Week 1 Topic 3 - Microanatomy of the nervous system Flashcards
Who discovered that the brain is not a single continuous entity but composed of individual cellular units?
In 1906, Ramóny Cajal and Camillo Golgi were jointly awarded the Nobel Prize in physiology and medicine for their
discovery that the brain is not a single continuous entity but composed of individual cellular units.
What are the two major types of cells that the cells of the nervous system differentiate into during development?
We now know that during development, the cells of the nervous system differentiate into two major cell types:
- neurons – the
cells responsible for fast communication along large networks – and the - supporting glial subtypes.
How do neurons communicate?
Neurons communicate by passing electrical signals along their elongated form and they’re converting this into a chemical signal to activate an electrical signal in the next neural network.
How fast does information travel between neurons?
Information travels at different speeds
in different neurons, ranging from 1 mile per hour, the speed of a tortoise, to 268 miles an hour, which is faster
than most Formula 1 racing cars.
Are neurons homogenous or heterogeneous?
Neurons are not homogeneous, they are heterogeneous. They come in many forms specialised for their particular function within the nervous system.
Can neurons both receive signals and send signals to other cell types?
On the left, we have a classical neuron which both receives signals from and sends signals to
other neurons and has a long, extended shape.
However, some neurons can both receive signals and send signals to other cell types.
For example, sensory neurons can be activated by changes in the skin cells, and lower motor
neurons can stimulate muscle movement.
Some neurons, such as interneurons, can actually send and receive signals with multiple other neurons.
Describe the dense lobe structure in the cerebellum.
Even within brain regions, neurons can vary widely.
For example, in the cerebellum, the brain region that primarily coordinates movement, there is a dense lobe structure.
The dense layer in these lobes is generated by millions of small granule cell neurons, which feed into one of the largest types of neuron in the brain, the Purkinje cells, with other interspersed basket and Golgi neurons.
What are Purkinje cells?
one of the largest types of neuron in the brain
Purkinje cells release a neurotransmitter called GABA (gamma-aminobutyric acid), which exerts inhibitory actions on certain neurons and thereby reduces the transmission of nerve impulses. These inhibitory functions enable Purkinje cells to regulate and coordinate motor movements.
What are Golgi neurons?
The Golgi cell acts by altering the mossy fibre - granule cell synapse. The Golgi cells use GABA as their transmitter. The basal level of GABA produces a postsynaptic leak conductance by tonically activating alpha 6-containing GABA-A receptors on the granule cell.
What are granule cells?
Granule cells are the only intrinsic excitatory neurons, the other four neuron types (Purkinje, basket, stellate, and Golgi) involved in computation are all inhibitory and target deep cerebellar nuclei, soma of Purkinje cells, and dendrites of Purkinje and granule cells, respectively.
What are mossy fibres?
Mossy fibers are the axons of dentate granule cells in the hippocampal region. In the normal hippocampus, these axons of granule cells elongate within the dentate hilus and stratum lucidum, and innervate hilar cells and CA3 pyramidal cells.
Provide a rich excitatory drive to the cerebellar cortex. They originate from several regions in the brain and spinal cord
Which glial cells directly interact with neurons?
But neurons do not function in isolation, they are supported by multiple types of glia. Those that directly interact
with neurons – oligodendrocytes, astrocytes, microglia – and ependymal cells, who line the ventricles of the brain
and the central canal of the spinal cord (similar to epithelial/skin cells). We will now go through each of these cell
types one by one.
What are ependymal cells?
line the ventricles of the brain
and the central canal of the spinal cord (similar to epithelial/skin cells).
What are the 5 functions of astrocytes?
Astrocytes have many known functions, including
- distribution of nutrients from the blood supply to neurons,
- maintenance of extracellular ionic balance and
- tissue repair.
- They can also regulate synaptic activity by direct
contact with synapses, in what is known as the ‘tripartite synapse’, and - signal between each other independently
of neurons via gap junctions – small gaps in the cell membrane that leak charged ions.
What are the functions of microglia?
Microglia, as inferred by the name, are smaller than astrocytes and function as the resident immune cells of the
brain.
1. In this function, they clear debris, recruit other cells to sites of damage and aid in tissue repair.
- In addition
to debris clearance, they can also degrade synapses – which is essential for synaptic pruning during development
but may make matters worse by preventing recovery when neurons undergo chronic stress during disease.
What are the functions of oligodendrocytes?
The next type of glia, oligodendrocytes, play the same role in the brain as Schwann cells in the periphery. 1. They wrap their processes around neuronal axons secreting the lipid myelin, generating a protective myelin sheath.
2. This sheath also increases the speed of neuronal signalling by insulating the passing of electrical charge along the
axon, in a process called saltatory conduction.
3. Recent data also shows that oligodendrocytes also provide
metabolic support to neurons, aided by their proximity.
4. Demyelinating diseases, like multiple sclerosis, cause
degeneration of the myelin sheath, preventing the brain communicating adequately with the body.
What is saltatory conduction?
The process which insulates the passing of electrical charge along the
axon - the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials
What happens when different cell types - neurons and/or glia don’t function as they should?
We have now seen that many different cell types contribute to the proper functioning of the brain and, therefore,
it is not surprising that dysfunction of any of these cell types can lead to disease.
Neurons and glia cohabit in a
very delicate balance.
What is Neuroinflammation?
Neuroinflammation is the activation of glia within a nervous system. This neuroinflammation
may initially be a defence response to threat, to protect neurons. But chronic activation can lead to the over or
aberrant activation of astrocytes and microglia and toxicity to neurons.
Altered function of astrocytes and
oligodendrocytes can also directly disturb synaptic transmission.
Therefore, these changes can result in
vulnerability of neurons both in neurodevelopmental and neurodegenerative diseases.
What is Neuronal morphology?
Neuronal morphology, or shape, is
- refined during development to fit the function of neurons and is,
- therefore, highly variable.
What does the extent of dendritic arborisation reflect?
The extent of dendritic arborisation, or branching, reflects the level of input that a neuron requires
– as dendrites are the main sites of neuronal input. For example, cerebellar Purkinje cells are highly branched,
as they receive many inputs and are the only input of the entire cerebellar cortex.
What is the longest axon in the body?
Axonal length can also vary widely, determining the distance of output in the network. The longest axon in the
body is from the lower motor neurons, which is one meter in length, which is quite incredible for a single cell. To
give you an equivalent – if the cell body was the size of a ping pong ball, the axon would be 380 meters long, just
under four football fields in length.
What are dendritic spines and what do they do?
Neurons also have microstructures called dendritic spines. These are small protrusions from dendrites which
form the postsynaptic side of a synapse with axon tunnels from other neurons. Dendritic spines come in different
forms, from long and thin to mushroom shaped. Their shape and size will affect how they receive and transmit
input. Those with a larger surface area provide more space capacity for neurotransmitter receptors and, thus,
generally form stronger, more stable synapses rather than the more transient, filopodial types. Spines are also
plastic and can increase in size during learning and memory.
What are filopodia?
that function as antennae for cells to probe their environment. Consequently, filopodia have an important role in cell migration, neurite outgrowth and wound healing and serve as precursors for dendritic spines in neurons