Homeostasis in the nervous system

Question 1

What is the neuronal microenvironment composed of ?

Answer 1

Glia
Capillaries
Neurons
Extracellular space

Question 2

What is extracellular space composed of?

Answer 2

Extracellular matrix
Brain extracellular fluid (interstitial fluid)

Question 3

What can uncontrolled neuronal influence of brain extracellular fluid lead to?

Answer 3

Neuronal dysfunction
Neuronal death

Question 4

How can neuronal activity change the composition of the BECF?

Answer 4

Increase K+ conc
Changes in Ca+ conc
Changes in O2, glucose and CO2 conc
Increase in H+,, leading to acidifcation

Question 5

How could a change in BECF composition change neuronal activity?

Answer 5

Increase in K+ conc can elevate resting potential
-> Brings the cell closer to ap firing potential, increasing neurotransmitter release

Question 6

How is the neuronal microenvironment regulated?

Answer 6

Blood brain barrier
CSF in ventricular system
Neurons
Glial cells

Question 7

How was the blood brain barrier identified?

Answer 7

Intravenous injection of dyes
- Dyes pass across leaky capillaries
- Stain soft tissue
- No staining in the brain

Question 8

Why does the brain not get stained?

Answer 8

The capillaries are less leaky than those in the spinal cord

Question 9

Function of brain blood barrier

Answer 9

Protect neurons from fluctuations in concentrations of substances in the blood

Question 10

How is the brain blood barrier maintained?

Answer 10

Tight junctions between endothelial cells
Thick basement membrane
Astrocytic endfeet

Question 11

How do endothelial cells maintain the brain blood barrier?

Answer 11

Prevents paracellular diffusion of materials

Question 12

How does the thick basement membrane maintain the bbb?

Answer 12

Acts as a physical barrier

Question 13

How do astrocytic end feet maintain the bbb?

Answer 13

Interact with blood vessels and form a capsule

Question 14

What is the difference between an exchanger and a cotransporter?

Answer 14

Exchanger is in opposite directions, cotransporters are in the same direction

Question 15

What molecules pass the bbb easily?

Answer 15

Small, uncharged or lipid soluble molecules

Question 16

What is an example of a facilitated transporter in bbb?

Answer 16

Glut1

Question 17

What is an example of an exchanger in bbb?

Answer 17

Na - H exchanger

Question 18

Where is cerebrospinal fluid produced?

Answer 18

Choroid plexuses

Question 19

What are the circumventricular organs function?

Answer 19

Form tight junctions (in the form of ependymal cells) beneath the blood vessels

Question 20

Why are there leaky areas of the bbb?

Answer 20

To allow secretion of hormones
Osmoreceptors
Temperature control centres

Question 21

Function of the ventricular system?

Answer 21

Increased buoyancy
Physical protection
Maintains appropriate level of ions
Removes waste products

Question 22

How does the ventricular system increase the buoyancy of the brain?

Answer 22

The brain doesn’t move with full weight when moving around

Question 23

What does the cerebral aqueduct lead to?

Answer 23

The 4th ventricle where it thins through the medulla and becomes the central canal

Question 24

What is in CSF?

Answer 24

Electrolytes
Amino acids
Proteins
Osmolality

Question 25

What is exchanged between CSF and BECF?

Answer 25

Macronutrients Micronutrients Ions

Question 26

What is exchanged between BECF and CSF?

Answer 26

Metabolic waste products Neurotransmitters

Question 27

What areas does the CSF circulate around?

Answer 27

- 3rd ventricle - 4th ventricle - central canal - foramens - outer brain - sinuses - venus system

Question 28

What happens to CSF at the superior sagittal sinus?

Answer 28

CSF is absorbed from the subarachnoid space into the venous blood system

Question 29

How much CSF is produced a day?

Answer 29

500 mls

Question 30

What is an ependymal cell?

Answer 30

A specialised glial cell that line the ventricles

Question 31

What are the stages of CSF secretion?

Answer 31

1. Ultrafiltration of plasma into ECF across normal 'leaky' capillaries 2. Selective absorption of substances into csf across choroidal epithelial cells 3. Free movement of substances from CSF to BECF across ependymal cells

Question 32

What are the 3 types of meninges?

Answer 32

Pia mater Arachnoid mater Dura mater

Question 33

Describe pia mater

Answer 33

Covers the surface of brain and blood vessels and allow diffusion between CSF and BECF

Question 34

Describe arachnoid mater

Answer 34

Cells linked by tight junctions preventing diffusion between CSF and plasma

Question 35

Describe dura mater

Answer 35

Thick inelastic membrane with 2 layers split to form intercranial sinuses Prevents too much movement

Question 36

How do things enter the dura mater?

Answer 36

Arachnoid granulations push through dura mater

Question 37

What is the mechanism of csf absorption?

Answer 37

Arachnoid granulations push up through the dura matter into the venous sinus - The csf is transported in vesicles driven by pressure build up

Question 38

What is hydrocephalus a result of ?

Answer 38

Dilation of ventricular system Obstruction in ventricular system Interrupted csf absorption

Question 39

What are the symptoms of hydrocephalus?

Answer 39

Increased intercranial pressure Less of brain cells Loss of brainstem reflexes

Question 40

Where do neurons and astrocytes terminate transmission?

Answer 40

Tripartite synapse

Question 41

How is neurotransmission terminated?

Answer 41

Neurotransmitters are removed from synaptic cleft and recycled Via neurons and astrocytes

Question 42

How is glutamate neurotransmission terminated?

Answer 42

EEAT transports glutamate back into the cell for recycling Astrocytes convert glutamate to glutamine

Question 43

What is the main excitatory neurotransmitter?

Answer 43

Glutamate

Question 44

What occurs if glutamate is left in the cleft?

Answer 44

Excitotoxicity

Question 45

How is K+ removed from extracellular space?

Answer 45

Astrocytes and neurons Sodium potassium ATPase pump, moves against gradient back into the cell

Question 46

What happens when astrocytes sense high K+ in ECF?

Answer 46

Convert glucose into lactate to excite neurons

Question 47

How does extracellular K+ affect astrocyte function?

Answer 47

Astrocytes drive K+ into ECF Can drive K+ to be taken up in the cell, increasing glucose metabolism More glucose allows better K+ uptake via ATPases

Question 48

Why do neurons have a resting membrane potential of -65mV and glia have -85mV?

Answer 48

Neuronal membranes are more permeable to Na+ than astrocytic membranes Astrocytes are more sensitive to extracellular K+ changes

Question 49

What creates a syncytium?

Answer 49

Astrocytes coupling to each other via gap junctions

Question 50

How is a gap junction formed?

Answer 50

Connexins form a connexon on 1 membrane 2 connexons in different membranes form a gap junction.

Question 51

What is spatial buffering?

Answer 51

Regulation of extracellular potassium concentration

Question 52

What is neurovascular coupling?

Answer 52

Neurons are coupled to vasculature

Question 53

Describe the process of neurovascular coupling

Answer 53

Increased neuron firing rate leads to an increase in astrocyte Ca2+ levels -> Leads to a release of vasoactive substances from the astrocyte -> Blood vessels and diameter change

Question 54

What do MRI allow imaging of ?

Answer 54

3d structural images of the brain

Question 55

What is the function of a PET scan?

Answer 55

Exploits the use of glucose

Question 56

What is the function of an fMRI scan?

Answer 56

Exploits the use of oxygen

Question 57

What is BOLD in terms of fMRI?

Answer 57

Blood Oxygenation Level Dependent

Question 58

What state is the person undergoing fMRI in?

Answer 58

Unconscious state