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002 - 6120 - Vet Neurobiology > (02) Neurohistology > Flashcards

(02) Neurohistology Flashcards

1
Q

What are the structural and functional units of the nervous system? What are they specialized to do?

A
  • neurons

- conduct electrical signals

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2
Q

What is the expanded portion of the neuron that contains the nucleus? How large are the nuclei? How do they stain (what’s the name) and why? How does the cytoplasm stain? What are the clumps of RER and polyribosomes detected in stained tissue sections referred to as?

A
  • cell body
  • very large
  • leptochromatic (stains lightly due to active transcription of many genes)
  • basophilically
  • Nissl bodies
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3
Q

What are the extensions of the cell body that are specialized to receive input from other nuerons? how many can there be? Why do the initial portions of dendrites stain basophilically? What are the small protrusions called? What purpose do they serve?

A
  • dendrites
  • one to many
  • presence of Nissl bodies
  • dendritic spines
  • expand dendritic surface area as sites of synaptic content
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4
Q

What are neuronal processes that project to and synapse with dendrites or cell bodies of other neurons or with non-neuronal targets (muscle)? What are these specialized to do?

A
  • axons

- conduct regenerative, all or none, electrical impulses called action potentials

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5
Q

How many axons per neuron? What are the swellings found along the axon or at its terminal branches called? What happens at these sites?

A
  • one typically
  • axonal varicosities/boutons
  • sites where synapses occur
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6
Q

Are axons myelinated or non-myelinated? How do the stain and why?

A
  • can be either

- they don’t stain, lack Nissl bodies

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7
Q

What is a specialized point of functional contact between neurons or between a neuron and a target organ called? What do these allow?

A
  • a synapse

- allow neurons to communicated with one another or with their target cells

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8
Q

What is a collection of neuron cell bodies situated in the PNS called?

A

ganglion

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9
Q

What term is used in the special sense to describe a collection of neuronal cell bodies in the CNS (accumulation of gray matter)?

A
  • nucleus
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10
Q

What are bundles of axons that extend out from the brain as cranial nerves and from the spinal cord as spinal nerves called? What are they surrounded by?

A
  • nerves

- connective tissue sheaths

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11
Q

What is a bundle of axons (nerve fibers) within the CNS called? Is connective tissue present around the the nerve fibers in the CNS?

A
  • tract

- no

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12
Q

What is a neuron that has one process that bifurcates called? Where is this type found?

A
  • unipolar (pseudounipolar)

- spinal and cranial ganglia

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13
Q

What is a neuron that has 2 processes called? How common? where are they found?

A
  • bipolar neuron
  • relatively rare
  • retina of eye and certain cranial ganglia
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14
Q

What is a neuron that has many processes called? How many axons and dendrites? How common?

A
  • Multipolar neurons
  • typically 1 axon and 2 or more dendrites
  • most common type
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15
Q

What type of neuron is related to innervation of muscle and glands? What does activation of these neurons lead to?

A
  • motor (efferent)

- some motor event (ie muscle contraction)

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16
Q

What neurons are related to the transfer of sensory information (pain, touch, etc)? example?

A
  • sensory (afferent)

- neurons of spinal (dorsal root) ganglia

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17
Q

What neurons are neither motor nor sensory? What are they responsible for?

A
  • interneurons

- for the various spinal reflexes

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18
Q

What are non-neuronal cells that provide support and protection for neurons called? How many of these relative to neurons?

A
  • glial cells

- 10:1

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19
Q

How many types of glial cells does CNS have? PNS?

A
  • 4

- 1

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20
Q

What are the CNS glial cells with relatively large leptochromatic nuclei that play an active role in brain function called? What roles do they play in brain function?

A
  • Astrocytes
  • influence activity of neurons, contact blood vessels and control local blood flow in CNS (contribute to integrity of Blood brain barrier)
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21
Q

What CNS glial cells are responsible for forming myelin sheaths around and spinal cord axons? What is myelin composed of primarily? What does it serve as? Nature of their nuclei?

A
  • oligodendrocytes
  • lipids
  • an electrical insulator that allows for rapid transmission of action potentials.
  • small, round pachychromatic (darkly stained) nuclei
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22
Q

What are the smallest of the glial cells? What are they sometimes referred to as? What percentage of the glial cell population do they represent? What do they represent? What do they underlie?

