Histology of the Central Nervous System (Dennis) Flashcards
Typical neuron:
Cell body with large nucleus, well developed nucleolus and nissi substances/bodies (ribosomal activity since neurons are very active)
Dendrites:
Axon:
-Extend from perikaryon (extensive branching)
Has numerous dendritic spines that increase the receptive surface area
-Long axon emerges from the axon hillock
What is a neuropil?
Dense network of fibers and their branches and synapses together with glial filaments
Anterograde axonal transport:
Cell body > axon
Uses kinesin, microtubule associated motor protein
Slow transport
Fast transport
- Anterograde movement of substances (0.2-4mm/day) and typically cytoskeletal elements
- bidirectional movement of organelles (20-400 mm/day), may include endocytosed toxins and viruses
How does synaptic communication work?
Nerve impulse transmitted from one neuron to effector cells (unidirectional)
Electrical signal from presynaptic cell converted to chemical signal that affects postsynaptic cell (via neurotransmitters)
Presynaptic terminal:
Bouton contains mitochondria and synaptic vesicles > release NT via exocytosis
Modularities of synapses:
Dendrites are not the only place neurons contact each other. Can be axon to cell body, axon to axon etc. Allows different signals to come in at the same time
What is electrical synapse?
Flow of electrical current between neurons via gap junctions and links pre and postsynaptic neurons
Contains connexon proteins that form gap junctions that link the pre and postsynaptic membranes. Allows ions to pass through the junctions.
Astrocytes
Has large number of long branching processes
Proximal regions have intermediate filaments made of GFAP (glial fibrillary acid protein)
Functions of astrocytes:
Has perivascular feet that loop around blood vessels to establish BBB
Also reuptake NTs to keep neurons from firing often
Also regulate ionic environment around the cell
What do oligodendrocytes do?
Wrap axons in myelin via extended processes in the CNS
Wraps axons from multiple neurons (promiscuous, numerous contacts)
What are ependymal cells?
- Columnar cuboidal cells lining the ventricle and central canal of spinal cord
- Apical end may have cilia and microvilli that facilitate movement and absorption of CSF
- Joined apically by apical junctional complexes to create boundary for the fluid
Choroid plexus:
Thin layer of cuboidal ependymal cells + vascular pia mater
Found on roofs of 3rd and 4th ventricles
Start to filter things from the blood and release the filtrate as CSF
Functions of the choroid plexus
Removes H2O from blood and releases it as CSF
CSF fills the ventricles, central canal of SC, subarachnoid and perivascular spaces
Features of the choroid plexus
- Blood vessels have a branching system with fibrous core and cuboidal/columnar epithelium
- Epithelial cells rest on basal lamina with long bulbous microvilli projecting from them
- Tight junctions connect the epithelial cells contributing to the blood CSF barrier. Basically helps the BBB formed by astrocytes.
Functions of microglia:
CNS monocytes. Behave like macrophages
Remove damaged or unactive synapses or other fibrous components
Immune defense against microbial invaders in CNS
Spinal cord
Central mass of gray matter; butterfly shape
Contains the Ventral, dorsal and lateral horns.
Central canal of spinal cord
Lies in the central commissure lined with ependymal cells and contains CSF
3 layers of the cerebellar cortex
Molecular layer - has neuropil and neuronal cell bodies
Purkinje cells - has dendrites
Granular layer - small densely packed neurons (granule cells)
Cerebellar medulla located deep to this
What is the old layer of cerebral cortex?
Archicortex
What makes up most of the cerebral cortex?
Neocortex consisting of 6 layers
Cells of the neocortex:
Pyramidal cells - pyramid shaped cell bodies
Granule (stellate) cells - small neurons with star shaped cell bodies
Cells of Martinotti - small polygons with few short dendrites
Fusiform cells - spindle shaped cells oriented perpendicular to surface
Horizontal cells of Cajal - spindle shaped cells oriented parallel to surface
What are the cortical layers of the cerebral cortex?
Molecular layer - fibers, neuroglial cells and horizontal cells of Cajal
External granular layer - small pyramidal cells/granule cells
External pyramidal layer - larger pyramidal cells
Inner granular layer- small granule cells
Ganglionic layer - extremely large pyramidal cells (Betz cells)
Multiform (polymorphic layer) - diverse shaped cells
Alzheimer’s disease:
Memory failure, eventually motor skills, speech and sensation
Characterized by thinning of gyri especially frontal and temporal lobes
Histology of alzheimers:
Plaque, tangles and neuron loss
Amyloid B plaques - amorphous, pink masses in the cortex
Neurofibrillary tangles - flame skeins formed by abnormal accumulation of tau
Substantia nigra:
- Large mass of grey matter containing dark pigmented multipolar neurons
- Neurons have neuromelanin pigment which contains dopamine which inhibits brain areas dedicated to movement
- Important role in fine control of motor function
Parkinson’s clinical features:
Tremor, slow movement, rigidity from degeneration of neurons in the substantia nigra > loss of dopamine
Histology of Parkinson’s disease:
Lewy bodies are rounded pink-staining inclusions w pale halo
Aggregates of alpha synuclein
