Nerve Flashcards
Neurons - describe the cell structure
- nerve cell body (soma):
- large euchromatic nucleus
- prominent nucleolus
- Nissl substance (RER, ribosomes –> contains RNA)
- axon hillock
- cytoplasmic processes:
- axons (one per neuron)
- ensheathed by Schwann cells
- may be myelinated
- dendrites (many per motor neuron; none for sensory neuron)
ID the tissue
Motor neurons in toluidine blue stain
note the large nucleus and nucleolus
These types of nerve pathways use a single neuron
Sensory and motor nerves
Ganglia
clusters of nerve cell bodies outside of the CNS
Two types:
- sensory
- autonomic (motor)
a) sympathetic
b) parasympathetic
b1) enteric
These types of nerve pathways use two neurons
Autonomic motor nerves
- first neuron cell body resides in CNS
- second neuron cell body resides in peripheral
ganglia
epineurium, perineurium, endoneurium
Types of peripheral nerve connective tissue investments
Perineurium surrounds fascicles while endoneurium are around individual nerve fibers
Describe the photo
Peripheral nerve axons tend to separate from the epi/perineurium in cross section
ID the tissue
Peripheral nerves tend to be “wavy” in longitudinal section; allows nerve to stretch with skin
ID the tissue
Peripheral nerve, wavy
ID the tissue
Nerve bundle in trichrome stain, surrounded by collagen
These cells form the blood-nerve barrier
Perineurial cells
- have tight junctions & gap junctions
- restrict cell entry (no lymphocytes, plasma cells)
- control transport
- are contractile
Describe
Peripheral nerve cross section
Schwann Cells
All peripheral axons are supported by Schwann cells
one Schwann cell will invest multiple unmyelinated axons; however, many Schwann cells will be needed to invest the full length of an axon
Describe
All peripheral axons are supported by Schwann cells
S=Schwann cell nucleus
F=fibroblast
There are NO nerve cell nuclei here; most nuclei in peripheral nerv are schwann cell nuclei
Myelin sheath
Wraps up in the Schwann cell; insulate and permits fast condution
Very lipid rich so looks empty in stain
Describe
Cross section of an axon
Type III Collagen in top right corner
Neurofilaments are IFs
Microtubules for cargo transport
Neurilemma is cytoplam of Schwann
Describe
Myelin (lipid-rich) is generally not well-preserved in most preparations
neurokeratin
residual protein elements in myelin sheath following lipid extraction
neurilemma
Schwann cell cytoplasm
Nodes of Ranvier
one of the myelin interruptions
region where cell depolarizes
allows for saltatory conduction
Sensory neurons and somatic motor neurons are myelinated; autonomic neurons are not
Describe
Schmidt-Lanterman incisures (clefts)
Channels within myelin that runs continuously from axon to Schwann cell
Connects cytoplam of Schwann cell from outer to inner when it’s wrapped up
Describe
Schmidt-Lanterman incisures (clefts) – gaps in myelin; these are the white spaces between the purple myelins sheaths surrounding the *
Here they used a lipophilic dye which stains the myelination purple
Sensory neurons
- examples:
- dorsal root ganglion
- cranial sensory nerve ganglia
- pseudounipolar neurons
- morphology:
- central nucleus
- ring of satellite cells complete because there are no dendrites to disrupt them
- synapses do not occur
Autonomic Neurons
- examples:
- sympathetic
- parasympathetic (CNs)
- multipolar neurons
- morphology:
- eccentric nucleus
- dispersed satellite cells; there are synapses with lots of axons coming in and lots of dendrites present
- synapses are abundant
Enteric ganglia
enteric plexuses
Describe
myenteric (Auerbach’s) plexus
They have eccentic nuclei which means they must be multipolar – they are enteric (autonomic) neurons
Most of the tissue in the frame is smooth muscle of the gut wall
Nerve regeneration
Pseudounipolar
Sensory nerves are pseudounipolar
Multipolar
Somatic motor & Visceral motor (autonomic) are multipolar
Describe
Dorsal root (aka spinal) ganglion
This is a photo of cell bodies, because you can see the nuclei – it’s not in the CNS, so must be dorsal root ganglion
Because the nuclei are in the center, we know they are sesory cells, which are also pseudounipolar
The arrowed nuclei are schwann cells
Describe
In the ganglion between the brackets, the nuclei are eccentric so they must be multipolar neurons (likely autonomic neurons)
they’re surrounded by dense irregular with adipocytes
The smaller bundle to the left is a bundle of axons, not another ganglion because there are no cell bodies
Describe
Spinal Ganglion (DRG)
Where you can see a nuclues, it is in the middle, and there are complete circles of satellite cells surounding the cell body
These are SENSORY NEURONS
Describe
Autonomic Ganglion
The nuclei are eccentric and therefore these must be multipolar
The satellite cells are dispersed, not surrounding in complete circles
These are AUTONOMIC NEURONS
Myelinated axonal regions have what type of ratio with Schwann cells?
1:1 if the axon is mylinated
If it’s not mylinated, one Schwann cell may wrap around multiple axons
Review
Reticular fibers mostly Col III
Endoneurium has external lamina
Silver stains of nerve fibers
Make axons look dark, mylination is light
Describe
Most peripheral nerves will be a mix of myelinated and unmyelinated axons
The dark pink rings around the axons are the neurolemma or Schwann cell cytoplasm that stains very well and surrounds the myelin sheath surrounding the axon
The dark dots are Schwann cell nuclei
Describe
This is an image of an axon
Surrounding the axon are the layers of Schwann cell cytoplasm and myelin sheath
The mesaxon (break in the Schwann cell) is at the 5 o’clock position
The Schwann cell has an external lamina that runs all the way around, looks like a fuzzy outline
There are reticular fibers (Col III) in the top right and bottom right corners
The circles inside the axon are microtubules
The dots inside the axon are neurofilaments
And the large body in the axon is the mitochondria
