Neurohistology Flashcards
What are the nervous tissues and neurons derived from?
They are ectodermally derived
Both the skin and nervous system are derived from the ectoderm, even though one is internal and one is external
Nervous tissue is one of the four basic types of tissue in the body. Its consists of two principle cell types, what are these?
Neurons are described as being excitable, what does this mean?
Neurons are excitable cells with long cytoplasmic extensions specialised for reception of stimuli and conduction of a nerve impulse (action potentials) via an axon
Tell me about neuronal cell division
Is there an exception to this?
Neurons do not undergo cell division and replication
The exception is Olfactory neurons. These are a minority and do undergo cell division and replication.
However, a majority of neuronal cells do not do this
Whats are dendrites and their role?
They recieve information from adjacent axons
(They sit close to cell body and are branched)
Whats the role of axons?
They send information from one end of the neuron to another (this transmission is faster if the axon is myelinated)
Whats the role of the axon hillock?
Signals from the cell soma are summated at the axon hillock. This hillock is considered the ‘trigger zone’ which must reach threshold potential to achieve an action potential
Tell me about the Hillock and axon initial segments (AIS)?
They are both rich in voltage-gated Na+ channels- where signals are summated
These do not have any myelin
What does the Nodes of Ranvier have an accumulation of?
Voltage gated Na+ channels
Label the structure of this neuron
What is used to identify dendrites and why is this used?
MAP2 (microtubule associated protein)
This is a neuron specific cytoskeletal protein which is found in dendrties
A good dendritic marker as it is only found here
Whats used to identify axons?
ßIV Spectrin
This is a cytoskeletal protein which is found in axons as well as some non-neuronal cells
Name some neuronal subtypes?
What is the role of each one?
- Motor neurons: Relay commands from brain and spinal cord to muscles and glands
- Sensory neurons: Are excited by specific stimuli
- Interneurons
Label this motor neuron
The arrows indicate the direction of signal transmission
Cell soma diameter: ranges from 5-135 µm
What is a Golgi stain used for?
The Golgi stain is a method using silver nitrate and potassium dichromate to densely stain an entire single neuron including its dendrite and axon branches.
It results in silver precipitation (from silver chromate) inside the neurons
Only a small subset of neurons are stained with the Golgi method, so the entire structure of those few neurons that are stained is visible for study
Cell bodies of multipolar motor neurons are found where and have what size?
They are large and found in the ventral horn of the spinal cord
How are motor neurons in the spinal cord displayed when stained?
They display a large pale staining nucleus and a prominent nucleolus and Nissl bodies
What does Nissl substance stain?
It stains rough endoplasmic reticulum and polyribosomes
The Nissl stain gives a good indication for what?
Protein synthesis
The Nissl substance is largely absent where?
In the axon
Label this sensory neuron
Arrows indicate the direction of signal transmission
Bring in afferent information
What are ganglia?
Aggregations of nerve cells (ganglion cells) outside the CNS
What are the dorsal root ganglia surrounded by?
A connective tissue capsule, which is continuous with the peripheral nerve
Where we find psudounipolar cells
Individual ganglion cells are surrounded by what?
A layer of flattened satellite (fibroblast) cells
What are integrative neurons also known as?
Interneurons
What are the three types of integrative neurons, label each one?
Arrows indicate direction of signal transmission
How are some characteristics of integrative neurons?
Multipolar
Has short axons
What neurons are multipolar ?
Motor neurons
Integrative neurons
What polarities do sensory neurons have?
Unipolar
Bipolar
Multipolar
What is the cerebral cortex (Neocortex) divided into?
Are these layers found in the white or grey matter?
What does each layer house?
The cerebral cortex is divided into 6 layers
These layers are found in the grey matter
The layers are each housing neurons whose morphology is characteristic of that layer
(The cerebral hemispheres are outlines in the blue in the image)
What are the 6 layers of the neocortex?
Tell me about potential; size, presence of cell bodies
- Layers 1,2,6 have no neuronal cell bodies
- Layers 3,4,5 have neuronal cell bodies
- Pyramidal cells found in layer 3 and 5
- Pyramidal cell in layer 5 is much larger than in 3
- Pyramidal cells are the starting point for motor systems in the body
- pyramidal cells give off efferent information
- Granule nerons are small and have integrative features and are foun in layer 2 and 4
Deep in the grey matter is what?
