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COT - Exam 1 > 7.3 - Lecture - Nerve > Flashcards

7.3 - Lecture - Nerve Flashcards

1
Q

What are the three neuron classifications

A
  • unipolar (pseudounipolar)
  • bipolar
  • multipolar
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2
Q

What defines each of the three classification types

A
  • they are based on the relationship of the cell body (soma) to the peripheral processes, i.e. axons and dendrites
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3
Q

Nissl Bodies

A
  • in the LM sometimes help to recognize cell bodies of neurons
  • representing large amount of basophilic ER
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4
Q

Axodendritic Synapses

A
  • axon synapsing on a dendrite
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5
Q

Presynaptic element

A
  • part of synapse that contains a region specialized for the vesicular release of NT
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6
Q

Postsynaptic element

A
  • part of synapse that contains membrane receptors that convert the chemical signal from the NTs into a membrane potential
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7
Q

Axosomatic synapse

A

axon synapsing on the soma of a neuron

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8
Q

axoaxonic synapse

A
  • axon synapsing on the exposed portion of an axon - nearer to the soma on the axon
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9
Q

What are the two locations/names for presynaptic elements

A

1) Bouton en passant - if the presynaptic element occurs along the length of the axon
2) terminal bouton if the presynaptic element occurs at the end of the axon

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10
Q

What is a Dendritic spine in relation to a synapse

A
  • postsynaptic element normally occurs here
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11
Q

Axon hillock

A
  • typically the area of a cell at which an AP (spike) is generated
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12
Q

Describe an AP in Myelinated axons

A
  • spikes propagate via saltatory conduction

- spikes are regenerated at nodes of Ranvier

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13
Q

Describe an AP in unmyelinated axons

A
  • spikes travel more slowly due to the lack of a myelin sheath
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14
Q

Oligodendrocyte

A

= the support cell of the CNS responsible for making myelin

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15
Q

Schwann Cell

A

= the support cell of the PNS responsible for making myelin

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16
Q

What are the two appearances of myelin sheaths in EM

A

alternating:
1) major dense lines
and
2) Intraperiod lines

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17
Q

Major Dense Lines

A

= two apposed cytoplasmic faces of the unit membrane

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18
Q

Intraperiod lines

A

= two apposed extracellular faces of the unit membrane

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19
Q

Inner mesaxon

A

= ending of cell membranes contributing to the myelin

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20
Q

Outer mesaxon

A

= ending of cells membrane contributing to the myelin that connects to the cell body of the support cell

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21
Q

Glial cells

A

= non-neuronal cells
- fxns: scaffolding, metabolic support of neurons, contributing to the blood-brain barrier
include:
- astocytes, fibrous astrocytes, protoplasmic astrocytes, microglia

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22
Q

Astocytes (astroglia)

A
  • in the CNS
  • contain unique intermediate filament - glial fibrillary acidic protein (GFAP) - useful for recognition by antibody staining
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23
Q

Glial Fibrillary acidic protein (GFAP)

A
  • a unique intermediate filament

- found in astrocytes in the CNS

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24
Q

Ganglia

A
  • collections of cell bodies outside the CNS
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25
Q

Satellite cells

A
  • support the neuronal cell bodies in the ganglia
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26
Q

Nucleus (not organelle)

A
  • a discrete group of cell bodies inside the CNS (in the brainstem mostly)
    e. g. brainstem nuclei, paraventricular nucleus, lateral geniculate nucleus
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27
Q

Grey matter

A
  • CNS organization largely containing neuronal cell bodies, neuropil, and glial cells
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28
Q

Neuropil

A

mesh of axons and dendrites

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29
Q

white matter

A
  • CNS organization largely containing axons + oligodendrocytes
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30
Q

The three covering of the brain

A

are meninges - three layers of fibrous tissue

1) pia mater - thin/wispy
2) Arachnoid mater
3) Dura mater - extremely tough

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31
Q

Subarachnoid space

A
  • common site of brain hemorrhage
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32
Q

Two classifications of neurons in the periphery

A

1) Sensory

2) Motor

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33
Q

Motor neurons in the PNS

A
  • motor neurons of the spinal cord - directly control skeletal muscle
  • axons of motor neurons from specialized NMJs with the muscle fibers and post-synaptic region of the muscle cell plasmalemma= motor end plate
  • leave the spinal cord and pass through ventral roots
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34
Q

Sensory Neurons in PNS

A
  • pass through the dorsal root ganglion

- cell bodies are located in the DRG

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35
Q

Motor end plate

A

= the post-synaptic region of the muscle cell plasmalemma

36
Q

ANS

A
  • innervates organs and glands
  • has 2 divisions
    1) parasympathetic
    2) Sympathetic
    3) Enteric NS - in the gut
37
Q

Sympathetic ganglia

A

located between the spinal cord and organ of innervation

38
Q

Parasympathetic ganglia

A

located immediately adjacent to the innervated organ

39
Q

Perineurium

A
  • CT encircles large nerve fibers
40
Q

Epineurium

A

= CT that is adventitial between the nerve fiber and surrounding structures

41
Q

Endoneurium

A

= fine CT immediately surrounding axons

42
Q

Endoneurial tubes (Schwann tubes)

