2.2 Flashcards
(14 cards)
- How is the peripheral nervous system (PNS) developed?
The PNS is derived from neural crest cells, which migrate from the neural tube and differentiate into diverse cell types—including sensory neurons (e.g., dorsal root ganglia), autonomic ganglia (sympathetic and parasympathetic), enteric neurons, and Schwann cells—to form the extensive network that connects the CNS to the rest of the body.
- What are neural crest cells and what is their significance in neural development?
Neural crest cells are a multipotent cell population that emerge from the lateral edges of the neural tube. They migrate throughout the embryo and give rise to many structures of the PNS as well as other cell types, making them essential for the formation of sensory, autonomic, and peripheral support cells.
- How are new neurons generated and positioned within the CNS during development?
New neurons are born in the ventricular zone (VZ) of the neural tube, where mitotic progenitor cells divide. After birth, many neurons migrate—often guided by radial glial processes—to their appropriate positions, establishing the layered structure of the CNS and forming the basis for neural circuits.
- What role do radial glial cells play during CNS development?
Radial glial cells serve both as neural progenitors and as a scaffolding system that guides the migration of postmitotic neurons from the ventricular zone outward to form the cortical layers and other organized CNS structures.
- Where does cell proliferation occur in the developing CNS, and what happens to the newborn neurons?
Cell proliferation occurs in the ventricular zone (VZ). Here, progenitor cells divide to generate neurons, which then migrate outward to form specific brain regions; this migration is essential for establishing proper neural networks and circuit connectivity.
- How is neural identity established during early development?
Neural identity is set up by diffusible signaling molecules that act in gradients. Bone Morphogenetic Proteins (BMPs) from the roof plate provide dorsal (lateral) signals, while Sonic hedgehog (Shh) from the notochord and floor plate delivers ventral (medial) signals. These gradients instruct cells about their positional fates within the neural tube.
- What is the specific role of Sonic hedgehog (Shh) in neural patterning?
Shh is secreted by the notochord and floor plate, providing a ventralizing signal that specifies the fate of cells in the ventral neural tube, including the generation of motor neurons and interneurons essential for forming motor circuits.
- How do Bone Morphogenetic Proteins (BMPs) influence neural development?
BMPs are secreted from the roof plate and create a dorsal signaling environment in the neural tube. They promote dorsal cell fates, such as the formation of sensory neurons, ensuring that the appropriate regions of the CNS develop their specific identities.
- Describe the organization of the spinal cord in terms of neural circuits. How are sensory and motor pathways arranged?
In the spinal cord, the dorsal (posterior) horn is specialized for processing sensory inputs (with neurons receiving afferent signals from dorsal root ganglia), while the ventral (anterior) horn contains motor neurons that send efferent outputs via the ventral roots to muscles. This dorsal-ventral segregation forms the basic template for spinal neural circuits.
- How does the neural tube differentiate during the vesicle stages?
During differentiation, the neural tube develops into primary vesicles (prosencephalon, mesencephalon, and rhombencephalon) and then secondary vesicles. These stages culminate in the formation of major brain regions such as the telencephalon (cerebral cortex, basal ganglia, amygdala, hippocampus), diencephalon (thalamus, hypothalamus), midbrain, pons, cerebellum, and medulla, as well as the spinal cord.
- In what way do diffusible signals help establish neural circuits?
Diffusible signals like Shh and BMPs set up positional information within the neural tube, guiding the differentiation of neurons with specific identities. This molecular patterning is crucial for forming functional neural circuits that underlie sensory, motor, and integrative processes.
- How do neural crest cells contribute to the formation of neural circuits outside the CNS?
Once they migrate from the neural tube, neural crest cells differentiate into peripheral neurons (including sensory and autonomic neurons) and supporting cells, which together establish the circuits that transmit information between the CNS and peripheral organs.
- What is the importance of the ventricular zone (VZ) in CNS development?
The ventricular zone (VZ) is the proliferative region of the neural tube where neural progenitor cells multiply. It supplies the neurons and glial cells that, after migration and differentiation, form the structured neural circuits of the mature CNS.
- Summarize how signaling molecules provide positional cues during neural tube development.
Signaling molecules such as BMPs and Shh are secreted from the roof plate and floor plate, respectively, creating opposing gradients. These gradients provide cells with positional cues that determine their fate—whether they become part of the dorsal sensory networks or the ventral motor circuits—ultimately shaping the organizational layout of the CNS.
