axons and Nerve Impulses ● ● Axons end in axonal terminals Axonal terminals contain vesicles with neurotransmitters ● Axonal terminals are separated from the next neuron by a gap ○ synaptic Cleft - gap between adjacent neurons ○ Synapse - junction between nerves Nerve Fiber Coverings ● ● Schwann Cells - produce myelin sheaths in jellyroll like fashion Nodes of Ranvier - gaps in myelin sheath along the axon Application ● ● ● In multiple Sclerosis the myelin sheath is destroyed. The myelin sheath hardens to a tissue called sclerosis. This is considered an autoimmune disease. Neuron Cell Body Location ● Most are found in the CNS ○ Gray Matter - cell bodies and unmyelinated fibers ○ Nuclei - clusters of cell bodies within the white matter of the CNS ● Ganglia - collections of cell bodies outside the CNS Functional Classification of Neurons ● Sensory (afferent) neurons ○ carry impulses from the sensory receptors cutaneous sense organs ○ Proprioceptors - detect stretch or tension ● Interneurons (association neurons) ○ found in neutral pathways in the central nervous system ○ connect sensory and motor neurons ● Motor (efferent) neurons ○ carry impulses from the CNS Structural Classification of Neurons ● ● ● Multipolar Neurons - many extensions from the cell body Bipolar Neurons - one axon and one dendrite Unipolar Neurons - have a short single process leaving the cell body ● ● ● Irritability - ability to respond to a stimuli Conductivity - ability to transmit an impulse The plasma membrane at rest is polarized ○ Fewer positive ions are inside the cell than outside the cell