L11 Homeostasis - Pt 2 Flashcards
What is the ventricular system?
Ventricular system is a series of hollow cavities filled with cerebrospinal fluid which run throughout the brain to the spinal cord.
Describe the structure of the ventricular system and the flow of CSF. Give examples of the functions of the CSF
What is the role of the ventricular system?
- Provides Physical protection - Buffer.
- Maintains appropriate levels of ions.
- Removes waste products.
What is in the CSF?
- Lower K+ compared to plasma.
- Amino acids are lower than plasma
- Proteins are lower than plasma.
What is exchanged from CSF to BECF?
- Macronutrients - Glucose
- Micronutirents - Vitamins
- Ions - HCO3-
What is exchanged from BECF TO CSF?
- Metabolic waste products - CO2
- Neurotransmitters.
What is secreted by the choroid plexus?
The cerebrospinal fluid (CSF)
Describe the flow of the cerebrospinal fluid (CSF)
Absorbed from the subarachnoid space to the venous blood system at the superior sagittal sinus
Where does the flow of cerebrospinal fluid (CSF) circulate around?
It circulates around the ventricles and central canal
How much CSF is produced each day?
Approx - 500 mls each day.
What are the specific roles of capillaries, choroidal epithelial cells, and ependymal cells in the exchange of substances between blood plasma, extracellular fluid (ECF), cerebrospinal fluid (CSF), and brain extracellular fluid (BECF)
- Ultrafiltration of plasma into ECF across normal ‘leaky’ capillaries
- Selective absorption of substances into CSF across choroidal epithelial cells
- Free movement of substances from CSF to BECF across ependymal cells
What are meninges?
The meninges are a vital set of membranes that protect the central nervous system (CNS), which includes the brain and spinal cord
What are the 3 layers of the meninges ?
Dura mater: The outermost, toughest layer.
Arachnoid mater: The middle, web-like layer.
Pia mater: The innermost, delicate layer that adheres directly to the CNS tissue.
What absorbs the CSF?
Arachnoid Granulations. They act as one-way valves, allowing CSF to flow from the subarachnoid space into the venous bloodstream.
What are the adaptations of arachnoid granulations?
What is hydrocephalus?
Hydrocephalus is a medical condition characterized by an abnormal buildup of cerebrospinal fluid (CSF) within the ventricles (cavities) of the brain.
What are the consequences of hydrocephalus?
- Increased intracranial pressure
- Loss of cells within the brain.
- Loss of brainstem reflexes.
Can you describe the structure of the ventricular system and the flow of CSF?
Can you give examples of the main functions of CSF?
What is the name of the thing between the Pia mater and the Arachnoid mater?
Subarachnoid space
Which menigeal layers are leptomeninges?
Pia mater
Arachnoid mater
What do neurons and astrocytes do to maintain homeostasis?
They terminate neurotransmission at the tripartite synapse to presynaptic terminal to postsynaptic terminal- recycling of neurotransmitters
What does neurons and astrocytes do in context to K+ composition?
Neurons and astrocytes remove K+ from the extracellular space
What can affect astrocyte function?
Increased glucose metabolism and increased K+ uptake
How does increase in extracellular K+ affect astrocyte function?
- K+ Buffering (Spatial Buffering)
- Neurotransmitter modulation.
- Metabolic changes
- Signalling and communication
- Vasoregulation.
What is astrocytes syncytium?
The term “astrocyte syncytium” refers to the network of astrocytes in the brain that are extensively interconnected via gap junctions.
What does astrocytic syncytium allow?
It allows spatial buffering
What can gap junctions create?
They can create a syncytium
How does astrocytic syncytium allow spatial buffering?
It redistributes K+ to areas of decreased activity
Can also transport sugars, amino acids, cAMP, Ca2+
Define the term neurovascular coupling
Neurovascular coupling (NVC) is the physiological process that links neural activity to changes in cerebral blood flow (CBF)
How does neurovascular coupling manipulate blood flow to a specific area?
Increased neuron firing rate -> Increased asctrocyte Ca2+ -> Release of vasoactive substances from astrocyte -> Blood vessel diameter changes.
Recall two types of functional imaging techniques
Positron emission tomography (PET) – exploits glucose use
Functional magnetic resonance imaging (fMRI) – exploits oxygen use
Why are PET and fMRI used to generate 3D structural images of the brain?
Active neurons need more glucose and oxygen
More blood is directed to these areas
Two techniques detect changes the subsequent changes in blood flow
Positron emission tomography (PET) – exploits glucose use
Functional magnetic resonance imaging (fMRI) – exploits oxygen use
What does fMRI do?
Functional magnetic resonance imaging (fMRI) – exploits oxygen use
What acronym does the fMRI follow ?
Blood Oxygenation Level Dependent (BOLD) - more oxygen = stronger signal
