Microanatomy Flashcards
1
Q
Cells within the CNS
A
- Neurons
- Glia: astrocytes, oligodendrocytes, microglia
- Ependymal cells (of the choroid plexus): simple cuboidal epithelium
- Endothelium
- Cells of the meninges
- Little ECM in the CNS, instead up to 20% of the volume of the brain is CSF
- Accumulation of water results in cerebral edema
2
Q
Grey vs white matter
A
- Grey matter contains neuron cell bodies, as well as glial cells, axons, and dendrites
- Neuropil is the fiber rich region btwn cell bodies (contains dendrites, axons, glia)
- Grey matter is on the inside of the spinal cord (butterfly shape) and on the outside of the brain (cortex)
- White matter contains long-distance myelinated axons, astrocytes and oligodendrocytes
- White matter is on the outside of the spinal cord and the inside of the brain
3
Q
Neurons
A
- Cell bodies have a large euchromatic nucleus w/ prominent nucleolus (active protein synthesis)
- Also contain lots of RER and polyribosomes (Nissl bodies)
- Axon hillock and the rest of the axon is devoid of nissl bodies
- Dendrites and spines have nissl bodies in proximal areas (to soma)
- Retrograde transport provides a point of access for toxins and viruses into CNS
4
Q
Classification of neurons
A
- Number of processes: can be unipolar (like in DRGs: have one long axon continuous w/ dendrites), bipolar (one long dendrite, then cell body, then axon), or multipolar (typical neuron, many dendrites off the body to one axon)
- Arrangement of processes
- NT type
- Shape of cell body, direction of transmission, location in body
5
Q
Synapses and spines
A
- Presynaptic cell has vesicles to store NTs, and the active zone which is the site of vesicle fusion and NT release
- Postsynaptic component can be found on dendrites (axo-dendritic synapse), cell bodies (axo-somatic), or axons (axo-axonic)
- The postsynaptic area (postsynaptic density) contains the NT receptors
- Spines are branches off dendrites that accept presynaptic input (majority of excitatory synapse location), are involved in learning
- Abnormal spine morphology/# are hallmarks of neurological diseases like fragile X and AD
6
Q
Synaptogenesis
A
- Formation of new synapses
- Most neurons are generated prior to birth
- Synapse # increases over the first few years of like, followed by a period of pruning
- During pruning the synapse # can fall by 50%
- The increase in synapse # reflects more connections, not more neurons
- Likewise, the growth of brain size early in life is due to an increase in dendritic processes, not in neuron #
7
Q
Glia cells
A
- 3 classes in the CNS: astrocytes, oligodendrocytes, microglia
- Play many important roles in normal CNS function, including structural support
8
Q
Astrocytes 1
A
- Stellate cells that express glial fibrillary acidic protein (GFAP) and are connected to each other by gap junctions
- Regulate the ECF by adjusting ion concentration and clearing excess glutamate (which could cause harm to neurons)
- Since neurons have limited ability to combat ROS, astrocytes are required to couple w/ neurons and prevent oxidative stress-induced cell death
- Also store glycogen
9
Q
Astrocytes 2
A
- Have processes that ensheath the synapse, and play a role in synaptic formation/remodeling
- Astrocyte processes can terminate in endfeet to form the layer glia limitans at the brain surface and around blood vessels
- Neuron activity triggers the release of vasoactive substances by astrocytes to increase blood flow to the region due to the higher metabolic demand
10
Q
Reactive gliosis
A
- Hypertrophy of the cell body of astrocytes, increase growth of processes, expression of GFAP, and proliferation
- This can serve to limit the extent of neuronal injury and enhance neuronal survival
- But this can also lead to edema, inflammation (release of cytokines), and/or form a glial scar that inhibits axonal regeneration
11
Q
Oligodendrocytes (OD)
A
- Responsible for myelin formation in CNS (schwann cells responsible for myelin in PNS)
- Unlike schwann cells, a single OD can myelin ate multiple axons
- The process of myelination is not complete in the prefrontal cortex until the third decade in life
- Demyelinating disorders (MS, transverse myelitis) can be cause by genetic factors, infections, AI rxns, and the environment
12
Q
Microglia (MG)
A
- Resident macrophages (smallest glial cells in the brain)
- Identify and phagocytose infectious agents in the CNS, remodel local environment, and participate in synaptic pruning
- Following injury they are responsible for the removal of dying cells and cellular debris
13
Q
BBB 1
A
- Endothelial cell tight junctions form the BBB, preventing large or hydrophilic molecules from exiting the blood
- Hormones, O2, and CO2 can still freely diffuse, and molecules needed for function (glc, AAs) are transported across the endothelium
- Endothelium in the CNS have high abundance of mito
- Astrocyte endfeet are not part of the BBB, but early on in development they induce the formation of the tight junctions
14
Q
BBB 2
A
- BBB protects the brain from most common bacterial infections, except syphilis and lyme disease
- BBB becomes more permeable during times of inflammation
- In certain regions (circumventricular organs) the BBB is interrupted
- This is to allow the brain to respond to chemical changes in the blood and to secrete neuropeptides into the blood
15
Q
Circumventricular organs
A
- The median eminence and neurohypophysis are involved in the regulation and release of pituitary hormones
- The area postrema (located in the medulla) contains chemoreceptors to trigger vomiting (can also detect bacteria and drugs)
