Neuroscience Lecture 1 PDF

Introduction to Nervous System Dr. Doha Al-Afifi Objectives:  At the end of the course the student should be able to: Identify different parts of the nervous system. Define the function of each part. Understand the anatomical basis of neurological disorder.  Organization of The Nervous Sy...

Introduction to Nervous System Dr. Doha Al-Afifi Objectives:  At the end of the course the student should be able to: Identify different parts of the nervous system. Define the function of each part. Understand the anatomical basis of neurological disorder.  Organization of The Nervous System The Nervous System is compromised of two major parts or, Subdivisions:  The Central Nervous System (CNS),  The Peripheral Nervous System(PNS).  The brain and spinal cord form the central nervous system (CNS),  The cranial, spinal, and autonomic nerves and their ganglia form the peripheral nervous system (PNS). Peripheral Nervous System  Consist of 12 pairs of Cranial Nerves and 31 pairs of Spinal Nerves, With their associated ganglion make up the peripheral nervous System.  A) Motor (or efferent) fibers of peripheral nervous system which are of two types:  Somatic motor fibers that terminate in skeletal muscles.  Autonomic fibers that innervate cardiac, smooth muscle and glands.  The termination of the somatic fibers in the skeletal muscle occur at the motor end plate which resembles (synapse).  B) The sensory (or afferent) fibers of peripheral nerves.  Transmit signals from receptors of various types. Each afferent fibers conduct impulses toward the brain and spinal cord from particular receptor with which it is connected.  The motor root originating from anterior horn cell(AHC), leaves the cord ventrally, Whereas the sensory root enter the cord on the dorsal side. Motor and sensory roots at each spinal level unite distal to the DRG to become a mixed spinal nerve. There are 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal. Each spinal nerve divides into a dorsal and ventral ramus. The dorsal and ventral rami both contain motor and sensory fibers  The dorsal ramus runs posteriorly to supply sensory innervation to the skin over the spine and muscular innervation to the paraspinal muscles at that segment. The ventral ramus differs, depending on the segment within the body. In the thoracic region, each ventral ramus continues as an intercostal nerve. In the lower cervical to upper thoracic (C5–T1) region, the ventral rami unite to form the brachial plexus. In the mid-lumbar to sacral regions, the ventral rami intermix to form the lumbosacral plexus Function of the Nervous System  The CNS integrates and controls the entire nervous system,  Receiving information (input) about changes in the internal and external environments,  Interpreting and integrating this information, and providing signals (output) for the execution of activities, such as movement or secretion.  The PNS connects the CNS to the tissues and organs of the body. Hence, the PNS is responsible for conveying input and output signals to and from the CNS.  Signals passing to the CNS are called afferent, whereas those passing away from the CNS are called efferent. The nervous system can be divided functionally into: Three systems extend through all regions of the nervoussystem 1. The somatosensory system that conveys information from the skin and the musculoskeletal system to areas of the brain. 2. The somatic motor system that transmits information fromthe brain to skeletal muscles. 3. The autonomic system that provides bidirectional communication between the brain and internal organs (e.g:smooth muscle, cardiac muscle, and gland cells. In the peripheral nervous system Neurons that convey information into the central nervous system are afferent. Neurons that transmit information from the central system to peripheral structures are efferent. Neurons that connect only with otherneurons are interneurons. Central Nervous System (CNS)  1) Brain Cerebrum (Cerebral hemisphere) Brain stem Cerebellum 2) Spinal cord Central Nervous System  The central Nervous system Consists of two main parts  A) Intracranial:  1) Cerebrum ( cerebral cortex):It is formed by two cerebral hemisphere connected to each other by corpus callosum.  The cerebral hemisphere consists of 4 lobes( frontal , parietal, temporal, occipital)  Function: Thinking, movement , speech , memory, vision, sensory processing  2) cerebellum :  Function: Posture, balance, Coordination of voluntary  motor activity, maintenance of equilibrium.  3) brain stem:  Midbrain  Pons  Medulla Oblongata  Function: Basic body Function( breathing ,heart rate,  sleep, consciousness) Central Nervous system Central Nervous System  B) Spinal Part: consists of  A)spinal cord: lies with in the spinal canal and ends at the lower border of 1st lumber vertebrae.  It is formed of grey matter surrounded with white matter.  Grey matter: it resembles H letter ( with two anterior Horn and two posterior Horn)  White matter : contain Ascending and descending nerve fibers arranged in to tracts).  