15 CNS Histology - A Flashcards
What are neurons?
cells that respond to stimuli through electrochemical mechanisms
– Excitable or inhibitory
What are Glia?
support cells involved in conduction speed, repair, neurotransmitter maintenance
Describe the cell body of a “Typical” neuron.
Cell body is large & has a large, euchromatic nucleus with a well-developed nucleolus
- Nissl substance/bodies
What happens to a neuron, when you increase the amount of dendritic spines?
it increases receptive area
Where does the long axon of a “Typical” neuron emerge from?
emerges from an axon hillock
What are Nissl substances/bodies of a “Typical” neuron?
large, basophilic masses of free polysomes & RER
What is the distal end of an axon called?
Terminal arborization
- some have branching, collateral branches
Ends of axons usually have small what?
telodendria
- dilation of branch ends & contact postsynaptic cell
Describe a multipolar neuron.
Describe bipolar neuron.
Describe unipolar neuron.
Describe anaxonic neuron.
For neuronal synapse communication, is the transmission unidirectional or bidirectional?
synaptic transmission is unidirectional
Synapses = Sites where nerve impulses are transmitted from one neuron to another, or from neurons and other effector cells
Synapses convert an electrical signal (nerve impulse) from the _____________ into a chemical signal that affects the ___________.
- presynaptic cell
- postsynaptic cell
Most synapse communication between nerves act by releasing what?
Neurotransmitters - small molecules that bind receptor proteins
Describe what the presynaptic terminal bouton of a chemical synapse contains.
mitochondria & synaptic vesicles –> release NT via exocytosis
Describe what the postsynaptic cell membrane of a chemical synapse contains.
receptors for the neurotransmitter
ion channels to initiate a new impulse
What is a 20- to 30-nm-wide intercellular space that separates pre- & postsynaptic membranes in a chemical synapse?
synaptic cleft
Describe the electrical synapse of a neuron.
Permit direct, passive flow of electrical current from one neuron to another
- potential difference (voltage) generated locally by presynaptic action potential
How does current flow occur and links pre- & postsynaptic membranes (2nm) in electrical synapses of neurons?
Gap junctions
What proteins permit diffusion of small molecules & electric current flow in an electrical synapse of neurons?
Connexon
What are the five (5) types of Glial cells?
- Neuropil
- Astrocyte
- Ependymal cell
- Microglial cell
- Oligodendrocyte
What is a neuropil?
type of Glial cell
fibrous intercellular network of cellular processes emerging from neurons & glial cells
What are characteristics of Astrocytes?
- large number of long, branching processes
- proximal regions are reinforced with intermediate filaments made of glial fibrillary acid protein (GFAP)
They form a vast network of delicate terminals contacting synapses & other structures
Terminal processes of a single astrocyte typically associate 1M+ synaptic sites
What are characteristics of Oligodendrocytes?
Type of Glial cell.
- Extend many processes that wrap repeatedly around a portion of a nearby axon
- Cytoplasm gradually moves out: leaves compacted layers of cell membrane, collectively termed myelin. Forms a myelin sheath.
Will enwrap axons from multiple neurons - a given axon is covered by many oligodendrocytes
Usually appear as small cells with rounded, condensed nuclei & unstained cytoplasm
What are characteristics of Ependymal cells?
- Columnar or cuboidal cells that line the fluid-filled ventricles of the brain & the central canal of the spinal cord
- Apical end may cilia & long microvilli
– Facilitate movement of CSF
– Likely involved in absorption
• Joined apically by apical junctional complexes & there is no basal lamina
What are characteristics of Microglia?
A type of Glial cell.
- Less numerous than oligodendrocytes or astrocytes
- Migratory, will remove damaged or unactive synapses or other fibrous components
- Major mechanism of immune defense in the CNS, removing any microbial invaders
- Originate from monocytes
What has a central mass of grey matter that has the shape of a butterfly?
- Ventral, dorsal, & lateral horns
What lies in the central commisure of grey matter of a spinal cord?
Central canal
- lined by ependymal cells and contains CSF
What does white matter consist of for a spinal cord?
White matter consists of ascending tracts of sensory fibers & descending motor tracts
The sharply folded cerebellar cortex is organized with three (3) layers. What are they?
