1. Neurocytology Flashcards
General Organization of the Nervous System Anatomically: • Central – CNS: – \_\_\_\_. – Spinal cord. – Neural parts of the \_\_\_\_.
• Peripheral – PNS:
– ____ nerves.
– ____.
– ____.
brain eye peripheral nerves ganglia nerve endings
Function of Nervous System • Peripheral – PNS – Receive information: sensory - \_\_\_\_. – Transmit response to effector organ: motor – \_\_\_\_.
• Central – CNS
– Integration
– Analysis
– Response
afferent
efferent
General Organization of the Nervous System Cell components • CNS: - Neurons - Glia --- \_\_\_\_ --- Oligodendrocytes --- \_\_\_\_
• PNS:
– Neurons
– ____ Cells.
– ____ Cells.
• Only common cell type: ____
astrocytes microglia satellite schwann neurons
Cell types: Neuron
• Highly specialized, excitable. • Structure: – \_\_\_\_: • Nucleus and most organelles. – Dendrites: • Tree-like processes: dendritic tree. – Axon: • \_\_\_\_ process. • Originates at the \_\_\_\_. • Ends in the \_\_\_\_. • Telodendron endings: \_\_\_\_.
• In response to NT, cell responds by changing the cxn of ions, resulting in a change of currents ◦ Can respond in a specific way • \_\_\_\_ terminals of telodendron ◦ Synaptic terminals • 3 divisions are related to the three regions: ◦ Dendrites/soma = \_\_\_\_ region ◦ Axon = \_\_\_\_ region ‣ Transmits the AP ◦ Synaptic terminal = \_\_\_\_ region ‣ Releases a NT
soma single axon hillock telodendron synaptic terminals
cytoplasmic
receptor
conductive
effector
The Neuron: Soma
• Soma:
– Nucleus (with prominent
____) + cytoplasm (a.k.a. ____ [“around the nucleus”]).
– Abundant ribosomes: often associated with the ER → ____ or ____ substance.
– Prominent Golgi apparatus.
– Abundant mitochondria.
• \_\_\_\_ active neurons • Soma contains all components of secretory pathways • ER is easily stainable and visible ◦ \_\_\_\_ stain in many neurons
nucleolus perikaryon Nissl bodies Nissl's substance metabolically granulated
The Neuron: Dendrites
• Dendrites: – \_\_\_\_ (“tree-like”). – Primary receiving site for synaptic information. – Surface may show dendritic spines: increase \_\_\_\_.
arborescent
surface area
The Neuron: Axon
• Axon: – Starts at the \_\_\_\_. – Initial segment: proximal region of the axon where \_\_\_\_ start. – Diameter usually remains \_\_\_\_. – May be myelinated: myelin sheath from initial segment to telodendron. – May have \_\_\_\_ branches.
• Axon hillock = area where AP begins ◦ Cxn of \_\_\_\_ is different here from the rest of the axon • Aren't always myelinated • Only the \_\_\_\_ are myelinated (not soma or dendrites)
axon hillock
AP
constant
collateral
ion channels
axons
Types of Neurons
• Based on the number of ____ emerging from the soma:
– ____ neurons:
• Two processes.
– ____ neurons:
• One short process that divides into two branches.
– ____ neurons:
• Many processes.
• Single axon.
• More than one dendrite.
processes
bipolar
pseudounipolar
multipolar
Types of Neurons
• Bipolar neuron: • Two processes. • \_\_\_\_ axon emerges from either side of the soma. •Common in \_\_\_\_ structures: – \_\_\_\_ – Olfactory epithelium – \_\_\_\_ and \_\_\_\_systems
• Either side is similar \_\_\_\_ • Place where input and output is produced is not \_\_\_\_ ◦ Bottom: effector; but upper process would then be the sensory part
single sensory retina vestibular auditory visually equivalent
Types of Neurons
• Pseudounipolar neuron:
• Single axon divides a ____ distance from the
soma.
• Axon branches:
– ____: information from the periphery.
– ____: ends in the spinal cord or brainstem.
• ____ of cranial and spinal nerves.
- Good at transmitting information ____
- One branch: transmits information from ____; would induce a response in the other end of branch which would reside in ____
- Transmits information without any form of ____
short peripheral central sensory ganglia quickly PNS CNS integration
Types of Neurons
• Multipolar neurons:
– Many ____.
– ____ axon.
– Examples:
• ____ cell of the cerebral cortex.
• ____ cell of the cerebellar cortex.
dendrites
single
pyramidal
purkinje
Synaptic Terminals and Synapses
• Synapse:
– Junction between the ____ terminal
of an axon and the ____ membrane receptor surface (a dendrite or a muscle cell).
