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Neuro > Ch 4- Cellular Components > Flashcards

Ch 4- Cellular Components Flashcards

0
Q

how is primary growth route determined?

A

by factors intrinsic to particular neurons and particular sites to be innervated which appears invariantly across individuals of a particular species
- CNS paterning is controlled by some chemical properties of the areas of termination described as a “chemical affinity” for appropriate target tissue.

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1
Q

what happens as axon grows?

A
  • increase in both rER and Golgi apparatus
  • nissl body precursors appear as small granules on one side of the nucleus
  • cytoplasmic glycogen is reduced
  • increase in ribosomes and mitochondria
  • neurofilaments and microtubules become more abundant
  • growth cones appear - the tips of the initial outgrowth and are on each branch
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2
Q

the nervous system is divided into 2 main parts

A
  1. the central nervous system - composed of the brain and spinal cord within the bony skull and vertebral column.
  2. peripheral nervous system - composed of ganglia and peripheral nerves
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3
Q

sensory neurons

A

detect events occurring in the periphery, often through specialized endings called receptors.

  • their cell bodies are located in the dorsal root ganglia of the spinal cord
  • a peripheral axon innervates the receptor and a central axon conveys signals into the spinal cord or brain (CNS).
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4
Q

how does a signal from a sensory neuron travel?

A
  1. the signals begin at the receptor
  2. travel down the peripheral axon
  3. past the cell body
  4. down the central axon and into the CNS.
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5
Q

where are skeletal motor neurons located?

A

in the CNS gray matter of the spinal cord and brain

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6
Q

where do axons of skeletal motor neurons go?

A

they enter the PNS through spinal nerves or cranial nerves and innervate striated muscle.

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7
Q

what are smooth muscle of various organs innervated by?

A

postganglionic axons of the sympathetic and parasympathetic systems

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8
Q

key fact of interneurons

A

all their axons are confined to the CNS

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9
Q

projection neurons

A

are interneurons that leave one brain region and travel to another.
- many release excitatory neurotransmitters.

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10
Q

what are some projection neurons called?

A

upper motor neurons; because they strongly influence motor neurons

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11
Q

local interneurons

A

have axons that ramify in the immediate vicinity of their cell body.
most of them release inhibitory neurotransmitters

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12
Q

neuroglia

A

they are the non-neuronal cells in the CNS and perform supporting functions for neurons and ependymal cells

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13
Q

the ventricular system

A

a series of cavities in the brain that contain cerebrospinal fluid which is produced in the ventricles and flows out over the external surfaces of the brain and spinal cord.

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14
Q

meninges

A

several layers of connective tissue in the brain and spinal cord that contain CSF and envelop the CNS.
- blood vessels course through the meninges and penetrate the CNS from its outer surfaces

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15
Q

what are cells from the PNS derived from?

A

embryonic neural crest cells

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16
Q

two types of peripheral neurons

A
  1. dorsal root ganglion which are the primary sensory neurons
  2. autonomic postganglionic cells which innervate smooth muscles and glands.
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17
Q

what are the supporting cells of the PNS?

A

satellite cells and Schwann cells.

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18
Q

soma aka perikaryon

A

the region of the motorneuron containing the nucleus - the cell body

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19
Q

branches of axons known as…

A

axon collaterals

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20
Q

the cone-shaped region of the cell body from which the axons orginiates…

A

axon hillock

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21
Q

the region between the axon hillock and the beginning of the myelin sheath is known as…

A

the initial segment

- this is the anatomical location for the initiation of the action potential

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22
Q

telodendria

A

small branches whose tips are button-shaped and contain terminal boutons at the distal end of the axon and its collaterals

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23
Q

how are most neurons polarized?

A
  • many dendrites are unmyelinated and carry information toward the cell body
  • one axons will be myelinated and carry impulses away from the cell body
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24
Q

what is special about sensory neurons which conduct information from receptors in the periphery?

A

they have a single myelinated axon that passes by the cell body on its way to the CNS

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25
Q

nissl bodies

A

aggregations of rER and are found around the nucleus and in the proximal parts of the dendrites. their presence reflects the intense protein synthesizing activity of the neuronal cell body.

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26
Q

neurofibrils

A

fibrillar structures around the nucleus and in the axon.

- seen especially well in silver dyes.

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27
Q

golgi technique

A

the only stain which demonstrates the neuron with all its processes.