A
  • microglia
  • brain macrophages
  • 4% (under normal circumstances)
  • intrinsic immune effector cells of the CNS
  • the inflammation response that occurs following damage to CNS and invasion of microorganisms
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23
Q

What are the glial cells that are columnar epithelial cells that make up the ependyma which line the cerebrospinal fluid (CSF) filled ventricle system of the brain and the central canal of the spinal cord? What do their apical surfaces contain? What does this allow them to do?

A
  • ependymal cells

- cilia (circulate CSF throughout CNS), microvilli (absorb CSF)

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24
Q

Modified ependymal cells associated with capillaries in ventricles make up what?

A
  • choroid plexus that produces CSF
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25
Q

What are the supporting cells of the PNS? What are they associated with? In myelinated nerves, what are they responsible for?

A
  • Lemmocytes (Schwann’s cells)
  • all peripheral nerve fibers
  • forming the myelin sheath (analogous to olidendrocytes in the central nervous system)
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26
Q

Are glial cells capable of reproduction? What happens when control over cell division is lost? What are among the most deadly or malignant forms of cancer?

A
  • yes (neurons can’t divide)
  • primary brain tumors
  • astrocytomas and glioblastomas
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27
Q

Myelinated axons are invested with what? What does this make them?

A
  • membranous, lipid sheath

- largest and fastest conducting nerve fibers

28
Q

What is a highly organized multilamellar structure? What is it formed by in the CNS? in the PNS?

A
  • myelin
  • plasma membrane of olligodendrocytes
  • lemmocytes (Schwann’s cells)
29
Q

In PNS myelin, myelination occurs when an axon attains what diameter? What is required to provide myelin for one axon in the PNS?

A
  • > 1 um

- a chain of lemmocytes

30
Q

In the PNS, a typical myelinated axon has what structure?

A
  • axon, surrounded by lemmocyte myelin sheath, surrounded by lemmocyte cytoplasm, surround by basal lamina, surrounded by endoneurium. The lemmocyte wraps around the nerve fiber (axon) several times producing a membranous sehath that varies in thickness depending on the number of times the lemmocyte wraps around the axon
31
Q

In CNS, a single oligodendrocyte will provide myelin for how many axons? Each axon is myelinated by how many oligodendrocytes? Do CNS myelinated axons have a basal lamina and endoneurium?

A
  • multiple axons
  • multiple oligodendrocytes
  • no
32
Q

Do axons in the CNS regenerate following injury? in PNS? What is this due to?

A
  • no
  • yes
  • CNS myelin contains several proteins that inhibit axonal regeneration
33
Q

What is an electrical insulator that allows increased speed of conduction along an axon?

A
  • myelin
34
Q

How do myelinated axons in PNS differ from CNS (two ways)?

A
  • chemical composition

- cell type that produces the myelin

35
Q

Why in H & E and triple-stained sections does myelin appear like spokes of a wheel around the axon?

A
  • appearance is artifactual in tissue processing (dehydration in alcohols, clearing in xylene) dissolves lipid components of myelin
36
Q

What are breaks in the continuity of the myelin sheath that occur regularly in both the PNS and CNS? What are they intervals between? Where do they occur (in CNS and PNS)? Do they increase speed of conduction?

A
  • nodes of ranvier
  • adjacent segments of myelin
  • junction of two oligodendrocytes (in CNS), two lemmocytes (in PNS)
  • yes
37
Q

Non-myelinated axons are what size and speed?

A
  • < 1 um; slow conducting
38
Q

How are non-myelinated axons arranged in PNS? How many axons does a lemmocyte typically enclose? What clumps and stains poorly with routine histological stains? What is a group of axons and associated lemmocytes surrounded by?

A
  • embedded in infoldings of the plasma membrane of a chain of lemmocytes
  • 5-20
  • axoplasm
  • basal lamina & endoneurium
39
Q

In CNS, are non-myelinated axons associated with oligodendrocytes? How do they run? How are they separated from one another?

A
  • no
  • they run free
  • by astocytic processes
40
Q

What is the destructive removal of myelin called? How much slower do they become?

A
  • Demyelination
  • 10x slower, sometimes stop altogether (a number of diseases are associated with breakdown of myelin in brain, spinal cord and peripheral nerves - degenerative myelophathy affects spinal cord in older dogs)
41
Q

What are the two classification schemes for Peripheral nerve fibers?

A
  • nerve fiber diameter (I-IV)

- compound action potential (A (alpha, beta, etc), B, C)

42
Q

What surrounds each myelinated axon, or a group of non-myelinated axons?

