APPH3753Fundnervoussytem - Fundamentals of the Nervous...

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Unformatted text preview: Fundamentals of the Nervous System Three functions of the nervous system 1- sensory (afferent) input: sensory receptors that work with the NS. 2- integration: processing and interpreting of data from the sensory input 3. motor (efferent) output: a response initiated by integration. Organization: CNS: (central nervous system) - brain - spinal cord (PNS) Peripheral Nervous System - cranial nerves (12 pairs) - spinal nerves (31 pairs) Communication lines between CNS and the rest of body An Overview of the Nervous System Central Nervous System (CNS) Responsible for integrating, processing, and coordinating sensory input Responsible for integrating, processing, and coordinating motor output It is the seat of intelligence, memory, learning, and emotion An Overview of the Nervous System Peripheral Nervous System (PNS) Provides sensory information to the CNS and carries motor commands away from the CNS Can be divided into: Afferent division Brings sensory information to the CNS Efferent division Carries motor commands to muscles and glands Divisions: - Sensory (afferent) division Somatic (skin, muscle, joints) and visceral (organs) sensory neurons Conducts impulses from receptors to the CNS - Motor (efferent) division Motor neurons Conducts impulses from the CNS to effectors (muscles and glands) Motor Divisions: Somatic Nervous System - Voluntary - Conducts impulses from CNS to skeletal muscles Autonomic Nervous System - Involuntary - Conducts impulses from CNS to cardiac muscles, smooth muscles, and glands. - Divisions: - Sympathetic - Parasympathetic CENTRAL NERVOUS SYSTEM (brain and spinal cord) Information processing Sensory information within afferent division Motor commands within efferent division PERIPHERAL NERVOUS SYSTEM includes Somatic nervous system Autonomic nervous system Parasympathetic division Special sensory receptors provide sensations of smell, taste, vision, balance, and hearing RECEPTORS Visceral sensory receptors monitor internal organs, including those of the cardiovascular, respiratory, digestive, urinary, and reproductive systems Somatic sensory receptors monitor skeletal muscles, joints, skin surface; provide position sense and touch, pressure, pain, and temperature sensations Skeletal muscle EFFECTORS Sympathetic division • Smooth muscle • Cardiac muscle • Glands Two types of cells in the nervous system. 1- Neurons (nerve cells) Transmit impulses 2- Glia: support, nourish and protect neurons. “glue” Glia: (neuroglia) PNS: 1- Schwann cells: cells produce a white fatty substance called myelin around the large nerve fibers of the PNS. Also called neurolemmocytes. 2- Satellite cells: surround neuron cell bodies and may help regulate chemical environment. Myelin Sheath and Neurilemma CNS: Astrocytes: - connecting neurons to blood supply - projections with bulbous ends that cling to neurons and capillaries - ½ of neural volume - BBB Microglia: - small and remain stationary. When disease or inflammation is present they become mobile and phagocytize microbes. (macrophages) CENTRAL CANAL Ependymal cells Gray matter Neurons Microglial cell Myelinated axons Internode Myelin (cut) White matter Axon Oligodendrocyte Astrocyte Axolemma Myelin sheath gap Unmyelinated axon Basal lamina Capillary Neuroglia are found in Peripheral Nervous System Central Nervous System contains contains Satellite cells Schwann cells Surround neuron cell bodies in ganglia; regulate O2, CO2, nutrient, and neurotransmitter levels around neurons in ganglia Surround all axons in PNS; responsible for myelination of peripheral axons; participate in repair process after injury Oligodendrocytes Myelinate CNS axons; provide structural framework Astrocytes Microglia Ependymal cells Maintain blood-brain barrier; provide structural support; regulate ion, nutrient, and dissolved-gas concentrations; absorb and recycle neurotransmitters; form scar tissue after injury Remove cell debris, wastes, and pathogens by phagocytosis Line ventricles (brain) and central canal (spinal cord); assist in producing, circulating, and monitoring cerebrospinal fluid Oligodendrocytes: - Line up along the thicker neuron fibers - Produce myelin sheath around axons Ependymal cells: - line central cavities of brain and spinal cord, creating a barrier between CNS cavities and tissues surrounding cavities - cilia circulates the cerebrospinal fluid Neurons (nerve cells): - Conducts messages in form of nerve impulses - Has longevity - Amitotic - Have a high metabolic rate Functionally composed of: - A receptive (input) region - A conducting component (generates and propagates an action potential) - A secretory (output) component - neurotransmitter Dendrites Cell body Axon Terminal boutons Stimulated by environmental changes or the activities of other cells Contains the nucleus, mitochondria, ribosomes, and other organelles and inclusions Conducts nerve impulse (action potential) toward synaptic terminals Affect another neuron or effector organ (muscle or gland) Mitochondrion Nucleus Nucleolus Nissl bodies (clusters of RER and free ribosomes) Dendritic spines Axon hillock Neurons are composed of - Cell body - Processes Cell body: (perikaryon or soma) - Most neuron cell bodies located within CNS - Clusters of cell