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Histology Exam 5 > Neurohistology > Flashcards

Neurohistology Flashcards

1
Q

what make the Central Nervous System

A

brain and spinal cord

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2
Q

What make the Peripheral Nervous System

A

cranial nerves, spinal nerves, ganglia, named nerves and associated terminals (sensory receptors and motor endings)

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3
Q

How massive is the brain alone?

A

Your brain contains an estimated 80 billion neurons!

Each neuron can receive 10,000 synapses

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4
Q

What is the Is Nervous tissue composed of?

A

neurons and supporting cells

and extracellular matrix

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5
Q

Whats the Efferent neurons? What does it do?

A

The efferent nerves, otherwise known as motor or effector neurons, carry nerve impulses away from the central nervous system to effectors.

  • controls movement
  • controls the state of the viscera
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6
Q

Whats the Afferent neurons? What does it do?

A

In the nervous system, afferent neurons (otherwise known as sensory, receptor neurons, and afferent axons), carry nerve impulses from receptors or sense organs toward the central nervous system.

  • monitors the environment (internal and external)
  • integrates (sensory, motor, alertness, desire…etc).
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7
Q

3 facts about neurons

A
  • are excitable cells, they “fire” action potentials
  • function to send and receive information via synapses (or gap junctions in some neurons)
  • are post mitotic –> they are highly specialized and do not divide
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8
Q

4 Facts about Supporting cells

A

-They greatly outnumber neurons, ~10:1) are “non-conducting.
-physical support
-electrical insulation
-metabolic exchange
blood-brain barrier

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9
Q

Structure of a neuron

A
  • Neuron has a cell body (soma), two types of specialized processes (dendrites-recieving and an axon-forwarding)
  • Neurons receives excitatory and inhibitory innervation (input)
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10
Q

Neuronal Plasticity

A

Neurons can pull their axons back and shorten if they are deprived

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11
Q

Neuron Morphologies 3 types.

A

Bipolar
– retina and CN VIII
–1 axon 1 dendrite

Uni/Pseudounipolar
– sensory (afferent) neurons [in sensory ganglia]
–1 process (the axon

Multipolar
– motor and interneurons
–1 axon and 2 or more dendrites

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12
Q

4 Functions of Dendrites

A
  • are utilized to collect information from other neurons or about a stimulus (sensory neurons)
  • typically have a greater diameter than axons, are unmyelinated and form dendritic trees (arbors)
  • contain all organelles, except Golgi
  • often give rise to spines, which are used to increase the receptive surface area of a neuron
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13
Q

Staining of the neuronal Soma

A

contains Nïssl substance (stains with basic dyes and correspond to stacks of rough endoplasmic reticulum)

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14
Q

Content of Soma

7 in total

A 
Perinuclear cytoplasm contains: mitochondria
Golgi apparatus
Lysosomes
Microtubules
Neurofilaments
Transport vesicles
Nissl bodies and free ribosomes
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15
Q

Neuron Dimensions

A

Each neuron has only one axon, but this axon can split an innervate multiple targets.

axons can range in diameter from 0.5 to 20 microns in diameter

axons can be relatively short or travel more than a meter to their target

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16
Q

Neuronal Physiology described by different sections.

A

axon hillock

initial segment – where action potentials are generated

Action potentials run away from the cell body toward terminals
Conduction velocity depends on axon size (diameter) and myelination state

17
Q

Axonal myelin sheath Types according to location.

A

The myelin sheath (lipid rich layers) is composed of concentric layers of either:

  • Oligodendrocytes in the CNS (several axons per oligo).
  • Schwann cell membrane (one axon per Schwann cell) in the PNS
18
Q

Where is the unmyelinated axon>

A

the axon hillock, initial segment and terminal arborizations are devoid of myelin

19
Q

Which are the Demyelinating Diseases

A

Multiple Sclerosis
Myelin sheath is destroyed via microglial phagocytosis and lysosomal degradation

Vitamin B12 deficiency-affects spinal cord, optic nerves and peripheral nerves

Tabes dorsalis-side effect of untreated syphilis, affects discriminative touch, vibration, and proprioception

20
Q

2 Types of synapses.

A

Electrical – in reality these are gap junctions, between interneurons and excitatory cells in the cortex, common in invertebrates

Chemical – presynaptic and postsynaptic elements, synaptic cleft of 20 – 30 nm

21
Q

3 Sub-Types of synapses.

A

Axodendritic – axon to dendrite
Axosomatic- axon to soma
Axoaxonic- axon to axon

22
Q

Describe the Two main classes of synapses.

