Fundamentals of the Nervous System PDF

Fundamentals of the Nervous System: Structure Dr. Ajith Sominanda Associate professor in Anatomy College of Medicine Qatar University  Objectives ◼ State the major function of the nervous system...

Fundamentals of the Nervous System: Structure Dr. Ajith Sominanda Associate professor in Anatomy College of Medicine Qatar University  Objectives ◼ State the major function of the nervous system (NS) and its structural basis ◼ Describe the organization of the nervous system Describe the structural and functional classification of NS List the parts of CNS and PNS ◼ Describe the structure of a neuron and neuroglia (Revise the nervous tissue) ◼ Classify neurons according to structure and function ◼ State the functions of neurons and neuroglia ◼ Describe the composition of gray matter and white matter 2  The major function of the nervous system (NS) and the structural basis Nervous system is the master control and the communication system of our body (organ systems). Nervous system receives information and stimuli from external and internal environments of the Motor output Sensory input > - integration > - body, transmit and communicate those information, process these information and responds accordingly Peripheral nervous system receives, transmits to and from the CNS y · Gr CNS and parts of PNS (ganglia) process these information Neurons and neural networks are https://www.alamy.com/illustration-of-a-hand- structurally organized in CNS and touching-a-hot-stove-element-and-reaction-in-the- bodys-neural-circuits-image PNS perform these functions  Organization of the nervous system Structural classification ◼ Central nervous system ◼ Brain ◼ Spinal cord ◼ Peripheral nervous system ◼ Sensory receptors of sense organs ◼ Peripheral nerves and ganglia 4 Central Nervous System: Components and major functions ◼ CNS consists of brain and spinal cord ◼ Contains: Neural tissue Connective tissue Blood vessels ◼ Functions of the CNS ◼ Process, integrate and coordinate sensory data ◼ Process Motor commands & control activities of peripheral organs ◼ Higher functions (e.g. intelligence, memory learning, behavior) 5  Peripheral Nervous System Includes all neural tissue outside the CNS (peripheral nerves and ganglia) Functions: Deliver sensory information to the CNS (input or 6 afferent signals) Relay motor commands from CNS to peripheral tissues and systems (output or efferent signals)  · Functional Divisions of the Nervous System Afferent division Efferent division ◼ Carries sensory ◼ Carries motor commands information from from CNS to PNS PNS to CNS 7  Afferent (Sensory) Division Detect changes or respond to stimuli ( internally & externally) Neurons and specialized cells Special & complex sensory organs (e.g., eyes, ears) Somatic sensory fibers (from skin, skeletal muscles, joints) and visceral sensory fibers (from viscera) 8 Efferent (Motor) Division Somatic nervous system (SNS) Controls voluntary and involuntary (reflexes) skeletal muscle contractions Autonomic nervous system (ANS) Controls subconscious actions Contractions of smooth muscle and cardiac muscle, and glandular secretions Divisions: ▪ Sympathetic division has a stimulating effect (Crazy reaction) ▪ Parasympathetic division has a relaxing effect (Calm reaction) 9  Nervous tissue ① e Consists - of supportive cells (neuroglia) - and Neurons that process and transmit nerve signals - 10 Revise the nervous tissue learnt already Nervous tissue t Ghansists Nerouns that Process and transmis Supporting nerve signals. cells (neuroglia)  Structure of Neuron Typical (multipolar) neuron, common in the CNS, consists of: Cell body (soma) Cell processes ◼ Short, branched dendrites (afferent) ◼ Long, single axon (efferent) 12  Structure of a Neuron: Cell Body I ◼ Cytoplasm is called Perikaryon ◼ Large nucleus and nucleolus ◼ Mitochondria for energy production 13  Structure of a Neuron: Cell Body