cells of the nervous system

What are neurons?

Excitable cells that integrate and relay information in a circuit

What are glia?

Supporting cells that maintain homeostasis, protect and assist neuron function

How many neurons and glia does the human body have?

85 billion of each

What does Nissl staining allow?

Distinguish between neurons and glia

Nissl bodies

Granular structure formed from rough ER and ribosomes

What does Nissl staining stain?

Cell nucleoli - appear as dark round dots in microscopy
Nissl bodies

Cresyl violet stains what?

Nucleic acids

Soma

Cell body of a neuron

What does the soma contain?

Nucleus, ribosomes, rough ER, golgi and densely packed mitochondria

What does a golgi stain do?

Highlights the architecture of neurons
Not taken up by all neurons - a few are stained at random
Can visualise all 4 main compartments of a neuron

What are the 4 main compartments of a neuron?

Soma, dendritesm axons and pre-synaptic terminals

Microtubules in neurons

Hollow tubes made of tubulin polymers that run longitudinally down neurotes (dendrites and axons)

Microfilaments of neurons

Made of actin
Run longitudinally and are membrane associated

Neurofilaments

Long protein molecules wound together
Very strong

Why are microtubules and microfilaments polar?

So that monomer units can be added and removed

Axon hillock

Widest part of the axon - joined to the soma

Axon initial segment

First generation site of action potentials

Axon collaterals

Branches of the axon

Axon terminal (bouton)

End of the axon

Why do axons not take up the Nissl stain?

It stains the nucleus

How do axons vary in length?

From 1mm to 1m

How do axons vary in diameter?

1um to 25um

Immunohistochemistry

Localizing antigens or proteins in tissues using labelled antibodies

What can immunohistochemistry be used for in neurons?

To find specific sodium channels in the axon by synthetically creating antibodies that will bind to the target ion channel then creating a second flourescent antibody that will bind to the first Ab

How could you identify the axon initial segment?

Immunohistochemistry of sodium channels

Neuronal divergence

Axons from one preganglionic cell synapse on numerous ganglionic cells through collaterals

What does neuronal divergence allow?

Innervation of many other neurons

How is the pre-synaptic terminal specialised?

Synaptic vesicles, lots of mitochondria and specific proteins but no microtubules

Synaptic cleft

Gap between pre and post synaptic neurons

Terminal arbour

Branching of axons to give many pre-synaptic terminals for each axon/collateral

Boutons empassent

Occurs when a pre-synaptic terminal is placed midway along an axon and not at the terminal

Axoplasmic transport

Movement of material from the soma down the axon

How was slow axoplasmic transport discovered?

By tying a knot in an axon
A bulge formed above the knot due to protein accumulation where transport was blocked

How was fast axoplasmic transport discovered?

Using radioactive amino acids to mark proteins

Anterograde transport

Down the axon away from the soma

Retrograde transport

Movement up the axon towards the soma with dynein use

What type of material is transported axoplasmically?

Mitochondria, lipids, vesicles, proteins and other organelles

How does material travel down the axon?

Down microtubules and kinesin with ATP requirement

How fast can material travel axoplasmically?

1000mm per day

Horseradish peroxidase

HRP - can be injecyed into the SC and it will be transported either antero or retro labelling other neurons
Used to show neuronal connections

Dendritic tree/arbour

Dendrites branches together

Neuronal convergence

Axons from numerous preganglionic cells synapse on a single ganglionic cell

The larger the dendritic tree...

The greater convergence as it can be innervated by many other neurons allowing the neuron to integrate information

Dendritic spines

Small ridges on dendrites

What do dendritic spines do?

Increase the surface area of the dendrites
Isolate chemical reactions in a microenvironment

What happens to dendritic spines if they are inactive?

The neuron has plasticity and can take in the spine

What happens if the dendrite is active and requires more spines?

The neuron will produce them

What are abnormalities in dendritic spines linked to?