White matter composed of myelinated fibres
The meningeal layers of the neocortex can be observed:
Are the pyramidal and granule neurons unique in the cortex?
No
Tell me about the Cytoarchitecture of the cerebellar cortex
It has three layers within the grey matter with a variety of cell types
(with myelination in the white matter which is deep in the grey matter)
What are the three layers of the cerebellar cortex?
What cells are found in each layer?
- Outer molecular layer: Basket cells, stellate cells (2 types of neuronal cells)
- A single layer of Purkinje cells: Purkinje cells (specific cells, only found in cerebellum, robuse dendritic tree structure)
- A granular layer: Granule cells (most abundant neuron on brain) and golgi cells
This layer is densely packed with cells compared to the others which have a relatively sparse arrangment
What are the largest cell in the cerebellum?
The purkinje neurons
Tell me about the characteristic shape of the purkinje neurons?
- pear shaped cell bodies
- distinctive tree (in moleuclar layer)
- Has a single axon
What type of information do purkinje cells recieve?
Afferent information
What are the smallest cells in the cerebellum?
Granule cells
What do Neuroglial cells function in?
Metabolism and support of neurons
What are the Neuroglial cells found in the CNS?
Astrocytes
oligodendrocytes
ependymal cells
microglia
What are the neuroglial cells found in the PNS?
Schwann cells
Satellite cells
What 2 neuroglial cells form myelin sheaths around axons?
Oligodendrocytes and Schwann cells
What do astrocytes provide?
Structural and metabolic support for neurons
What are the different types of astrocytes?
Where are they found?
The astrocytes are names something different dependent on their location in the body
- Fibrous (in white matter)
- Protoplasmic (in grey matter)
- Müller glia (in retina)
- Radial glia (specialised cells in developing CNS)
What does the blood-brain barrier form?
Glial-limiting membrane around blood vessels and along CNS surface
Whats the blood brain barrier composed of?
Endothelial cells joined by tight junctons
Tell me about what can/cannot diffuse through the blood brain barrier
It prevents the diffusion of solutes and fluid into the brain and spinal cord
Allows: O2, CO2, lipid soluble molecules (hormones)
Doesn’t allow: >500 Dalton’s MW not permissible e.g. certain drugs
The integrity of the blood brain barrier depends on what?
Its highly dependent on astrocytes ‘end feet’
Label this blood brain barrier
What is the role of Microglia?
They serve as an immune function within the CNS. Much like macrophages, they are able to phagocytose cell debris in response to injurt
They don’t have quite the same power as macrophages though
What happens when an injury is detected by microglia?
They normally exist as ‘resident microglia- observing the nervous system’ but become ‘activated’ upon CNS damage and actively move towards the site of injurt
They release cytokines which can help and hind recovery
When they aren’t activated they look small and flattened
What do oligodendrocytes form?
Myelin sheath around CNS axon.
Can one oligodendrocytes myelinate a single axon or several?
One oligodendrocytes can myelinate several axons
Name some diseases that affects oligodendrocytes?
MS (multiple sclerosis)
Leukodystophies
Are oligodendrocytes one of the first or last cells to form during development?
They are one of the last cell types to form during development
What do schwann cells form?
Myelin sheath around PNS axons
Can one schwann cell activate one or many axons?
One schwann cell is able to myelinate one axon
Schwann cells play a key role in the organisation of what?
The organisation of connective tissue sheaths around peripheral nerves during development and regeneration
myelination
What does myelin consist of and provide?
Myelin consists of roughly 80% lipid
It provides insulation as well as enhanced conduction velocity for action potentials (saltatory conduction)
myelination in schwann and oligodendrocytes
Tell me about conduciton in unmyelinated neurons?
Unmyelinated axons have ‘continuous conduction’ of action potentials due to passive current flow (low conduction)
What happens with unmyelinated neurons in the PNS and CNS?
PNS: Schwann cells ‘envelope’ unmyelinated axons contacting 1 or more axons
CNS: unmyelinated axons are not associated with glial cells
Give an example of an unmyelinated axon?
Sensory fibres carrying pain, temperature, itch
What has a larger diameter; myelinated or unmyelinated axons?
myelinated has a larger diameter
