Astrocytes | Nervous system physiology | NCLEX-RN | Khan Academy

Summary

This video explains the crucial roles of astrocytes, star-shaped glial cells in the central nervous system. Astrocytes support the brain and spinal cord by providing structural scaffolding, forming glial scars after injury, and maintaining homeostasis for optimal neuronal function. They contribute to the blood-brain barrier, protect neurons, and help clear synapses by removing neurotransmitters. Astrocytes also influence neuron and glial communication. With their wide range of functions, they are essential for the proper functioning of the nervous system, making them one of the most versatile and hardworking cell types in the body.

Takeaways

• 😀 Astrocytes are glial cells in the central nervous system, derived from neural stem cells.
• 🌟 The name 'astrocyte' comes from the Greek word for 'star cell' because of their star-like appearance under a microscope.
• 🧠 Astrocytes have numerous highly branched processes and special structures called end-feet at the ends of their processes.
• 🔧 Astrocytes perform a wide variety of functions, including providing structural support to the brain and spinal cord.
• ⚡ Astrocytes form a 'glial scar' in response to injury, helping to wall off the affected area and promote healing.
• 🩹 This process, known as gliosis, involves astrocytes proliferating and migrating to injury sites, contributing to scar tissue formation.
• 💧 Astrocytes maintain homeostasis by regulating ion concentrations in the interstitial fluid, ensuring an optimal environment for neurons.
• 🍭 Astrocytes also release lactate, which provides energy to neurons that have limited internal energy stores.
• 🛡️ Astrocytes help form the blood-brain barrier, preventing large molecules in the bloodstream from entering the central nervous system.
• 🧹 Astrocytes assist in clearing neurotransmitters from synapses, ensuring effective communication between neurons by resetting synapses after each use.
• 🔄 Overall, astrocytes are critical for the function and health of the central nervous system, playing a role in nearly every aspect of its operation.

Q & A

What are astrocytes and how did they get their name?

Astrocytes are glial cells of the central nervous system that are derived from neural stem cells. They got their name from the Greek words meaning 'star cell' due to their star-like appearance when observed under a microscope, as they have highly branched processes.

What is the function of astrocytes' end-feet?

Astrocytes' end-feet are specialized structures at the tips of their processes. They play a crucial role in the blood-brain barrier, where they cover blood vessels, preventing large molecules from entering the central nervous system unless necessary. They also surround synapses to help clear neurotransmitters and maintain proper neural communication.

How do astrocytes contribute to the structural support of the central nervous system?

Astrocytes provide the structural framework for the central nervous system by occupying a large portion of the space in the brain and spinal cord. They create the scaffold that holds neurons and other glial cells in place, contributing to the overall structure of the CNS.

What happens to astrocytes when there is an injury in the CNS?

In response to CNS injury, astrocytes proliferate and migrate to the injury site. They form a protective tissue called the glial scar by growing thicker, longer processes around the injury. This helps wall off the damaged area, similar to scar tissue in other parts of the body.

What is gliosis and why is it important?

Gliosis, also known as astrogliosis or reactive astrocytosis, is the process where astrocytes respond to injury in the central nervous system by proliferating and forming a glial scar. This process is crucial for limiting damage and providing structural support during the repair of the CNS after injury.

What role do astrocytes play in maintaining homeostasis in the CNS?

Astrocytes help maintain homeostasis in the CNS by regulating the interstitial fluid around neurons. They monitor and adjust the concentrations of ions, particularly potassium, to ensure a stable environment for proper neuronal function. They also release lactate to neurons when oxygen or glucose supply is insufficient.

How do astrocytes support neurons during metabolic stress?

Astrocytes support neurons during periods of metabolic stress by releasing lactate into the interstitial fluid. Since neurons have limited internal energy stores, lactate provides an alternative fuel source to maintain their activity when oxygen and glucose are scarce.

What is the blood-brain barrier and how do astrocytes contribute to it?

The blood-brain barrier is a protective barrier that prevents large molecules in the blood from entering the central nervous system, unless specifically allowed. Astrocytes contribute to this barrier by covering blood vessels with their end-feet, helping regulate the movement of substances between the blood and the brain/spinal cord.

How do astrocytes help clear neurotransmitters from synapses?

Astrocytes help clear neurotransmitters from synapses by surrounding the synaptic cleft with their end-feet. This process is crucial to resetting the synapse after neural communication, ensuring that neurotransmitters are removed efficiently so the synapse can be used again for proper signaling.

Why are astrocytes considered essential in the CNS?

Astrocytes are considered essential because they perform a wide range of functions that are vital for the proper functioning of the CNS. They provide structural support, assist in injury repair, regulate the neural environment, maintain the blood-brain barrier, and facilitate neurotransmitter clearance, making them indispensable for maintaining homeostasis and neural communication.