#6. Brain: development, CSF, ventricles, BBB Flashcards
What does the brain and spinal cord develop from?
The ectoderm
What is a neural tube?
This is what the ectoderm arranges into to for the brain and the spinal cord.
What are the primary brain vesicles?
- prosencephalon
- mesencephalon
- rhombencephalon
When do the primary brain vesicles develop?
In the womb, 3-4 weeks
What are the secondary brain vesicles?
- Telencephalon
- Diencephalon
- Mesencephalon
- Metencephalon
- Myelencphalon
Where does the telencephalon come from?
the prosencephalon
Where does the diencephalon come from?
the prosencephalon
Where does the mesencephalon come from?
the mesencephalon
where does the metencephalon come from?
the rhombencephalon
Where does the myelencephalon come from?
the rhombencephalon
When do the secondary brain vesicles develop?
5 weeks into pregnancy
What does the telencephalon become in the adult brain?
cerebrum
What does the diencephalon become in the adult brain?
the talamus, the hypothalamus, and the epithalamus
What does the mesencephalon become in the adult brain?
the midbrain
What does the metencephalon become in the adult brain?
the pons and the cerebellum
What does the myelencephalon become in the adult brain?
the medulla oblongata
What are the walls in the adult brain that come from the secondary brain vesicles?
the cerebrum, the thalamus, hypothalamus, and epithalamus, midbrain, the pons and the cerebellum, and the medulla oblongata.
What are the cavities in the adult brain?
- lateral ventricles (x2)
- third ventricle
- aqueduct of the midbrain (cerebral aqueduct)
- fourth ventricle (upper and lower)
What forms the brainstem?
the midbrain, the pons and cerebellum and the medulla oblongata.
What are the midbrain, the pons and cerebellum and the medulla oblongata grouped together as?
the brain stem
True of False: the brain stem is continuous with the spinal cord.
True
Where is the cerebellum?
posterior to the brain stem
Where is the diencephalon?
superior to the brainstem
What makes up the diencephalon?
the thalamus, the hypothalamus and the epithalamus
What is the cerebrum and where is it located?
it is the largest part of the brain and sits on the diencephalon.
Are the cranial meninges continuous with the spinal meninges?
yes
Is there an epidural space around the brain?
no
How many layers are in the dura mater in the brain?
2 - the periosteal (external) and the meningeal (internal)
Is there a space between the periosteal and the meningeal layer of dura mater in the brain?
no, they are fused together EXCEPT where they separate to enclose the dural venous sinuses (ie. the superior sagittal sinus).
What are the dural venous sinuses made of and what do they do?
- endothelial-lined venous channels.
- they drain blood from the brain and deliver it into the internal jugular veins
What are the 3 extensions of dura mater?
- falx cerebri
- falx cerebelli
- tentorium cerebelli
What do the extensions of dura mater do in the brain?
They separate different parts of the brain
What is the purpose of falx cerebri?
To separate the 2 hemispheres of the cerebrum
What is the purpose of the falx cerebelli?
to separate the 2 hemispheres of the cerebellum
What is the purpose of the tentorium cerebelli?
it separates the cerebrum from the cerebellum
True of False: The arachnoid mater is the same as the spinal cord but the pia mater changes to accommodate the higher need for the blood brain barrier.
False. the arachnoid mater and the pia mater are the same as in the spine.
How does blood get tot he brain?
the internal cartoid artery and the vertebral arteries
How does blood leave the brain?
the dural venous sinuses that drain into the internal jugular veins
How much of the body weight is the brain?
2%
How much of the oxygen and glucose does the brain consume in the body?
20%
Why does the brain need so much oxygen and glucose?
So the neurons can make enough ATP
Can the brain cells store glucose?
No, this is why there needs to be a constant supply of glucose to the brain.
How long does it take for an interruption in the blood flow to start to impair the neuronal function?
1 or 3 minutes.
How long does it take for total oxygen deprivation to cause permanent brain damage?
about 4 minutes.
What happens if the blood entering the brain has low levels of glucose?
- mental confusion
- dizziness
- convulsions
- loss of consciousness
What type of junctions are in the blood brain barrier?
tight junctions
What makes up the BBB?
- tight junctions sealing the endothelial cells of capillaries
- a thick basement layer that surrounds the capillaries
- astrocytes
What are astrocytes?
- a type of neruoglia
- star shaped
What do astrocytes do?
-their processes press up against the capillaries and secrete chemicals that maintain the permeability characteristics of tight junctions
What can cross the BBB?
- some water soluble substances via active transport (ie. glucose)
- creatinine, urea, and ions cross slowly
- lipid-soluble substances (O2, carbon dioxide, alcohol, most anesthetic agents)
What does not cross the BBB?
proteins and most antibiotic drugs
What can cause a breakdown of the BBB?
trauma, certain toxins, and inflammation
What is the CSF?
- clear, colorless liquid
- mainly water
What does the CSF do?
- protects the brain and spinal cord from chemical and physical injuries.
- carries small amount of O2, glucose, and other needed chemicals in blood to neurons and neuroglia
What is continuously circulating through the cavities in the brain, spinal cord and in the subarachnoid space?
CSF
What is the total volume of CSF in adults?
80-150 mL
What is in the CSF?
small amounts of glucose, proteins, lactic acid, urea, cations, anions and some WBC’s
What separates the 2 lateral ventricles in the cerebrum?
the septum pellucidum: a thin membrane
What are the functions of the CSF?
- mechanical protection - shock absorbing medium that protects brain and SC from jolts. - fluid also keeps brain floating in the cranial cavity
- Homeostatic function - the pH of CSF affects pulmonary ventilation and cerebral bloodflow
- Circulation - minor exchange of nutrients and waste products b/w blood and nervous tissue
Where is CSF formed?
in the choroid plexuses
What are choroid plexuses?
networks of blood capillaries in the walls of the ventricles
How is the CSF formed?
-substances from the blood plasma (mostly water) are filtered from the capillaries through the ependymal cells to produce CSF.
What covers the capillaries of the choroid plexuses?
ependymal cells along with tight junctions
What do ependymal cells have to do with the blood-cerebralspinal fluid barrier?
because of the tight junctions b/w the ependymal cells the fluid must pass THROUGH the cells which creates the barrier.
What is the purpose of the BBB?
protecting the brain and spinal cord from blood-borne substances
Is the CSF in all ventricles?
Yes
True or False: BBB = tight junctions of brain capillary ependymal cells?
False. the BBB = tight junctions of brain capillary endothelial cells
True or False: Blood-CSF barrier = tight junctions of endothelial cells?
False. blood-CSF barrier = tight junctions of ependymal cells
What is the circulation route of CSF?
- lateral ventricles (CSF is formed in choroid plexuses)
- travels through the interventricular foramina
- 3rd ventricle (more CSF from choroid plexuses)
- through the cerebral aquaduct
- 4th ventricle (more CSF is formed in the choroid plexuses)
- CSF can go down the central canal
- travels to subarachnoid space in spine (through 2 lateral apertures and 1 median aperture) then to the arachnoid villi.
What happens to the CSF in the arachnoid villi?
CSF is reabsorbed into blood
What is an arachnoid granulation?
a cluster of arachnoid villi