Cognitive impairment

Cognitive impairment

Loss of ability to think logically; concentration and memory are affected

Unipolar neuron

A neuron with one process extending from its cell body

Bipolar neuron

A neuron with one axon and one dendrite attached to its soma

Pseudounipolar neuron

Neuron with two axonal roots. The two roots appear to leave the cell body as a single process

Multipolar neuron

A neuron with a single axon and multiple dendrites; the most common type of neuron in the nervous system.

Function of unipolar neurons

Sensory

What type of neuron is a dorsal root ganglion?

Unipolar

Why are unipolar neurons reliable relays of information?

Small area for receiving input making them highly specialised

Function of bipolar neurons

Sensory neurons

What type of neuron is a retinal bipolar cell?

Bipolar

What type of neuron are the majority in the brain?

Multipolar

What do multipolar neurons have?

High levels of convergence

Pyramidal neurons

Distinct apical and basal dendritic trees with a pyramidal soma

Where are pyramidal neurons located?

Neocortex and hippocampus

Stellate neurons

Star shaped dendritic tree

Where would you find stellate neurons?

Neocortex

Interneurons

Neurons within the brain and spinal cord that communicate internally and intervene between the sensory inputs and motor outputs

Sensory neurons

Neurons that carry incoming information from the sensory receptors to the brain and spinal cord

Motor neurons

Neurons that carry outgoing information from the brain and spinal cord to the muscles and glands

How can we identify what type of neurotransmitter a neuron uses?

Use GFP
Add to a neurotransmitter gene promoter sequence
All neurons containing a given NT will flouresce

Glia

Cels that fill space around neurons

What is the gap size between neurons and glia?

20nm

What is the difference between neurons and glia in terms of proliferation?

Glia can proliferate throughout life but neurons can't

Where are glia found?

CNS, PNS or ENS

Enteric nervous system

The nervous system of the gastrointestinal tract. It controls secretion and motility within the Gi tract, and is linked to the central nervous system.

CNS homeostatic glia

Astrocytes

PNS homeostatic glia

Satellite cells

CNS myelinating glia

Oligodendrocytes

PNS myelinating glia

Schwann cells

CNS phagocytic glia

Schwann cells/macrophages

ENS homeostatic glia

Eneteric glia

Satellite cells

Surround neuron cell bodies in PNS

Oligodendrocytes

Form myelin sheath in CNS

Microglia

Act as phagocytes, eating damaged cells and bacteria, act as the brains immune system

Schwann cells

Supporting cells of the peripheral nervous system responsible for the formation of myelin.

Astrocytes function

Glycogen stores of the brain - astrocytic endfeet can take up glucose
Control the environment surrounding neurons
Control movement of substances into/out of neurons from vasculature
Buffer extracellular potassium
Form blood brain barrier coupling neuronal activity to the blood supply

What can astrocytes be studied using?

GFAP

GFAP

Glial fibrillary acidic protein

Astrocytic endfeet

Encircle blood vessels to allow transpirt control

What can glycogen be metabolised into in astrocytes?

Lactate

Fibrous astrocyte

Astrocyte found in white matter

Protoplasmic astrocyte

Found in grey matter

Radial glial cells

Type of astrocyte
Key in development

Muller cells

Funnel-shaped glial cells (astrocytes) that aid light transmission through the retina

Ependymal cells

Produce CSF in ventricles
Type of astrocyte

Bergmann cells

Astrocytes in cerebellum

Tripartite synapse

Presynaptic neuron, postsynaptic neuron and astrocytes

How can astrocytes terminate neurotransmitter activity?

They can take in neurotransmitter present in the synaptic cleft, terminating NT activity and allowing NT recycling back to the presynaptic terminal

What percent of glial cells are microglia?

15%

Function of microglia

Control and remove tissue debris and allow neuron growth
Undertake synaptic pruning - must be activated to become phagocytic

Synaptic pruning

Removing unused synapse by phagocytosis

Synaotic pruning in neurodegenrative diseases

Removeing unsued sunapse by phagocytosis - makes it worse