Neuronal Activity L2.2

Question 1

what are two ways neurons propagate information?

Answer 1

• transmission of an altered electrical potential ( needs repolarisation )
• Release of chemical neurotransmitters ( needs re-uptake)

Question 2

Describe the neuronal membrane

Answer 2

• it is a lipid bilayer
• acts as an insulator
• controls the diffusion of ions across the membrane

Question 3

How are ion concentrations distributed across the neuronal membrane?

Answer 3

• K+ has a higher concentration in the intracellular space.
• Na+ and Cl- have a higher concentration in extracellular space,
• this results in a potential cross the membrane -80mV and -40mV

Question 4

How are ions transported across the membrane to generate action potentials?

Answer 4

through:
- Ions Channels: Voltage-gated or molecularly gates (e.g glutamate)
they allow ions to transport along the ionic concentration gradient
- Ion Pumps: Release ions across the membrane AGAINST the concentration gradient

Question 5

what is a key concept about the energy requirements for generating excitatory or inhibitory signals?

Answer 5

• Generating excitatory or inhibitory only needs kinetic energy that is already available.
• Restoring electrochemical potential needs LOTS of additional energy that can only be met by increases in metabolism

Question 6

what are neurotransmitters and how do they transport information?

Answer 6

are endogenous chemicals that transmit signals across the synapse from one neuron to another by opening ion channels
- they are packaged into synaptic vesicles on the presynaptic side of the synapse and bind to specific receptors on the postsynaptic side

Question 7

what are the requirements for neurotransmitter function?

Answer 7

• A precursor enzyme on the presynaptic side
• Sufficient amount of neurotransmitters to affect postsynaptic neurons
• specific postsynaptic receptors
  biochemical mechanism for deactivation

Question 8

list the major types of neurotransmitters

Answer 8

• Amino acids: Glutamate, glycine, GABA
• Mono-amines: Serotonin, histamine, dopamine, nor-adrenaline
• Peptides: Opioids, cocaine, amphetamine
• Others: Acetylcholine, adenosine, nitric oxide.

Question 9

what is a key concept regarding neurotransmitter reuptake?

Answer 9

neurotransmitter reuptake in the presynaptic space is essential to keep neuronal activity.
- reuptake and recycling also need a lot of extra energy from increases in metabolism

Question 10

why postsynaptic neurons need lots of energy?

Answer 10

• releasing chemicals (aka neurotransmitters)
• keep resting potent
• processing signals

Question 11

why doesn’t the brain have enough energy to support its activity?

Answer 11

• the brain needs ‘real-time’ top-up of energy to support its processes from the arterial blood supply

Question 12

Aerobic (6 points)

Answer 12

aerobic:
1. happens in the presence of 02
2. end product = pyruvate ( carbon)
3. makes 36 ATP/ glucose
4. slow process and involves TCA cycle
5. energy source: glucose,fatty acid,keton bodies
6. efficient ATP production when 02 is there:
- theres little gycogen in the brain so brain relies on a ontinous supply of glucose from bloodstream rather than stored
- amount of ATP produce is based on how much energy the brain uses

Question 13

what is localisation of function and what tecniques are used ?

Answer 13

is where different areas perform different functions and so more activity in one area of brain more blood flow to that area
- techniques like PET or fMRI are used to provide regional info on brain activity

Question 14

what do PET/fMRI rely on?

Answer 14

1. regional changes in brain activity
2. changes in :
   - blood flow
   - metabolism
   - oxygen levels

Question 15

What is neurovuscular coupling?

Answer 15

process where CBF is regulated by neural activity

Question 16

what do glial cells release during neurovascular coupling?

Answer 16

glial cells, more so astrocytes, release vasoactive substances like
- k+ ions
- adenosine
- nitric acid (NO)

Question 17

steps for Neurovascular coupling: (9 steps)

Answer 17

1. neurons become active due to a stimulus
2. release neurotransmitters like glutamate into synaptic cleft
3. glutamate binds to receptors at end feet of astrocytes
   4.activated astrocytes release vasodilators like arachidonic acid which promotes dilation of blood flow
   5.astrocytes also take up excess k+ ions released during neuronal activity
4. k+ ions,NO and adenosine diffuse from the synapses into the smooth muscle of nearby arterioles
5. peri-arteriolar neurons make NO(nitric acid) which diffuses into the smooth muscle of arterioles helping with relaxation and vasodolation
   8.smooth muscle cells in arterioles relax due to combines effects of adenosine,NO,k+ ions leading to an increase of diameter in blood vessel
6. therefore an increase in blood flow to the active brain regions= helps keep homeostasis within brain environment

Question 18

role of astrocytes? ( 6 point) short

Answer 18

1. respond to neurotransmitters
2. vasodilator releasese
3. k+ regulation (during neuronal activity k+ are released so astrocytes remove excess k+ to stop overactivity in neurons and support blood vessel dilation since k+ helps widen blood vessel)
4. interaction with endothelial cells (help with nutrients exchnage and also astrocytes communicate with endothelial cells to keep blood-brain-barrier)
5. Regulation of neurotransmitter
   uptake (astrocytes absorb neurotransmitters like glutamate from synaptic cleft which help end signaling process)
6. respond to metabolic changes ( can detect brain metabolism like low oxygen or glucose level)

Question 19

difference between diamagnetic and paramagentic

Answer 19

1. diamagnetic (02Hb) = No magnetic effect
   - have all electrons paired so they create a weak and opposite response to the magnetic field (B)
2. paramagentic (dHb)= influences B die to unpaired electrons
   - strong attraction to magnetic field due to its unpaired electrons therefore creating BOLD contrast that help map brain activity

Question 20

what type of hemoglobin is venous and arterial bloos ?

Answer 20

venous= deoxygenated Hb
Arterial= oxygenated Hb

Question 21

does how much material in B affect distortion?

Answer 21

yes, for example, 02Hb and Hb can distort local B
- these lead to spin de-phasing( H nuclei in water lose their sync)
- losing transverse magnetisation
- because of de-phasing the transverse magnetisation of hydrogen protons decay faster near dHb( deoxygenated hemoglobin)
- this causes signal loss in MRI (aka distortion )

Question 22

what does BOLD contrast depend on? ( 3 processes)

Answer 22

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