Homeostasis in the Nervous Tissue 1 & 2

Question 1

Explain why the composition of brain extracellular fluid (BECF) must be tightly regulated

Answer 1

-The BECF can influence neurons and be influenced by neurons
-Uncontrolled, this can lead to neuronal dysfunction and neuronal death

Question 2

Explain the purpose and structure of the blood brain barrier

Answer 2

-The BBB is there to protect neurons from fluctuations in concentrations of substances in the blood
-Tight junctions between endothelial cells
-Thick basement membrane
-Astrocytic endfeet
-There are leaky areas of the BBB, choroid plexus and circumventricular organs

Question 3

Describe the function of cerebrospinal fluid (CSF)

Answer 3

-Provides physical protection (buffer)
-Maintains appropriate levels of ions
-Removes waste products

Question 4

Describe the ventricular system and the flow of CSF

Answer 4

4 ventricles that include 2 lateral ventricles (1 in each cerebral hemisphere), the third ventricle in the diencephalon, and the fourth ventricle in the hindbrain

CSF to BECF
-Macronutrients e.g. glucose
-Micronutrients e.g. vitamins
-Ions e.g. HCO3

BECF to CSF
-Metabolic waste products e.g. CO2
-Neurotransmitters

CSF secreted by choroid plexus, circulates around the ventricles and central canal

Absorbed from the subarachnoid space to the venous blood system at the superior sagittal sinus

Question 5

Explain how neurons and astrocytes regulate BECF

Answer 5

-Neurons and astrocytes terminate neurotransmission at the tripartite synapse
-Neurons and astrocytes remove K+ from the extracellular space
-Increases in extracellular K+ affect astrocyte function
-Astrocytes can share with neurons the energy stored in glycogen, but not by the direct release of glucose into the BECF. Instead, astrocytes break glycogen down to glucose and even further to lactate, which is transferred to nearby neurons where it can be aerobically metabolised

Question 6

Explain how astrocytes behave functionally like a syncytium and the benefits of this

Answer 6

-Astrocytic syncytium allows spatial buffering
-Gap junctions create a syncytium
-Redistributes K+ to areas of decreased activity
-Astrocytes’ ability to function as a syncytium enables coordinated activity and communication between these cells, providing essential support and regulation of brain function

Question 7

Describe the relationship between astrocytes, neurons and blood vessels

Answer 7

-Blood vessels in the brain are closely regulated by astrocytes and neurons to ensure a constant supply of oxygen and nutrients to support neuronal activity
-Astrocytes, neurons, and blood vessels work together to regulate brain function by ensuring an adequate supply of oxygen and nutrients to neurons, removing waste products and toxins, and maintaining the proper balance of ions and other substances in the brain

Question 8

Recall two types of functional imaging techniques

Answer 8

PET - exploits glucose use
fMRI - exploits oxygen use
(active neurons need more oxygen and glucose)