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Histology Unit 1 > Nervous Tissue > Flashcards

Nervous Tissue Flashcards

1
Q

Do neurons possess an external (basal) lamina?

A

No!

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2
Q

Pseudounipolar vs bipolar vs multipolar?

A

pseudo-unipolar is the soma or cell body is attached to the side, bipolar is only 1 axon and 1 dendrite off the soma, and multipolar is multiple dendrites off the soma

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3
Q

Where is nervous tissue highly vascularized and why?

A

It is most vascularized where there are many neuronal cell bodies because the neurons have no glycogen storage

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4
Q

What does the cell body of a neuron contain?

A

Also called the soma, it contains the genetic material and most of the protein synthetic capacity of the neuron. There is a centrally placed nucleus with a prominent nucleolus. Relatively little heterochromatin due to the large variety of proteins produced by it

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5
Q

What is Nissl staining?

A

Histological sections of nerves are often only stained using basic dies rather than H&E so you can see the key features of cell bodies well.

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6
Q

What is the perikaryon and what does it contain?

A

It is the portion of the cell body surrounding the nucleus. It contains Nissl bodies / granules which are collections of free ribosomes and rough ER which synthesize the bulk of proteins used by the neuron

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7
Q

What is the neuropil?

A

the area surrounding the soma of neuronal cells in CNS, made up mostly of Muller glial cells attached to nuclei, axons, and dendrites

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8
Q

How do the neuropil and perikaryon differ in the CNS vs PNS?

A

CNS:
Perikaryon - rich in Nissl bodies, highly basophilic granular staining
Neuropil - minimal connective tissue, densly packed with neuronal processes, glial cell processes, and blood vessels
PNS:
Perikaryon - very small Nissl bodies, giving a homogenous basophilic staining to the cytoplasm of most ganglion cells
Neurophil - substantial amount of connective tissue in addition to neuronal processes and glial cells

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9
Q

What packaging organelle is found in the perikaryon and why?

A

The Golgi apparatus, due to the large amount of carbohydrates added to membrane proteins on the neuron. Also, it is needed to make lysosomes.

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10
Q

What organelles can be found throughout a neuron?

A

Mitochrondria to supply ATP, and lysosomes active in autophagy.

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11
Q

What are the three types of filamentous organelles found within the neuron and their functions?

A
  1. Microtubules - 25 nm - cytoskeletal support and movement of materials in cell, especially down the axon
  2. Neurofilaments - 10 nm - the intermediate filament of neurons, function in cytoskeletal support
  3. Microfilaments - 5 nm - actin. Hard to see, most prominent in developing neurons and regenerating axons.
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12
Q

How do the filaments of nervous tissue appear?

A

Microtubules - like donuts in cross sections
Neurofilaments - like dots in cross sections. they are very ARGYROPHILIC - like type 3 collagen
Microfilaments - difficult to see

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13
Q

What is the function of smooth ER in neurons?

A

Found throughout - it’s a reserve membrane pool to sequester calcium and for phospholipid synthesis

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14
Q

What are two inclusions found in neuronal cells?

A
  1. Lipofuscin - pigmented breakdown products that cannot be disposed of by the neuron. Accumulate during aging.
  2. Melanin - inclusions found in some neurons that synthesize monoamines (i.e. dopamine)
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15
Q

What is the function of a dendrite and how is it best visualized?

A

They are the major receptive surface of the neuron. Technically part of the perikaryon surface. Their job is to conduct postsynaptic excitatory and inhibitory (graded) potentials to the cell body. They contain longitudinally arrayed microtubules and neurofilaments.

Silver-staining techniques make it easy to see the overall form of the dendrites.

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16
Q

What is the axon hillock?

A

Conical elevation on cell body giving rise to a single narrow process - the axon initial segment.

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17
Q

Where does the axon initial segment end? What is it important?

A

It is the place where the axon potential is generated. It ends where the first myelin wrapping begins around the axon proper

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18
Q

What is an action potential?

A

An all-or-none (non-graded) electrical signal conducted along the axon

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19
Q

What is the main, distinguishing feature between the organelles of the axon and the organelles of the dendrite?

