Neurons and Their Components

Myelin

  • Definition: Myelin is a fatty substance that surrounds the axons of neurons, serving as an insulator and facilitating rapid electrical signal transmission.

Nucleus

  • Definition: A nucleus refers to a collection of cell bodies within the central nervous system.

  • Common Terms for Cell Body:

    • Cell Body

    • Soma

    • Perikaryon

Cell Body Structure

  • Contains usual organelles such as:

    • Nucleus

    • Ribosomes

    • Rough Endoplasmic Reticulum (ER), also known as chromatophilic substance

    • Golgi Apparatus

    • Mitochondria

  • Neurofibrils:

    • Structure that maintains cell shape and integrity.

  • Types of Clusters of Cell Bodies:

    • Ganglia: A cluster of cell bodies found in the Peripheral Nervous System (PNS).

    • Nuclei: A cluster of cell bodies found in the Central Nervous System (CNS).

Dendrites

  • Definition: Dendrites are branching extensions of the cell body.

  • Functions:

    • Increases surface area for receiving input signals.

    • Contains cytoplasm and organelles.

    • Some dendrites have thorny structures called dendritic spines.

Axon

  • Definition: The axon is the part of the neuron that transmits incoming information to the axon hillock by graded depolarizations.

  • Characteristics:

    • Typically, there is one axon per neuron.

    • It is a projection of the cell body that arises from the axon hillock.

    • Can vary in length from short to long (up to 1 meter).

    • May branch into axon collaterals.

    • Usually has terminal branches, approximately 10,000.

  • Function: Axons are the conduction components of neurons; they transmit electrical impulses.

  • Terminals:

    • Act as the secretory component of neurons, releasing neurotransmitters (Nt's).

  • Organelles in Axons:

    • Contains organelles but lacks rough ER and Golgi apparatus, thus relying on the cell body for protein synthesis.

    • Axons degrade quickly when damaged.

  • Axolemma:

    • The plasma membrane of the axon.

Molecular Transport in Axons

  • Molecular Traffic:

    • There is a constant two-way transport of molecules inside the axon.

  • Anterograde Transport:

    • Refers to the movement of materials from the cell body to the axon terminal.

    • Functions include:

    • Delivery of mitochondria and replacement molecules for the axolemma.

    • Neurotransmitter synthesis.

    • Transport Mechanism: Transported by the protein kinesin.

  • Retrograde Transport:

    • Refers to the movement of materials from the terminal back to the cell body.

    • Functions include:

    • Degradation and recycling of molecules and organelles.

    • Transport Mechanism: Transported by the protein dynein.

Vesicle Transport Mechanism

  • Concept: Motor molecules can attach to receptors on vesicles or organelles and carry these organelles along the microtubule tracks of the cytoskeleton.

  • Powered by: ATP, suggesting an active transport mechanism.