PHYS: EEG & Regulation of Cortical Excitability

Question 1

How do our lower centres keep us awake, and in what 2 forms of cortical stimulation?

Answer 1

• Brainstem keeps cortex awake by passing excitatory impulses into our cortex.

2 forms:

1. Direct neuronal stimulation - neurons that dump them.
2. Neurohormonal systems - diffuse out of synapses/spill over of NTs.

Question 2

• The reticular formation in the brain controls what?
• It has ____ and ____ areas.

Answer 2

• General area/system for control of the overall excitation level of the brain.
• In the reticular formation of pons & midbrain.
• Reticular system has both inhibitory and excitatory areas.

Question 3

Explain the reticular excitatory area and its function.

Answer 3

Sends signals upwards and downwards:

• Upward through thalamus:
  
  1. Rapid transmission (milliseconds) to excite cerebrum through gigantocellular neurones (ACh)
  2. Build up progressively (seconds to minutes) through large number of smaller neurons, also excitatory (NA, Dopamine) - controls longer term excitation of brain
• Downwards antigravity muscles:
  
  • maintains tone
  • controls levels of spinal reflexes

Question 4

Explain the reticular inhibitory area and its function

Answer 4

• Located in reticular formation of medulla
• Inhibits excitation of REA via serotonergic projections
  
  • Seratonin is inhibitory here

Question 5

Which 4 systems are involved in neurohormonal control?

Answer 5

• Noradrenaline system (locus coeruleus)
  
  • excitatory, wakefulness and non-REM sleep
• Dopamine system (substantia nigra, arcuate, VTA)
  
  • excitatory/inhibitory (region dependent)
• Serotonin system (raphe nuclei)
  
  • inhibitory, induction of sleep, pain control, mood
• Acetylcholine system (gigantocellular neurons)
  
  • excitatory, acutely awake, excited nervous system and REM sleep.

Question 6

Match the neurohormonal modulatory systems to the diagrams

Answer 6

Question 7

What are the most abundant excitatory and inhibitory neurotransmitters in the CNS?

Answer 7

Glutamate

• Most abundant excitatory NT in CNS
• binds NMDA or AMPA receptors (both ionotropic).
• GABA precursor (requires glutamate decorboxylase).

GABA

• Chief inhibitory NT in CNS.
• Binds GABA_A (Cl- Channels) or GABA_B (GPCR -> K+ channel) receptors.

Question 8

What excites the excitatory area?

Answer 8

• Peripheral sensory signals
  
  • pain signals strongly excite the brain’s attention
• Feedback (once away this keeps us awake)
  
  • Cortex activation (motor/thought) –> REA –> cortex acviation (thalamic feedback also)
  • +ve feedback; any cerebral activity –> awake mind
  • Corticothalamic loops fires up fires down fires up fires down

Question 9

What are the normal EEG patterns?

Answer 9

• Beta rhythm
  
  • Alert/aroused/concentrating/REM sleep
  • Small amplitude, High frequency.
• Alpha rhythm
  
  • Awake relaxed/eyes closed
  • medium amplitude medium frequency
• Delta rhythm
  
  • Deep sleep
  • large amplitude low frequency
• Gamma rhythmn
  
  • higher cognitive/attentional state
  • very high frequency

Question 10

How are EEGs used clinically?

Answer 10

• Coma
  
  • Widespread cortical damage.
    
    • Consciousness requires functioning cortex.
  • Damage to ascending reticular excitatory area.
• Seizures
  
  • Brief episodes of abnormal excessive or synchronous neuronal activity in the brain.

Question 11

• What does fMRI do?
• Spatial resolution: good/bad?
• Temporal resolution: good/bad?

Answer 11

• Measures oxygenated blood flow and hence functional usage of bloow flow
• Spatial resolution good, temporal resolution bad
  
  • although unclear whether precise