NURS1108 Introduction to Anatomy & Physiology PDF

NURS1108: Introduction to Anatomy & Physiology Dr. Jermaine H. Whyte FMS- UWI [email protected] Nervous System Introduction Objectives • Discuss the structural and functional divisions of the nervous system; • List the basic functions of the nervous system; • Identify the structural...

NURS1108: Introduction to Anatomy & Physiology Dr. Jermaine H. Whyte FMS- UWI [email protected] Nervous System Introduction Objectives • Discuss the structural and functional divisions of the nervous system; • List the basic functions of the nervous system; • Identify the structural and functional classification of neurons; • Describe resting membrane potential including its resting membrane electrochemical basis; Content • Organization of the nervous system • Developmental aspects of neurons Body’s Two Main Communication Systems • Endocrine system: releases chemicals into blood and other bodily fluids • Nervous system: unified collection of neurons and supporting cells that, with the endocrine system, regulate the body’s response to change; combines electrical and local chemical signals o Neurons: main functional cells of nervous system; receives and responds to sensory information Functions of the Nervous System Introduction • Organs of the Nervous System o Brain and spinal cord o Sensory receptors of sense organs (eyes, ears, etc.) o Nerves connect nervous system with other systems Divisions of the Nervous System CNS • The central nervous system integrates information – The CNS integrates incoming (sensory) signals and responds with outgoing (motor) command signals. – Its components are vertically stacked according to the degree of signal integration they provide. • Spinal cord provides the least amount of integration. – Cylinder of nervous tissue about three feet long – Encased by vertical bone. – Extends down back from base of skull. CNS • The central nervous system – The spinal cord • The cord ends at the first or second lumbar vertebra • Breaks into a fan of nerves called the cauda equina • Integrates and reacts automatically to some sensory signals; relays others to the brain – Spinal cord sits beneath the brain • Has about 100 billion neurons • Has about 30 trillion glia cells, which provide support to the neurons CNS Brain – The subdivisions of the brain are stacked according to the degree of integration they provide. • Brainstem – merges with the spinal cord; serves as the central clearinghouse for nerve signals; integrates signals specific to core physiological processes • Cerebellum – integrates signals in the regulation of body movement • Diencephalon – contains the hypothalmus, which integrates and regulates additional core body processes. Brain – The subdivisions of the brain are stacked according to the degree of integration they provide. • Cerebrum – consists of right and left cerebral hemispheres; home to the highest degree of integration; each hemisphere is essentially connected to the opposite side of the body. Peripheral Nervous System PNS • The PNS transmits information – The PNS is a network of sensory receptors that detect internal and external environmental change and nerves • Nerves are bundles of neurons and axons • Two-way traffic – Anatomically, PNS consists or cranial nerves, which originate from the brain and spinal nerves, which originate from the spinal cord. PNS • The somatic division is voluntary – Receives signals from special receptors in the sense organs (eyes, ears, etc.) and from somatic receptors in other body tissues (skin, muscles, etc.). – Somatic sensory nerves convey sensory signals to the brain, where they are integrated into conscious experience. – In response signals are sent along motor nerves to skeletal muscles. PNS • The autonomic division is involuntary – The autonomic nervous system operates automatically and unconsciously. – Autonomic sensory (afferent) nerves receive signals from visceral receptors that monitor internal conditions such as blood pressure. They send signals to the CNS. – Autonomic motor (efferent) nerves convey signals from the CNS to effect changes in smooth muscle, cardiac muscle, and glands. – Autonomic nerve signals may cause increased activity (excitation) or decreased activity (inhibition) of the target tissue or organ. Introduction • All Neural Tissue within the body o Contains two kinds of cells: • Neurons: o cells that send and receive signals • Neuroglia (glial cells): o cells that support and protect neurons Neurons • Neurons are specialized for intercellular communication and are supported by cells called neuroglia • The Structure of Neurons o o o o Cell body (soma) Short, branched dendrites Long, single axon Axon terminals Neuron Structure Connective Tissue Coverings of a Nerve CT Coverings of a Nerve Neurons • Structural Classifications of Neurons o Multipolar neurons: • Common in the CNS • Include all skeletal muscle motor neurons o Unipolar neurons: • Found in sensory neurons of PNS o Bipolar neurons: • Found in special sensory organs (sight, smell, hearing) Dendrites – receptive regions Cell Body – biosynthetic center and receptive region Axon – impulse generating and conducting region Axon Terminals – secreting regions Neurons • Three Functional Classifications of Neurons o Sensory neurons: • Afferent neurons of PNS o Motor neurons: • Efferent neurons of PNS o Interneurons: • Association neurons Neurons • Three Types of Sensory Receptors o Exteroceptors: • External senses (touch, temperature, pressure) • Distance senses (sight, smell, hearing) o Proprioceptors: • Monitor position and movement (skeletal muscles and joints) o Interoceptors: • Monitor internal systems (digestive, respiratory, cardiovascular, urinary, reproductive) • Internal senses (taste, deep pressure, pain) Neuroglia • Neuroglia o Half the volume of the nervous system o Many types of neuroglia in CNS and PNS Neuroglia • Four Types of Neuroglia in the CNS o Astrocytes: large cell bodies with many processes o Oligodendrocytes: smaller cell bodies with fewer processes o Microglia: smallest and least numerous neuroglia with many finebranched processes o Ependymal cells: cells with highly branched processes; contact neuroglia directly Neuroglia Glial Cells • Several types of glial cells in CNS – Astrocytes • Most abundant; shaped like stars. From a cell body, they send out projections that grip and stabilize neurons and capillaries • Control the condition of extracellular fluid • Serve as neuronal stem cells Glial Cells – Microglia • Roaming scavenger cells; engulf, digest, and destroy invading organisms and foreign matter; clean up debris of dead cells following an injury – Oligodendrocytes • Synthesize myelin sheath of CNS axons Glial Cells – Ependymal cells • Line brain cavities called ventricles • Produce cerebrospinal fluid • May act as neuronal stem cells Neuroglia • Neuroglia of the Peripheral Nervous System o Satellite cells: • Also called amphicytes • Surround ganglia • Regulate environment around neuron o Schwann cells: • Also called neurilemmocytes • Form myelin sheath (neurilemma) around peripheral axons • One Schwann cell sheaths one segment of axon: o many Schwann cells sheath entire axon Schwann Cells and Peripheral Axons The Anatomical Organization of the NS Recommended Reading • McConnell, T. H. & Hull, K. L. (2011). Human form and function: Essentials of anatomy& physiology. Philadelphia: Wolters Kluwer, Lippincott Williams & Wilkins. • Shier, D., Lewis, R. & Butler, J. (2002). Hole’s human anatomy & physiology. New York: McGraw Hill. • Tortora, Gerard J. & Derrickson, Bryan H. (2011). Principles of anatomy and physiology. Somerset, New Jersey: John Wiley & Sons.