II Neurofibrils: ◼ Bundles of neurofilaments ◼ Provide support for dendrites and axon ◼ Maintain cell shape Nissl bodies: ◼ Dense areas of RER and ribosomes ◼ Produce neurotransmitters ◼ Make neural tissue appear gray 14  Structure of a Neuron: Cell Processes BrineuraimTrim suma (cell body) ↳ 15  Cell Processes: Dendrites O %* ◼ Highly branched ◼ Receive information from other neurons (afferent) ◼ Occupies most of neuron surface area 16  Neuronal Synapse Telodendrion (axon) Axon terminal Mitochondrion Synaptic vesicles Presynaptic membrane Postsynaptic Synaptic membrane cleft ◼ neurotransmitters => Neurons communicate each other through synapses by releasing - ◼ Neurotransmitters are chemical messengers (e.g. Acetylcholine, - adrenaline, noradrenaline, serotonin) 17  Cell Processes: Axon Arises at a cone- like point (axon hillock) Longest process, usually covered by myelin sheath outside CNS Occasional branching, gives collaterals Carries electrical signal (action potential) to target 18  Nodes of Ranvier Gaps in myelin sheath because sheath is formed by many individual Schwann cells 19  Cells of Nervous System: Neuroglia ◼ Neuroglial cells are supportive cells in the nerve tissues ◼ But possesses diverse unctions: f ◼ Supportive function ◼ Metabolic function ◼ Defensive function 20 Neuroglial Cells in CNS I ▪ Astrocytes: ▪ Most abundant (half of neural tissues) ▪ ▪ s Versatile neuroglia Large cell bodies and many star-shaped processes ▪ Form & maintain theC BBB · is ▪ Ependymal cells: ▪ Line cerebrospinal fluid- filled cavities of brain & SC ↳ ne 21 Neuroglial Cells in CNS II ▪ Oligodendrocytes ▪ Smaller cell bodies with fewer processes - form fatty insulating myelin - sheath around CNS - nerve fibers ▪ Microglia ▪ Smallest and least = " numerous neuroglia - with many fine- branched processes – Defensive function (phagocytic) 22  Neuroglial Cells in PNS ▪ Satellite cells ▪ Surround neuronal cell bodies ▪ Acts as supportive and protective cushioning cells ▪ Regulate environment (gases, nutrients & neurotransmitters) around neuron 23  Neuroglial Cells in PNS ▪ Schwann cells ▪ Form myelin sheath around peripheral nerve axons ▪ Many Schwann cells en-sheath entire axon ▪ Thus, there are gaps at regular intervals – Nodes of Ranvier ▪ Axon can regenerate when damaged ▪ Outer most covering layer is the neurilemma 24 Schwann Cells and Axons in PNS Myelin is a whitish fatty material Protects and insulates axons Increases transmission rate of impulses along nerve fibers 25 Schwann Cells vs Oligodendrocytes ◼ Each oligodendrocyte cell ◼ Wraps around many fibers ◼ Lacks neurilemmal covering Injured nerves in PNS regenerate but those in CNS do not injured d earate Oligodendrocytes - ifitgets injured a te Schwann cells - if if itgets 26 Anatomical classification of neurons  Organization of the Nervous System (summary) Organization of the Nervous System Central Nervous System (CNS) (brain and spinal cord) Integrate, process, and coordinate sensory data and motor commands Sensory information Motor commands within within afferent division efferent division Peripheral Nervous System (PNS) includes (neural tissue outside the CNS) Somatic nervous Autonomic system (SNS) nervous system (ANS) Parasympathetic Sympathetic division division Receptors Effectors Smooth muscle Special sensory Visceral sensory Somatic sensory Cardiac receptors receptors receptors muscle monitor smell, taste, monitor internal monitor skeletal Glands vision, balance, and organs muscles, joints, Skeletal Adipos hearing and skin surface muscle e 28 tissue  Reference Essentials of Human Anatomy and Physiology Elaine N. Marieb Tortora’s Principals of Anatomy and Physiology of Gerard J Tortora Thank you Nervous system (NS) -- I Peripheral - Central nervous - system (CNS) ner vous system (PNS) - Eory Attor - - division division -3 I Somatic nervous Autonomete system - - JSymphatheic division Farasympathetic division