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SMS Week 2 > Nervous Tissue > Flashcards

Nervous Tissue Flashcards

1
Q

What glial cells are present in the CNS?

WHat glial cells are present in the PNS?

A

CNS: astrocyte, oligodendrocytes, microglia, ependymal cells

PNS: Schwann cells, satellite cells

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2
Q

Which one has against connective tissue, PNS or CNS?

A

PNS only

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3
Q

Embryologically, what forms the PNS? WHat forms the CNS?

A

Neural crest forms the PNS (sensory neurons, motor neurons, glia, etc)

Neural tube forms the CNS (neurons and glia)

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4
Q

What cells are mitotically active in the nervous system?

A

neurons are NOT

glial cells maintain mitotic capbility

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5
Q

Where are pyramidal neurons located? WHere are purkinje fibers located?

A

hippocampus

Cerebellum

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6
Q

What is the term for all the neural tissue that contains all the synapses, processes, axons, dendrites and glial cells?

A

neuropil

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7
Q

WHat cells line the canal of the spinal cord?

A

ependymal cells

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8
Q

What stain will strongly strain RER?

A

the Nissl stain

it forms Nissle bodies = clumps of RER (there’s lots of RER in neurons because they need lots of proteins)

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9
Q

What filaments make up the cytoskeleton of the neuron cell body?

A

a class of intermediate filemtns called neurofilaments

microtubules ar epresent as well, but moreso in the axons

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10
Q

What are the two major pigments that can be picked up by neurons?

A

lipofuscin (from breakdown of lipids in lysosomes)

neuromellenin (in locus cerruleus and substantia nigra)

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11
Q

WHy does the axon hillock stain white under stains?

A

there’s no RER in the hillock. the RER is what’s being stained.

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12
Q

WHat do dendrites do for a neuron?

A

provides receptive areas for receipt of input

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13
Q

What is the example of naked nerve ending?

What are two examples of encapsulated nerve endings?

A

Merkel’s cells are associated with naked nerve endings in the skin (touch)

The encapsulated nerve endings are meisner’s corpuscles (touch) and pacinian corpuscles (pressure)

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14
Q

What are the places an axon can send information?

A
  1. another nerve cell in the CNS
  2. autonomic ganglia in the PNS
  3. effector organ in the PNS
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15
Q

What are some general characteristics of axons?

A
  1. usually single, but can have collateral braches
  2. myelinated or non myelinated
  3. variable length
  4. constant diameter
  5. have terminal branches
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16
Q

Which axon fibers tend to be non-myelinated?

A

the small ones = C fibers

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17
Q

If an axon terminal branches to form up to 1000 or more terminals, what is it called?

A

telodendria

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18
Q

Swellings at the end of axon terminals are called what?

A

terminal boutons

end-feet

knobs

telodendria

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19
Q

What are some characteristics of the plasma membrane of neurons?

A

it’s semipermeable and electrically active

integral membrane proteins serve as channels/carriers for ions or receptors for NT

they maintain the resting membrane potential and also propagate action potentials

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20
Q

What forms the synaptic vesicles for NT secretions?

A

the golgi apparatus

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21
Q

What really determines the characteristics of different nerve cell types?

A

the arrangement of the dendrites

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22
Q

What is the initial segment of a neuron?

A

It’s the region of the axon that extends from the cell body to the beginning ot myelination

It is the site of impulse initiation due to lower threshold of excitability

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23
Q

What is the content of an axon?

A

NO RER or ribosomes

synaptic vesicles in the terminals

microtubules running parallel to the long axis of the axons

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24
Q

What do terminal ends of the axon do? What are the different types?

A

THey form synapses - specialized communicating junctions - with other nerve cells or effector organs

  1. axo-dendritic
  2. axo-somatic
  3. axo-axonal
  4. Serial, like axo-axo-dendritic
  5. Dendrodendritic (very rare)
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25
Q

What are the NT released into?

A

the synaptic cleft between the axon terminals and their targets

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26
Q

What are 4 things you’d find at an axon terminal?