A

= tubes in which axons travel made by schwann cells

- important structures in axon regeneration

43
Q

Describe the characteristic nuclear morphology of a neuron

A
  • large spherical euchromatic nucleus

- contains very prominent nucleolus (tells you the nucleus is active)

44
Q

What are Nissl Bodies and the Nissl Stain

A
  • correspond to stacks of ER that fill the neurons because they are very actively producing proteins
  • shown by the Nissl Stain - accumulating in cytoplasmic globules of dye = nissl bodies - charcateristic of neurons
45
Q

Golgi Stain

A
  • stains only 1-5% of the neurons –> allows visualization of a neuron and its processes
  • myelin disturbs Golgi stain
46
Q

Describe the typical characteristics/morphology of a local process or dendrite

A
  • multiple dendrites emerge from soma at different sites and branch extensively at less than 90 degree angles
  • dendrites tape with increasing distance from cell body
  • appears studded with Golgi stain
47
Q

Describe the typical characteristic/morphology of a distal process or axon

A
  • one axon
  • emerges from cell body at a specialized region = axon hillock
  • maintains fix diametere throughout its long course
  • branches emerge at 90 degree angles
  • appears smooth in Golgi stain
48
Q

Describe the fine structures of dendrites

A
  • microtubules
  • mitochondria
  • large dendrites - contain ER, ribosomes, neurofilaments
  • dendritic spines
49
Q

What are dendritic spines

A

= specialized evaginations of dendritic plasmalemma that receive signals
- each spine can move (increase or decrease in size) - they are highly dynamic - each receives a synapse

50
Q

Describe the fine structures of an axon

A
  • neurofilaments
  • microtubules
  • stray mitochondria
  • no rER or free ribosomes
51
Q

Describe the morphology of axons in Nissl stains

A
  • axons don’t stain with nissl (because do not contain ER)
52
Q

Describe the morphology of axons in H and E stains

A
  • eosinophilic core = axon
  • white space = myelin
  • can see perpindicular line = indicating node of Ranvier of myelinated axons (in longitudinal sections)
53
Q

Describe the morphology of axons in osmium and what osmium stains for

A
  • Osmium is a heavy metal stain for lipids

- therefore it will show myelin staining around myelinated axons

54
Q

Compare myelination of axons in the CNS and PNS

A
  • in PNS 1 schwann cell contributes 1 internode of myelin to a single axon
  • in CNS 1 oligodendrocyte contributes internodes to multiple axons
55
Q

Describe the morphology of unmyelinated axons in H and E stains and their relation to the myelin-producing cells

A
  • they appear as froth in H and E stains
  • many unmyelinated axons are enveloped by a single supporting cell - which offers partial support (not to the level of myelination though)
  • i.e. Schwann cells that are not involved in myelinating an axon encapsulate a group of unmyelinated axons
56
Q

Describe the different axonal terminations

A
  • axo-dendritic (on a dendrite)
  • axo-spinous (on the dendrite spine)
    the above ones are the most common
  • axo-somatic (on the soma)
  • axo-axonic (on the inital segment of an axon)
  • in rare cases dendrites can have vesicles and be presynaptic to other vesicles
57
Q

What are the two types of synapses and are they differentiable in EM?

A
  • The two types are excitatory and inhibitory and they are differentiable in EM
58
Q

Describe the characteristics of Excitatory Synapses

A

use the acronym WEAR

  • Wide synaptic cleft
  • Excitatory
  • Asymmetric synapse
  • Round Vesicle
59
Q

Describe the characteristics of Inhibitory Synapses

A

use acronym PINS

  • Pleomorphic vesicles
  • Inhibitory
  • Narrow Synaptic Cleft
  • Symmetrical Synapse
60
Q

Describe the multipolar classification of neurons

A
  • Multiple processes into and out of the cell body- Multiple dendrites + multiple axons
    ex. Chandelier cells with “candles” axons - effective rapid inhibitory neuron - shuts down cells very effectively
    ex. Purkinje Neurons
61
Q

Describe the Bipolar classification of neurons

A
  • morphologically simlified neurons
  • 1 input process
  • 1 output process
  • only found in retina and olfactory bulb
62
Q

Describe the Unipolar classification of neurons

A
  • only found in sensory ganglia of the PNS –> DRG
  • AP initiation and summation happens at sensory end
  • AP signal doesnt have to go though the cell body (unlike multipolar or bipolar neurons)
  • almost always myelinated
  • have satellite cells (subclass of Schwann cell)
63
Q

2 Differences of CNS and PNS

A
  • supporting cells/elements

- response to injury

64
Q

Describe the relative size of a supporting cell

A
  • essentially equivalent to nucleolus of neuron –> (might only apply to unipolar neurons???)
65
Q

