homeostasis in the nervous tissue Flashcards
what is the relationship between brain extracellular fluid (BECF) and activity in a neuron?
they influence each other - change in BECF influences activity in a neuron and vice versa
therefore BECF composition must be tightly controlled
what happens if BECF is not tightly controlled?
neuronal dysfunction / neuronal death
how could a change in BECF composition change 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 leading to unspecific receptor activation
what is the function of the blood brain barrier?
to protect neurons from fluctuations in concentrations of substances in the blood
how is the blood brain barrier maintained?
- tight junctions between endothelial cells
- thick basement membrane
- astrocytic endfeet (ends of astrocytes)
how do important molecules get through BBB?
- facilitated transport
- exchangers
- co-transporters
- increased numbers of mitochondria = active transport
- small, uncharged, lipid soluble can pass through
what are the leaky regions of the BBB?
- choroid plexuses - part of ventricular system where cerebrospinal fluid is made
- circumventricular organs
why are there leaky areas of the BBB?
- hormone release (from hypothalamus and pituitary gland)
- osmoreceptors (brain needs to know fluid levels)
- temperature control centers and fever
how do we regulate neuronal microenvironment, including BECF?
- blood brain barrier
- cerebrospinal fluid in ventricular system
- neurons
- glial cells (esp astrocytes)
what is exchanged from CSF to BECF?
- macronutrients e.g. glucose
- micronutrients e.g. vitamins
- ions
what is exchanged from BECF to CSF?
- metabolic waste products e.g. CO2
- neurotransmitters
what is the flow of cerebrospinal fluid?
- secreted by choroid plexus (leaky part of BBB)
- circulates around ventricles and central canal
- absorbed from the subarachnoid space to the venous blood system at the superior sagittal sinus
what are the 3 types pf meninges?
- pia mater - innermost membrane, very thin, leaky
- arachnoid mater - tight junctions so selective
- dura mater - tough, outermost layer
how is CSF absorbed?
absorbed through arachnoid granulations and arachnoid villi
what happens if CSF cannot circulate properly?
hydrocephalus
- obstruction in ventricular system causes build up of CSF in brain
- pushes down on brain stem causing death of cells and loss of brainstem reflexes
what are the two main functions of the CSF?
- protection
- regulation of ions
what is the function of neurons and astrocytes in regulating neuronal microenvironment?
- terminating neurotransmission at the tripartite synapse
- remove K+ from the extracellular space
how do neurons and astrocytes terminate neurotransmission at the tripartite synapse?
transporters which absorb neurotransmitters into the cell which are then recycled
how do neurons and astrocytes remove K+ from the extracellular space?
Na+/K+ ATPase pump moves K+ inside the cell against conc. gradient
how do astrocyte membrane potentials vary from neurons?
neurons resting potential = -65mc
glia resting potential = -85mv
why do astrocytes and neurons have different resting membrane potentials?
- neuronal membranes are more permeable to Na+
- astrocytes have higher K+ selectivity
how do astrocytes get rid of potassium to maintain conc. gradient?
astrocytes couple to each other and form syncytium (gap junctions)
- redistributes K+ to areas of decreased activity
what does syncytium do?
- allow redistribution of K+
- neurovascular coupling
what is neurovascular coupling?
coupling of neurons to vascular system (arterioles)
1. increased neuron firing
2. increased Ca2+ in astrocytes
3. release of vasoactive substances from astrocyte
4. blood vessel diameter changes
two types of functional imaging techniques to view the brain?
positron emission tomography (PET) - exploits glucose use
functional magnetic resonance imaging (fMRI) - exploits oxygen use