A

The axon contains few, if any, ribosomes beyond the initial segment

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20
Q

How are microtubules arranged in the axon and what is the function?

A

They are involved in axonal transport, having their (+) ends towards the axon terminal. (-) ends are towards the cell body. Anterograde movement is towards the + end, retrograde is towards the - end

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21
Q

What are the two families of motor proteins for microtubule movement? What do they have in common?

A

They are both ATPases.
Kinesin - anterograde movement towards + end, or axon terminal
Dynein - retrograde movement towards - end, or cell body

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22
Q

What forms myelin?

A

Tight wrapping of glial cell plasma membrane. Adjacent membranes are bound by adhesion molecules (integral membrane proteins) of myelinating cells.

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23
Q

What is the function of a node of Ranvier?

A

Since the myelin acts as an insulator, they are regions where the action potential can be renewed. Breaks in the myelin are nodes

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24
Q

What stain is used to visualize myelin and how does it stain?

A

Osmium tetroxide. Stains dark brown or black and leaves the axon itself unstained.

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25
Q

What two factors increase conduction speed?

A

Myelination and axon diameter.

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26
Q

What are Schwann cells?

A

Cells forming myelin in the PNS. They are surrounded by external lamina and can only form one myelin segment. HOWEVER, they can organize the axons of several unmyelinated nerves

27
Q

What are oligodendrocytes?

A

Cells forming myelin in the CNS. They lack external lamina but can form several myelin segments. They do not envelop unmyelinated axons at all! unlike schwann cells

28
Q

What is Multiple Sclerosis (MS)?

A

A demyelinating disease caused by autoimmunity to unique proteins found in myelinating cells

29
Q

What is the external lamina important for the PNS?

A

PNS axons are repaired following nerve damage via PNS axon regeneration, which uses the external lamina of Schwann cells as a guide to know where to go.

30
Q

What does it mean for an axon to “arborize”?

A

Upon reaching its target, the axon of a CNS or PNS neuron branches repeatedly

31
Q

What is a varicosity / bouton?

A

The branch of arborization containing many synaptic vesicles filled with chemical neurotransmitters

32
Q

What is a synapse and what are its three components?

A

They are membrane specializations designed for one-way conduction between cells using chemical transmitters.

  1. Presynaptic membrane - membrane of varicosity where synaptic vesicles crowd
  2. Synaptic cleft - extracellular space around 15-20 nm wide
  3. Postsynaptic membrane - Place on target cell that contains receptors and ion channels to be activated by the transmitter

These membranes appear more electron dense than normal membranes

33
Q

What proteins hold synaptic vesicles to the cytoskeleton?

A

They are tethered to actin via synapsin

34
Q

What proteins are contained in the plasma membrane of vesicles?

A
  1. v-SNARE - docking protein

2. Fusion protein

35
Q

What is the function of t-SNARE?

A

It is the target SNARE, the docking protein in the presynaptic membrane.

36
Q

What is the mechanism of vesicular release of neurotransmitters / regulatory secretion of neurons and glands?

A

Ca+2 influx caused by depolarization leads to phosphorylation cascade where synapsin is phosphorylated, releasing the vesicle from actin. v-SNARE of vesicle binds t-SNARE of membrane, allowing fusion protein to bind to the presynaptic membrane. Contents of vesicle are released into synaptic cleft. v-SNARE and fusion protein will be once again taken up by endocytosis of plasma membrane.

37
Q

How are neurotransmitters cleared?

A

Transmitter pumps and transmitter-degrading enzymes rapidly clear the synaptic cleft of the transmitter

38
Q

What is a motor end plate?

A

neuromuscular junction. It is a specialized synaptic contact made of neuronal and skeletal muscle components. Axon arborization forms tangle on surface of skeletal muscle cell, usually in mid-region of muscle cell

39
Q

What is a synaptic trough?

A

The depression of a muscle cell where the axon arborization is embedded in a neuromuscular junction. It contains many mitochondria and nuclei.

40
Q

What is the active zone?

A

The area where the presynaptic membrane is marked by density and a crowding of synaptic vesicles

41
Q

What are junctional folds?

