Homeostasis in the Nervous Tissue

Question 1

the neuronal microenvironment is composed of…

Answer 1

brain extracellular fluid,
glia,
capillaries,
other neurons.

Question 2

the neuronal microenvironment is regulated by…

Answer 2

the brain blood barrier,
cerebrospinal fluid from choroid plexuses,
and glial cells.

Question 3

what is the purpose of the blood brain barrier?

Answer 3

it protects neurons from fluctuations in concentrations of substances in the blood.

Question 4

what is the purpose of the blood brain barrier?

Answer 4

it protects neurons from fluctuations in concentrations of substances in the blood.

Question 5

what are some examples of substance fluctuations in the blood?

Answer 5

increased amino acid concentration after a meal,
increases in K+ and H+ after exercise,
circulating hormones,
and toxins.

Question 6

how do important molecules get through the blood brain barrier?

Answer 6

facilitated diffusion (glucose) and co-transporters (Na+/K+/Cl-),
and there are lots of mitochondria for active transport / ATP in endothelial cells.

Question 7

how does the blood brain barrier relate to the treatment of CNS disorders?

Answer 7

molecules that are small / uncharged / lipid soluble can pass through the barrier,
disorders like Sz, depression, chronic pain and epilepsy can be treated by small molecule drugs.

Question 8

what is the purpose of having leaky areas in the blood brain barrier?

Answer 8

for hormone release,
osmoreceptors,
and for temperature control centres.

Question 9

cerebrospinal fluid regulates the composition of…

Answer 9

brain extracellular fluid.

Question 10

describe the flow of cerebrospinal fluid.

Answer 10

fluid starts in the 2 lateral ventricles secreted by choroid plexus,
the fluid circulates around the ventricles and central canal,
then is absorbed from subarachnoid space into the blood system.

Question 11

the Meninges are a layer in what space?

Answer 11

a layer in the subarachnoid space.

Question 12

what are the layers of Meninges that surround the brain tissue and Spinal Cord?

Answer 12

Pia mater,
Arachnoid mater,
and Dura mater.

Question 13

what is the Pia mater?

Answer 13

it covers the surface of the brain and blood vessels, allowing for diffusion between cerebrospinal fluid and brain extracellular fluid.

Question 14

what is the Arachnoid mater?

Answer 14

cells linked by tight junctions preventing diffusion between cerebrospinal fluid and plasma.

Question 15

what is the Dura mater?

Answer 15

is thick, inelastic membrane that splits into 2 layers to form intracranial sinuses.

Question 16

how are substances exchanged between cerebrospinal fluid and brain extracellular fluid.

Answer 16

across the Pia mater into subarachnoid space,
across ependymal cells linking to the ventricles,
the cerebrospinal fluid is also a ‘waste management’ system.

Question 17

what is hydrocephalus?

Answer 17

dilation of the ventricular system caused by an obstruction somewhere in the ventricular system,
causes an increase in intracellular pressure and can lead to a loss in brain cells or Brainstem reflexes.

Question 18

what is the process of absorption of cerebrospinal fluid in the sinus?

Answer 18

the subarachnoid spaces pushes through arachnoid mater into the sinus,
this is called arachnoid granulation,
if pressure is higher in the cerebrospinal fluid than in the venous blood then the fluid will move out of the subarachnoid space and into the sinus.

Question 19

what are the steps of cerebrospinal secretion?

Answer 19

ultrafiltration of plasma into the extracellular fluid,
osmotic and hydrostatic pressure drives substances out of the capillaries and into extracellular fluid,
ion transfer drives water into cerebrospinal fluid,
and K+ are absorbed back into extracellular fluid.

Question 20

what is astrocytic syncytium?

Answer 20

cells of different astrocytes are coupled together by gap junctions – electrically coupled.

Question 21

what are gap junctions?

Answer 21

2 proteins (1 in one cell membrane, 1 in another) that an join together to form a continuous pore.

Question 22

how can astrocytes communicate with blood vessels, such as arterioles and capillaries?

Answer 22

astrocytic end feet bind to the arteriole and can influence how contracted or dilated the smooth muscle is.

Question 23

in relation to astrocytes and blood vessels, what happens if the firing rate increases?

Answer 23

the astrocyte’s Ca2+ rate increases,
causing the release of vasoactive substances from astrocytes,
and the blood vessel diameter increases.

Question 24

name two types of functional imaging techniques:

Answer 24

PET scan and fMRI.

Question 25

CT and MRI scans form what image, but can’t measure what?

Answer 25

computed tomography and magnetic resonance imaging techniques allow for 3D structural images of the brain, but they don’t measure brain activity.

Question 26

CT and MRI scans form what image, but can’t measure what?

Answer 26

computed tomography and magnetic resonance imaging techniques allow for 3D structural images of the brain, but they don’t measure brain activity.

Question 27

active neurons need what?

Answer 27

glucose and oxygen.

Question 28

more blood flow if directed to what areas?

Answer 28

active areas.

Question 29

PET and fMRI scans detect the changes in what?

Answer 29

subsequent changes in blood flow.

Question 30

how do PET scans work?

Answer 30

add positron emitting isotopes into reagents, like glucose,
the decay of the isotopes causes emission of 2 positrons in opposite directions,
gamma ray detectors in the scan machine register these positrons.

Question 31

what are some cons of PET scans?

Answer 31

the images produced have low spatial resolution, showing the activity of many cells,
the risk of radiation.

Question 32

how do fMRI scans work?

Answer 32

uses electromagnetic waves to disrupt the state of H atoms,

oxyhaemoglobin and deoxyhaemoglobin distort the magnetic resonance properties of H atoms differently.

Question 33

what are some pros of fMRI scans?

Answer 33

the scan process is faster,
it is non-invasive,
and has better spatial resolution.

Question 34

how do astrocytes maintain homeostasis?

Answer 34

by terminating neurotransmitters at the tripartite synapse,

they also recycle neurotransmitters to presynaptic terminals.