Nervous system notes pdf biology 12

The net effect is a calcium wave that propagates from cell to cell. In general, there are two types of astrocytes, protoplasmic and fibrous, similar in function but distinct in morphology and distribution. Protoplasmic astrocytes have short, thick, highly branched processes and are typically found in gray matter. Fibrous astrocytes have long, thin, less branched processes and are more commonly nervous system notes pdf biology 12 in white matter.

Highly branched processes and are typically found in gray matter. Yet increasingly crucial, these cells are found in all regions of the brain and spinal cord. Protoplasmic and fibrous, glial modulation of synaptic transmission in the hippocampus”. Glia derive from the neural crest. Not only does the ratio of glia to neurons increase through evolution, some glial cells function primarily as the physical support for neurons.

They also have been involved in neuronal circuits playing an inhibitory role after sensing changes in extracellular calcium. They are also thought to act as neural stem cells. Their differentiation abilities are more restricted than those of neuroepithelial cells. In the developing nervous system, radial glia function both as neuronal progenitors and as a scaffold upon which newborn neurons migrate. In the mature brain, the cerebellum and retina retain characteristic radial glial cells.

These cells help regulate the external chemical environment. Like astrocytes, they are interconnected by gap junctions and respond to ATP by elevating intracellular concentration of calcium ions. They are highly sensitive to injury and inflammation, and appear to contribute to pathological states, such as chronic pain. Are found in the intrinsic ganglia of the digestive system. They are thought to have many roles in the enteric system, some related to homeostasis and muscular digestive processes. These cells are found in all regions of the brain and spinal cord.