Histology - Nervous System Flashcards
Nueroglial cells
Aka glia
Non-conducting cells located close to neurons
CNS central neuroglia - oligodendrocytes, microglia, astrocytes, and ependymal cells
PNS peripheral nuerolgia - Schwann cells and satellite cells
Fx - providing physical support and protection for neurons
Insulating nerve cell bodies and processes (myelin)
Reparising neuoranal injury
Regulating the internal fluid environment of the CNS
Clearing neurotransmitters from synaptic clefts
Facilitating metabolic exchange between the vascular system and neurons
Nissl bodies
Rough ER and polyribosomes - appear as clumps of basophilic material
Neuronal type of dorsal root ganglia
Pseudo-unipolar neurons
Neuronal cell type of the retina
Bipolar neurons
Purkinje and pyramidal cells
Found within the CNS
Afferent processes of neurons
Dendrites - they receive information from other neurons or from the environment
Dendrites are generally unmyelinated
Lack golgi but otherwise organelle profile similar to that of the cell body
Dendritic spines
Increase surface area and are the sites of synapses
Efferent processes of neurons
Axons - initial segment located below or distal to the axon hillock (where action potentials are generated)
Recurrent axonal branching
Near the cell body
Collateral axonal branching
Near the target
Organelle profile of axons
Arrays of microtubules and neurofilaments
Mitochondria
Vesicles
Derivatives of smooth ER
Direction of axonal transport
Biderectional
Anterograde - via kinesin motors - moves organelles and secretory vesicles along microtubules
Retrograde - moving endosomes via dynein motors
Types of synapses
Axosomatic
Axodendritic
Axoaxonic
Most common form of synapse in humans
Chemical synapses
Excitatory synapses
Allow Na+ to enter postsynaptic cells, dpolarizing the membrane and causing an action potential
Inhibitory synapses
Allow Cl- to enter postsynaptic cells, hyperpolarizing the membrane and making acxtion potentials less likely
Astrocytes
Provide physical and metabolic support for neurons and form the blood-brain barrier.
Fibrous astrocytes are found in white matter, while protoplasmic astrocytes are found in gray matter
Oligodendrocytes
Produce myelin and myelinate CNS axons
Microglia
Resident macrophages in the CNS, derived from monocytes
Note the elongated nuclei of microglia
Ependymal cells
Line the ventricles in the brain and the central canal of the spinal cord. These columnar, epithelial-like cells absorb cerebrospinal fluid. In the choroid plexus, ependymal cells are modified to secrete CSF.
Satellite cells
Provide physical and metabolic support for cell bodies in ganglia
Schwann cells
Myelinate axons and support both myelinated and unmyelinated axons in the PNS
Protoplasmic astrocytes
Gray matter - form BBB
Fibrous astrocytes
White matter - processes are longer and thinner than protoplasmic astrocytes - also contribute to the BBB
What accounts for ~80% of primary brain tumors?
Tumors originating from fibrous astrocytes
What embryonic cell population are Schwann cells derived from?
Neural crest cells
What type of cells do Schwann cells support?
Both myelinated and unmyelinated cells of the PNS
Difference between myelination of axons by oligodendrocytes in CNS and Schwann cells in PNS?
Schwann cells only myelinate portions of one axon whereas oligodendrocytes may myelinate segments of more than one axon
Arrow - node of Ranvier (where two Schwann cells meet - unmyelinated portion of axon)
Circle - Schmidt-Lanterman clefts appear as pink arrow heads with the white bubbles of myelin - remaining cytoplasm of Schwann cells - likely play a role in nourishment of the myelinated axons
Guillain-Barre syndrome
Acute inflammatory demyelinating polyradiculoneuropathy
Large accumulations of lymphocytes, macrophages, and plasma cells around nerve fivers within nerve bundles (fascicles).
Large segments of myelin are damaged, leaving the axons exposed to the extracellular matrix.
T-cell mediated immune response directed against myelin, causing its destruction - slowing or blocking nerve conduction
Pt exhibits sxs of muscle paralysis, loss of muscle coordination, and loss of sensation
Multiple sclerosis
Attacks myelin in CNS.
Characterized by immune-mediated damage to myelin which becomes detached from the axon and is eventually destroyed.
Destruction of oligodendrocytes occurs, so new myelin cannot be made.
Myelin basic protein appears to be the major autoimmune target of this disease.
Chemical changes in the lipid and portein constituents of myelin produce irregular, multiple plaques throughout the white matter of the brain.
Sxs depend on the area in the CNS that is damaged. Typically characterized by distinct episodes of neurologic defects such as unilateral vision impariment, loss of cutaneous sensation, lack of muscle coordination and movement, and loss of bladder/bowel control.
Endoneurium
Loose CT that surround individual nerve fibers
Collagen type III secreted by Schwann cells
Occasionally fibroblasts, mast cells, and macxrophages are in the endoneurium
Perineurium
Specialized CT that surrounds nerve fascicles
Metabolically active diffusion barrier that maintains the ionic milieu of the ensheathed nerve fibers, contributes to the BBB
Perineural cells have characteristics of both fibroblasts and smooth muscle cells
Epineurium
Dense irregular CT that surrounds and binds nerve fascicles into a common bundle
Often associated with adipose
Often blends with tunica adventitia of blood vessels
Cerebrum: gray matter of cerbral cortex and its distinct layers
Purkinje cells
Molecular layer of the cerebellum
Mostly dendrites of Purkenje cell bodies
Where are pseudounipolar neurons typically found?
The dorsal root ganglion
Fibrous astrocytes stained with glial fibrillary acidic protein (GFAP)
Cells with blue stained nuclei - oligodendrocytes
Remember:
Fibrous astrocytes - white matter
Protoplasmic astrocytes - gray matter
Cells with large nuclei - oligodendrocytes
Left - microglial
Right - oligodendrocytes
Ependymal cells (at the lateral ventricle)
