PNS Histology Flashcards

Schwann Cell
Terms Definitions
The myelinating cell of the PNS is the ___ ___, this cell is ___, espcially following nerve injury.
Schwann cellmitotic
The myelinating cell in the CNS is the ____.
oligodendrocyte
The Schwann cell is ___ and myelinates ____ axon at a time. The oligodendrocyte is not____ but can myelinate ____ axons at one time.
- mitotic- one- not mitotic- many
All nerves in the PNS are surrounded by ___ ____, even though not all nerves are myelinated. This is not the case in the CNS.
- Schwann cells
Nerve fibers are ____ surrounded by sheaths of cells of ___ _____ (_____).
- axons- ectodermal origin (Schwann cells)
In the PNS, axons not ensheathed by the Schwann cell membrane are enveloped by ?
- clefts of Schwann cells
Areas on a myelinated nerve fiber between two myelinated areas are called ___ __ ___.
nodes of ranvier
unmyelinated axons do not have ___ __ ____.
nodes of ranvier
in the CNS, unmyelinated axons project between ___ and ___ cell processes.
- neuronal - glial
In the PNS, you have a ___ ___ made of collagen, you do not have this in the CNS.
- basal lamina
In the PNS, a ____ axon is embedded in the ___ ___.
- axon- Schwann cell
A Schwann cell is able to house numerous ____ in cytoplasm invaginations, but with this arrangement ___ does not occur b/c the Schwann cell cannot wrap around all the axons.
- axons- myelination
The ___ is the ____ ____ ____ that surrounds the PERIPHERAL ___ and fills the space between nerve fiber bundles.
- epineurium - external fibrous coat- nerve
The epineurim in the PNS is made of ____, ____, and ___ _____.
- collagen- fibroblasts- blood vessels
The epineurium provides ___ ___ and ____ for the nerve.
- structural support- elasticity
Nerve fibers are arranged in ___ to form nerves.
- bundles
what kind of cell is found in the PNS, but not the CNS?
- fibroblast
each individual nerve bundle/fasicle is surrounded by a ____.
- perineurium
The perineurium consists of :
- flattened epithelial like cells
The flattened epithelial like cells of the perineurium are connected by ___ ____ to protect the nerve fiber from ___ ____.
- tight junctions- toxic macromolecules
Each nerve fiber in the PNS is surrounded by Schwann cells. The ____ surrounds the Schwann cells.
- endoneurium
The endoneurium consists of:
- reticular cells- collagen fibers
each individual PNS nerve fiber is covered by a thin delicate cytoplasmic sheath of the Schwann cell, called the ____.
- neurilemma
The Neurilemma is the outermost ___ ____ of a ___ ____ that surrounds an axon.
- cytoplasmic layer- Schwann cell
The neurilemma forms the outermost layer of the ___ ___ in the PNS, and lays over the ___.
- nerve fiber- endoneurium
Nerve fibers are myelinated by Schwann cells at only ___ ____ on the fiber.
- one point
early on in myelination a Schwann cell encloses many axons, but as mitosis continutes it becomes segregated to a ___ ___. The lips of the Schwann cell envelpiong process extend around the axon is a spiral fashion forming the ___ ___.
- single axon- intraperiod line (IPL)
each wrap is ___ to the previous wrap.
internal
As the cytoplasm is lost in the spiral myelinating process, a ____ ___ ___ forms.
- major dense line
Compaction:
- sheath becomes more mature, number of turns around axon increases, lamallae of the sheath become more compact
Some areas of myelin do not compact, these areas are called ____ ____ ____.
Schmidt-Lanterman Clefts
Schmidt-Lanterman clefts allow for passage of newly synthesized ___ ____ (protein, lipids) from the ___ ___ ___ to the ___ ___.
- myelin components- Schwann cell cytoplasm- myelin proper
Myelin, both in the CNS and PNS, is ___ % protein and ___% lipid.