• Synaptic terminal:
– Specialized neuronal structure for the
transmission of a ____ (neurotransmitter) in response to an action
potential.
• Postsynaptic membrane does not have to belong to another ____
presynaptic
postsynaptic
chemical message
neuron
Classification of Synapses
• Based on their location on the \_\_\_\_ neuron: – \_\_\_\_ synapse: • Axon terminal ending on the soma of a neuron. – \_\_\_\_ synapse: • Axon terminal ending on another axon terminal. – \_\_\_\_ synapse: • Axon terminal ending on a dendrite. – \_\_\_\_ synapse: • Axon terminal facing a dendritic spine
• Axoaxonic are common
◦ Postsynaptic controlled in activity by controlling the releaser of NT
◦ Typical of neurons that are ____ on the PSN
• Axodendritic are the most ____ contact
postsynaptic axosomatic axoaxonic axodendritic axospinous
inhibitory
“traditional”
Designation of groups of neurons and axons
PNS: – \_\_\_\_: Cluster of neurons. • Sensory • Motor – Nerves, rami (sing. ramus), or roots: Axons derived from a ganglion.
• CNS:
– ____: Aggregate of functionally and structurally related neurons.
– ____: Clusters of neurons arranged in a layer.
– ____ (cerebral cortex): Clusters of neurons arranged in longitudinal groups.
– ____, fasciculus, or ____: Bundles of axons.
– ____: darker tissue of the brain and spinal cord, consisting mainly of nerve cell bodies and
branching dendrites.
– ____: lighter tissue of the brain and spinal cord, made of axons connecting different parts
of grey matter to each other.
ganglia nucleus stratum lamina tract lemniscus gray matter white matter
Support Cells
PNS
• ____ cells
• ____ cells (ganglion glia)
CNS (Glial Cells) • Oligodendrocytes – \_\_\_\_ - gray matter – \_\_\_\_ - white matter • Astrocytes – \_\_\_\_ - white matter – \_\_\_\_- grey matter • Microglia – macrophages
schwann
satellite
perineuronal
interfascicular
fibrous
protoplasmic
Schwann Cells and Myelination
• Derive from the \_\_\_\_. • Cover most of the surface of all axons in \_\_\_\_ nerves. • Envelop axons in a sheath of myelin: facilitates transmission of action potentials. • One axon: myelin sheaths from \_\_\_\_ Schwann cells • \_\_\_\_: – Segments of axons covered with myelin. • Nodes of Ranvier: – Gaps without \_\_\_\_ between internodes – Function: nerve signal boost; \_\_\_\_.
- Similar embryological origin to ____ (derive from neural crest)
- Some of the axon will be covered by the ____ itself, and the myelin sheath
- Need many Schwann cells to cover an axon in myelin
neural crest peripheral multiple internodes myelin saltatory conduction
neural crest
schwann cell
Development of the Myelin Sheath
- During ____, the axon is close to a schwann cell
- After Schwann cell precursor attaches, it begins to ____ around
development
wrap
Development of the Myelin Sheath
____ movement
• Wrapping creates consecutive ____
◦ Embed ____ of Schwann cell
clockwise
layers
cytoplasm
Development of the Myelin Sheath
- Closer to axon - the more ____
- Outside layer, the ____ still present
compacted
cytoplasm
Development of the Myelin Sheath
• Formation of ____: most of ____ of Schwann cell is removed, and deposition of specific ____ that form the sheath
spiral
cytoplasm
proteins
Schwann Cells and Myelination
• Bands that are more and less \_\_\_\_ Repetitive structure ◦ Cytoplasm bordered by \_\_\_\_ ◦ Extracellular space bordered by outer leaflet of \_\_\_\_ ‣ \_\_\_\_ ‣ Very small
electron dense
inner leaflets
PM
intraperiod line
Development of the Myelin Sheath
Compact myelin is formed by the ____-mediated apposition of the external leaflets of the bilayer membrane (forming the ‘____’), which will further facilitate ____-mediated apposition of the internal leaflets and the extrusion of the cytoplasm (forming the ‘____’).
• Two proteins that Schwann cells deposit: • Green = PLP ◦ \_\_\_\_ leaflets ◦ Interact with \_\_\_\_ domain • Red = MBP ◦ \_\_\_\_ leaflet ◦ Interact with \_\_\_\_ • \_\_\_\_ is important for transmission of AP in neurons
proteolipid protein (PLP)
double intraperiod line
myelin basic protein (MBP)
major dense line
outer EC inner cytoplasm structure
Schwann Cells and Myelination
• Myelin sheath is electron dense due to ____
layering
Organization of the Peripheral Nerves
Nerve \_\_\_\_: structural component of peripheral nerves. – Axon. – +/- Schwann cells → +/- Myelin sheath. – Surrounded by \_\_\_\_ (CT).
