Flashcards in Principles of Neuroscience Lecture 16 Homeostasis Deck (31)
How is blood pressure maintained at a near constant rate?
Changing the heart rate
What factors affect blood pressure?
Why is regulation of blood pressure important? (2)
We need to keep a constant blood flow to the brain
High blood pressure damages blood vessels
How is blood glucose level regulated?
Insulin and glucagon
What is cellular homeostasis in a neuron?
What must be maintained?
Regulation of synthesis of ion channels & GPCR etc. -> controlling the excitability.
Stretch of a cell can damage it
Too many ion channels changes the excitability of a cell
How do some organisms maintain cell volume? How does this relate to maintenance of neuron volume?
Osmoconformers change their internal concentration so they are in equilibrium with the environment. In this way there is no movement of water in or out of the cell.
This is done by taking in or excreting electrolytes
Making osmolytes (longer term)
This is not a option for neurons, because changing the concentration of electrolytes changes the excitability of the cell
What is osmolality?
This is the electrolyte-water balance in the body
Describe the differences in osmolality among different species. What dictates plasma osmolality in these organisms?
Sharks have high osmolality
Fresh water animals have low osmolality
Terrestrial animals are somewhere in the middle
Exercise affects ... ?
Failure to ... Causes ... In osmolality when exercising
Rehydrate during exercise
Increased osmolality when exercising leads to ...
Reduced mental and physical performance
Differentiate between hypertonicity and hypotonicity
Hypertonicity: too much solute / salt
Hypotonicity: too much water
What does the body do to reduce hypertonicity?
What shouldn't be done, why?
(Reduce appetite for salt)
Increased water retention
Drinking more water doesn't really do much good becaus it increases your volume and thus blood pressure
What does the body do to reduce hypotonicity?
Increase salt retention
Increased salt appetite
Increase urine production
Give a rough outline of neural control of osmolality
Gut -> (vagus) -> CNS -> Kidneys
Which areas in the brain are important for osmolality regulation? Differentiate between the two
Frontal cortex: perception of thirst
Lamina Terminalis: sensor of osmolality
Name a few important regions within the Laminate terminalis
What do these nuclei do?
They swell or shrink according to whether we are hypo or hyperosmolar. This is detected, and they increase or decrease their firing activity. This information is sent to the hypothalamus for regulation and the Insula cortex for the perception of thirst
What is the main function of the region of the frontal cortex that deals with osmoregulation?
It tells us that we are thirsty so that we will drink more
It is fed information about osmolality from the Lamina Terminalis
What is special about SFO & OVLT? Where are they located?
SFO and OVLT have leaky blood brain barriers, so stuff from the blood can come in contact with these cells.
In this way, the composition of the blood can be detected
What is the function of SON?
Where is it?
The SON is in the hypothalamus
It contains magnocellular neurons that release AVP down into the posterior pituitary to be released into the blood stream
How do neurons detect changes in osmolality?
They fire more rapidly when the cell is shrivelled due to an increase in osmolarity
Decrease in osmolarity -> cell swells -> decreased firing rate
When the osmolality of the external environment of the sensory neurons in the Lamina Terminalis increases, firing rate ...
Change in osmolality results in: (3)
1. Change in cell size
2. Change in volume
3. Change in ionic strength
When osmolality detector cells swell/ stretch, they ... their activity.
These cells stretch when ...
Decrease their activity
The individual is hypo osmolar
When osmolality detector cells shrivel, they ... their activity
These cells shrivel when ...
The individual is hyper-osmolar
The change in activity of the osmolality detector cells is due to ...
Trp channels associated with the cytoskeleton
How do the osmolality receptor cells bring about change in osmolality?
Trp channels open when the cell shrivels. Sodium rushes in and the conductance of the cell increases
Describe how AVP is released
1. The OVLT osmolality receptor cells signal to Magnocellular neurons in the hypothalamus: SON, PVN
2. These neurons make AVP
3. AVP is transported down the axon to the posterior pituitary
4. At the lobe at the bottom of the posterior pituitary, the neurons release AVP into the capillary bed.
5. The hormone circulates to the collecting ducts in the kidneys
Which hormone is important for osmoregulation
How does AVP bring about a change in osmolality
1. Circulates in blood to the kidney
2. Bonds to receptors on the cells of the collecting duct
3. Signal transduction pathway, second messengers etc.
4. Aquaporin proteins are synthesised by ER, embedded in the membrane
5. Vesicles transport the aquaporins to the membrane.
6. Water moves out of the collecting duct, back into the blood