bodies in CNS are called nuclei - Few/clusters of cell bodies in PNS are called ganglia - Rough ER called Nissl bodies. Details of Neuron Structure Soma consists of: Nucleus Nucleolus Ribosomes (clusters are called chromatophilic substance—create gray matter) Mitochondria Golgi apparatus Lack centrosomes—cannot reproduce Processes - Cellular processes are called either tracts (in CNS) or nerves (in PNS) - Dendrites - have large surface area to receive chemical signals as well as conduct electrical signals (graded potentials) - Axons - single in each neuron, transmit graded potential away from cell body to axonal terminal (generates action potential) - Axon hillock arises from the cell body into the axon (graded potential) - Profuse branching at end of axon called terminal branches or telodendria. At the tips there are bulbous structures storing neurotransmitters. Substances travel continuously up and down the axon. Anterograde: substances move from cell body to terminal axon Retrograde: substances move from terminal axon to cell body. Plasma membrane of axon is axolemma. - Electrochemical signals transmitted with the aid by myelin sheath (protein-lipoid) which insulates nerve fibers (long axons) and increases the transmission - Nodes of Ranvier also aid in the transmission of nerve impulses. - saltitory conduction - Myelinated processes form the white matter of nervous tissue and unmyelinated processes form the gray matter of nervous tissue. In the spinal cord, gray matter forms the H- shape in the center while white matter surrounds it. In the brain, gray matter forms the thin outer cortex with white matter filling the inside Classification of neurons: Structural Functional Structural: Neurons are classified as to how many processes extend from their cell body Multipolar: three or more processes extend from cell body - posses single axon - most common type of neuron in the CNS Bipolar: two processes (axon and dendrite) extend from opposite sides of neuron. - rare in adult but may be found in retina and olfactory mucosa (special senses). Unipolar: one process extending from cell body and forms central and peripheral processes - Central process associated with secretory region - Peripheral process associated with sensory region (receptor). - Found in ganglia of PNS where they function as sensory neurons Functional Classification of Neurons 1. Synapses with another neuron Collateral branch Axon Neuron Synapses with another neuron Dendrites Neuron 2. Neuromuscular synapses Neuromuscular synapses Terminal arborization Terminal boutons Skeletal muscle 3. Neuroglandular synapses Neuroglandular synapses Gland cells A neuron may innervate (1) other neurons, (2) skeletal muscle fibers, b or (3) gland cells. Synapses are shown in boxes for each example. A single neuron would not innrvate all three. Functional: Sensory (afferent) neurons - transmit impulses from sensory receptors toward CNS Unipolar neurons - skin or internal organs to CNS for interpretation Bipolar neurons - special sense organs, retina Motor (efferent) neurons - carry impulses away from CNS to organs Multipolar neurons - cell body located within CNS and neurons form neuromuscular junctions with effector (muscle or gland) cells Association neurons (interneurons ) transmit impulses within CNS (usually sensory to motor); found in CNS only; mostly multipolar and 99% of neurons in body. Also called connecting neurons. RECEPTORS PERIPHERAL NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM Interoceptors Exteroceptors Afferent fibers Sensory neurons in peripheral ganglia Proprioceptors Interneurons EFFECTORS Skeletal muscles Somatic motor neurons Efferent fibers Skeletal muscle fibers Visceral effectors Smooth muscles Glands Cardiac muscle Adipose tissue Visceral motor neurons in peripheral Postganglionic motor ganglia fibers Preganglionic fibers Visceral motor neurons in CNS = Somatic (sensory & motor) = Visceral (sensory & motor) The Nerve Impulse The “speed” of the impulse depends on: Presence of a myelin sheath Lack of a myelin sheath Fast impulse Slow impulse Myelinated axons with a large diameter Fast impulse Up to 140 m/sec Unmyelinated axons with a small diameter Slow impulse Less than 1 m/sec Anatomical Organization of the Nervous System Organization in the CNS Gray matter organization Neural cortex Nuclei Gray matter on the surface of the brain Neuron cell bodies in the interior of the CNS White matter organization Bundles of CNS axons that form ascending and descending columns CENTRAL NERVOUS SYSTEM GRAY MATTER ORGANIZATION Neural Cortex Gray matter on the surface of the brain PERIPHERAL NERVOUS SYSTEM GRAY MATTER Ganglia Collections of neuron cell bodies in the PNS Nuclei Collections of neuron cell bodies in the interior of the CNS WHITE MATTER Nerves Bundles of axons in the PNS Centers Collections of neuron cell bodies in the CNS; each center has specific processing functions. Higher centers are the most complex centers in the brain WHITE MATTER ORGANIZATION Tracts Bundles of CNS axons that share a common origin and destination RECEPTORS TRACTS EFFECTORS Centers and pathways that connect the brain with other organs and systems in the body Ascending (sensory) tracts Descending (motor) tracts Columns Several tracts that form an anatomically distinct mass The Synapse ...
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