A
  1. NT vesicles
  2. presynaptic dense projections
  3. neurofilaments
  4. mitochondria
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27
Q

What is the importance of presynaptic dense projections in the terminals? (also called presynaptic grid)

A

it’s an electron dense material on the cytoplasmic side of the membrane.

it provides sites for the vesicles to approach and fuse with the presynaptic membrane

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28
Q

What are some characteristics of the post synaptic structure?

A

It has receptor integral membrane proteins to interact with the neurotransmitters

interaction with the NT may cause an electrical change in the postynaptic nerve

it’s electron dense material at the cytoplasmic side of post-synaptic membrane

it may be thicker or the same thickness as the presynaptic density

MUCH less compplex than presynaptic dense projections

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29
Q

What is a peptidergic neurons?

A

It’s a neuron that packages the neurotransmitters into vesicles within the cell body and then transports them to the axon terminals via fast axonal transport via kinesins. the vesicles are then exocytosed

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30
Q

How is a small-molecule secreting neuron different from a peptidergic neuron?

A

In small molecule secreting neurons, the golgi makes empty vesicles that are transported to the axon terminals by fast transport and that’s where they are constantly being packaged, recycled and repackaged

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31
Q

Describe the slow component of axonal transport?

A

It is ONLY in the orthograde direction

It transports non-packaged molecules and cytoskeletal components

0.5 to 3 mm per day

mechanism unclear

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32
Q

Describe the fast component of axonal transport.

A

It can be orthograde (400 mm/day) or retrograde (200-300 mm/day)

In the orthograde direction it transports synaptic vesicles, mitochondria and other membrane associated proteins

In the retrograde direction it transports worn out membranes of synaptic vesicles, old mitochondira, etc.

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33
Q

What is the importnat clinical issue with retrograde axonal transport?

A

Viruses can travel to cell bodies that way

ravies does this

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34
Q

For fast axonal transport, what motor cells are used for the orthograde direction? How about the retrograde motor?

A

othograde = kinesin

retrograde = dynein

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35
Q

What two glial cell types form macroglia?

A

astrocytes and oligodendrocytes

36
Q

What are the two types of astrocytes?

A

fibrous (white matter) and protoplasmis (gray matter)

37
Q

What do astrocyte processes terminate as? WHere

A

they terminate as “end feet”

they insinuiate themselves between nerve cells and processes and also end on blood vessels

  1. they form a layer outside the basement membrane of the endothelial cells - they help to form tight junctions between the endothelial cells to make the BBB
  2. THey end on the inner surface of the pia mater to form the external glial limiting membrane
  3. They end on the basal surface of ependymal cells to form the internal glial limiting membrane
38
Q

What are the likely function of astrocytes?

A
  1. structural support
  2. uptake of excess potassium form extracellular space following prolonged neuronal activity
  3. phagocytosis and scar formation after injury (gliosis)
  4. Isolation of nerve terminals and fibers form their neighbors
  5. regulation of the entry of substances to the interneuronal space
39
Q

How can you distinguish an oligodendrocytes from an astrocyte?

A

the nucleus will stain darker in oligodencrotyes

they’ll have fewer projections

40
Q

What is the function of oligodencrocytes?

A

myelination of CNS axons

they have arms, each of which will myelinate a different internode

41
Q

What is the funciton of microglia?

A

they are macrophages of the nervous system, derived from monocytes, and actively phagocytic

42
Q

What do ependymal cells do?

A

they line the central canal of the spinal cord and the ventricles

in the ventricles they have cilia that beat and move CSF

They are possibly involved with the transport of substances form the CSF to the brain, and secretion into the ventricles

43
Q

What kind of cells are ependymal cells?

A

simple cuboidal o columnar epithelium; ciliated

44
Q

In the roof of the ventricles, the ependymal cells are modified to make what?

A

choroidal epithelium covering the choroid plexus

45
Q

What do choroidal epithelial cells do?

A

they control the composition of CSF produced by the choroid plexus

they prevent movmeent of plasma proteins from the capillaries of the choroid plexus into the CSF by having tight junctions between adjacent choroidal epithelial cells

46
Q

What are the three layers of connective tissue that bind together groups of axons in peripheral nerves?

