Week 3 part 1

Question 1

What are the two ways in which neurons communicate information?

Answer 1

1. By transmitting electrical potential

2. Releasing chemicals - neurotransmitters

Question 2

What is a lipid bi-layer?

What are its two functions?

Answer 2

A membrane that neurons possess on the outside.

1. It serves as an insulator
2. Control the diffusion of ions (charged atoms or charged molecular groups across the membrane.

Ionic concentrations across membranes are not balanced! It means neurons do not exist at neutral electrical potential (somewhere between -80 and -40 mV).

Question 3

How do neurons generate spontaneous electrical activity?

Answer 3

By transporting ions across neuron membrane. Ions are moved through ion channels.

Question 4

What are the two types of ion channels?

Answer 4

1. Ion channels: allow ionic transport along their concentration gradient - they open at a particular voltage or by the action of another media.
2. Ion pups: release ions across the membrane, against their concentration gradient.

Question 5

What type of energy is required for the transmission of an altered electrical potential?

Answer 5

Kinetic energy (only)

Question 6

What energy is required for the repolarization of of the membrane (restoration of ionic concentrations to what they normally were before activity was generated)?

Answer 6

It requires input of energy. This energy requirement can be met by increasing tissue metabolism.

Question 7

What is neurotransmitters and how do they operate?

Answer 7

Neurotransmitters are endogenous chemicals that transmit signals across the synapses from one neuron to the other by opening ionic channels.

Question 8

How neurotransmitters are classified?

Answer 8

Based on their molecular character:

1. Amino acids: glutamate, glycine, GABA
2. Peptides: opioids, cocaine, amphetamine
3. Monoamines: serotonin, histamine, dopamine, noradrenaline
4. Others: acetylcholine, adenosine, nitric oxide

Question 9

What is neurotransmitter reuptake and why it is important?

Answer 9

It is essential to maintain neuronal activity. Concentration of neurotransmitters, needs o be restored to their original level in presynaptic side. Reuptake and recycling also require a lot of additional energy, which is met by further increases in tissue metabolism.

Question 10

How energy demand in the brain maintained?

Answer 10

By the process of hydrolysis, where the third phosphate group of ATP and a lot of free energy is released. - ATP is also known as the currency of the brain. ATP production is linked to its utilization - which means its concentration is relatively constant.

Question 11

Describe two processes breaking down glycogen to create ATP.

Answer 11

1. Aerobic glycolysis:
   - using oxygen in order to produce this breakdown
   - this in turn allows glucogen molecules to enter what is known as the TCA cycle
   - as a result we have production of 36 molecules of AATP
   - limitation: it is slow
2. Anaerobic glycolysis - without the input of oxygen:
   - produces relatively small amount of energy because only two molecules of ATP are produced, its however 100 times faster
   - disadvantage: it generates lactate accumulation, which is equivalent to sprinting muscular activity. This is not optimal for human brain.

Question 12

How the real time replenishment of oxygen and glucose is maintained in the brain?

Answer 12

By the arterial blood supply.

Question 13

Which type of the artery is the main source of blood in the brain?

Answer 13

Carotid artery (4-10 mm)

Question 14

How capillaries make efficient transport of oxygen and glucose?

Answer 14

Its small size of 10-50 microns, makes the network very wide and close proximity to the cells (red blood cell is about 7.5 microns).

Question 15

How does the velocity changes when arterial blood leaves the aortic arch?

Answer 15

It slows down to 10-250 millimeters per second in the small arteries deep in the brain.

Question 16

What is neurovascular coupling?

Answer 16

The process by which regional CBF or better yet rCBF is regulated by neuronal activity. Increase in activity of neurons trigger the production of substances that relax the smooth muscle wall of arteriole in order to increase their diameter and deliver increased amount of blood.
CBF - ml of blood circulated per time frame.
The main molecule responsible for this effect is nitric oxide, which can be secreted by astrocytes after they sense changes in the activity of neurons.

Question 17

What are the main three variables contrasting the BOLD?

Answer 17

1. The increase in blood flow triggered by the increase in cellular activity
2. The magnetic properties of the haemoglobin in the blood
3. The mismatch between the increase in blood flow and the increase in oxygen metabolism in neurons

Question 18

How oxygen is transported in red blood cells?

Answer 18

By haemoglobin molecules.

Question 19

What is haemoglobin? What are the two types of haemoglobin?

Answer 19

It is a protein complex with four structures known as heme groups each of which carry oxygen.
Haemoglobin has different magnetic states depending on its oxygenation state.

• Oxygenated heamoglobin as known as diamagnetic - has no intrinsic magnetic character.
• Deoxygenated haemoglobin on the other hand is a paramagnetic molecule which is to say that it can acquire magnetic properties in the presence of the external magnetic field.

Question 20

What happens when oxygen leaves haemoglobin?

Answer 20

Four unpaired electrons are left in the rest of the molecule which have a large magnetic moment. These are responsible for giving the deoxygenated heamoglobin its strong paramagnetic character.

Question 21

What is magnetic susceptibility?

Answer 21

The physical parameter that describes the magnetic character of a substance or in this case a molecule. Deoxygenated heamoglobin because of its four unpaired electrons has much more larger magnetic susceptibility than oxygenated heamoglobin.

Question 22

How Ogawa et al. showed that the amplitude of the BOLD contrast depends on oxygen metabolism?

Answer 22

They showed that BOLD contrast was directly proportional to the depth of anaesthesia of the rodent. At higher levels of anaesthesia, the local metabolism of neurons falls - therefore the local oxygen utilization also falls. Therefore BOLD contrast depends on the relationship between changes in rCBF and changes in CMRO.

Question 23

What did the Fox and Raichle found in terms of reactive hyperaemia?

Answer 23

they found that neurons appear to supply themselves with a lot of oxygen - far in excess of the amount they need.

Question 24

Is BOLD activity related to electrical activity or synaptic activity/

Answer 24

Synaptic activity