Neuroglia and Neurons Overview

Astrocytes

  • Meaning of Astro: The term "astro" comes from the Greek word for star, referring to their star-shaped appearance.
  • Function:
    • Astrocytes support neurons by anchoring them to nearby blood vessels (capillaries) and help maintain the structure of the nervous system by keeping neurons located closely together.
    • They allow nutrients and oxygen from capillaries to diffuse effectively to neurons.
    • Other functions: Recycling neurotransmitters and maintaining the extracellular environment. However, the primary role of holding neurons and capillaries together is vital for neuronal health.

Microglia

  • Meaning of Micro: The prefix "micro" signifies small size.
  • Role:
    • Microglia serve as the primary immune defense in the central nervous system (CNS).
    • They act as scavengers, cleaning up debris and removing dead cells or damaged neurons.
    • They respond to injury or infection by phagocytosing pathogens such as bacteria or viruses, thus preventing infection. If ineffective, conditions like meningitis can occur.
    • They can be thought of as substitute white blood cells due to the blood-brain barrier's restricting access to conventional white blood cells from the bloodstream.

Ependymal Cells

  • Location: Found lining the lateral ventricles in the brain.
  • Function:
    • Ependymal cells contribute to the circulation of cerebrospinal fluid (CSF). They possess cilia that help propel CSF through the ventricular system.
    • CSF is essential for maintaining brain health; it cushions the brain and aids in nutrient exchange between neurons and blood vessels.

Oligodendrocytes

  • Meaning: "Oligodendrocyte" can be broken down into three parts: "oligo" (few), "dendro" (branches), and "cyte" (cell). Therefore, it refers to a cell with few branches.
  • Function:
    • Oligodendrocytes produce the myelin sheath that insulates axons in the CNS.
    • This myelin sheath is crucial for the efficient transmission of electrical impulses along the nerve fibers.
    • Degeneration in myelin sheaths can be associated with neurodegenerative diseases, such as various forms of dementia.

Schwann Cells

  • Similar to oligodendrocytes but function in the peripheral nervous system (PNS).
  • Schwann cells wrap around the axons of neurons to help form myelin sheaths.

Satellite Cells

  • These are found in the PNS and are thought to provide support to the neuronal cell bodies, but their exact function remains less clear compared to other neuroglial cells.

Neurons

  • Neurons are the cells responsible for sending electrical signals throughout the nervous system.
  • Structures of a neuron include dendrites (receiving signals), soma (cell body), and axon (sending signals).

Nerve Structure

  • Nerves are composed of bundles of neurons wrapped in connective tissue.
  • Endoneurium: wraps individual neuron fibers.
  • Perineurium: surrounds groups of fibers (fasicles).
  • Epineurium: encases the entire nerve.

Types of Nerves

  • Sensory nerves: Carry signals toward the CNS (e.g., optic nerve).
  • Motor nerves: Carry signals away from the CNS (e.g., oculomotor nerve).
  • Mixed nerves: Contain both types of fibers (e.g., vagus nerve).

Cranial Nerves Overview

  1. Olfactory Nerve: Sensory; innervates nasal mucosa for smell.
  2. Optic Nerve: Sensory; innervates the retina in the eye for vision.
  3. Oculomotor Nerve: Motor; controls most eye movements.
  4. Trochlear Nerve: Motor; innervates the superior oblique muscle of the eye.
  5. Abducens Nerve: Motor; innervates the lateral rectus muscle of the eye.
  6. Trigeminal Nerve: Mixed; sensory for face and motor for chewing.
  7. Facial Nerve: Mixed; involved in facial movements and taste.
  8. Vestibulocochlear Nerve: Sensory; responsible for hearing and balance.
  9. Glossopharyngeal Nerve: Mixed; innervates tongue and throat structures for taste and swallowing.
  10. Vagus Nerve: Mixed; regulates heart and digestive tract activities, innervating thoracic and abdominal organs.
  11. Accessory Nerve: Motor; innervates neck muscles.
  12. Hypoglossal Nerve: Motor; innervates tongue muscles for speech and swallowing.

Summary Notes

  • Each glial cell has a specific function that contributes to the overall health and operation of neurons.
  • Understanding the distinct types of CNS and PNS cells aids in recognizing how nerves conduct signals and maintain homeostasis in bodily functions.