A
  • endoneurium
43
Q

What surrounds the entire nerve?

A
  • epineurium
44
Q

What surrounds each nerve fascicle (a bundle of axons)? What does it consist of? What does it participate in?

A
  • perineurium
  • perineural epithelium and collagenous connective tissue
  • forming a blood-brain barrier that limits the passage of water-soluble substances and proteins from blood into the endoneurial compartment
45
Q

What is a progressive disease of spinal cord in older dogs? Where does it begin? What is it associated with? clinical signs? as it progresses?

A
  • degenerative myelopathy
  • thoracic spinal cord
  • degeneration of myelin sheaths
  • wobble, drag or cross feet
  • knuckle at feet until it cannot stand
46
Q

What is a specialized region located on a peripheral terminal branch of an axon of a primary afferent neuron? What can it serve as? What does this do? Does number per neuron vary?

A
  • receptor
  • a transducer
  • converts environmental energy (sensory stimuli) into depolarizing ionic current (nerve signals)
  • yes - several (small receptive field), to several dozen (large receptive field)
47
Q

What is an organized collection of receptor cells, with which the dendritic zones of afferent neurons synapse? What modifies the excitability of the these receptor cells?

A
  • sense organ

- environmental energy (ie receptor cells act as transducers)

48
Q

What are the sense organs? Neurons that synapse on receptor cells are of which type? of what pole?

A
  • retina, cochlea, vestibular apparatus, taste buds, and olfactory epithelium
  • SSA or SVA
  • commonly bipolar rather that unipolar
49
Q

What are the three ways receptors are classified?

A
  • morphology, location, modality (energy sensitivity)
50
Q

(Receptor morphology classification) terminal branches ramifying among epithelial cells, very common especially in the skin (pain, itch thermal)

A
  • free nerve endings
51
Q

(Receptor morphology classification) consists of terminal expansions of an afferent axon which are joined to modified epidermal cells (in skin and mucous membranes)

A
  • tactile discs
52
Q

(Receptor morphology classification) each receptor is encapsulated by lemmocytes and perineural epithelium (examples: Pacinian corpuscles, tactile corpuscles, muscle spindles)

A
  • encapsulated
53
Q

(receptors on location) associated with skin and subcutaneous tissue (GSA)

A
  • exteroreceptors
54
Q

(receptors location) associated with muscles, tendons, and joints (GSA)

A
  • proprioceptors
55
Q

(receptor location) located in viscera

A
  • interceptors (GVA)
56
Q

(receptor modality) detect mechanical deformation (touch, pressure, vibration)

A
  • mechanoreceptors
57
Q

(receptor modality) detect changes in temperature (some detect warmth, some - cold)

A
  • thermoreceptors
58
Q

(receptor modality) detect damage to tissue (pain receptors); also detect itch

A
  • nociceptors
59
Q

(receptor modality) detect light on the retina of the eye

A
  • electromagnetic
60
Q

(receptor modality) detect chemical molecules, including: taste receptors, olfactory
receptors, arterial oxygen receptors in the aortic arch and carotid bodies, blood osmolarity
in the hypothalamus and blood glucose and fatty acid receptors in the hypothalamus.

A
  • chemoreceptors
61
Q

What are protective connective tissue sheaths surrounding the brain and spinal cord?

A
  • meninges
62
Q

(meninges) outermost layer consisting of coarse, irregular connective tissue; composed of collagen and elastic fibers

A
  • dura mater (hard mother)
63
Q

(meninges) innermost layer of meninges? Forms thin protective membrane that adheres to what? Does it consist of flattened fibrocytes superficial to elastic and collagen fine fibers that extend into the numerous depressions and fissures on the surface of the brain and cord? Is it very vascular?

A
  • pia mater (tender mother)
  • surface of brain and spinal cord
  • yes
  • yes
64
Q

(meninges) middle layer of meninges, consists of a distinct membrane and numerous fibrous trabeculae on its inner surface? What does this trabecular network form? What does the subarachnoid space contain? What forms at points in the subarachnoid space where it is dilated? Why are these clinically important?

A
  • arachnoid
  • structural framework for subarachnoid space (lies between arachnoid and pia mater)
  • CSF
  • cisterns
  • spinal taps are done here
65
Q

What is the function of CSF?

A
  • protect, support, and nourish the CNS

002 - 6120 - Vet Neurobiology (23 decks)

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