- Molecular layer
- Purkinje cells
- Granular layer
Describe the molecular layer of the cerebellar cortex.
has much neuropil & scattered neuronal cell bodies
Describe Purkinje cells of the cerebellar cortex.
extend dendrites throughout the molecular layer as a branching basket of nerve fibers
- Conspicuous in H&E-stained sections
Describe the granular layer of the cerebellar cortex.
contains various very small, densely packed neurons (i.e., granule cells) & little neuropil
What is organized into folia with the _______ medulla located deep?
The cerebellar cortex!!
- cerebellar
Biologically, older parts of the cerebral cortex are arranged into three layers. What is this called?
Archicortex
What is the majority of the cerebral cortex (about 90%) called? How many layers does it consist of?
neocortex
consists of 6 layers
The neocortex has a variety of cells, divided into five (5) different morphological types. What are they?
- Pyramidal cells
- Stellate (granule) cells
- Cells of Martinotti
- Fusiform cells
- Horizontal cells of Cajal
Describe pyramidal cells of the neocortex.
pyramid-shaped cell bodies with the apex directed towards the
cortical surface
• Huge upper motor neurons of the motor cortex (Betz cells), are the largest pyramidal cells
Describe stellate (granule cells) of the neocortex.
small neurons with a cell body the shape of a star (look like granules in micrographs)
Describe cells of Martinotti of the neocortex.
small polygonal cells with a few short dendrites
Describe fusiform cells of the neocortex.
spindle-shaped cells oriented at right angles to the surface of the cerebral cortex
Describe horizontal cells of Cajal of the neocortex.
small & spindle-shaped but oriented parallel to the surface
(least common)
What are the 6 cortical layers of the neocortex?
- Molecular (plexiform) layer
- Outer/external granular layer
- Pyramidal cell layer
- Inner/internal granular layer
- Ganglionic layer
- Multiform cell layer
Here are more examples of the 6 cortical layers of the neocortex.
Describe and name the first cortical layer of the neocortex.
Molecular (plexiform) layer
superficial layer containing dendrites & axons of cortical neurons; sparse neuroglia & horizontal cells of Cajal
Describe and name the second cortical layer of the neocortex.
Outer/external granular layer
dense population of small pyramidal cells & stellate cells, mixed with axons & dendrites from deeper layers
Describe and name the third cortical layer of the neocortex.
Pyramidal cell layer
pyramidal cells of moderate size predominate, Martinotti cells are also present
Describe and name the fourth cortical layer of the neocortex.
Inner/internal granular layer
consists mainly of densely packed stellate cells
Describe and name the fifth cortical layer of the neocortex.
Ganglionic layer
large pyramidal cells & smaller numbers of stellate cells & cells of Martinotti make up this layer
Describe and name the sixth cortical layer of the neocortex.
Multiform cell layer
wide variety of cell types (small pyramidal cells, cells of Martinotti, stellate cells & fusiform cells in the deeper part)
What is the choroid plexus and what support cell type are associated with it?
Elaborately folded & highly vascular tissue, found in the roofs of the 3rd & 4th ventricles, & in parts of lateral ventricular walls
• Contains a thin layer of well-vascularized pia mater covered by cuboidal ependymal cells
What is the choroid plexus responsible for?
Removes H2O from blood & releases it as CSF
– Contains Na+, K+, & Cl– ions
– Very little protein
– Only cells include sparse lymphocytes
- Completely fills ventricles, central canal of SC, subarachnoid & perivascular spaces
- Arachnoid villi provide absorption pathway for CSF back into the venous circulation
Histologically speaking, how do Choroid plexus’ look like? Cell type, structure, etc.
Branching system of blood vessels which run in fronds composed of a fibrous core covered by cuboidal/columnar epithelium → villous structure
- Capillaries & vessels are large, thin-walled
- Epithelial cells rest on a basal lamina
- Long bulbous microvilli project from the epithelial cells
- Tight junctions (zonula occludens) between epithelial cells contribute to a blood-CSF barrier
Describe what a “Typical” neuron looks like.
- Cell body
- Nissl substance/bodies - Numerous dendrites
- Long axon covered by myelin
Describe the dendrites of a “Typical” neuron.
Numerous dendrites extend from the perikaryon
- Extensive branching/arborization
- Numerous dendritic spines ↑↑ receptive area
- Spines are plastic
Where is the site where excitatory or inhibitory stimuli are initiated on a neuron?
The initial segment of an axon (which originates from the axon hillock)
