Brain formation and fluids Flashcards
Cerebrum/central hemispheres
telencephalon
Thalamus and hypothalamus
Diencephalon
Telecephalon and diencephalon
Prosencephalon
Midbrain
Mesencephalon
Pons and cerebellum
Metencephalon
Medulla
Myelencephalon
myelencephalon and metencephalon
Rhombencephalon
Development of the nervous system
Forms early in embryonic life - 3rd week
Develops from ectodermal layer
Neural groove develops in the mid line and neural cells proliferate and form a neural tube
Neural tube forms spinal cord, at the cephalic ( head) end it swells and flexes to form the brain
Neuropores
Posterior and anterior neuropores HAVE to close for formation of brain and spinal cord
Posterior - end of spine
anterior - brain
folic acid can help
vertebral column more rapidly than spinal cord
3rd month of development - neural tube
Spinal cord extends the entire length of the embryo,spinal nerves pass through the intervertebral foramina at their level of origin
How does the neural tube and vertebral column develop past 3 months
Vertebra column and dura lengthen more rapidly than the neural tube/spinal cord ,spinal cord stops and spinal nerves have to run down
Spinal nerves run obliquely from their origin to corresponding level
Large region of vertebral column with no spinal cord
Cauda equina
Nerve fibers below the terminal end of the spinal cord
Can access to cerebrospinal fluid within vertebral column and inject anaesthia without affecting spinal cord
Where does spinal cord terminate
Where does dural sac and subarchnoid space terminate
Spinal cord l2-l3
s2
What is the filum terminale
Below l2-l3
Threadlike extension of the piwqqqa mater forms the filum terminale
Attached to the periosteum of the first coccygeal vertebra and marks the tract of regression of spinal cord
What does the prosencephalon give rise to
ONLY ONCE ANTERIOR neuropore has closed
Forebrain
Telencephalon and diencephalon
Secondary vesicles - cerebrum , hypothalamus
What does the mesencephalon give rise to
Midbrain
Mesencephalon
secondary vesicles - mid brain
What does the rhombencephalon give rise to
Hindbrain
Metencephalon and myelencephalon
secondary- pons, cerebellum,
Ventricular system in the brain formation
spaces within neural tube
Either side: from superior to inferior
Lateral ventricles, third ventricles, aqueduct
4th ventricle
Cortical development - synapses and prunation
Synapses form fastest at 2-3 years old,
prunation/elimination at birth of nuerones
3 meninges of the brain
Dura mater subdural space Arachnoid mater subarachnoid space Pia mater BRain
DURA MATER - 2 layers
Thickest
Superficial- endosteal layer
Deep- meningeal, continuous with dura of spinal cord
2 layers close together except for areas where meningeal layer dips down into brain fissures
Falx cerbri
Layer of dura meter
Throuhg hemisphere
Vertical fold
Longitudinal fissure
tentorium cerebelli
fold lying above the cerebellum and below the cerebrum
roofs over the posterior cranial fossa, opening (tentorial notch )remains to allow the midbrain to pass through
Space occupying legion e.g. tumour
Dura is tough and immovable - brain may be pressed against tentorial notch
ARACHNOID mater
Seperated from dura by subdural space and seperated from pia by subarachnoid ( CSF)
Blood vessels and cranial nerves lie in subarachnoid space
Arachnoid bridges over sulci ( grooves) of brain
Arachnoid projects through dura into venous sinuses( arachnoid villi forming arachnoid granulations) in some places
ARACHNOID VILLI
One way valves
allow CSF to drain into sinuses and then venous system
Pia mater
thinnest
closesly follows brain surface, extends down to sulci
Cerebral arteries entering brain have covering of pia mater
Headache - how is it detected
brain itself has NO pain receptors
Stretching/irritation of meninges or blood vessels causes headache
Bacterial meninigitis
Inflammation
Build up of fluid ( cerebral oedema) and increase in internal pressure = reduced blood supply
Diagnosis by CSF - high white cells, high protein, low glucose
What fills the ventricle system
CSF- ultrafiltrate of blood
How does CSF leak
From 4th ventricle via 2 apertures - median and lateral
goes into subarachnoid space
Function of CSF
Removes waste products
Transports signalling molecules
Renders the brain buoyant
Supports, cushions and evenly distributes pressure on teh brain
flows all around brain, at arachnoid granulations at TOP - CSF absorbed into SSS
How does CSF get secreted
ACTIVELY by choroid plexus tissue
Choroid plexus
Network of capillaries seperated from ventricles by choroid epihtelial cells
Hydrocephalus
Because CSF is continuously poduced ,blockages in circulation, drainage or excess production cause increase in intracranial pressure
- occur at interventricular foramen and cerebral aqueduct
- new born = ventricular and skull dilation
- adults - cranial cavity is closed , increase in cranial pressure headaches etc
How to relieve cranial pressure
Shunt to remove excess fluid
Blockage can be caused by tumour - removing tumor relieves pressure
Blood brain barrier
Tight junctions between epithelial cells
Atrocytes on brain side- regulate blood flow , close connections with basement membrane of epihtelial cells
How do substances cross blood brain barrier
Water soluble - straight through paracellular
Lipid soluble - transcellular lipophilic pathway
Transport proteins
Receptor mediated transycotsis , insulin
Absorpitive transcytosis - albumin
CSF from subarachnoid to saggital sinus
The CSF from the subarachnoid space is eventually reabsorbed through outpouchings into the superior sagittal sinus (SSS) known as the arachnoid granulations.