30% protein70% lipid
major protein in PNS myelin is:
- Proglycoprotein
Poglycoprotein is a ___ ___ found in the ___ and the ___.
- transmembrane protein- IPL - MDL
Schmidt clefts are only in the ___.
PNS
Myelin basic proteins make up 20% of myelin and are found within the ___.
- major dense line
if you lose a myelin basic protein, what component of myelin would you lack?
- major dense line
In the PNS, myelin basic protein is not essential for formation of the ____ since PNS also has __ _____. In the CNS you have to MBP for MDL formation.
- major dense line- Po glycoprotein
A collection of nerve cell bodies outside the CNS is called a ___ ____.
- nerve ganglion
In the CNS, nerve cell bodies are called:
- nuclei
Each neuron cell body in the PNS is surrounded by ___ ___, which function as glial or supportive cells.
- satellite cells
The satellite cells that around a nerve cell body are surrounded by ___ ___ .
basal lamina
There are two types of nerve ganglia in the PNS categorized based on morphology and function and direction of impulse. What are they?
- sensory ganglion- autonomic ganglion
What are the two types of sensory ganglia?
- cranial sensory ganglia- associated with cranial nerve- spinal sensory ganglia- associated with dorsal root ganglia of spinal nerves)
Sensory ganglia are ___ ganglia since they send impules to the brain.
- afferent
Dorsal root sensory ganglia have ____neurons that send one thin process to the CNS. The other thicker processes go to the ____. These neurons have ___ as large as ____ in diameter.
- pseudounipolar- periphery- perikaryia - 100 micrometers
Since dorsal root ganglia are ___ and the perikarya do not receive impulses, there are no ____ within the ganglia itself.
- pseudounipolar- synapses
With sensory ganglia, nerve fibers are found in ____, nerve cell bodies are found at the ____, and there is a centrally located ___ with a darker nucleolus.
- bundles- peripheray- nucleus
Autonomic ganglia are distributed within the ___ and ___ divisions of the auonomic nervous system.
- sympathetic- parasympathetic
Autonomic ganglia appear as ___ ____ in autonomic nerves.
- bulbous dilations
Autonomic ganglia found in the walls of the digestive tract are called ____ ____. These ganglia are not surrounded by connective tissue, but rather by the ___ of the organ and only have a few ___ cells.
- intramural ganglia- stroma- satellite
Autonomic ganglia include ___ _____ ___ ___ and ___ ___ __ ____.
- submucosal plexus of Meissner- myenteric plexus of Auerbach
the submucosal plexus of meissner is in ____. the myenteric plexus of auerbach is in ___ ___.
- glands- secretion- smooth muscle- peristalsis
Autonomic ganglia are ____ neurons that are ___ shaped, and have a small diameter of 15-45 micrometeres. The nucleus is round and ___ placed, and the cytoplasm contains ____ bodies.
- multipolar- star- eccentrically - Nissl bodies
Nissl bodies are part of the ___.
RER
Neuron cell bodies of autonomic ganglia are surrounded by a layer of satellite cells, although in intramural ganglia, only a few satellite cells are found
autonomic ganglia do ____, but dorsal root ganglia do not do this.
- synapse
cell bodies in autonomic ganglia are not grouped but are ___ b/w nerve fibers.
scattered
rarely are neurons able to divide so degeneration is a permanent loss. But Schwann cells, glial cells, and ganglionic cells can ___.
divide
The olfactory nerve CNI is not a nerve.
Neurons can divide in the ___ ___. This is an exception. usually this can't happen.
nasal epithelium
when a peripheral nerve axon is severed, degenerative changes occur, called ___ ____.
Wallerian degeneration
If the proximal axon stays in tact with the perikaryion, it can ____, but degrades 1-2 internodes.
-regenerate
the distal segement degernates and is removed by what?
Schwann cellsmacrophages
Axonal injury causes the following events in the perikaryon.
