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 (NS) and its structural basis ◼ ◼ Describe the organization of the nervous system ➢ Describe the s...

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 body, transmit and communicate those information, process these information and responds accordingly Peripheral nervous system receives, transmits to and from the CNS CNS and parts of PNS (ganglia) process these information Neurons and neural networks are structurally organized in CNS and PNS perform these functions https://www.alamy.com/illustration-of-a-handtouching-a-hot-stove-element-and-reaction-in-thebodys-neural-circuits-image 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 afferent signals) ◼ Relay motor commands from CNS to peripheral tissues and systems (output or efferent signals) 6 Functional Divisions of the Nervous System Afferent division ◼ Carries sensory information from PNS to CNS Efferent division ◼ Carries motor commands from CNS to PNS 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 Parasympathetic division has a relaxing effect 9 Nervous tissue Consists of supportive cells (neuroglia) and Neurons that process and transmit nerve signals 10 Revise the nervous tissue learnt already 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 15 Cell Processes: Dendrites ◼ ◼ ◼ 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 membrane Synaptic cleft ◼ Neurons communicate each other through synapses by releasing neurotransmitters ◼ Neurotransmitters are chemical messengers (e.g. Acetylcholine, adrenaline, noradrenaline, serotonin) 17 Cell Processes: Axon Arises at a conelike 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 functions: ◼ Supportive function ◼ Metabolic function ◼ Defensive function 20 Neuroglial Cells in CNS I ▪ ▪ ▪ ▪ ▪ ▪ ▪ Astrocytes: Most abundant (half of neural tissues) Versatile neuroglia Large cell bodies and many star-shaped processes Form & maintain the BBB Ependymal cells: Line cerebrospinal fluidfilled cavities of brain & SC 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 finebranched 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 26 Anatomical classification of neurons Organization of the Nervous System (summary) Organization of the Nervous System Central Nervous System (CNS) (brain and spinal cord) Peripheral Nervous System (PNS) (neural tissue outside the CNS) Integrate, process, and coordinate sensory data and motor commands Sensory information within afferent division Motor commands within efferent division includes Somatic nervous system (SNS) Autonomic nervous system (ANS) Parasympathetic division Receptors Special sensory receptors monitor smell, taste, vision, balance, and hearing Effectors Visceral sensory receptors monitor internal organs Somatic sensory receptors monitor skeletal muscles, joints, and skin surface Skeletal muscle • Smooth muscle • Cardiac muscle • Glands • Adipose tissue Sympathetic division 28 Reference Essentials of Human Anatomy and Physiology Elaine N. Marieb Thank you