Neurodevelopment happens to be something that I'm particularly weak on, and the first chapter of our text jumps right into it, for better or for worse.
A section titled: "A note on times and ages" is in part this inspiration for this post. This section points out some very basic clinical conventions used to delimit certain periods of neural development:
1. Pregnancy is timed from the 1st day of the last menstrual period.
2. An 8-week old ball of cells is called a fetus.
3. The embryonic period is divided in to 23 Carnegie stages (not sure where Carnegie comes from), with the neural folds appearing at stage 8.
More on development:
By the end of the 3rd week the neural folds have begun to fuse with one another to form the neural tube. The cells that line the tube will eventually become the neurons that make up all of the neurons in the CNS.
Neural crests are what give rise to many neuroglia and other cells outside of the nervous system. These cells migrate extensively.
An interesting fact of the brain is that during development there are many more neurons formed than will go on to exist when the animal is an adult. Evidence has shown that in vertebrates cells that died were those that failed to make synaptic connections. Unfortunately, there is currently no evidence to suggest that adult human brains regenerate neurons (with the exception of an area of the hippocampus and olfactory neurons).
The developing nervous system is conventionally divided into 5 parts and their names change as the organism develops:
- Telencephalon $\rightarrow$ Cortex
- Diencephalon $\rightarrow$ Thalamus/Hypothalamus
- Mesencephalon $\rightarrow$ Midbrain
- Metencephalon $\rightarrow$ Pons and Cerebellum
- Myelencephalon $\rightarrow$ Medulla Oblongata
Here's a nice breakdown from the text:
Another interesting part of neural development is the construction of the meninges. The meninges are a membraneous tissue that protect the brain. The meninges is somewhat like plastic wrap for the brain, at least upon initial visual inspection.
Key parts of the brain:
- Spinal cord
- Least differentiated part of the nervous system
- pair of nerves is connected to the spinal cord (dorsal sensory root, ventral motor root)
- H-shaped spatial organization with gray matter as the H and white matter in the surrounding area
- Gray matter in the spinal cord is important for reflexes
- Medulla oblongata
- A continuation of the spinal cord
- Pons
- Two-part structure
- Tegmentum
- ascending/descending tracts
- Basal pons
- Provides connections between the cortex of a cerebral hemisphere and that of the contralateral cerebellar hemisphere
- Midbrain
- Dorsal region
- Tectum: lower level visual/auditory control
- Red nucleus/substantia nigra: important in motor control
- attached to the mid brain via the superior cerebellar peduncles
- Cerebellum
- Extremely large, contains most of the neurons of the brain
- Important for muscular compensation during movement
- Diencephalon
- Central core of the cerebrum
- Largest component is the thalamus
- Epithalamus and pineal gland constitute an endocrine organ
- Interestingly, the retina is a derivative of the diencephalon
- Telencephalon
A human brain (!) :
No comments:
Post a Comment