A
  1. epineurium (the external, tough layer of dense collagen)
  2. Perineurium (envelopes bundles of fasicles of fibers and includes numerous epithelioid-like cells on the inner aspect)
  3. Endoneurium (delicate collagen around individual axons - contacts the basement of schwann cells which cover the axon)
47
Q

Unmyelinated fibers of the PNS consist of an axon and what?

A

a sheath of Schwann, or neurilemma

48
Q

Describe a Sheath of Schwann

A
  1. schwann cell embraces a number of small axons (C fibers)
  2. eventually eac axon gains its’ own trough in the periphery of the schwann cell
  3. the axons still remain outside the schwann cell membrane even though they are engulfed by it
  4. the area of membrane that encloses over the axon is called a mesaron
49
Q

what is the collective term fo a group of unmyelinated fibers encompassed in a single Schwann cell?

A

a bundle of remak

50
Q

Where do unmyelinated fibers occur in the pNS?

A

a. Axons of most post-ganglionic autonomic neurons
b. Axons of small sensory neurons in dorsal root ganglia

51
Q

WHat do myelinated fibers of the PNS consist of?

A

axon

myelin

schwann cells

52
Q

What is the major consistuent of myelin?

A

lipids 80%

protein 20%

53
Q

What will myelin look like…

when fresh?

stained with osmium?

stained with H&E?

A

fresh: glistening white

Osmium: black empty rings - like black cheerios

H&E: network of residual proteins called neruokeratin (the lipid is removed in the fixation)

54
Q

What are nodes of ranvier?

A

periodic interruptions in the myelin sheath

the space between adjacent schwann cells along the length of the axon

55
Q

What are internodes?

A

Segments of myelin between adjacent Nodes of Ranvier

56
Q

Sometimes there are areas where the myelin didn’t wrap quite right and the cytoplasm wasn’t squeezed out. THese form oblique clefts in the myelin under stainig. WHat are these called?

A

Schmidt-Lantermann clefts

57
Q

What is the myelin jelly-roll theory?

A
  1. the myelin is formed by a spiral wrapping of the Schwann cell membrane around hte nerve fiber
  2. cytoplasm of the SC is squeezed out and compation results in the formation of intraperiod and major dense lines

ONE schwann cell will form ONE segment of internode on ONE axon with the nucleus in the cytoplasm of the final wrap

58
Q

Largest axons will have the —— myelin and the —— internodes, and are the most —— conducting.

A

Largest axons have the thickest myelin and the longest internodes –
and are the most rapidly conducting

59
Q

What forms the major dense lines in myelin? THe intraperiod lines?

A

the major dense lines are former cytoplasmic surfaces of schwan cell membranes that fuse together

the intraperiod liens are former outer surfaces of schwann cells that fuse and ecome thin

60
Q

What are the internal and external mesaxons?

A

the regions where the SC meets itself as it encircles the axon initially (internal) and where it overlaps itself on the outermost turn (external)

61
Q

What do the nodes of ranvier look like in the PNS?

A

it’s partially covered by loosely interdigitating cytoplasmic processes of the schwann cell

the basement membrane is outside the SC and inside the endoneurium

62
Q

Do unmyelinated fibers in the CNS have a glial cell?

A

no

63
Q

What glial cell myalinates fibers int he CNS? Describe how.

A

oligodendrocyte

one oligodencrocyte may myelinate more than one axon - 10 to 40

Oligodendrocyte cell body is located distant form the axon so there is little cytoplasm in the outer wrap and never a nucleus

64
Q

How are nodes of ranvier in the CNS different from thos ein the PNS?

A

in the CNS the internodal distance is shorter and the node is exposed to the extracellular space because ther eis no oligodendrocyte process covering it (as in the PNS)

There isn’t a basement membrane outside the myelin - no connective tissue

65
Q

Are there any schmidt lantermann clefts in the CNS?

A

No - differen cell, different type of wrapping

66
Q

How do action potentials doncut down myelinated axons?

A

it’s faster because it uses slatatory conductoin - it jumps from node to ndoe

this correlates with the fact that the N of R have the highest concentration of sodium channels anywhere on the nerve cell

67
Q

Where are sensory ganglia?

