Histology of the CNS (Dennis) Flashcards
1
Q
What are the attributes and structural features of the neuron?
A
- cell body: large nucleus w/ well-developed nucleolus and Nissl substance/bodies
- Nissl substance/bodies: corresponds w/ staining properties of ribosomes, direct relation with the metabolism of the neuron
- dendrites: extend from perikaryon, extensive branching/arborization, numerous dendritic spines increased in receptive area, spines are plastic (can appear/regress based upon need)
- axon: emerges from axon hillock (where soma decides whether AP will be propigated)
- neuropil: dense network of nerve fibers and their branches and synapses, together w/ glial processes (b/c neurons do not contain CT so this is a structural component)
2
Q
What do the following letters in the photo correspond w/?
- N:
- G:
- Np:
- CB:
- D:
- DS:
A
- N: neuronal cell bodies
- G: glial cells
- Np: neuropil
- CB: cell body
- D: dendrite
- DS: dendritic spine
3
Q
What are the 4 possible structure types of a neuron?
A
- multipolar neuron: cell body more localized toward dendrites, multiple dendrites, one long axon (most common)
- bipolar neuron: two poles, one pole from the dendrite with fewer outbranches compared to a multipolar neuron, and one pole from the axon (most commonly found in retina)
- unipolar: single axon that spans the length of the processes, one process is short (central process) and is generally centered toward CNS, while the other process is longer (peripheral process) and generally extends in the periphery, the dendrites are arborizations at the end of the of the peripheral process
- anaxonic neuron: multiple dendrites surrounding soma that receives dendritic info but does not send any outgoing info b/c there is no axon
4
Q
- nerve impulses transmitted from one neuron to effector cells
- unidirectional
- converts electrical signal (nerve impulse) from presynpatic cell into a chemical signal that affects the postsynaptic cell
- most act by releasing NT’s
A
synpatic communication
5
Q
What is the structure and function of a chemical synapse?
A
- presynaptic terminal bouton: contains mito and synpatic vessicles (release NT via exocytosis)
- synpatic cleft: 20-30 nm intercellular space, separates pre- and postsynaptic membranes
- postsynaptic cell membrane: receptors for NT’s and ion channels to initiate a new impulse
6
Q
What do these letters correspond w/ in the following photos?
T1:
D:
T2:
TB:
M:
V:
A:
C:
What is occurring in the gray area that the arrows are pointing to in the larger photo?
A
What do these letters correspond w/ in the following photos?
T1: presynaptic terminal
D: dendrite
T2: 2nd presynaptic terminal
TB: terminal bouton
M: mito
V: vesicle
A: actin filaments
C: caveolae
*axons have synaptic vesicles (containing NT’s) while dendrites do not, this is how you can distinguish the two*
What is occurring in the gray area that the arrows are pointing to in the larger photo?
- synaptic clefts where synaptic transmission is occurring
7
Q
What are the 3 possible structural variances of chemical synapses within the nervous system?
A
- axodendritic synapse: axon contacts dendrites (common)
- axosomatic synapse: axon contacts soma (cell body)
- axoaxonic synapse: axon contacts axon
*the variance in possible synapses provides an outlet for impulse modulation within the nervous system*
8
Q
Describe the structure and function of an electrical synapse:
A
- direct, passive flow of electrical current between neurons via gap junctions
- link pre- and postsynaptic membranes (2 nm)
- contain connexon proteins that link pre- and postsynaptic membranes
9
Q
- cells that contain large number of long, branching processes
- proximal regions of the cells are reinforced w/ intermediate filaments made of glial fibrillary acid protein (GFAP)
- form a vast network of delicate terminals contacting synapses and other structures
- terminal processes of a single astrocyte typically a/w 1M+ synaptic sites
- have reuptake proteins (perineural feet) that can remove NT’s from the synaptic cleft, thus moderating signal transmission
- establish blood brain barrier: their processes have perivascular feet that block certain substances cannot cross into the nervous system
A
astrocytes
10
Q
- columnar or cuboidal cells that line the brain ventricles and the central canal of the spinal cord
- apical end may have cilia and long microvilli (facilitate movement of CSF, likely involved in absorption)
- joined apically by apical junctional complexes
- no basal lamina present
A
ependymal cells
11
Q
- found in the roofs of the 3rd and 4th ventricles and parts of lateral ventricular walls
- thin, elaborated folded layer of well-vascularized pia mater covered by cuboidal ependymal cells
- removes H20 from blood and releases it as CSF: contains Na+, K+, and Cl- ions; very little protein; only cells are sparse lymphocytes
- CSF completely fills ventricles, central canal of SC, subarachnoid, and perivascular spaces
- arachnoid villi provide absorption pathway for CSF back into venous circ
A
choroid plexus
12
Q
What features should you look for when identifying the choroid plexus histologically?
A
- branching system of blood vessels which run in fronds composed of fibrous core covered by cuboidal/columnar epithelium > villous structure
- capillaries and vessels are large, thin-walled
- epithelial cells rest on basal lamina
- long bulbous microvilli project from epithelial cells
- tight junctions (zonula occludens) between epithelial cells contribute to blood-CSF barrier
13
Q
- less numerous than oligodendrocytes or astrocytes
- migratory, will remove damaged/inactive synapses or other fibrous components
- major mechanism of immune defense in CNS, removing any microbial invaders
- originate from monocytes
A
microglia
14
Q
- extend processes that wrap nearby axons in myelin
- wrap axons from multiple neurons
- a single axon may be wrapped by many of these cells
- usually appear as small cells w/ rounded, condensed nuclei and unstained cytoplasm
A
oligodendrocytes
15
Q
- a group of cells comprised of neurolemmocytes (Schwann cells) and satellite cells, both neural crest cell derived
- neurolemmocytes (Schwann cells): myelinate peripheral nerves providing electrical insulation; one Schwann cell per neuron
- satellite cells: found in dorsal root ganglion, provide structural and metabolic support for neuronal cell bodies
A
peripheral ganglia
23
Q
What are the 6 layers of the neocortex portion of the cerebral cortex?
