Regulation of Cortical Excitability and EEG

Question 1

What are the types of cortical stimulation (awakening)?

Answer 1

2 forms:

Direct neuronal stimulation

Neurohormonal systems

Question 2

What happens if there is no cortical excitation?

Answer 2

Coma; cerebrum is useless without constant activation by the lower centers

Question 3

What drives wakefulness?

Answer 3

Reticular formation which sits in the brain stem and its activity radiates out to the cerebral cortex

Question 4

What are the 2 parts of the reticular formation?

Answer 4

Excitatory area

Inhibitory area (sleepiness results from activation)

Question 5

What kind of action does the inhibitory area perform?

Answer 5

Its only known function is to inhibit the excitatory area from activating the rest of the brain. No direct effect on the cortex observed.

Question 6

What CN is located directly inferiorly to the excitatory area? Why is this important?

Answer 6

CN5 (trigeminal nerve)

CN5 recieves sensory signals which can activate the excitatory area.

Question 7

Where in the brainstem does the reticular excitatory area sit?

Answer 7

In reticular formation of pons and midbrain.

Question 8

Where does the reticular excitatory area send signals?

Answer 8

Upwards towards the cortex and downwards towards antigravity muscles and controls levels of spinal reflexes

Question 9

What do antigravity muscles do in response to excitatory area stimulation?

Answer 9

They become stronger and produce higher amounts of tension

Question 10

What are the types of actions that the Reticular Excitatory Area has?

Answer 10

1) Rapid transmission to excite the cerebrum. (gigantocellular neurones: excitatory and produce acetylcholine) [rapid action rapid destruction]
2) Progressive build up for seconds to minutes. Large number of smaller neurons, slower signal: Also often excitatory and controls long term excitation of the brain. (Dopamine, Noradrenaline, Serotonin)

Question 11

What is the locus coeruleus?

Answer 11

The origin of the noradrenaline system.

Question 12

What does the noradrenaline system do?

Answer 12

It acts mostly in an excitatory way in fibers spread throughout the cortex.

It is active during wakefulness and non-REM sleep and inactive during REM sleep.

Question 13

What is the action of the dopamine system?

Answer 13

Can be both excitatory and inhibitory.

Fibers innervate specific regions of the brain

Question 14

Where is the dopamine system located?

Answer 14

Starts off at substantia niagra, arcuate vasciculus and VTA

Question 15

What does the serotonin system do?

Answer 15

Usually inhibitory, fibers to diencephalon and specific cortex regions.

Induces sleep, controls pain, and mood control

Question 16

Where is the serotonin system located?

Answer 16

Raphe nuclei

Question 17

What does acetylcholine system do?

Answer 17

Usually excitatory and causes feeling of being acutely awake and excited nervous system.

It also drives REM sleep

Question 18

Where is the acetylcholine system located?

Answer 18

Gigantocellular neurons in REA

Question 19

Why are Glutamate and GABA the most important neurotransmitters to understand?

Answer 19

They are the most abundant excitatory neurotransmitters in CNS.

Question 20

What does glutamate do?

Answer 20

Binds NMDA (Na and Ca channel) and AMPA (Na channel) and produce exctation. It is excitatory.

Question 21

What does GABA do?

Answer 21

It is the most common inhibitory NT in CNS and it binds GABAa (Cl channels) or GABAb (GPCR -> potassium channels)

Question 22

What enzyme converts glutamate to GABA?

Answer 22

Glutamate decarboxylase

Question 23

What excites excitatory area?

Answer 23

Peripheral sensory signals. (Pain signals strongly excite the brain)

Feedback:
Cortex activation (motor/thought) -> REA -> Cortex activation (thalamic feedback does the same)
+ve feedback; any cerebral activity.

Question 24

What are some functional brain imagine techniques used?

Answer 24

Electroencephalography (EEG)

Positron Emission Tomography (PET)

Functional Magnetic Resonance Imaging (fMRI)

Question 25

What are the types of resolution that can be achieved from imagine of the brain?

Answer 25

Spatial resolution which gives accuracy of location in space Temporal resolution which gives accuracy in determining the timing of activity.

Question 26

What is the best method of scanning for spatial resolution? What is the worst?

Answer 26

Worst: EEG Best: PET

Question 27

What is the best and worst scanning method for temporal resolution?

Answer 27

Excellent: EEG Pretty bad: fMRI Terrible: PET

Question 28

What is electroencephalography?

Answer 28

An old technique in which the electrical current moving in the brain is measured via many small electrodes.

Question 29

What are the limitations of EEG?

Answer 29

The current has to flow through both the cranium and the scalp and so changes in electric potential are only detected if they are major.

Question 30

What is EEG good for?

Answer 30

Diagnosing pathologies of electrical activity, sleep abnormalities, coma, confirmation of brain death, psychiatric disorders-gamma rhythm

Question 31

What kind of signals can EEG detect?

Answer 31

Volume currents which become distorted as they follow lines of least resistance through the skull tissue.

Question 32

What do corticothalamal loops tell us? How do they show up on the EEG?

Answer 32

The brain is keeping itself awake which means no external signals are likely activating them (i.e occipital lobe synchronous waves show eyes are closed). they show up as synchronous alpha waves.(8 - 13 Hz)

Question 33

What happens to EEG pattern during deep sleep?

Answer 33

Waves are much larger due to corticothalamal loops. During dreams (REM sleep) the waves are smaller again.

Question 34

What are the types of rhythms of EEG?

Answer 34

Beta rhythm (small amplitude high frequency resulting in alert cortical state) Alpha rhythm (Awake medium amplitude medium frequency waves resulting in awake and relaxed state) Delta rhythm (Large amplitude low frequency which is seen in deep sleep) Gamma rhythm (has very high frequency and is consistent with elevated states of consciousness)

Question 35

What happens when GABA is knocked out?

Answer 35

If you suppress inhibitory signal of GABA you create excitation which is seen as a lower amplitude higher frequency signals.

Question 36

What is a coma?

Answer 36

Widespread cortical damage resulting in loss of consciousness. Damage to ascending reticular activating systems causes permanent sleep

Question 37

What causes seizures?

Answer 37

Brief episodes of abnormal excessive or synchronous neuronal activity in the brain.

Question 38

Above what point of the pons is damage going to induce a coma?

Answer 38

Above the entry of CN5

Question 39

What are the types of seizure effect?

Answer 39

Momentary loss of awareness (absence seizure) Uncontrolled jerking movement (tonic-clonic seizure)

Question 40

How are PET scans conducted?

Answer 40

a "tracer" containing positron-emitting isotopes of organic molecules/compounds is injected intravenously (Fluoridated glucose 18F-FTG) and this flows to area of highest metabolic needs (most active) and so brain activity will use the fluoridated glucose resulting in it showing up on the scan.

Question 41

What are the spatial and temporal resolution of PET scans?

Answer 41

Spatial resolution = 5 - 10mm Temporal resolution = minutes

Question 42

What conditions are PET scans good for diagnosing?

Answer 42

Cancers

Question 43

What does fMRI measure?

Answer 43

Haemoglobin dissociation (Hb:O vs Hb + O) When group of neurons fire more signals they increase their metabolic rate and therefore that creates more oxygenated blood flow to the area and in turn more oxygen dissociation from haemoglobin