Basic Cellular Physiology of Brain Function

Question 1

What valuable neuronal insights do mice provide?

Answer 1

a. Enables cellular + genetic study and manipulations
b. Similar structural and circuit organisation (ex. hippocampus is involved in spatial navigations + special amendments in both brains)
c. Similar cellular and synaptic proteins, structures and mechanisms (i.e stimulus causing action potential in human nerve cell causes an action potential in mouse nerve cell)
d. Capacity for similar complex behaviours to some extent

Question 1

What are some structural differences between the human and mice neurons?

Answer 1

Human brain:
* 2700x larger
* Has 1000x more neurons (80 billion vs 80 million)
* Different glia
* Has a convoluted cortex + larger frontal lobes
* Has a greater complexity

Question 2

How are neurons arranged in the hippocampus?

Answer 2

In the hippocampus the neuron is localised into a denser nucleus.

The neuronal soma are packed together and extend dendritic + axonal processes to communicate with neurons in different regions.

Inputs received from the cortex –> neuron –> output sent elsewhere in the hippocampus (the CA3 region).

Question 3

Outline the structure of a neuron.

Answer 3

1. Dendrites: processes extending from the soma that receive the synaptic inputs.
2. Soma (cell body): integrates the synaptic inputs together + site of metabolic and genetic processes
3. Axon hillock: specialised region where the action potential is initiated.
4. Axon: single, long, cylindrical process that conducts the action potential to the nerve terminal end (may be myelinated).
   5: Presynaptic nerve terminal: site where the electrical signal gets converted to a chemical signal and communicated to other nerve cells.

Question 4

How do neurons generate and transmit action potential?

Answer 4

1. Transient change in membrane potential of 100mV
2. Triggered in ‘all or nothing’ fasion when voltage threshold is reached
3. Rapid depolarisation (Na+ influx through voltage gated Na+ ion channels)
4. Repolarisation (K+ efflux through voltage gated K+ ion channels)
5. Stronger stimuli can result in multiple action potentials.

Question 4

What are neural circuits and what are the two ways in which they can exist?

Answer 4

Neural circuits: collections of neurons with specific inputs and outputs.

Can exist as local circuits of longer range circuits.

Local circuits –> one brain region (ex. local inhibitory interneuron in the hippocampus, which comprise about 10% of all hippocampal neurons)
Longer range circuits –> project to other regions (ex. CA3 to CA1, CA1 to EC)

Question 5

What are the functions of different neuron subparts?

Answer 5

1. Stimulation of synaptic input give a small depolarizing potential in the dendrites.
2. These spread to the soma, where all different inputs get integrated.
3. If inputs cross the voltage threshold, an action potential is initiated.
4. Action potential occurs first at the Axon hillock –> down the axon –> nerve terminal
5. Action potential also ‘back propagates’ to the dendrites in many mammalian neurons
6. This is recorded by double and triple patch clamp recording from a single cortical neuron.

Question 6

What is neuronal excitability?

Answer 6

A term expressing how easy it is for a nerve cell to fire action potential.

Question 7

What are potential ways to alter excitability?

Answer 7

• ability to reach threshold
• channels generating or regulating APs
• Ion concentrations
• Physical damage
• Axonal conduction
• Processes at synapse

Question 8

Identify 4 glial cells.

Answer 8

Ependymal cells, oligodendrocytes, astrocytes and microglia.

Question 8

Distinguish between increases and decreases in excitability.

Answer 8

Increases in excitability: death of an inhibitory neuron
a. inhibitory neuron cannot transmit AP
b. Easier to get AP/increased AP frequency
c. Excessive/inappropriate response or seizures

Decreases in excitability: death of an excitatory neuron
a. Excitatory neuron cannot transmit AP
b. Harder to get AP/decreased AP frequency
c. Prevent/reduce response

Question 8

What is the function of microglia?

Answer 8

Microglia are specialised glial cells that are macrophage-like cells in the CNS.

Their functions are:
i. Immune cells + surveillance
ii. Sculpting neural circuits
iii. Synapse elimination
iv. Clear up cellular debris

Question 9

Outline key features of oligodendrocytes.

Answer 9

Oligodendrocytes are specialised glial cells with multiple axons that wrap themselves around neurons present in the CNS.
Function:
i. myelination of central axons
1. increases in myelin is associated and required for learning
2. precursor cells can differentiate into oligodendrocytes as required
ii. metabolic + trophic support of axons

Question 9

What is the function of ependymal cells.

Answer 9

Ependymal cells are ciliated-epithelial glial cells that line the ventricles of the brain. Function is to produce + regulate CSF, brain metabolism, clearance of waste from the brain.

Question 10

What is the function of astrocytes?

Answer 10

Astrocytes are star-shaped glial cells with many processes that envelop synapses made by neurons.

Their functions are:
i. Homeostasis via ion transmitter, water, metabolites regulation
ii. Integral part of the blood brain barrier
iii. Formation and elimination of synapses