Lesson 6 Flashcards
Brain stem
continuous with spinal cord
= medulla oblongata
= pons
= midbrain
Cerebellum
posterior to brain stem
Diencephalon
- superior to brain stem
= thalamus
= hypothalamus
= epithalamus
Cerebrum
- largest part of the brain
- sits on diencephalon
Protective Coverings of the Brain
Cranium & cranial meninges surround and protect the brain
Cranial meninges are continuous with the spinal meninges
Dura mater
*no epidural space around the brain
-outer meningeal layer
-made up of 2 layers - periosteal layer (external)
- meningeal layer (internal)
-these 2 layers are fused together except where they separate to enclose the dural venous sinuses
Dural venous sinuses
-endothelial-lined venous channels
-drain blood from the brain and deliver
it into internal jugular veins
3 extensions of dura mater separate parts of the brain
- Falx cerebri:
- Falx cerebelli:
- Tentorium cerebelli:
Falx cerebri:
Separates the 2 hemispheres of the cerebrum
Falx cerebelli
Separates the 2 hemispheres of cerebellum
Tentorium cerebelli
Separates the cerebrum from
the cerebellum
Blood flows to brain mainly via
-the internal carotid
-vertebral arteries
blood flows out of brain via
dural venous sinuses which drain into the internal jugular veins
Brain is what % of total body weight?
How much oxygen and glucose does it consume?
2% total body weight
20% oxygen and glucose
Oxygen and glucose make what in brain?
ATP
Interruption in blood flow for 1 or 2 minutes
impairs
neuronal function
total deprivation of oxygen for about 4 minutes may cause
Permanent injury
Supply of glucose must be consistent because?
none stored in brain
Symptoms of low glucose
mental confusion ⬥dizziness ⬥convulsions ⬥loss of consciousness
Blood Brain Barrier made up of
- tight junctions that seal together endothelial cells
of capillaries in the brain + - a thick basement layer that surrounds the
capillaries + - astrocytes (their processes press up against the
capillaries and secrete chemicals that maintain
the permeability characteristics of tight junctions)
What crosses Blood brain barrier
- some water-soluble substances cross by active transport (ie glucose)
- creatinine, urea, ions cross slowly
- lipid-soluble substances (O2, carbon dioxide, alcohol,
most anesthetic agents) - proteins and most antibiotic drugs do not cross
- trauma, certain toxins and inflammation can cause a
breakdown of the BBB
What is CSF
-clear, colourless liquid
-mainly water
-protects the brain and spinal cord from chemical and physical injuries
-also carries a small amount of O2, glucose and other needed chemicals in blood to the neurons and neuroglia
-CSF continuously circulates through
the cavities in the brain + spinal cord and
around the brain + spinal cord in the subarachnoid
space
CSF
total volume =
80-150 mL in adult
CSF contains
small amounts of glucose, proteins, lactic acid,
urea, cations, anions and some WBCs
ventricles -cavities within the brain filled with CSF
*2 lateral ventricles
-1 in each hemisphere of the cerebrum
-septum pellucidum: thin membrane
that separates the lateral ventricles
*third ventricle
*fourth ventricle
CSF
functions
- Mechanical protection
-shock absorbing medium that protects
brain + SC from jolts
-fluid also keeps brain floating in the
cranial cavity - Homeostatic function
-the pH of CSF affects pulmonary
ventilation & cerebral blood flow - Circulation
-minor exchange of nutrients + waste
products btw blood and nervous tissue
Formulation of CSF in Ventricles
-CSF is formed in choroid plexus
-choroid plexuses are networks of blood capillaries in the walls of the ventricles
-ependymal cells joined by tight junctions cover
the capillaries
Formulation of CSF in Ventricles - filtration
-substances from blood plasma (mostly water) are filtered from the capillaries through the ependymal cells to produce CSF
-because of the tight junctions btw ependymal cells, fluid must pass through the ependymal cells, creating a blood-cerebrospinal fluid barrier
-this protects the brain + SC from harmful blood-borne
substances
Formation of CSF in Ventricles - junctions
-so BBB is made up of tight junctions btw brain capillary endothelial cell
-and the blood-CSF barrier is made up of tight junctions btw ependymal cells
Circulation of CSF
- Lateral ventricles
- Third ventricle
- Fourth ventricle
- Central canal
- Subarachnoid space
- Arachnoid villi
Arachnoid villi
-CSF is reabsorbed into blood through arachnoid villi
-arachnoid villi are fingerlike extensions of arachnoid that project into dural venous sinuses
-a cluster of arachnoid villi = granulation
