Neurohistology

Question 1

what make the Central Nervous System

Answer 1

brain and spinal cord

Question 2

What make the Peripheral Nervous System

Answer 2

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

Question 3

How massive is the brain alone?

Answer 3

Your brain contains an estimated 80 billion neurons!

Each neuron can receive 10,000 synapses

Question 4

What is the Is Nervous tissue composed of?

Answer 4

neurons and supporting cells

and extracellular matrix

Question 5

Whats the Efferent neurons? What does it do?

Answer 5

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

Question 6

Whats the Afferent neurons? What does it do?

Answer 6

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).

Question 7

3 facts about neurons

Answer 7

• 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

Question 8

4 Facts about Supporting cells

Answer 8

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

Question 9

Structure of a neuron

Answer 9

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

Question 10

Neuronal Plasticity

Answer 10

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

Question 11

Neuron Morphologies 3 types.

Answer 11

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

Question 12

4 Functions of Dendrites

Answer 12

• 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

Question 13

Staining of the neuronal Soma

Answer 13

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

Question 14

Content of Soma

7 in total

Answer 14

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

Question 15

Neuron Dimensions

Answer 15

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

Question 16

Neuronal Physiology described by different sections.

Answer 16

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

Question 17

Axonal myelin sheath Types according to location.

Answer 17

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

Question 18

Where is the unmyelinated axon>

Answer 18

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

Question 19

Which are the Demyelinating Diseases

Answer 19

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

Question 20

2 Types of synapses.

Answer 20

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

Question 21

3 Sub-Types of synapses.

Answer 21

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

Question 22

Describe the Two main classes of synapses.

Answer 22

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)

Question 23

What is Kiss and Run Vesicle Trafficking

Answer 23

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.

Question 24

Describe the Events in membrane movement at the synapses.

Answer 24

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

Question 25

Describe the CNS Organization

Answer 25

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”

Question 26

Describe the PNS Organization

Answer 26

``` 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 ```

Question 27

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

Answer 27

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

Question 28

2 Types of Ganglia

Answer 28

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 ```

Question 29

Describe the morphology of Satellite Cells

Answer 29

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

Question 30

Describe the structure of Satellite Cells

Answer 30

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.

Question 31

4 types of Glial Cell

Answer 31

Fibrous astrocytes Oligodendrocytes Protoplasmic astrocytes Microglial Cells

Question 32

Describe Astrocytes structure

Answer 32

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

Question 33

Describe astrocytes Function

Answer 33

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

Question 34

Describe microglial Function

Answer 34

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

Question 35

What is the The Ependyma

Answer 35

lines the internal ventricular chamber of the CNS | is composed of epithelial cells (cuboidal or columnar)

Question 36

What is Choroid Plexus

Answer 36

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

Question 37

Describe Responses to Injury | Degeneration

Answer 37

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)

Question 38

Describe Responses to Injury | Regeneration

Answer 38

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