Brain organisation and CSF Flashcards
What are the 3 primary brain vesicles?
Prosencephalon
Mesencephalon
Rhombencephalon
What does the prosencephalon divide into?
Telencephalon
Diencephalon
What does the Rhombencephalon divide into?
Metencephalon
Myelencephalon
What does the telencephalon develop into?
The telencephalon develops into the cerebrum and lateral ventricles.
What does the diencephalon form?
The diencephalon forms the thalamus, hypothalamus, epi- thalamus, and third ventricle.
What does the metencephalon become?
The metencephalon becomes the pons, cerebellum, and upper part of the fourth ventricle.
What does the myelencephalon form?
The myelencephalon forms the medulla oblongata and lower part of the fourth ventricle.
What does the mesencephalon give rise to?
The mesencephalon (mes -en-SEF-a-lon), or midbrain, gives rise to the midbrain and aqueduct of the midbrain (cerebral aqueduct).
What are the 4 major parts of the brain?
Brain stem
Cerebellum
Diencephalon
Cerebrum
What makes up the brain stem?
Midbrain
Pons
Medulla Oblongata
What are the 3 layers of the cranial meninges?
The outer dura mater
The middle arachnoid mater
The inner pia mater
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What two layers make up the dura mater of the brain?
Periosteal layer (which is external)
Meningeal layer (which is internal)
Where do the dura layers of the brain split apart?
The dural layers around the brain are fused together except where they separate to enclose the dural venous sinuses (endothelial-lined venous channels) that drain venous blood from the brain and deliver it into the internal jugular veins.
What 3 extensions of the dura mater separate parts of the brain?
Falx cerebri
Falx cerebelli
Tenatorium cerebelli
What does the falx cerebri separate?
Cerebral hemispheres
What does the falx cerebelli separate?
Two hemispheres of the cerebellum
What does the tentorium cerebelli separate?
The cerebrum from the cerebellum
What are the main blood supplies to the brain?
Internal carotid arteries
Vertebral arteries
How does the blood drain from the brain?
The dural venous sinuses drain into the internal jugular veins to return blood from the head to the heart
What percentage of an adults body weight comes from the brain?
In an adult, the brain represents only 2% of total body weight
How much oxygen and glucose is used by the brain?
It consumes about 20% of the oxygen and glucose used by the body, even when you are resting
What substances are able or not able to cross the Blood Brain Barrier?
A few water-soluble sub- stances, such as glucose, cross the BBB by active transport.
Other substances, such as creatinine, urea, and most ions, cross the BBB very slowly.
Still other substances—proteins and most antibiotic drugs—do not pass at all from the blood into brain tissue.
However, lipid-soluble substances, such as oxygen, carbon dioxide, alcohol, and most anesthetic agents, are able to access brain tissue
What is CSF?
Cerebrospinal fluid (CSF) is a clear, colorless liquid composed primarily of water that protects the brain and spinal cord from chemical and physical injuries.
What is the total volume of CSF in an adult?
The total volume of CSF is 80 to 150 mL (3 to 5 oz) in an adult.
What does CSF contain?
CSF contains small amounts of glucose, oxygen, proteins, lactic acid, urea, cations (Na , K , Ca2 , Mg2 ), and anions (Cl– and HCO3–); it also contains some white blood cells.
What is the septum pellucidum?
Anteriorly, the lateral ventricles are separated by a thin membrane, the septum pellucidum
Where does the 3rd ventricle lie?
The third ventricle is a narrow slitlike cavity along the midline superior to the hypothalamus and between the right and left halves of the thalamus.
What are the 3 basic functions of the CSF?
Mechanical protection
Homeostatic function
Circulation
Explain the mechanical function of the CSF?
CSF serves as a shock-absorbing medium that protects the delicate tissues of the brain and spinal cord from jolts that would otherwise cause them to hit the bony walls of the cranial cavity and vertebral canal.
The fluid also buoys the brain so that it “floats” in the cranial cavity.
Explain the homeostatic function of the CSF?
The pH of the CSF affects pulmonary ventilation and cerebral blood flow, which is important in maintaining homeostatic controls for brain tissue. CSF also serves as a transport system for polypeptide hormones secreted by hypothalamic neurons that act at remote sites in the brain.
Explain the circulation function of the CSF?
CSF is a medium for minor exchange of nutrients and waste products between the blood and adjacent nervous tissue.
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What is responsible for the majority of CSF production?
The majority of CSF production is from the choroid plexuses, networks of blood capillaries in the walls of the ventricles.
Explain how the CSF is produced?
Function of ependymal cells?
Ependymal cells joined by tight junctions cover the capillaries of the choroid plexuses. Selected substances (mostly water) from the blood plasma, which are filtered from the capillaries, are secreted by the ependymal cells to produce the cerebrospinal fluid. This secretory capacity is bidirectional and accounts for continuous production of CSF and transport of metabolites from the nervous tissue back to the blood.
Because of the tight junctions between ependymal cells, materials entering CSF from choroid capillaries cannot leak between these cells; instead, they must pass through the ependymal cells. This blood–cerebrospinal fluid barrier permits certain substances to enter the CSF but excludes others, protecting the brain and spinal cord from potentially harmful blood-borne substances. In contrast to the blood–brain barrier, which is formed mainly by tight junctions of brain capillary endothelial cells, the blood–cerebrospinal fluid barrier is formed by tight junctions of ependymal cells.
Explain the circulation of the CSF?
The CSF formed in the choroid plexuses of each lateral ventricle flows into the third ventricle through two narrow, oval openings, the interventricular foramina. More CSF is added by the choroid plexus in the roof of the third ventricle. The fluid then flows through the aqueduct of the midbrain (cerebral aqueduct), which passes through the midbrain, into the fourth ventricle. The choroid plexus of the fourth ventricle contributes more fluid. CSF enters the subarachnoid space through three openings in the roof of the fourth ventricle: a single median aperture and paired lateral apertures, one on each side. CSF then circulates in the central canal of the spinal cord and in the subarachnoid space around the surface of the brain and spinal cord.
Explain the reabsorption of the CSF?
CSF is gradually reabsorbed into the blood through arachnoid villi, fingerlike extensions of the arachnoid that project into the dural venous sinuses, especially the superior sagittal sinus. (A cluster of arachnoid villi is called an arachnoid granulation.) Normally, CSF is reabsorbed as rapidly as it is formed by the choroid plexuses, at a rate of about 20 mL/hr (480 mL/day). Because the rates of formation and reabsorption are the same, the pressure of CSF normally is constant. For the same reason, the volume of CSF remains constant.
Explain hydrocephalus?
Abnormalities in the brain—tumors, inflammation, or developmental malformations—can interfere with the circulation of CSF from the ventricles into the subarachnoid space. When excess CSF accumulates in the ventricles, the CSF pressure rises. Elevated CSF pressure causes a condition called hydrocephalus. The abnormal accumulation of CSF may be due to an obstruction to CSF flow or an abnormal rate of CSF production and/or reabsorption. In a baby whose fontanels have not yet closed, the head bulges due to the increased pressure. If the condition persists, the fluid buildup compresses and damages the delicate nervous tissue. Hydrocephalus is relieved by draining the excess CSF. In one procedure, called endoscopic third ventriculostomy (ETV), a neurosurgeon makes a hole in the floor of the third ventricle and the CSF drains directly into the subarachnoid space. In adults, hydrocephalus may occur after head injury, meningitis, or subarachnoid hemorrhage. Because the adult skull bones are fused together, this condition can quickly become life-threatening and requires immediate intervention.
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