A

The areas of invagination continuous with synaptic cleft throughout the neuromuscular junction which increase the surface area of the synapse. It is included in the synaptic trough. The external lamina is found in this area, which also contains the degradative enzymes for the neurotransmitter Ach. Active zone is found on presynaptic side, and the postsynaptic side contains the Ach receptor.

42
Q

What are satellite cells of muscles?

A

Another name for Schwann cells, they allow the external lamina to continue around the surface of the axon arborization. This is continuous through the synaptic cleft and down into the junctional folds.

43
Q

What is myasthenia gravis?

A

body produces antibodies to Ach receptors, preventing binding and resulting in muscular weakness.

44
Q

What is white matter vs gray matter?

A

White matter - mostly axons and few neuronal cell bodies in CNS (myelin)
Gray matter - mostly neuronal cell bodies and fewer axons. Highly vascularized

45
Q

What are nuclei?

A

Collections of neuronal cell bodies in CNS that have similar morphology, connections, and function

46
Q

What are tracts?

A

White matter in CNS collections of axons that have a common origin and destination (i.e. spinothalamic tract to the thalamus)

47
Q

What creates the blood-brain barrier?

A

Endothelial cells within the CNS forming Zonula Occludens with their neighbors

48
Q

What are the three collagenous tissue coverings of the CNS?

A

Dura mater - thick, tough dense irregular collagenous connective tissue
Arachnoid mater - thinner, collagenous tissue composed of many trabeculae which form the subarachnoid space below it
Pia mater - A delicate collagenous tissue following the contours of the brain

49
Q

What is the function of the choroid plexus?

A

It is a group of cells that lines the ventricles of the brain. It functions in producing the cerebrospinal fluid

50
Q

What are ependymal cells?

A

Cells that line the ventricles of the brain. Modified ones produce the CSF in the choroidal plexus

51
Q

What are microglia?

A

Phagocytic cells of monocyte origin from the CNS

52
Q

What are astrocytes?

A

A supporting type cell

53
Q

What are collections of cell bodies in the PNS? Connections of axons?

A

Ganglia. - often found between layers of smooth muscle in GI tract
Nerves.

54
Q

Where are neuronal satellite cells in the PNS?

A

they can be found encapsulating some ganglion cells, which are generally between the layers of smooth muscle. They are associated with the cell body

55
Q

What is the perineurium?

A

individual nerve fascicles are wrapped in dense collagenous wrapping, they provide a barrier

56
Q

What is the epineurium?

A

The outermost collagenous sheath around large nerves close to the CNS. It is continuous with the dura.

57
Q

What is the endoneurium?

A

Loose connective tissue matrix formed by type III collagen (reticular fibers) and type I collagen fibers surrounding the individual axons within the nerve.

58
Q

How can peripheral nerves be identified by LM?

A

Longitudinal / oblique sections stain with eosin and have a wavy arrangement of axons. Neuronal cell bodies are basophilic and typically much larger than nearby cells, with large nucleoli.

Transverse sections look light in staining, and the nerve typically has a frothy “vesiculated” appearance because the myelin dissolves from the tissue embedding procedure.

59
Q

What type of neurons are sensory in the PNS typically and where do they enter the CNS?

A

Sensory fibers always enter the dorsal horn of the spinal cord via its dorsal root. However, they always travel in the same axonal bundles of motor nerves. They are generally pseudo-unipolar cells that reside in dorsal root ganglia or cranial nerve ganglia.

60
Q

What is an example of a visceral motor function?

A

Secretion of an endocrine product via a gland. Or contraction of smooth muscle in GI tract

61
Q

What are the two subdivisions of the motor PNS?

A
  1. Somatic - under conscious control. i.e. skeletal muscle

2. Visceral / autonomic - smooth muscle / glands

62
Q

Where do motor neurons exit the spinal cord?

A

Via ventral roots, but they still join the sensory axons peripherally.

63
Q

What is a fascicle? A lemniscus?

A

Fascicle - small bundle (of nerves)
Lemniscus - ribbon, generally describing sensory fibers in brainstem

ways of describing white matter in CNS

Histology Unit 1 (9 decks)

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