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.