\_\_\_\_: group of nerve fibers. – Surrounded by \_\_\_\_ (CT): forms the \_\_\_\_ barrier. – Fascicles contain \_\_\_\_ and \_\_\_\_ nerve fibers.
____: group of fascicles:
– Surrounded by ____ (CT).
In PNS, you will only find ____ of neurons; therefore all the nuclei are from the ____ cells
Capillaries are located outside of the ____
fiber
endoneurium
fascicles perineurium nerve-blood barrier myelinated unmyelinated
nerve
epineurium
axons
schwann
perineurium
Organization of the Peripheral Nerves: Myelin and the Nodes of Ranvier
• Processes of myelin sheath are \_\_\_\_ at NR • Sheaths are \_\_\_\_ at NR • Surrounding whole structure, basal domain, is the \_\_\_\_ ◦ Produced by the \_\_\_\_ cell • Bottom: ◦ Myelin is highly stained ◦ Single nerve contains fibers of many \_\_\_\_
interdigitated thinner basal lamina schwann cell diameters
Peripheral nerves
• ____ acid
◦ ____
with high affinity for myelin
osmic
heavy metal
Peripheral nerves (H&E)
• ____ is outside basal lamina, produced by fibroblasts
endoneurium
Development of Myelinated and Unmyelinated Peripheral Nerves
- ____ axons get surrounded by Schwann cells.
- Axons enlarge, become sheathed by myelin: ____ nerve fiber.
- Unmyelinated nerve fibers: axons remain ____ and embedded in recesses of the Schwann cell ____
• Both axons are present with Schwann cells
◦ If not, they would be too ____
• Axons that are ____ are usually the ones that are being myelinated (they grow in diameter)
◦ Depositing PLP and MBP
• Smaller ones are moved to periphery of schwann cells and
embedded in ____ of the PM of the schwann cell
◦ The ____ of the schwann cell protects both the axon and itself
embryonic
myelinated
small
membrane
fragile
larger
infoldings
BL
Ganglia: Sensory Ganglia
• Sensory ganglia: e.g. \_\_\_\_ nerve and trunks of \_\_\_\_, facial, \_\_\_\_, and vagal cranial nerves. • Surrounded by \_\_\_\_(CT). • Clustered \_\_\_\_ neurons. • \_\_\_\_ nerve fibers. • Satellite cells: – \_\_\_\_cell-like cells. – Associated with the \_\_\_\_.
• Part of the ____ nerves, transmitting sensory information
posterior spinal trigeminal glossopharyngeal epineurium pseudounipolar myelinated schwann basal lamina
afferent
Sensory Ganglia
• Here, we see the ____ of neurons
◦ Nuclei of ____ are visible
• Whole ganglion is surrounded by ____
somas
neurons
epineurium
Sensory Ganglia
• Soma of ____ neuron surrounded by ____ cells
Surrounding the complex of the neuron and satellite cells is the ____
◦ Separating one neuron from the next
pseudounipolar
satellite
BL
Autonomic Ganglia
• Typical of ganglia in the autonomic (sympathetic and parasympathetic) system.
• Surrounded by ____.
• ____ arranged, small ____
neurons.
• Small ____ axons, mostly ____.
• Fewer ____ cells than spinal ganglia: no
____.
epineurium randomly multipolar diameter unmyelinated satellite
Autonomic Ganglia
• Not as well organized as ____ ganglia
• Some similarities
◦ Somas
◦ Whole thing is surrounded by ____
sensory
epineurium
Autonomic Ganglia
• Less ____ in terms of population of neurons
• Soma of each neuron surrounded by ____
cells
◦ Organization is not as well defined as
____ ganglia
• Absence of ____ surrounding the entire structure
• ____ between connective tissue and satellite cells → not separated
neatly by basal lamina
dense
satellite
sensory
continuation
Support Cells of CNS
LETS GO!
YAY
CNS Support Cells: Oligodendrocyte (OD)
• A.k.a. Oligodendroglia.
• Axon myelination in the ____.
• Protruding cytoplasmic ____ wrap the axons
and produce myelin.
• Each OD provides a myelin sheath to ____ axons.
• Post-____.
• Loss of ODs:
– ____: loss of myelin in areas of brain and spinal cord, impairment of axonal conductance.
