NERVOUS SYSTEM د. شيرين PDF

NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM Brain Spinal Cord Autonomic nervous Somatic nervous system system Sympathetic Parasympathetic nervous system nervous system A...

NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM Brain Spinal Cord Autonomic nervous Somatic nervous system system Sympathetic Parasympathetic nervous system nervous system Anatomical speaking in the nervous system has to parts 1.central nervous system =brain +spinal cord(it's responsible for processing of formation and decision making) 2_peripheral nervous system = carinal nerves and spinal nerves responsible for the transmission of electrical signals Physiological Speaking and nervous system 2parts 1-somatic nervous system voluntary control of skeletal muscles 2- autonomic nervous system=involuntary control of internal organs Physiological Brain 2parts 1-higher Brain areas /responsible for thickening and memory 2-lower brain area=homeostasis spinal cord has 31 segments each segments exhibits of spinal nerves 51 pairs of spinal nerves 1-cervical region 8S, thoracic region 12S,lumbar region 5S Sacral region 5S.coceygel1S The spinal cord is responsible for a transmission between brain and body tissue  What function of nervous system 1.CNS receive his information from body tissue through peripheral nerves afferent singles 2. Store information memory with CNS 3. Integrated formations processing with CNS 4 CNS send information to the tissues through peripheral nerves efferents signals  Introduction Human CNS contain >100 billion neurons 50-100 times this number glial cells About 40% human genes participating its formation Specialized function of muscle – contraction Specialized function of neurons – integration & transmission of nerve impulse Along with endocrine, nervous system forms the major control system for body functions  Structure of Neuron Structural and functional unit of nervous system Consists of nerve cell body with all its processes axon and dendrites All neurons contain one and only one axon But dendrites may be absent one or many Axon carries impulses from the soma towards a centrifugal directions (away from soma) Dendrites brings impulse from distance centripetally (towards the soma) Nerve cell means a neuron where as nerve cell body means soma  Classification of Neuron 1. Depending upon the number of poles 2. Depending upon the function 3. Depending upon the length of axon  1. Depending upon the number of poles a. Unipolar: Having only one pole From single pole both axon and dendrites arise Present in embryonic stage in human being b. Bipolar: Having two poles Axon arises one pole and dendrites other pole c. Multipolar: Nucleus having multipoles Axon arise one pole & all other pole give rise dendrites  2. Depending upon the functions Motor or efferent neurons: – Carry impulses from CNS to peripheral effector organs e.g., muscles/glands/blood vessels – Generally each motor neurons has long axon and short dendrites Sensory or afferent neurons: – Carry impulses from periphery to CNS – Generally each neuron has short axon a long dendrites  Axis cylinder Has long central core of cytoplasm- axoplasm Axoplasm covered by membrane – axolemma continuation of cell membrane of soma Axoplasm along with axolemma- axis cylinder Contain mitochondria, neurofibrils and axoplasm, vesicles Axis cylinder covered by neurilemma in non myelinated nerve fiber Nerve fiber insulated by myelin sheath – myelinated nerve fiber  Myelin Sheath Concentric layers of protein alternating with lipid Nerve fiber insulated by myelin sheath- myelinated nerve fiber Protein lipid complex wrapped around axon >100 times Outside the CNS (peripheral nerve) myelin produced by Schwann cells Inside the CNS myelin sheath produced by oligodendrogliocytes  CONTI Myelin is compacted when extracellular membrane protein (Po) locked extracellular portion of Po apposing membrane Not continuous sheath absent at regular intervals Where sheath absent – node of Ranvier (1µm) Segment between two node- internode (1mm)  Non myelinated nerve No myelin sheath formation Nerve fiber simply covered by Schwann cells, no wrapping No internode and node of Ranvier Neurilemma and axis cylinder close to each other In CNS no neurilemma FUNCTIONAL DIVISION OF NEURON Divided in to four zone: 1. Receptor or dendritic zone: – Multiple local potential generated by synaptic connection are integrated 2. Origin of conducted impulse: – Propagated action potential generated 3. Conductive zone:  Axonal process transmits Propogated impulse to the nerve ending  All or none transmission 4. Secretory zone:  Nerve ending where AP cause release of neurotransmitters Neurotrophins – Neurotrophic Factors Protein substances Play important role in growth and functioning of nervous tissue Secreted by many tissue in body e.g., muscles/ neurons/ astrocytes Functions: – Facilitate initial growth and development of nerve cells in CNS & PNS  Function of neurotrophins Promote survival and repair of nerve cell Maintenance of nerve tissue and neural transmission Recently – neurotrophins capable of making damaged neuron regrow Used reversing devastating symptoms ) ‫العالمات‬ ‫المدمرة‬of nervous disorders like Parkinson disease, Alzheimer's disease, Commercial preparation for treatment of some neural diseases  Type 1st protein identified as neurotrophin- nerve growth factor (NGF) Now many numbers neurotrophin identified 1. Nerve growth factors (NGF) – Promote early growth and development in neurons – Major action on sympathetic and sensory neurons especially neurons concerned with pain – sympathetic NGF (major actions on sympathetic neurons  Neuroglia Neuroglia or glia (glia- glue) supporting cells of nervous system Non excitable and do not transmit nerve impulse 10-50 time as many glial cells as neurons Capable of multiplying by mitosis Schwann cells invest axon also glial cells  Classification of Nerve fibers 1. Depending upon structure – Myelinated nerve fibers – Non myelinated nerve fibers 2. Depending upon distribution – Somatic nerve fibers (supply skeletal muscles) – Visceral or autonomic (supply internal organs) Depending upon origin – Cranial nerve (arising from brain) – Spinal nerve (arising from spinal cord)  Depending upon functions: – Sensory nerve fibers (afferent nerve fiber) – Motor nerve fibers (efferent nerve fibers) Depending upon secretion of neurotransmitter – Adrenergic nerve fibers – Cholinergic nerve fibers Depending upon diameter and conductions of impulse (Erlanger- gasser classification) Classified into three major groups: – Type A nerve fibers – Type B nerve fibers – Type C nerve fibers  Among these type A thickest fibers Type c thinnest fibers Except type C fibers all fibers are myelinated Type A nerve fibers further subdivided four groups: – Aα or Type I nerve fibers – Aβ or Type II nerve fibers – A or Type III nerve fibers – A