Lecture 10 - continues Flashcards
What are meninges?
3 layers that protect the outside of the brain and the spinal cord
What are leptomeninges?
- pia mater - super pliable and thin membrane that is quite permeable
- arachnoid mater - further towards outside. Contains tight junctions - things selectively move through it
Describe how leptomeninges have a different membrane
thinner membrane
What is the 3rd meninge?
dura mater - much thicker - for structure. Bits of the arachnoid space push into dura mater
Describe absorption of CSF
Evaginations of arachnoid membrane:
- arachnoid translations (up to 1cm)
- arachnoid villi
Increased absorption with increased intracranial pressure
Bulk movement of CSF across the cell in a vesicle into venous sinus. This is driven by pressure. The more CSF made, the higher the pressure and therefore the higher the movement of CSF transported
What if CSF cannot circulate properly?
Hydrocephalus
- 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
CSF isn’t able to leave the ventricles & starts pressing on other brain tissue around it
if caught early enough, it can be drained
What is the function of CSF?
physical function - buffering/preventing
practical function - remove waste and provide nutrients
What terminates neurotransmission at the tripartite synapse?
Neurons & astrocytes
- can recycle neurotransmitters to presynaptic terminals
- in astrocytes there is a glutamate transports that take glutamate out of the synapse. They are capable of converting glutamate to glutamine, which is less likely to be used as a neurotransmitter
How do neurons & astrocytes remove K+ from the extracellular space?
sodium potassium ATPase regulates the potassium in the extracellular space
How does increased extracellular K+ affect astrocyte function?
- increased glucose metabolism
- increased K+ uptake
- astrocytes are able to increase glucose metabolism which can help neurons, as they uptake K+
How do astrocyte membrane potentials vary from neurons?
- the equilibrium potential for K+in both neurons & glia is about -90mV
Why do neuron have a resting membrane potentials of -65mV and glia hybrid a resting membrane potentials of -85mV?
- neuronal membranes are more permeable to Na+ than astrocytic membrane
- astrocytes have high K+ selectivity than neurons
- the more selective av membrane is to K+, the more extracellular K+ will influence Vm
- astrocytes are more sensitive to extracellular K+ changes
How does astrocytic syncytium allows spatial buffering?
- gap junctions create a syncytium
- redistributes K+ to areas to decreased activity
- can also transport sugars, amino acids, cAMP, Ca+
- nearby astrocytes will uptake K+ and pass it through gap junctions to distant areas. The K+ is being pushed into the extracellular space in high concentrations by a neuron.
This is called ‘Spatial buffering’
What is neurovascular coupling?
- coupling activity from neurons to activity in our vascular system
- neuron firing rate increases
- astrocyte Ca2- increases
- release of vasoactive substances from the astrocyte
- blood vessel diameter changes
Blood vessel relax - more oxygen into area
Astrocyte can control how much blood enters the area
Describe functional imaging techniques
Magnetic resonance imaging (MRI) allows 3D structural images of the brain - but what about techniques that measure activity
- active neurons need more glucose and oxygen
- more blood is directed to these areas
- 2 techniques detect changes the subsequent changes in blood flow