A

The synaptic densities can have different morphologies; they can be:

Symmetrical–> associated with inhibitory synapses; the vesicles are elongated and contain an inhibitory neurotransmitter (GABA and/or glycine)

Asymmetrical–> associated with excitatory synapses; the vesicles are round and contain excitatory neurotransmitter (glutamate)

23
Q

What is Kiss and Run Vesicle Trafficking

A

Kiss-and-run fusion is a type of synaptic vesicle release where the vesicle opens and closes transiently. In this form of exocytosis, the vesicle docks and transiently fuses at the presynaptic membrane and releases its neurotransmitters across the synapse, after which the vesicle can then be reused.

24
Q

Describe the Events in membrane movement at the synapses.

A

when an action potential reaches the bottom, it depolarizes the membrane → there are voltage sensitive Ca++ channels here

the influx of Ca++ permits the binding of vesicles with fusion machinery

neurotransmitter is released → traverses the cleft → binds to a receptor → cellular event

25
Q

Describe the CNS Organization

A

The CNS is divided into:
white matter – myelinated axons
gray matter – cell bodies

Both of which contain:

  • Neurons and/or processes [somata, dendrites + axons]
  • Glia
  • Blood vessels
  • Connective tissue and ECM

A cluster of neuronal cell bodies in the CNS is a “nucleus”

26
Q

Describe the PNS Organization

A 
The PNS includes:  
-Nerves + nerve terminals/endings
-Ganglia – collections of neuronal cell bodies in the PNS
     Sensory
     Motor/Autonomic 
Both of which contain:
-Axons (or axons of passage)
-Supporting cells 
     Satellite cells
     Schwann cells
-Blood vessels
-Connective tissue
27
Q

What are the layers of Connective Tissue (CT) of Nerve

A

The CT in a nerve is arranged in three layers:
epineurium – dense CT, binds fascicles together
perineurium – Surrounds the nerve fascicle
endoneurium – loose CT

28
Q

2 Types of Ganglia

A

There are two types of ganglia (clumps of neuronal cell bodies outside the CNS):

Sensory ganglia
contain pseudounipolar neurons
no synapses
central projection into CNS

Autonomic ganglia
visceral motor ganglia
sympathetic or parasympathetic
contain multipolar neurons
synapses from other motor neurons
29
Q

Describe the morphology of Satellite Cells

A

Small cuboidal cells surrounding cell bodies in ganglia
Sensory- nucleus is in the center
Sympathetic: nucleus is not centrally located

30
Q

Describe the structure of Satellite Cells

A

are found mainly in ganglia and only nuclei are seen with routine stains

processes form a complete layer around the neuron, axons must penetrate the satellite cells to reach the soma of the neuron

supporting cells maintain a controlled environment around the neuron

Note the different arrangement in sensory vs. sympathetic ganglia.

31
Q

4 types of Glial Cell

A

Fibrous astrocytes
Oligodendrocytes
Protoplasmic astrocytes
Microglial Cells

32
Q

Describe Astrocytes structure

A

Astrocytes are the largest of the neuroglial cells. Two main types of astrocytes:

a. protoplasmic – gray matter
b. fibrous – white matter

Astrocytes have numerous tentacle-like processes with end-feet associated with:
neurons
blood vessels

33
Q

Describe astrocytes Function

A

They are supporting cells
Maintain the microenvironment of the neuron by mobilizing wastes and nutrients
Contribute to the blood brain barrier
Confine or metabolize neurotransmitters at the synapse
Synaptogenesis

34
Q

Describe microglial Function

A

are phagocytic cells, present only in small numbers

proliferate and are active in regions of injury (they can migrate) and disease

are small cells with darkly staining nuclei and typically have a few short, spiny processes

Originate outside of the brain during development

More closely related to macrophages than other neuronal cells

35
Q

What is the The Ependyma

A

lines the internal ventricular chamber of the CNS

is composed of epithelial cells (cuboidal or columnar)

36
Q

What is Choroid Plexus

A

The ependyma is specialized in regions, where it exists as small tufts of small vascular elements covered with modified ependymal cells  choroid plexus

The choroid plexus is responsible for the formation of cerebrospinal fluid within the ventricles

37
Q

Describe Responses to Injury

Degeneration

A

in the PNS, the axon distal to the injury undergoes Wallerian degeneration  the axon breaks down into fragments which are digested by Schwann cells

if a motor axon is cut, the muscle fiber innervated by that axon undergoes degeneration

the cell body of the damaged neuron undergoes chromatolysis (loss of Nissl substance)

38
Q

Describe Responses to Injury

Regeneration

A

in the PNS, Schwann cells develop processes that surround the injury site

the axon will sprout numerous neurites, if a neurite makes it across the scar into the surviving Schwann cell tube of the distal stump, the target can be reinnervated

regrowth of an axon can occur at ~2mm per day

Histology Exam 5 (1 decks)

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