LECTURE6.Cells of the Nervous System_e4277683e44a29f977daea51384a0f99

Introduction to the Nervous System

Cells of the Nervous System:

Overview of two main types of cells in the nervous system:

  • Neurons: Primary cells responsible for transmitting information through electrical impulses and chemical signals. Neurons consist of three main parts: dendrites, cell body (soma), and axon.

  • Glia: Supportive cells that provide a variety of functions, including protection, nourishment, and maintenance of homeostasis for neurons. Glial cells play a crucial role in maintaining the overall health and functionality of the nervous system.

Cell Structures

Main Components:

  • Cell Membrane: Protects and contains the cell, regulating the entry and exit of substances, thus maintaining cellular integrity.

  • Dendrite: Branch-like structures that receive signals from other neurons and relay them to the cell body for processing.

  • Cell Body (Soma): Contains the nucleus, which houses genetic material, and organelles that perform vital cellular functions.

  • Axon: A long, slender projection that transmits impulses away from the cell body to communicate with other neurons or muscles.

  • Oligodendrocyte: Type of glial cell found in the central nervous system (CNS) that creates myelin, a protective sheath that insulates axons to speed up signal transmission.

  • Node of Ranvier: Gaps between segments of myelin sheath that facilitate rapid signal transmission through saltatory conduction, allowing action potentials to jump from one node to another.

  • Myelin Sheath: Insulating layer surrounding axons that enhances the speed and efficiency of electrical signal conduction.

  • Synapse: Junction between neurons that allows communication through the release of neurotransmitters, ensuring effective signal transmission across nerve cells.

Diversity of Glial Cells

Morphologies of Glial Cells:

  • Glial cells exhibit a variety of shapes and functions, suggesting significant heterogeneity within this category. More than 90% of glial cells are classified as macroglia, which encompass astrocytes, oligodendrocytes, and ependymal cells.

Neurons and Glia Interrelation

Similarities:

  • Neurons and glial cells share fundamental characteristics, underscoring their specialized roles in the nervous system. Despite their specialization, both cell types retain essential components necessary for cellular functions and communication.

Special Cells:

  • While they are specialized for distinct functions—such as information transmission in neurons and support in glial cells—they both possess structures like axons, myelin sheaths, and organelles such as the endoplasmic reticulum and Golgi apparatus, suggesting a shared evolutionary background.

Membrane Extensions

Golgi and Endoplasmic Reticulum:

  • Membranes project from the cell body into dendrites, allowing for effective communication and integration of signals from multiple sources, enhancing neuronal functionality.

Cytoskeleton Role

Cytoskeleton's Function:

  • The cytoskeleton is a dynamic framework that determines the shape and structure of neurons and glial cells. It plays a crucial role in intracellular support and transport.

Types:

  • Microtubules (A): Hollow tubes made of tubulin that provide structural support and pathways for intracellular transport.

  • Neurofilaments (B): Intermediate filaments that provide tensile strength and structural integrity to neurons.

  • Microfilaments (C): Composed mainly of actin, these small structures are involved in cellular movement, shape maintenance, and movement of cellular components.

Cytoskeletal Elements

Three Major Types of Cytoskeletal Elements:

  • Actin Filaments (Microfilaments): Essential for cell movement, shape, and signaling.

  • Intermediate Filaments: Provide a supportive scaffold for the cell, helping to maintain shape and resist stress.

  • Microtubules: Key players in intracellular transport and maintaining cell structure, also crucial during cell division.

Continued Cytoskeleton Function

Cytoskeleton's Influence on Shape:

  • The cytoskeleton's dynamic nature is crucial for the functions of both neurons and glial cells, influencing their morphology and adaptability in response to environmental changes.

Motor Proteins Functionality:

  • Motor proteins, such as kinesin and dynein, facilitate the movement of vesicles and organelles along microtubules, which is essential for the transport of materials within neurons and for maintaining cellular homeostasis.

Axonal Transport

Active Transport Mechanisms along Axon and Dendrites:

  • Involves several components, including the synthesis and assembly of proteins in the cell body and their movement to the axon terminal.

  • Axonal Transport: The systematic movement of materials to and from the cell body, critical for maintaining neuron function.

  • Release of Neurotransmitters: This process is vital for the communication between neurons, enabling the transmission of signals across synapses.

  • Retrograde Transport: Recycling of materials back to the cell body for degradation or reuse, essential for cellular maintenance and health.

Protein Synthesis

Protein Assembly in Neurons:

  • Involves ribosomes, nuclear pores, lysosomes, and the endoplasmic reticulum, which collectively contribute to synthesizing and exporting proteins fundamental for neuronal functioning, particularly as secretory cells that release neurotransmitters.

Roles of Glial Cells

Myelination:

  • Glial cells like oligodendrocytes in the CNS and Schwann cells in the PNS form insulating myelin sheaths that enhance signal transmission efficiency and speed along axons.

Types of Myelination:

  • Central Nervous System (CNS): Oligodendrocytes create myelin for multiple axon segments.

  • Peripheral Nervous System (PNS): Schwann cells provide myelin to individual axons.

Nodes of Ranvier

Structure and Function:

  • Regular gaps between myelin sheaths, Nodes of Ranvier are essential for rapid signal transmission through saltatory conduction, allowing action potentials to propagate efficiently.

Saltatory Conduction Dynamics

Mechanism:

  • In myelinated axons, action potentials propagate by jumping from one Node of Ranvier to another, significantly speeding up signal transmission and improving the efficiency of neuronal communication.

Myelination Defects

Impact of Myelination Defects:

  • Observations in normal versus Shiverer mutant mice highlight the importance of myelination for proper nervous system function, as reduced myelination severely affects neural communication.

  • Interventions such as transfection with a normal gene have been explored and shown to improve myelination and restore functionality in affected neurons.

Astrocyte Functionality

Astrocytes:

  • These glial cells have complex processes that connect them to synapses, playing critical roles in supporting synaptic function and contributing to neurovascular coupling, reinforcing their importance in neural communication and support.

Microglia's Role

Microglia Functions:

  • Although crucial for CNS health and responding to damage or disease, the specific roles of microglia remain poorly understood even after extensive study over the past century, making them an important area for ongoing research.

Cerebrospinal Fluid Production

Ependymal Cells and Choroid Plexus:

  • Ependymal cells lining the ventricles and choroid plexus are responsible for producing cerebrospinal fluid (CSF), which is essential for cushioning the brain and spinal cord, providing nutrients, and removing waste.