• No Schwann cells in CNS
◦ These only wrap around axon of single cell; OD
does ____
• Mechanism of myelination is different
• Post-mitotic - cannot ____ (important in degeneration)
CNS "paddles" several mitotic multiple sclerosis
multiple
divide
CNS Support Cells: Oligodendrocyte Myelination in the CNS
• Myelinated CNS:
– Cell body of oligodendrocyte not in close ____ to the myelin sheath.
– Each oligodendrocyte provides a sheath for ____ axons.
– No ____ associated with the myelin.
– No ____ cytoplasmic processes.
– Nodes are contacted by cytoplasmic processes from ____.
proximity several BL interdigitating astrocytes
CNS Support Cells: Astrocytes
• Branching cells with cytoplasmic processes:
– ____: exchange of nutrients, gases and metabolites with capillaries.
Support CNS.
Help maintain ____.
Two types:
– ____.
– ____.
Connect capillaries in CNS with ____ cells
Substances that have to be sent to neurons must be absorbed first by ____, then xported to the neuron
end-feet BBB protoplasmic fibrous neuronal astrocyte
CNS Support Cells: Astrocytes
Two types: – Protoplasmic: • \_\_\_\_ matter. • processes \_\_\_\_ with \_\_\_\_ branches. – Fibrous: • \_\_\_\_ matter. • processes \_\_\_\_ with \_\_\_\_ branches.
Grey matter - protoplasmic
◦ ____; rich in bodies of neurons
◦ Cell is in close proximity to ____
White matter - fibrous
◦ Mostly ____
grey
short
many
white
long
few
CNS
BV
axons
The Blood-Brain Barrier
• CNS capillaries: \_\_\_\_ endothelium. • Substances can reach the nervous tissue only by \_\_\_\_ through the endothelial cells. • Main components: – \_\_\_\_ endothelium with \_\_\_\_. – \_\_\_\_. – Perivascular astrocyte \_\_\_\_.
continuous crossing continuous tight junctions basal lamina end-feet
CNS Support Cells: Microglia
• Resident ____ of the CNS:
– Phagocytosis of injured and dead neurons.
• Main cells to respond to injury.
• Produce ____ for leukocytes:
crossing of the brain-blood barrier.
• Cell-cell interaction Microglia/Astrocytes:
modulation ____ responses.
- Control immune response of brain in response to inflammation
- ____ elongated cytoplasmic processes
macrophage
chemoattractants
immune
long
Peripheral Nerve Regeneration I
• Intact motor neuron: – Innervation of skeletal muscle: \_\_\_\_. – Myelin sheath. – \_\_\_\_. – \_\_\_\_.
NMJ
basal lamina
endoneurium
Peripheral Nerve Regeneration II
- Injury to the nerve fiber: Proliferation of ____ cells to bridge the gap.
- Phagocytosis of myelin fragments by ____ cells and ____.
- ____ and swelling of the soma; degeneration of the distal (____) and proximal (____) axon segments.
• Schwann cells can ____ upon stimulation (not post-mitotic)
◦ Reason why we can regenerate PNS nerves
• Chromatolysis
◦ Reorganization of ____; reorganizing the secretory pathway
‣ Cannot be ____ as well anymore
◦ Swelling of the neuronal ____
• Axon degenerates in both ____ (retrograde for part connected to soma; anterograde for the other end up to telodendrum)
schwann schwann macrophages chromatolysis anterograde retrograde
divide Nissl substance stained soma directions
Peripheral Nerve Regeneration III
4. Axon sprouts: – One sprout grows \_\_\_\_ to re-innervate the muscle. – Remaining sprouts \_\_\_\_. – \_\_\_\_ cells guide the growth of the regenerating axon.
• Cytoplasmic processes produced from the part still attached to ____
◦ Most will degenerate, but if one reaches the other end: uses preexisting ____ cell structure to regenerate the complete axon
distally degenerate schwann soma schwann
Peripheral Nerve Regeneration IV
5. Regenerated axon reaches the muscle (several \_\_\_\_). – Schwann cells produce myelin. – Internodal segments are \_\_\_\_. – Diameter of axon is ≈ \_\_\_\_ of original: \_\_\_\_ conduction of nerve impulse
months
shorter
80%
slower
CNS Nerve Regeneration: Is it possible?
– Regeneration process starts as in the ____:
- ____ cells remove debris by phagocytosis.
- Regeneration process than stops:
• Absence of ____.
• Absence of mitotically active ____ cells: oligodendrocytes (myelinating cells in the CNS) do not ____.
____ is needed to tell the sprouts where to go
PNS microglial endoneurium schwann proliferate endoneurium
