BP exam 2 SAQs

1a) Who discovered the BBB?

1a) Paul Ehrlich

1b) What role do astrocytes play in forming the BBB?

1b)

• surround capillaries in CNS

• & secretes chemical that causes tightening

1c) why is there reason for leaky (weakened) areas in the BBB?

1c)

• homeostasis

• pituitary gland: endocrine and hormone reg

• pineal glad: melatonin release

• area postrema: toxicity monitor (vomitting)

2a-1) intermittent, low lvl depolarization (less neg) that creates small, short-lived changes in potential across axonal membrane—what are the changes called?

2a-1)

• graded potentials

• sub threshold events that aren’t strong enough to travel long distance

2a-2) Why was an AP not produced with low lvl depolarizing stimulation?

2a-2)

• threshold potential not reached

• need to depolarize (less neg) to open voltage-gated Na+ channels

2b-1) Then: more depolarizing stimulation is applied to giant squid axon and an AP is produced.

Why do the actions of the ion channels and movements across the axonal membrane cause the depolarization phase (the upsweep) of the AP and subsequent return to resting potential?

2b-1)

1. threshold reached to open voltage-gated Na+ channels (rapid)

2. upsweep (depolarization - less neg)

3. THEN: Na+ inactive & K+ channels open & flow

4. repolarization

5. delayed K+ close

6. hyperpolarization (more neg)

7. resting potential restored

3a) When neuron receives natural stimulation (from other neurons), why do APs first form at the axon hillock and not in the dedrites or the soma of a neuron?

3a)

• @ axon hillock bc high density (voltage-gated Na+ channels)

• EPSPs formed & detected here to determine if threshold reached

Not in dendrite or soma bc:

• ligand-gated channels w little/no voltage-gated channels to start AP

3b) Why does the size of AP remain same as it travels down unmyelinated axon?

3b)

• regenerative = continuous conduction bc of depolarizaiton (less neg) voltage-gated Na+ channels that trigger new AP

3c) If you place a stimulated electrode inside of a long axon midway b/w the soma of a neuron and the axon terminal (end foot) and provide sufficient stimulation to cause an AP, what direction would the AP travel?

3c)

• both directions bc middle stimulated

  • surrounding tissues not in refractory pd

3d) How would the shape of an AP change if you were to treat the axon w/ a chemical that selectively blocked voltage-gated K+ channels w/out altering the activity of any other channels?

3d)

• repolarization (reset) slowed bc depolarization (less neg) prolonged

• AP would have:

  • slower down slope (repolarization)

    • or incomplete repolarization

  • wider shape (longer duration)

  • risk of Na+ channels not working and K+ channels causing neuron dysfunction bc of it