B) Cauda Equina  SPINAL CORD HAS TWO MAIN FUNCTIONS:  convey information between neurons innervating peripheral structures and the brain.  To process information; An example is the reflexive movement of a limb away from a painful stimulus. Transection with in the spinal cord showing difference between white matter and grey matter IN CENTRAL NERVOUS SYSTEM The difference between white and gray matter in section of the central nervous system White matter is composed of axons, projections of nerve cells that usually convey information away from the cell body.  A bundles of axons that travel together in the central nervous system is called tract, lemniscus, fasciculus, column , peduncle or corpuscle. Areas of the central nervous system that appear gray contain primarily neuron cell bodies. These areas called gray matter. Groups of cell bodies in the central nervous system are called nuclei  Groups of cell bodies in the peripheral nervous system are called ganglion. NERVOUS SYSTEM SUPPORT AND PROTECTION  At the histologic level, the nervous system is composed of neurons and glial cells.  Nerve cells are extremely fragile and cannot survive without the protection of supporting cells. The brain and spinal cord, also very fragile, are protected from the surrounding bones of the cranial cavity and vertebral or spinal canal by three coverings or membranes, called the meninges The Nervous System  Nervous tissue is composed of two types of cells, neurons and glial cells. Neurons  They are responsible for receiving, processing and transmitting information.  They are electrically active and release chemical signals for target cells. Glial cells or , glia,  They are known to play a supporting role for nervous tissues.  Neurons are important, but without glial cells they would not be able to perform their function. Neuron  The basic structure (functional )unit of the nervous system is the neuron.  Each neuron has a cell body that receives nerve impulses and an axon that conveys the nerve impulse away from the cell body.  Function of Neuron:  neurons are specialized to receive information,  to transmit electrical impulses,  and to influence other neurons or effector tissues.     It composed of: A)Cell body(Soma):contain nucleus B) Axon: carry impulses away from the cell body. C) dendrites: carry impulses toward cell body.  The nervous system comprises neurons arranged in longitudinal series. Reflex and Relay  The serial arrangement forms two types of circuits: reflex and relay.  A reflex circuit conveys the impulses that result in an involuntary response such as muscle contraction or gland secretion. A relay circuit conveys impulses from one part of the nervous system to another.  For example, relay circuits convey impulses from sensory organs in the skin, eyes, ears, and so forth that become perceived by the brain as sensations.  Relay circuits are categorized according to their functions and are called functional paths, for example, pain path, visual path, or motor or voluntary movement path.  A functional path may consist of a series of only two or three neurons or as many as hundred of neurons. Reflex circuits may overlap with parts of A functional path may contain thousands or even millions of nerve cell bodies and axons. The nerve cell bodies may form pools or clumps, in which cases they are called nuclei or ganglia, or the nerve cell bodies may be arranged in the form of layers or laminae. The axons in a functional path usually form bundles called tracts, fasciculi, or nerves. Therefore, the entire nervous system is composed of functional paths whose neuronal cell bodies are located in the nuclei, ganglia, or laminae and whose axons are located in the tracts or nerves. The Meninges  The CNS is supported and protected by the meninges, three connective tissue membranes located between the brain and the cranial bones and between the spinal cord and the vertebral column. The meninges are, from external to internal,  the dura mater,  the arachnoid,  the pia mater. The meninges around the brain and spinal cord are continuous at the foramen magnum, the large opening in the base of the skull where the brain and spinal cord are continuous. Clinical connection (Meningitis)  Inflammation of the meningeal membranes surrounding the brain and spinal cord, due primarily to either a viral or bacterial infection of the meninges, may result in a lifethreatening condition of meningitis.  Less common causes include:  fungal, parasitic, and drug-mediated meningitis.  In adults,  neck stiffness and headache with fever, altered consciousness, vomiting, and aversion to bright light or loud noises are the primary symptoms of meningitis.  In children,  symptoms may be less apparent than in adults and consist of only irritability and drowsiness.  Pathogen access to the meninges may be blood borne or as the result of direct entry from the nasal cavities.  How to diagnose????????  Diagnosis most commonly is by lumbar puncture if there is no indication of elevated intracranial pressure in the patient. Bacterial meningitis is treated by antibiotics