What are the non-neuronal cells of the CNS

A
  • generally known as glia (glue)
  • support neuronal function and provide structure
    1) Macroglia
    1A) Astrocytes
    1B) Oligodendrocytes
    2) Microglia
66
Q

Describe astrocytes

A
  • star shaped marcoglial cells of CNS
  • provide structure to brain and fill space between neuronal processes (CNS doesnt have CT)
  • Contains intermediate filaments - GFAP in cytoplasm to provide structural support
  • maintain stable ionic medium around nucleus by taking up excess NT and regulating ionic composition
  • provide metabolic support to neurons
  • forms glial scar - by proliferating and forming scar in regions of CNS damage
67
Q

What are the types and localizations of the two types of astrocytes

A

1) Protoplasmic Astrocytes - in grey matter

2) Fibrous Astrocytes - in white matter

68
Q

Describe Oligodendrocytes

A
  • macroglial cells of CNS

- each cell gives rise to several processes that each forms myelin internode on a different axon

69
Q

Describe Microglia

A

= phagocytic cells that patrol the brain + spinal cord

  • are part of the Mononuclear phagocytic system (MPS)
  • derived from bone marrow - from monocytes (like macrophages, alpha-synoviocytes, osteoclasts)
  • incredibly dynamic cells - highly motile within nervous tissue
  • responsible for immune surveillance
70
Q

What are the nonneuronal cells of the PNS

A 
- nerves in periphery are ensheathed, organized, supported by CT + the microenvironment bathing the neuronal elements in PNS is strictly controlled by:
Epineurium
Perineurium
Endoneurium
External Lamina
Schwann Cells
Satellite Cells
71
Q

Function of epineurium in PNS - in relation to support cells it provides

A
  • dense CT sheath around perineurium

- separating perineurium from rest of tissues

72
Q

Function of perineurium in PNS - in relation to support cells it provides

A
  • collagen fibers with squamous cells

- surround and support nerves

73
Q

Function of endoneurium in PNS - in relation to support cells it provides

A
  • type III collage fibers (reticular fibers) - between myelin sheaths
74
Q

Function of external lamina in PNS - in relation to support cells it provides

A
  • basal lamina surrounding schwann cells
75
Q

Function of Schwann cells in PNS - in relation to support cells it provides

A
  • surround myelinated and unmyelinated axons in peripheral nerves
76
Q

Function of Satellite cells in PNS - in relation to support cells it provides

A
  • a subclass of Schwann Cell
  • encapsulate neuronal cell bodies in peripheral ganglia (DRG)
  • protect cell - joined together by gap JXNs - to separate it from ECF
77
Q

Which support cell is responsible for the glial function of physical support in CNS and PNS

A

CNS - Astrocyte

PNS - CT

78
Q

Which support cell is responsible for the glial function of Control of Microenvironment in CNS and PNS

A

CNS - Astrocyte

PNS - Schwann Cell/satellite cell

79
Q

Which support cell is responsible for the glial function of Myelin synthesis in CNS and PNS

A

CNS - Oligodendrocyte (multiple internode per cell)

PNS - Schwann Cell (1 internode per cell)

80
Q

Which support cell is responsible for the glial function of Defense/Immune in CNS and PNS

A

CNS - Microglia

PNS - Immune System

81
Q

What happens during peripheral nerve injury with respect to retrograde RXN?

A

Retrograde RXN

  • produce cell that completely cahnges morphology
  • Nissl substance dissolves
  • undergoes chromatolysis
82
Q

What happens during peripheral nerve injury with respect to Local Changes?

A
  • Axon terminals are completely dependent on the soma organelles
  • so the axon and its associated wrapped myelin cytoplasm are phagocytosed (but the schwann cell remains intact)
83
Q

What happens during peripheral nerve injury with respect to Anterograde RXN?

A
  • Distal Axon and myelin are phagocytosed
  • Schwann cells proliferate and form tubes = Schwann tubes = Band of Bungner
  • cell body begins heightened production and proximal axon sprouts and growth into the Schwann tubes
  • Schwann cells wil re-myelinated and guide the axon to its target
84
Q

What happens if their is failure of regeneration

A
  • traumatic neuroma occurs - results is sprouting axon cannot reach Schwann cell tubes and therefore cannot reach its target
85
Q

Describe Central Nerve (CNS) Regeneration

A
  • Regeneration in CNS is extremely rare
  • ECM (External lamina) does not exist in CNS and cannot guide axon sprouts
  • Schwann cells secrete chemical factors that attract and encourage growth of axon sprouts in PNS, but oligodendrocytes do not
  • Central myelin = a potent inhibitor of axonal growth in CNS
  • After CNS injury - astrocytes fill in the spaces and form a physical barrier (gliotic scar) to regeneration
86
Q

Why does regeneration work in the PNS but not CNS following nerve damge

A
  • largely due to the CT organization in the PNS
  • external lamina
  • ECM
  • schwann cells - which secrete chemical factors to aid targeting and encourage growth as well as form Schwann tubes/Bands of Bungner
    ==> all of these factors aid/guide the axonal growth and are not present in CNS

COT - Exam 1 (26 decks)

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