Dissolution of the Nissl substance - chromatolysis. Decrease in cytoplasmic basophilia. Increase in the volume of the perikarya.Migration of nuclei to a peripheral position in the perikarya.
during nerve regeneration, ____ cells proliferate giving rise to tube like structures which are surrounded by collagen of an _____.
- Schwann cells- endoneurium
Each ___ of the surviving neuron cell body splits into nerve fibers, aka ____, and reaches the ___ ___ tube of the degerating stump. This tube guides the axons during regrowth. Some axons/neurites reach peripheral tubes, while others reach central tubes a
- axon- neurites- Schwann cell
In nerve regeneration, only one fiber persists and becomes ____, this is usually the____ fiber.
- myelinated- largest
Enlargement of one fiber and elimination of the others, only occurs if the regenerating axons make sensory or motor contact with the appropriate receptor or effector endings in the periphary.
What are the two types of receptors?
- encapsulated receptors- nonencapsulated receptors
nonencapsulated receptors respond to ___ and ___ sensations. These are not ____ and are ___ ___ ___. They are found in the ____.
- pain and touch- not myelinated- free nerve endings- epidermis
Are Merkel discs/cells encapsulated or unencapsulated?
- unecapsulated
Merkel cells are specialized epithelial cell masses located in the ___ ___ of the ___.
basal layerepidermis
The merkel cell is enmeshed in a terminal branch of an underlying axon terminal and is senstive to ___. Thus it is called a ___.
- touch- mechanoreceptor
The outer connective tissue sheath of the hair follicle is surrouned by ____ ____ to form a ___ ___ that is sensitive to touch when the hair is perturbed or bent.
- unmyelinated nerve fibers- nerve ending
The Meissner corpuscle is _____ and ____ shaped, located just below the ____ in a ___ ____. It is made of a stack of flattened cells, and is sensitive to ____.
- encapsulated - bee-hive shaped- epidermis- dermal papilla- touch
more specifically the meissner corpuscle is in the ___ ____.
stratum spinosum
Pacinian corpuslces are also ____ and are located in the ___ of skin and respond to ___, ___, and ___. This receptor has a cylindrical core surrounded by ___ ____ of ___ and ___ ___ fibers.
- encapsulated- dermis- pressure, tension, vibrations- concentric lamellae - fibroblasts- thin collagen fibers
A Pacinian Corpuscle has an axon through its center that terminates at its expanded end.
Role of muscle spindles:
- relay sensory information to the CNS for : controlling muscle activity, posture, and regulating activities of opposing muscle groups (muscle tone) involved in walking and other motor activities
These spindles consist of a fluid-filled space with modified muscle fibers encased in groups within a connective tissue shell
Fibers outside the muscle spindle are called ___ fibers. Fibers inside the muscle spindle are called ___ fibers.
- extrafusal- intrafusal
2 types of intrafusal fibers:
- nuclear chain intrafusal fibers- small diameter, short- nuclear bag intrafusal fibers- larger fibers
Intrafusal fibers are richly ____ by ____ fibers that monitor the degree of stretch placed on these fibers.
- innervated - sensory
A __ ___ organ is found at the site where the skeletal muscle fibers insert on its ____.
- Golgi Tendon Organ- tendon
What function does the golgi-tendon organ have?
- proprioceptive sensory function
The golgi tendon organ is surrounded by a fibrous ____and the body consists of ____ that connects the skeletal muscle fibers with its tendon.
- capsule- collagen
The golgi tendon organ is innervated by ___ ___ ___ that terminates as endings around the ___ fibers.
type 1b sensory fiberscollagen
muscle tension ___ the fiber, which signals the force being developed within the muscle.
stretches
motor unit:
single axon and its association with a single muscle fiber/cell
An axon sends short terminals, called ___, to the surface of the muscle fiber to form a ____ junction. An action potential triggers release of ___ via ____at this junction.
- boutons- myoneural junction- acetylcholine- exocytosis
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