All bleeding eventually stops.
ATP production in mitochondria (purple) can lead to the formation of reactive oxygen species (ROS) that damage mitochondria. When an organelle is beyond repair, the cellular recycling system (green) kicks-in and targets them for mitophagy, a specialized form of mitochondrial degradation.
Image: A primary retinal ganglion cell expresses a red fluorescent protein targeted to mitochondria, a green fluorescent protein fused to the autophagosomal marker LC3, and a cyan fluorescent protein in the cytosol. This image reveals how autophagosomes (green) can contact individual mitochondria (purple), before their ingestion by mitophagy.
The Neural Tube
- the neural tube forms the brain and spinal cord
- fusion of neural groove extends rostrally and caudally
- begins at the level of 4th somite
- closes neural groove “zips up” in some species.
- humans appear to close at multiple points along the tube.
- leaves 2 openings at either end - Neuropores
- cranial neuropore closes before caudal
Failure for the neural tube to close correctly or completely results in a neural tube defect.
This transmission electron micrograph shows a Langerhans cell (purple) exiting an isolated epithelium to disseminate the HIV-1 infection. A long cytoplasmic extension of the Langerhans cell remains anchored between basal keratinocytes and contains a large vacuole with one HIV-1BaL virion (red) inside. Epithelial sheets were inoculated with the virus by centrifugation (i.e., spinoculation) for 2 hours and then fixed in Karnovsky’s fixative for electron microscopy.
Carnegie stage 13 Embryo showing neural tube and brain flexures
Rapid growth folds the neural tube forming 3 brain flexures:
- cephalic flexure - pushes mesencephalon upwards
- cervical flexure - between brain stem and spinal cord
- pontine flexure - generates 4th ventricle
Here a mouse retina is seen en face with these “J” retinal ganglion cells marked by the expression of one fluorescent protein. The millions of other entangled neurons are not marked and thus are invisible in this image. Image obtained with a confocal scanning microscope and pseudocolored.
- neural stem cells lie in the layer closest to the ventricular space, the ventricular layer
- this layer generates both neuroblasts and glioblasts
Neuroblasts - neurons arise first as neuroblasts and migrate along radial gial, their migration stops at cortical plate. Glioblasts - glia arise later as glioblasts
Both neurons and glia undergo a complex process of growth, differentiation and interaction over a long developmental time period.
Metaphase and Anaphase
Upon entry into anaphase, the mitotic spindle reorganizes dramatically: kinetochore fibers attached to chromosomes shorten, bringing chromatids toward the poles. The astral microtubules, which radiate from each spindle pole, elongate until they reach the cell surface. Meanwhile, a bundle of antiparallel microtubules, called the ‘central spindle,’ remains at the midpoint between the two poles. The central spindle and astral microtubules collaborate to position the division plane during cytokinesis.
Syringomyelia is a generic term referring to a disorder in which a cyst or cavity forms within the spinal cord. This cyst, called a syrinx, can expand and elongate over time, destroying the spinal cord. The damage may result in pain, paralysis, weakness, and stiffness in the back, shoulders, and extremities. Syringomyelia may also cause a loss of the ability to feel extremes of hot or cold, especially in the hands. The disorder generally leads to a cape-like loss of pain and temperature sensation along the back and arms. Each patient experiences a different combination of symptoms. These symptoms typically vary depending on the extent and, often more critically, to the location of the syrinx within the spinal cord.
Image: An idiopathic syrinx. See the thin light grey shape inside the spinal cord, placed at centre in the bottom half of the above image.