Lecture 4 Flashcards
meninges
three membraneous layers that surround the brain & SC
dura mater
- outermost layer directly under the skull
- tough and flexible
- protects brain from displacement
- two layers :
1.outer postereal layer - fibrous
2.inner meningeal layer - smooth
arachnoid mater
- middle layer
- lies closely against dura mater
- in some places, shows small protrusions into dura mater called arachnoid granulations/villi
- they transfer CSF from ventricles back into bloodstream
pia mater
- innermost layer
- projects into ventricles and fuses with ependyma
ependyma
- membraneous lining at the ventricles
- form structures called the choroid plexi that produce CSF
epidural space
potential space b/w the dura mater of the SC and the vertebral canal wall
subdural space
potential space b/w the dura mater and arachnoid mater
subarachnoid space
- real space b/w arachnoid mater & pia mater
- filled with CSF
- all blood vessels entering brain & cranial nerves pass through
fibrous septa
seperates the two dural layers
CSF
- clear, plasma like fluid produced within spaces called ventricles
- found in subarachnoid space
- central canal wall contains CSF
- functions :
1. functions as a cushion for neurons
2. brings nutrients to brain & SC
3. removes waste from system
CSF circulation pathway
- CSf passes from lateral ventricles to 3rd ventricle via intraventricular foramen
- from 3rd ventricle to 4th ventricle via cerebral aqueduct
- from 4th ventricle passes through medial & lateral apertures
- CSF flows through subarachnoid space of brain & SC
- finally reabsorbed into dural venous sinus through arachnoid granulations/villi
skull
- cranial cavity is rigid box with brain, blood vessels and CSF
- communicates with verterbal canal wall through foramen magnum and with tissues outside the cranium via foramina
intercranial pressure
because it is a rigid box, extensive bleeding or a tumour inside the cranium has little room for expansion and will lead to intercranial pressure
blood brain barrier
structures formed due to establishments of tight junctions b/w endothelial cells
purpose of BBB
- protect against circulating toxins or pathogens that could cause infections
- allows vital nutrients to reach brain
- helps maintain relatively constant levels of hormones nutrients & water in brain
circumventricular organs
- gaps in BBB
- not protected by BBB
- examples - pituary gland, pineal gland, subfornical organ
problem with BBB?
- in an infection in the brain, BBB makes delivery of antimicrobial agents to the brian very difficult
- can be too restrictive
Meningococcal disease
- meningococcal bacteria can bind to endothelial wall
- causes tight junctions to open slightly
- BBB becomes porous allowing bacteria and toxins to infect brain tissue
- leads to inflammation & sometimes death
endothelial cells
- line interior of all blood vessels
- wedged together closely to form tight junctions
- these allow small, fat soluble molecules to pass through the capillary wall and into brain tissue
- large molecules gain entry through transporter proteins