Introduction to Structure and Function of Nervous Tissue PDF

INTRODUCTION TO STRUCTURE AND FUNCTION OF NERVOUS TISSUE Dr. Entesar yaseen  Topic Outcomes 14.1 Describe the ultramicroscopic structure of a neuron. 14.2 Describe the structure of an unmyelinated and myelinated nerve fiber. 14.3 Describe various types of axonal tra...

INTRODUCTION TO STRUCTURE AND FUNCTION OF NERVOUS TISSUE Dr. Entesar yaseen  Topic Outcomes 14.1 Describe the ultramicroscopic structure of a neuron. 14.2 Describe the structure of an unmyelinated and myelinated nerve fiber. 14.3 Describe various types of axonal transport systems. 14.4 Describe the structure and function of various types of neuroglia cells. 14.5 List various neurotrophins  Overview of the Nervous System Definition: The nervous system is a complex network of neurons and supporting cells that coordinates body activities by transmitting signals between different body parts. Main Functions: Sensory Input: Collects information from sensory receptors about internal and external environments. Integration: Processes and interprets sensory data to determine appropriate responses. Motor Output: Activates effector organs (muscles and glands) to produce a response.  Divisions of the Nervous System Peripheral Nervous System (PNS): Components: All nerves outside the Central Nervous System CNS, including sensory and motor (CNS): neurons. Components: Brain and spinal cord. Subdivisions: Somatic Nervous System: Controls Function: Integrates voluntary movements by activating sensory information and skeletal muscles. coordinates responses; Autonomic Nervous System: responsible for higher Regulates involuntary functions (e.g., functions like thought heart rate, digestion) and is further and emotion. divided into the sympathetic and parasympathetic nervous systems. Rest and relax actions Flight-fight response Definition of Neuron: Neuron Structure Basic unit of the nervous system, crucial for signal transmission. Main Parts: 1. Cell Body (Soma): Contains the nucleus, cytoplasm, and essential organelles. 2. Dendrites: Short, branching extensions that receive incoming signals from other neurons. 3. Axon: A long, slender projection that carries impulses  Axonal Structure and Myelination Axon Characteristics: Varies in length and diameter, Myelin Sheath: influencing signal speed. Composed of glial cells (e.g., Surrounded by the Axolemma (axonal oligodendrocytes in CNS, membrane) for signal propagation. Schwann cells in PNS). Provides insulation and increases conduction velocity of action potentials.  Specialized Features and Synaptic Communication Nodes of Ranvier: Gaps in the myelin sheath that facilitate rapid signal conduction via saltatory conduction. Synaptic Terminals: End points of axons where neurotransmitters are released. Essential for communication with target cells (neurons, muscles, glands). Organelles in Neurons: High concentration of mitochondria for energy. Rough Endoplasmic Reticulum (Nissl bodies) for protein synthesis, crucial for neurotransmitter production. Structure of Myelinated Vs. Unmyelinated Nerve Fibers Myelinated Nerve Fibers: Unmyelinated Nerve Myelin Sheath: Fibers: Composed of multiple layers Lack of Myelin Sheath: of lipid-rich membrane from Axons are not insulated; glial cells (Schwann cells in they are surrounded by a PNS, oligodendrocytes in single layer of glial cell CNS). membrane. Insulates the axon, allowing Signal Transmission: for faster signal Slower conduction velocity transmission. due to continuous Nodes of Ranvier: conduction along the Gaps in the myelin sheath entire length of the axon. where ion channels are Structure: concentrated. Typically, thinner and may Facilitate saltatory be found in autonomic conduction, speeding up pathways and pain fibers. nerve impulses.  Axonal Transport Definition: Axonal transport is the process by which materials are moved along the axon, essential for neuron function and health. Importance: Supports the transport of organelles, proteins, and neurotransmitters between the cell body and synaptic terminals. Types: Anterograde Transport Retrograde Transport  Axonal Transport Anterograde Transport Definition: Movement of materials from the cell body to the axon terminal. Mechanism: Utilizes motor proteins such as kinesin that travel along microtubules. Function: Transports essential components like: Neurotransmitter precursors Synaptic vesicles Membrane proteins for synapse formation  Axonal Transport Retrograde Transport Definition: Movement of materials from the axon terminal back to the cell body. Mechanism: Utilizes motor proteins such as dynein that also travel along microtubules. Function: Transports signaling molecules, growth factors, and waste products. Plays a key role in: Neurotrophic signaling Recycling of synaptic components Definition: Neuroglia Neuroglia, or glial cells, are non-neuronal cells in the nervous system that support, protect, and maintain neurons. Types of Neuroglia: Central Nervous System (CNS) Glia: ❖ Astrocytes ❖ Oligodendrocytes ❖ Microglia ❖ Ependymal Cells Peripheral Nervous System (PNS) Glia: ❖ Schwann Cells ❖ Satellite Cells  Central Nervous System (CNS) Glia Astrocytes: Oligodendrocytes: Structure: Star-shaped cells with Structure: Fewer processes numerous processes. compared to astrocytes; can Function: Provide structural support, myelinate multiple axons. regulate blood flow, maintain the blood- Function: Form and maintain the brain barrier, and modulate myelin sheath around CNS neurotransmitter levels. axons, facilitating faster signal conduction. Microglia: Structure: Small, with branching processes; the immune cells of the CNS. Function: Act as macrophages, removing debris and dead neurons; involved in immune response and inflammation.  Peripheral Nervous System (PNS) Glia Schwann Cells: Structure: Wrap around single axons; can also support unmyelinated fibers. Function: Form the myelin sheath in the PNS, aiding in rapid signal transmission and supporting nerve regeneration. Satellite Cells: Structure: Flattened cells surrounding neuronal cell bodies in ganglia. Function: Provide structural support and regulate the microenvironment around neurons, contributing to homeostasis.  Neurotrophins Definition of Neurotrophins: Neurotrophins are a family of proteins essential for the growth, survival, and differentiation of neurons, playing a critical role in the development and maintenance of the nervous system.  List of Neurotrophins and Their Functions ▪ Nerve Growth Factor (NGF) Function: Promotes survival and growth of sympathetic and sensory neurons. ▪ Brain-Derived Neurotrophic Factor (BDNF) Function: Supports neuron survival and encourages synapse formation; vital for learning and mood regulation. ▪ Neurotrophin-3 (NT-3) Function: Essential for the survival and differentiation of various neuronal populations. ▪ Neurotrophin-4 (NT-4) Function: Like BDNF; promotes neuron survival and enhances synaptic plasticity. ▪ Ciliary Neurotrophic Factor (CNTF) Function: Supports motor and sensory neuron survival; provides neuroprotection. ▪ Glial Cell Line-Derived Neurotrophic Factor (GDNF) Function: Promotes survival of dopaminergic neurons; maintains peripheral neuron health.