1. Neurocytology Flashcards by J L

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

How well did you know this?

Not at all

Perfectly

Function of Nervous System
• Peripheral – PNS
– Receive information: sensory - \_\_\_\_.
– Transmit response to effector organ:
motor – \_\_\_\_.

• Central – CNS
– Integration
– Analysis
– Response

afferent

efferent

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

The Neuron: Dendrites

• Dendrites:
– \_\_\_\_ (“tree-like”).
– Primary receiving site for synaptic
information.
– Surface may show dendritic spines: increase \_\_\_\_.

arborescent

surface area

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Types of Neurons

• Multipolar neurons:
– Many ____.
– ____ axon.

– Examples:
• ____ cell of the cerebral cortex.
• ____ cell of the cerebellar cortex.

dendrites
single
pyramidal
purkinje

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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”

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Development of the Myelin Sheath

____ movement
• Wrapping creates consecutive ____
◦ Embed ____ of Schwann cell

clockwise
layers
cytoplasm

How well did you know this?

Not at all

Perfectly

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 1. ____ axons get surrounded by Schwann cells. 2. Axons enlarge, become sheathed by myelin: ____ nerve fiber. 3. 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 1. Injury to the nerve fiber: Proliferation of ____ cells to bridge the gap. 2. Phagocytosis of myelin fragments by ____ cells and ____. 3. ____ 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 ```