L11 Homeostasis in the Nervous Tissue I (Imported from Quizlet)

Glia, capillaries, other neurons, extracellular space

What is the neuronal microenvironment composed of?

Extracellular matrix, brain extracellular fluid (BECF)

What is included in the extracellular space?

Extracellular space

What is the purple/blue in this image?

The ECF that is found within parts of the ventricular system

BECF is used to distinguish from what?

Influence neurons and be influenced by neurons

What can BECF do?

Neuronal dysfunction, neuronal death

What does uncontrolled BECF composition lead to?

Tightly regulated

BECF composition must be __________ _______________

Increased K+ concentration

Changes in Ca2+ concentrations

Changes in O2, glucose and CO2 concentrations

Increased H+ thus acidification

Neurotransmitter concentrations change

How could BECF composition be changed by neuronal activity?

Increased K+ concentration in the BECF could elevate resting potential bringing the cell closer to threshold for firing an action potential

Increased neurotransmitter release

Increased neurotransmitter concentrations could lead to an unspecific neuronal activity

How could a change in BECF composition change neuronal activity?

1. Blood brain barrier

2. Cerebrospinal fluid (CSF) in the ventricular system

3. Neurons

4. Glial cells - focus on astrocytes

How do we regulate the neuronal microenvironment, including BECF?

Dyes pass across leaky capillaries

Stain soft tissues

But not in the brain - no staining

How did the intravenous injection of dyes reveal the blood brain barrier?

To protect neurons from fluctuations in concentrations of substances in the blood

What is the function of the blood brain barrier?

Increased amino acid concentrations after a meal

Increases in K+ and H+ concentrations after exercise

Circulating hormones

Inflammatory mediators

Toxins

What are the examples of some of the fluctuations in concentrations of substances in the blood?

Non selectively activate receptors, exciting or inhibiting neurons

What could increased amino acids do?

Depolarisation of neurons

What does an increased extracellular K+ cause?

Tight junctions between endothelial cells (transcellular route)

Thick basement membrane

Astrocytic endfeet

How is the blood brain barrier (BBB) maintained?

Formation of tight junctions between endothelial cells and may facilitate transport between BECF and blood

What can astrocytes induce?

Facilitated transport (e.g. Glut1)

Exchangers (e.g. Na-H exchanger)

Co-transporters (e.g. cation coupled Cl- transporters, NKCC1)

Increased numbers of mitochondria = active transport

Small, uncharged and/or lipid soluble can pass the BBB more easily (e.g. CO2, O2, nicotine, heroin, caffeine)

How do important molecules get through the BBB?

Choroid plexuses (make cerebral spinal fluid) - ventricular system

Circumventricular organs (green in the image)

What are the 2 leaky regions in the BBB?

Surrounds the ventricles

What does circumventricular stand for?

Ependymal, tight junctions

In these leaky areas of the BBB, ___________ cells beneath have _____ _____________

Hormone release (e.g. hypothalamus and pituitary gland)

Osmoreceptors (e.g. OVLT and SFO, hypothalamus)

Temperature control centres and fever - cytokines (e.g. OVLT)

Why have leaky areas of the BBB?

Open cavities (ventricles an central canal) filled with cerebrospinal fluid

What does the ventricular system contain?

Physical protection - buffer

What does the ventricular system provide?

Appropriate levels of ions

What does the ventricular system maintain?

Waste products

What does the ventricular system remove?

Choroid plexus

Cerebrospinal fluid is secreted by what?

The ventricles and central canal

What does cerebrospinal fluid circulate around?

Subarachnoid space

Cerebrospinal fluid is absorbed from the _____________ _______ to the venous blood system at the superior sagittal sinus

150, 30, 120

~____mls CSF in total, __ in ventricles, ___ in SAS

1400, 50

Cerebrospinal fluid reduces effective weight from _____g to <__g

Accelerating and decelerating injuries

What does cerebrospinal fluid decrease the risk of?

~500mls

How much CSF is produced per day (approx)?

3

How many times a day is CSF replaced?

Capillaries

~30% of CSF is made by what?

Specialised glial cells that line ventricles

What are ependymal cells?

1. Ultrafiltration of plasma into ECF across normal 'leaky' capillaries

2. Selective absorption of substances into CSF across choroidal epithelial cells (have tight junctions)

3. Free movement of substances from CSF to BECF across ependymal cells

Secretion of CSF

What is in CSF

What does this table show?

Pia mater, arachnoid mater, dura mater

What are the 3 types of meninges?

Covers surface of brain and blood vessels and allows diffusion between CSF and BECF

What does the pia mater do?

Cells linked by tight junctions, prevent diffusion between CSF and plasma

What does arachnoid matter have and what does it do?

Thick, inelastic membrane

2 layers - split to form intracranial sinuses

What is the composition of dura mater?

Arachnoid granulations (up to 1cm)

Arachnoid villi

Evaginations of arachnoid membrane

Intracranial pressure

Increased absorption with increased ...?

From ventricles across ependymal cells, from subarachnoid space across the Pia mater

Where does exchange between CSF and BECF occur?

Macronutrients (e.g. Glucose), micronutrients (e.g. vitamins), ions (e.g. HCO3-)

What is exchanged from CSF to BECF?

Metabolic waste products (e.g. CO2), neurotransmitters

What is exchanged from BECF to CSF?

Hydrocephalus

What if CSF cannot circulate properly, what happens?

Dilation of ventricular system

Obstruction in ventricular system or interrupted CSF absorption

Increased intracranial pressure

Loss of cells within the brain

Loss of brainstem reflexes

What happens in hydrocephalus?