Central Nervous system

Question 1

Differentiate between grey matter and white matter

Answer 1

1. grey matter: neuron cell bodies located here, glial cells, axons, and dendrites. fiber rich regions between cell bodies are called neuropil
2. white matter: long distance myelinated axon tracts. Astrocytes and oligodendrocytes are also present

Question 2

Describe the characteristics of synapses and spines.

Answer 2

• pre-synaptic component, characterized by presence of synaptic vesicles, the active zone: site of synaptic vesicle fusion and neurotransmitter release
• post-synaptic component: found of dendrites, cell bodies, or axons
• spines: small protrusions from dendritic staff where majority of excitatory glutamatergic synapses are found

Question 3

What are the characteristics of astrocytes?

Answer 3

• stellate cells that express glial fibrillary acidic protein (GFAP) and numerous processes. vimentin and intermediate filaments.
• function: maintain extracellular environment of CNS, regulate concentration of ions, clear excess glutamate, enhance neuronal ability to combat oxidative stress.
• have endfeet: forms glia limitans at brain surface and around blood vessels
• reactive gliosis: hypertrophy of cell body, increased growth of processes, increase in GFAP expression and proliferation–>limit neuronal injury or form glial scar to limit axonal regeneration

Question 4

What are the characteristics of oligodendrocytes?

Answer 4

• myelin formation in CNS
• can myelin ate multiple axons
• late event in CNS development

Question 5

What are the characteristics of microglia cells?

Answer 5

• resident macrophages of the brain, identify and phagocytose infectious agents that gain access to the CNS
• motile, can sample and remodel local environment
• possible participation in synaptic pruning
• removal of dying cells and debris

Question 6

Describe the basis of the blood brain barrier

Answer 6

• formed by endothelial cells of capillaries-prevents large or hydrophilic molecules from penetrating brain parenchyma
• tight junctions, limited vesicular transport, high mitochondria number

Question 7

what are the circumventricular organs?

Answer 7

• circumventricular organs: interrupted BBB
  1. median eminence and neurohypophysis-invovled in regulation of pituitary hormones
  2. area postrema-in medulla-chemoreceptor trigger zone for vomiting-detect blood borne substances

Question 8

Describe the characteristics of ependymal cells and the choroid plexus

Answer 8

• ependymal cells: ciliated simple cuboidal epithelium lining ventricles and central canal of spinal cord
• cilia assist in circulation of CSF through ventricles
• Choroid plexus made of ependymal cells- they have tight junctions and forms blood-CSF barrier
• active transport of Na+ -produces most of CSF

Question 9

What is the difference between CT and MRI?

Answer 9

CT=computed tomography
-uses ionizing radiation and forms cross sectional images. useful in evaluation of trauma, stroke, in emergency setting. but has poor CNS tissue contrast
MRI=magnetic resonance imaging
-detects RF signal from H nuclei in magnetic field
-optimal imaging of CNS
-many sequences possible

Question 10

What is the difference in T1WI and T2WI in MRI?

Answer 10

Water/CSF is dark in T1 and bright in T2

• brain lesions: dark in T1 and bright in T2
• vascular malformations: dark on T1 and T2
• Neoplasms: bright on post contrast T1 due to leakage of contrast due to breakdown of BBB