A
(from superficial to deep)
- molecular layer: largely fibers and neuroglial cells (know for exam)
- external granular layer
- external pyramidal layer
- inner granular layer
- ganglionic layer: extra-large pyramidal cells (Betz cells), especially in motor areas (know for exam)
- multiform (polymorphic) layer: contains cells w/ diverse shapes (know for exam)
*must know the highlighted layers by histo identification, must know the order of all layers*
24
Q
- most common neurodegenerative disease
- incidence increases w/ age, typical presentation is 70+ y/o
- sx: memory failure, progressing steadily to involve motor skills, speech, and sensation
- etiology unknown, small proportion of cases have a genetic association
- striking thinning of gyri, particularly those of the frontal and temporal lobes
- plaques, neurofibrillary tangles, and neuronal loss are identified on sections: amyloid (amyloid β) plaques (amorphous, pink masses in the cortex) and neurofibrillary tangles (flame-shaped skeins formed by abnormal accumulation of tau protein)
A
Alzheimer’s disease
25
Q
- large mass of gray matter containing multipolar neurons w/ dark pigment
- connections w/ the cortex, SC, corpus striatum, and reticular formation
- important role in fine control of motor function
- neurons contain numerous membrane-bound granules of neuromelanin pigment
- neuromelanin contains dopamine > inhibitory effects in brain areas dedicated to movement
A
substantia nigra
26
Q
- neurodegenerative disease
- clinical features: tremor, slow movement, and rigidity resulting from degeneration of neurons in the substantia nigra > loss of dopamine (etiology unknown)
- distinctive inclusions are seen in remaining neurons, Lewy bodies (rounded, pink-staining inclusions w/ pale halo; composed of aggregates of the protein α-synuclein and other proteins)
A
Parkinson’s disease
(middle photo is unaffected individual, 2 right sided photos are diseased individuals)
27
Q
What are the 3 layers of the cerebellar cortex?
A
(superficial to deep)
- molecular layer: has many neutrophil and scattered neuronal cell bodies
- Purkinje cells: extend dendrites throughout the molecular layer as a branching basket of nerve fibers (conspicuous in H&E stains)
- granular layer: contains various very small, densely packed neurons (i.e. granule cells) and little neuropil
(organized into folia w/ cerebellar medulla located deep)
28
Q
What do these letters stand for in the following photos?
- P:
- WM:
- Mol:
- Gr:
- BV:
A
- P: Purkinje cells
- WM: cerebellar medulla / white matter
- Mol: molecular layer
- Gr: granular layer
- BV: blood vessel
29
Q
Describe the histological structure of the spinal cord:
A
- central masses of gray matter has the shape of a butterfly: ventral, dorsal, and lateral horns
- central canal: lies in the central commissure of gray matter
- white matter consists of ascending tracts of sensory fibers and descending motor tracts
30
Q
What do these letters stand for in the following photo?
- D:
- L:
- V:
- FG:
- FC:
- R:
- F:
A
- D: dorsal horn
- L: lateral horn
- V: ventral horn
- FG: fasciculus gracilis
- FC: fasciculus cuneatus
- R: rootlet
- F: anterior (ventral) median fissure
31
Q
- bundles of nerve fibers individually surrounded by neurolemmocytes and CT
- multiple layers of neurolemmocyte membrane can unite as myelin sheath (composed mainly of lipid bilayers and membrane proteins, dependent on axon diameter, degraded by standard staining procedures)
- intervening regions that lack myelin are Nodes of Ranvier
A
peripheral nerves
32
Q
How do Schwann cells myelinate axons in the periphery?
A
- Schwann cell becomes aligned along axon and extends wide cytoplasmic process to encircle it
- growing process completely encloses axon but continues its spiral extension
- spiral wrappings become compacted layers of cell membrane (myelin) as cytoplasm leaves the growing process
- mature Schwann cell myelin sheath has up to 100 lamellae, w/ most cytoplasm in the outermost layer with the cell body
33
Q
What is the structural organization of nerves?
A
- endoneurium: immediately around neurolemmocytes, consists of reticular fibers, fibroblasts, and capillaries
- perineurium: enwraps fascicles of axons, neurolemmocytes, and endoneurium
- epineurium: dense, irregular fibrous coat in between fascicles and surrounding the peripheral nerve (c/w spinal meninges
34
Q
What do these letters stand for in the following photo?
- N:
- En:
- C:
- S:
A
- N: node of Ranvier
- En: endonerium
- C: capillary
- S: Schwann cell nucleus
35
Q
What do these letters stand for in the following photo?
- P:
- C:
- A:
- S:
- F:
- N:
- E:
A
- P: perinerium
- C: capillary
- A: axons
- S: Schwann cells/nuclei of Schwann cells
- F: nuclei of endoneurial fibroblasts
- N: small nerve
- E: endonerium
