neuro- dendrites and glia

Question 1

different types of cells present in the brain?

Answer 1

neurons
glial cells

Question 2

what are ways of histologically staining neural tissue?

Answer 2

• fixation: brain tissue is fixed for preservation using paraformaledehyde and then embedded into wax/frozen material, so that you have a block ready to check under a microtome.
• sectioning: a microtome can cut slices of a block of embedded brain tissues into micrometers.

Question 3

how can we visualise neural tissue?

Answer 3

the Nissl stain: comprised of a basic dye (cresyl violet) which stains the nuclei and the nissl bodies of the neuron.
nissl bodies are RNA rich structures such as the RER.

Golgi stain: comprised of a silver chromate solution, stains neurons and their projections.

Question 4

some facts about light microscopy? and electron microscopy?

Answer 4

• has a resolution of 0.1 micrometer
  space between neurons are 0.02 micrometer
• electron microscopes have an resolution of 0.1 nanometre. All of the insights into the fine structure of the neurone has come from electron microscopy.

Question 5

some more advanced techniques for observing parts of the brain?

Answer 5

• fluorescence microscopy and genetic manipulation techniques such as cre-lox
• enzyme which us cre, recognises some lox sites and inserts a fluorescent protein into the cells.
• allows researchers to look under the microscope and identify the areas of the brain with different colours.

Question 6

what are neurones ?

Answer 6

information processing cells
highly specialised for the conduction and transmission of chemical and electrical signals

Question 7

what does a prototypical neuron comprise of?

Answer 7

• cell body
• axon
  -dendrites

Question 8

describe the organelles contained in a cell body?

Answer 8

contains the same organelles found in all human beings
- nucleus
-RER
-SER
-Golgi apparatus
-mitochondria

Question 9

describe the neuronal cytoskeleton?

Answer 9

-the cytoskeleton is the internal ‘scaffolding’ that gives a neurone its characteristic shape. Comprised of microfilaments, microtubules and neurofilaments.

Microtubules: a polymer of the protein tubulin. Located in axons and dendrites. Important for axoplasmic transport (transport of mitochondria lipids organelles proteins etc from the cell body to the axoplasm)

Microfilaments: a polymer of the protein actin, found throughout the neurone but particularly abundant in axons and dendrites.

Neurofilaments: a type of intermediate filament. Particularly abundant in axons and important in regulating atonal shape.
It is a promising biomarker for neurodegenerative disorders (eg Alzheimer’s)

Question 10

Describe what an axon is and it’s types?

Answer 10

Axons are highly specialised neuronal projections that conduct nerve impulses within the nervous system

Axons are comprised of :
- axon hillock: tapers away from the cell body to form the initial part of the axon
- axon proper: axon can branch to form axon collaterals.
- axon terminal: site at which the axon comes into contact with another neurone at the synapse

Question 11

function of glial cells?

Answer 11

glial cells are able to myelinate axons.
Myelin is a membranous sheath that is able to wrap around and insulate axons
Gaps in myelin sheath are called nodes of ranvier and are highly enriched in voltage gated sodium ion Chanels.

Question 12

what are dendrites?

Answer 12

dendrites are highly specialised neuronal projections that recieve synaptic information from other neurones
Dendrites of a specific neurone are collectively termed as a dendritic tree

Dendrites of SOME neurones are covered with specialised structures called dendritic spines that are membranous sacs that protrude from the dendrites of some cells to receive synaptic input.
Dendritic spine structure is sensitive to type and amount of synaptic activity
A number of conditions have also been associated with abnormal dendritic spine number (Alzheimer’s, schizophrenia etc).

Question 13

how can we classify neurones?

Answer 13

• either by neuronal structure or gene expression

Question 14

classify neurones based on neuronal structure

Answer 14

number of projections- unipolar, bipolar, multipolar

number of dendrites - pyramidal, Stellate

connections: sensory, motor and intermediate.

axon length: Golgi type I (pyramidal) Golgi type II (stellate)

Question 15

classify neurones based on their gene expression

Answer 15

neurones can be classified based on the type of neurotransmitter they release

-cholinergic (Ach)
-gabanergic (GABA)
- dopamine
- serotonin
-noradrenaline

Question 16

what are glial cells?

Answer 16

-glial cells are known as the ‘support cells’ within the nervous system and can be classified into four categories based on its structure and function.
The four type of glial cells are. :

• Astrocytes
• microglia
• ependymal cells
• schwann/oligodendrocyte cells

Question 17

what are astrocytes?

Answer 17

-astrocytes are star shaped glial cells that function to regulate the extra cellular environment in the brain in a number of ways.

• astrocytes are the most numerous type of glial cell present within the human brain.
• they regulate the extra cellular environment in the brain by enclosing synaptic junctions and actively
  removing neurotransmitters from the synaptic cleft. This is important so there’s no more neurotransmitter left hanging around so that they don’t activate receptors.

Question 18

describe microglia and it’s functions?

Answer 18

-are a type of glial cell that functions as a phagocyte within the nervous system to remove neuronal and glial debris.
- accounts for approximately 5-15% of the total CNS cell number. They are broadly distributed between the brain and the spinal cord.

Microglia have been shown to function in:
- phagocytosis of neuronal and glial debris
- synaptic connection remodelling
- directing neuronal migration during brain development

Question 19

describe ependymal cells and their functions?

Answer 19

ependymal cells line the ventricular system and act as a physical barrier between the brain tissue and cerebrospinal fluid

ependymal cells have been shown to function in:
- osmotic regulation of the cerebrospinal fluid
- flow of cerebrospinal fluid
- directing cell migration during brain development

Question 20

what has a deficit in ependymal cell function been linked to?

Answer 20

• it has been liked to a condition called: “hydrocephalus”
• hydrocephalus is the swelling of the ventricular system

Question 21

what are oligodendrocytes and Schwan cells and what are their functions?

Answer 21

• glial cells that function to provide myelin. A membranous sheath around axons
  Both these cells differ in their locations and in some other characteristics:

Similarities: both of them function if provide myelin

Differences:
- oligodendrocytes are situated in the central nervous system
-schwann cells are situated in the peripheral nervous system
-oligodendrocytes can myelinate multiple axons whilst the schwann cells can myelinate only one singular axon.