A

dorsal root ganglia of all spinal enrves and the sensory ganglia of cranial nerves 5, 7,8,9 and 10

68
Q

Do sensory ganglia have synapses inside?

A

No - they hold pseudounipolar cells, so synapses aren’t necessary- one process goes to the periphery and the other goes to the CNS

69
Q

What type of peripheral glia cell is located in sensory ganglia?

A

satellite cells

70
Q

Describe satellite cells.

A

Very small cells which form a covering around each ganglionneuron; only the nucleus of these glial cells is demonstrated inlight microscopy

they might just be schwann cells - the satellite cell layer is ocnitnuous with the schwann cell sheath of the peripheral nerve and they share a continuous bsement membrane

71
Q

What connective tissue cells can also be found in sensory gnaglia

A

fibroblasts!

they are continuous with the endoneurium of the peripheral nerve

72
Q

The entire ganglion is surrounded by what?

A

a connective tissue capsule that is continuous with th perineurium and epineurium of the peripheral nerve

it extends into the ganglion to separate nerve ell bodies into groups

73
Q

How do sympathetic ganglia and parasympathetic ganglia differ?

A

sympathetic ganglia are discrete structures with CT capsules

parasympathetic ganglia are smal encapsulated structures in the head, but are isolated cell groups in the thoracid, abdominal and pelvic viscera

74
Q

What are the contents of autonomic ganglia?

A

synapses of the preganglionic fibers on the dendrives nand cell bodies of the post-ganglionic neuron

the cell bodie of the postganglionic neurons (multipolar)

satellite cells and schwann cells

connective tissue and fibroblasts

75
Q

What is one way you can differentiate sensory ganglia from autonmoic ganglia uder a microscope?

A

sensory ganglia have central nuclei

autonomic ganglia have eccentric nuclei and are often binucleate

76
Q

Which are the myelinated fibers: pre or postganglionic nerve fibers?

A

the pregnaglionis are myalinated B fibers

the postganglionic axons are small unmyelinated C fibers

77
Q

How do the satellite cells of the autonomic ganglia differ form that of sensory ganglia?

A

they don’t form as complete a covering of each nerve fiber as they do through autonomic

78
Q

Describe Wallerian degeneration?

A

it’s orthograde degeneration

the axon, axon terminals, and myelin disintegrate

sometimes the schwann cell sheath and CT layers remain intact, but not always

79
Q

Describe retrograde degeneration.

A

It’s degeneration in the cell body and or portion of axon still attached to the cell body

  • degeneration of axon and myelin sheath for a short distance toward the cell body
  • chromatolysis (cell body and nucleus swell, nucleus becomes eccentric, RER disintegrates and move to periphery
  • somtimes cell death without chromatolysis
80
Q

Which injury is worse: a crushing injury or a slice injury?

A

a crushing injury

regeneration can occur in the PNS if the growing axon can find and follow the tube of the schwann cells and connective tissue that’s left

it won’t be present in a crushing injury

81
Q

What happens first, reinnervation or remyelination?

A

reinnervation

82
Q

Is reinnervation specific?

A

not really

sensory fibers will innervate any sensory receptor and motor fibers will innervate any muscle

so the regenerated product is never as good as the original - sensation is less critical and movement is less discrete

the regenerated axons generally don’t retain their oriinal diameter either, so conduction velocity is decreased

83
Q

What is a traumatic neuroma?

A

a. Large heterogeneous mass of entangled nerve fibers, Schwann
cells, connective tissue cells, etc.
b. Sometimes develops as regenerating neurons are unable to overcome
the obstacles between the cut ends of the nerve
c. the afferent neurons involved in the neuroma still transmit messages
centrally which are often regarded as painful

84
Q

Why does regeneration typically not occur in the CNS?

A

THe Oligodendrocytes don’t retain that guiding tube

scar tissue produced by astroglia is a significant barrier as well

85
Q

WHat is a possible explanation for surprising CNS regeneration in some cases?

A

plasticity

  1. collateral sprouting and establishment of new connections
  2. unmasking of previously less significant connections that had redundant function
86
Q
A

SMS Week 2 (9 decks)

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