28
Q

Golgi apparatus

A

a complex of stacked, smooth-surfaced vesicles and cisternae which is widely dispersed in the cytoplasm immediately surrounding the nucleus.

29
Q

microtubules vs. neurofilaments

A
  • microtubules are found in the dendrites, soma and axon ad are similar to microtubules in other cells.
  • neurofilaments are smaller and most abundant in the axon.
  • they are both aligned longitudinally and thought to play a role in transport of substances and form scaffolding that maintain structure.
30
Q

two types of synapses occur in the nervous system

A

electrical and chemical

31
Q

chemical synapses are identified by 4 key characteristics:

A
  1. a presynaptic complement of membrane-bound synaptic vesicles
  2. aggregations of dense material in the cytoplasm immediately adjacent to the membrane of one or both sides of the junction
  3. distinct synaptic cleft or intercellular space
  4. the presence of mitochondria
32
Q

synaptic vesicles

A

contain neurotransmitters involved in the chemical transfer of info from one neuron to another

33
Q

electrical synapses

electrotonic

A

characterized by super close apposition of htemembranes of the pre- and post-synaptic cells.

  • the intercellular cleft appears to be absent but actually leaves a 2nm space
  • an ex is the cells of the hypothalamus that monitor the state of hydration in the body.
34
Q

neuroglia - where are they and what are the 3 types

A
  • there occupy the space between neurons and their processes (like nerve-glue)
  • astrocytes, oligodendrocytes, microglia
35
Q

neuroglia differ from neurons in 4 ways

A
  1. their processes are unpolarized (axons & dendrites cannot be distinguished)
  2. they are capable of proliferation in the mature nervous system
  3. their processes do not form synapses
  4. they are less electrically excitable than neurons and do not transmit action potentials
36
Q

astrocytes

A
  • “star-shaped”
  • processes extend around neural cell bodies and fibers separating them from each other and connective tissue
  • their processes terminate in closely opposed endfeet which form a “glial membrane” that may be a constituent of the blood brain and blood CSF barriers
37
Q

how to differentiate an astrocyte

A

it has an irregular shaped nucleus and contains many small patches of stained material (chromatin) rather than a single nucleolus.
- in the golgi technique, they have a furry appearance because their processes emerge from the neurons all over the place giving it a furry appearance.

38
Q

2 categories of astrocytes:

A

1- fibrous astrocytes: found in white matter and contain relatively more glial fibers
2- protoplasmic astrocytes: found in grey matter and present the classic furry appearance.

39
Q

function of astroglia

A
  • regulate blood flow in the brain by detecting changes in synaptic activity.
  • then release factors from their glial endfeet that affect arteriole smooth muscle, resulting in regional vasodilation or vasoconstriction.
40
Q

oligodendrocytes: where they are found

A
  • they are formed from myelin in the CNS.
  • they are predominant cell type found in white matter, typically in rows
  • in grey matter they are found near cell bodies and hence are known as perineuronal satellite cells
41
Q

oligodendroctyes: function

A
  • the formation and maintenance of the myelin sheath around large axons.
  • they wrap around the axon, synthesizing new membrane as it goes.
42
Q

interperiod line

A

the fused outer surfaces of the oligodendrocyte cell body and myelin sheath of an axon.

43
Q

ependymal cell

A

it is a non-neuronal cell found in nervous tissue. it lines the ventricular system that extends throughout the CNS and are arranged in a single layer.
- they rest directly upon the nervous tissue without any basal lamina.

44
Q

ependymal cell: function

A

the cilia may be involved in the movement of CSF or the absorption or secretion of chemicals.
- they form specialized junctions with one another and may participate in a brain-CSF barrier.

45
Q

choroid plexus

A

certain regions of the ventricles where the ependyma is modified and lies on an extensively folded basement membrane derived from connective tissue meninges. this is a rich vascular region and is a major site of secretion of CSF.

46
Q

tanycyte

A

an impt ependymal specialization in which a cell with a basal process extends through the nevous tissue to blood vessels or pia.
- these cells are thought to aid in transporting hypothalamic hormones into the pituitary.

47
Q

microglia

A

the macrophages of the brain and are the first line of immune defense.

