6

Question 1

why are the brain and the spinal cord protected from the general circulation in the body?

Answer 1

the ionic composition of the extracellular fluid around the neuron must be carefully controlled:
- cannot change the excitability of the membrane (eg with KCl injection > decreased K+ conc gradient > depolarisation > inactivation of the Na+ channel > no more AP produced)
- cannot have neurotransmitters floating around for no reason

Question 2

how are the brain and the spinal cord protected from the general circulation in the body?

Answer 2

through the Blood-Brain Barrier (BBB)

Question 3

describe the BBB

Answer 3

2 fold entity between:
- blood vessels and interstitial fluid
- blood vessels and cerebrospinal fluid (CSF)

Question 4

interstitial fluid

Answer 4

fluid bathing the neurons

Question 5

CSF

Answer 5

fluid in the ventricles

Question 6

why are the interstitial fluid and CSF considered mixable?

Answer 6

there is virtually free movement between these two due to diffusion, causing chemical composition to be almost identical

Question 7

Parkinson’s disease

Answer 7

• problems with dopamine and its associated receptors which result in muscle stiffness and dystonia (twitching, repetitive movements)
• you can’t simply inject patients with dopamine as it doesn’t readily cross the BBB
• L-DOPA is given instead. this is a precursor to dopamine that crosses the blood-brain barrier and gets converted once in there

Question 8

MSG

Answer 8

mono-sodium glutamate:
- leads to thirstiness and stiff neck
- cannot readily cross BBB but can activate glutamate receptors outside the brain and nervous system

Question 9

is the BBB continuous? why/why not?

Answer 9

no, though most of the brain is protected by it
- at some places it is essential for neurons to communicate freely with the bloodstream (eg hypothalamus)

Question 10

2 places in which the BBB is broken

Answer 10

• pituitary gland (releases hormones) is directly connected to the hypothalamus > thus, BBB is purposely broken to allow release of hormones
• circumventricular organs (around 3rd ventricle) the BBB is broken so neurons can sense specific chemical concentrations

Question 11

generally, BBB is broken in areas that

Answer 11

interact with the endocrine system or require sensitivity to metabolites in plasma

Question 12

3 types of brain encasings

Answer 12

• scull
• meninges
• reticular formation

Question 13

meninges

Answer 13

• Dura Mater
• arachnoid membrane
• pia mater
• subarachnoid space

Question 14

dura mater

Answer 14

very tough membrane, sac containing the brain and the spinal cord

Question 15

arachnoid membrane

Answer 15

much more delicate tissue

Question 16

pia mater

Answer 16

lies right on top of the brain; tethered to arachnoid by arachnoid ‘trabeculae’

Question 17

subarachnoid space

Answer 17

between the arachnoid membrane and Pia mater;
filled with CSF so the brain floats to protect from mechanical stress

Question 18

label a sectional view of the meninges of the brain

Question 19

reticular formation

Answer 19

a diffuse network of nerve pathways in the brainstem connecting the spinal cord, cerebrum, and cerebellum, and mediating the overall level of consciousness.

Question 20

how is the BBB placed in the subarachnoid space?

Answer 20

in between the blood vessels (capillaries to the brain tissue) and the brain tissue

Question 21

distinguish between typical capillaries and capillaries in the brain

Answer 21

• in endothelial lining of blood vessels, most contain large gaps (fenestrations) through which molecules can pass
• in the brain, endothelial cells are tightly bound leaving no gaps > this constitutes the BBB (everything has to be transported)

Question 22

label a diagram of the ventricles of the brain

Question 23

ventricles

Answer 23

cavities deep inside the brain filled with CSF to cushion the brain

Question 24

describe the structure/layout of the ventricles

Answer 24

• there is a large curving Lateral Ventricle (LV) inside each cerebral hemisphere
• the LV empties into the 3rd ventricle, right in the middle, deep in the brain under the cerebral hemisphere
• the 3rd ventricle communicates via a channel called ‘Aqueduct of Sylvius’ to the 4th ventricle
• from the 4th ventricle, we have the ‘Central Canal’ which goes in the middle of the spinal cord

Question 25

Ventricles - CSF

Answer 25

- CSF produced in the ventricle drains through the ventricle of the central canal - CSF then moves to outer parts of the brain (subarachnoid space) and finally exits at the top of the brain into large venous sinus (on the midline) - all the CSF eventually drains into either venous sinus or veins somewhere along the line - 1/2 CSF drains through 'Arachnoid villi' into the venous system

Question 26

arachnoid villi

Answer 26

out-pouching of the arachnoid tissue: - sticks out through dura matter into the venous sinus - allows CSF to drain into the venous system

Question 27

define the CSF and its contents

Answer 27

the bathing medium of the brain, containing highly regulated ionic content with few macromolecules

Question 28

how is the CSF produced?

Answer 28

from plasma by 'choroid plexus' which lines the ventricles (LV, 3rd, 4th)

Question 29

does the choroid plexus produce all CSF?

Answer 29

no; it produces some, but not all. some is produced in the capillaries inside the brain

Question 30

describe the choroid plexus

Answer 30

- made up of epithelial cells connected by tight junctions - dense network of capillaries ballooning out into the ventricular wall with tight junction so that everything has to be transported - produces CSF continuously (550 ml/day) to circulate (this is a cleansing mechanism)

Question 31

stats on the CSF

Answer 31

- has same osmolarity and [Na+] as blood - greatly reduced [K+], [Ca2+] and [Mg2+] - total volume on an average person is 215ml - cranial CSF is 140ml (25ml in ventricles, 115ml in subarachnoid space) and the spinal CSF is 75ml

Question 32

lumbar puncture

Answer 32

- also known as a spinal tap - a diagnostic, therapeutic procedure - collect sample of cerebrospinal fluid for analysis

Question 33

astrocytes

Answer 33

star-shaped glial cell of the central nervous system

Question 34

describe the walls of capillaries

Answer 34

- plastered with the 'end feet' of glial cells, particularly astrocytes - this provides a bridge between neurons and blood vessels

Question 35

how are the features of astrocytes useful to their placement?

Answer 35

- efficient at glycolysis - produce lactate as an end-product, which is used as a substrate for ATP production in neurons

Question 36

2 functions of astrocytes

Answer 36

- remove neurotransmitters - provide energy substrates for neurons and more

Question 37

how do astrocytes regulate local blood flow?

Answer 37

- astrocytes are already bridging the gap between BV and neurons, so they are in a good spot to signal BV when to dilate and to constrict (increase/decrease blood flow) - astrocytes have connection with the neuron at the synapse and when they detect increased signalling, they can send a metabolic signal outward to BV (opposite to nutrient flow), signalling neuronal activity level

Question 38

the effect of glutamate in synapses

Answer 38

- triggers Ca2+ release within astrocytes - Ca2+ wave travels through astrocytes and triggers prostaglandin (PGE2) release at end-foot - PGE2 causes vasodilation, leading to increased blood flow