  • they are not true neuroglia because they originate from hematopoietic stem cells, not from the neural tube.
  • they proliferate under pathological conditions and use phagocytosis.
48
Q

ganglia

A

neuron cell bodies in aggregates within the PNS

49
Q

3 types of ganglia

A

1- dorsal root ganglia
2- cranial nerve ganglia
3- autonomic ganglia

50
Q

two major types of dorsal root ganglion (DRG):

A

1- dorsal root ganglion neurons: is unipolar and has a smooth round cell body, surrounded by small satellite cells
2- satellite cells: a neural crest derivative. a connective tissue sheath surrounds the ganglion and is continuous with the connective tissue sheath of the peripheral nerve.

51
Q

description of dorsal root ganglion

A
  • its connected to the spinal cord by the dorsal root, which contains the central processes of the DRG cells and is therefore ONLY SENSORY.
  • contains both myelinated and unmyelinated fibers
  • motor fibers (axons of motor neurons and preganglionic autonomics) emerge from the cord in the ventral root and form peripheral (mixed) nerves by joining the peripheral processes of DRG cells just distal to the ganglion, in the intervertebral foramen.
52
Q

schwann cell and its function

A

is a neural crest derivative. its function is to produce the myelin sheath which surrounds fibers.

  • one schwann cell forms a myelin sheath around a segment of only one nerve fiber.
  • small fibers have a different relation to a schwann cell - groups of them are embedded in the cytoplasm of a single schwann cell.
53
Q

myelination of axons in CNS vs. PNS.

A

in the CNS, a single motor axon originating in the spinal cord ventral horn will be myelinated by oligodendroglial cells.

in the PNS, it will be myelinated by schwann cells

54
Q

endoneurium

A

each schwann cell-nerve fiber complex is completely embedded in a connective tissue matrix of collagen and fibroblast

55
Q

perineurium

A

bundles of endoneurium-embedded fibers are wrapped with perineurium.
perineural cells are connected with tight junctions and appear to form a barrier to the interchange of substances between nerve fibers and surrounding tissues.

56
Q

epineurium

A

the perineurial bundles are wrapped by another connective tissue matrix of collagen, fibroblasts and elastin.

57
Q

wallerian or anterograde degeneration

A

the distal portion separated from the nerve cell body undergoes a series of changes following a transaction of an axon in the PNS

58
Q

bands of “Bungner”

A

newly formed Schwann cells that line up in longitudinal bands and become phagocytic to aid in the removal of debris during anterograde degeneration.

59
Q

retrograde degeneration

A

changes that occur simultaneously with anterograde degeneration at the severed end of the proximal nerve stump attached to the nerve cell body.

60
Q

the clinical importance of retrograde degeneration

A

retrograde degeneration of the cut nerve fibers occurs for a distance of approximately two to four internodes into the proximal nerve stump. this allows the proximal end of the nerve to be surgically trimmed for better alignment of the severed ends after a traumatic lesion.

61
Q

how peripheral nerve fibers re-enter a lesion site

A

they can grow into the scar at the site of the lesion after approx. 7 days by axons growing across schwann cell bridges at the site of the lesion and enter hte distal stump.

62
Q

factors determinating success and rate of regeneration

A
  • mechanical problem of crossing disorganized debris at lesion site
  • fibers may grow in wrong direction
  • if a sensory fiber reinnervates a motor end plate it will be non-functional and vice versa
  • can be misdirected and grow into a mass leading to pain
63
Q

neuromas

A

nerve fiber masses that are frequently associated with pain and are therefore of clinical relevance

64
Q

chromatolysis or axonal reaction

A

the reaction of the nerve cell body to a section of its axon is striking and called chromatolysis.

65
Q

reaction of neural cell body to a section ie lesion

A
  • morphologically manifested at about 2 days and reaches max at 2-4weeks
  • disorganization of Nissl substance so the cell body loses characteristic staining pattern of nissl bodies due to changes in ribosomal organization (characteristic of neurons producing proteins at an accelerated rate)
  • alteration of nucleus location toward cell membrane
  • ## perikaryal (cell body) swelling
66
Q

correlation between survival of a neuron and how much axon is saved

A

the closer to the nerve cell body the axon is sectioned, the greater the probability that the entire nerve will degenerate.

67
Q

reactions of CNS neuronal replacement

A

severely limited - CNS axons do not regenerate as axons in PNS do.
however axonal sprouts of intact neurons can reinnervate affected areas but this is non-selective.

Neuro (12 decks)

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