Neuro Exam 4: Cns Fluid Compartments

Front 1

How much water weight does the brain consist of?

Back 1

80%

Front 2

What are the four major CNS fluid compartments of the brain?

Back 2

1) intracellular space of neurons and glia
2) interstitual fluid surrounding neurons and glia
3) CSF space (unique to CNS)
-separated from interstitial space by ependyma and pia
-solutes/water move freely between CSF and interstitial fluid (similar compositions)
4) Plasma
-special blood-brain barrier between plasma and interstitial fluid and between plasma and CSF (choroid plexus & arachnoid villi)

Front 3

Which ventricles are contained within the cerebral hemispheres?

Back 3

-Lateral ventricles
-Each one has a central part and frontal, temporal, and occipital horns
-Along the floor is a portion of the choroid plexus

Front 4

What is the choroid plexus?

Back 4

Tissue that secretes CSF

Front 5

What is the septum pellucidum?

Back 5

Separates the two frontal horns of the lateral ventricles from eachother

Front 6

What is the third ventricle?

Back 6

Midline structure located between the two thalami
-Choroid plexus is located int he roof of the third ventricle

Front 7

What is fourth ventricle?

Back 7

Midline structure with choroid plexus in its roof
-Pons/Medulla form floor
-Cerebellum forms roof

Front 8

What connects the lateral ventricle to the third ventricle?

Back 8

An interventricular foramen termed the foramen of Monro

Front 9

What connects the third ventricle to the fourth ventricle?

Back 9

The cerebral aqueduct (aka aqueduct of Sylvius)

Front 10

What connects the fourth ventricle to the subarachnoid space?

Back 10

Three foramina
-2 lateral foramina of Luschka
-1 midline foramen of Magendia

Front 11

What is the spinal cord subarachnoid space referred to as?

Back 11

The intrathecal space

Front 12

What are cisterns?

Back 12

Pockets of CSF between the brain and the skull (outside the brain)

Front 13

Where is the cisterna magna located?

Back 13

In the midline inferior to the cerebellum

Front 14

Where is the suprasellar cistern located?

Back 14

Superior to the pituitary and to the sella turcica

Front 15

Where is the supravermian cistern?

Back 15

Superior to the vermis of the cerebellum

Front 16

What are nerve root sleeves?

Back 16

Small meninges that contain CSF and extend along the proximal course of cranial and spinal nerves, generally to the location of the dorsal root ganglia

Front 17

How much CSF does the average adult have?

Back 17

-About 140 cc (of which 30 cc is located int he spinal subarachnoid space and 110 cc in the cranial cavity)

Front 18

How much CSF is formed per day?

Back 18

-About 500 cc (turned over about 3x per day so the average adult has about 150 cc of CSF)
-Half formed by choroid plexus and remainder formed around cerebral vessels and along walls of ventricles

Front 19

What are the arachnoid villi?

Back 19

small, finger-like projections of the arachnoid that extend into the dural venous sinuses (esp the superior sagittal sinus)
-some arachnoid villi project into veins that accompany spinal nerve roots exiting spinal canal
-become more prominent with age due to thickening and then referred to as arachnoid granulations

Front 20

How does the CSF flow?

Back 20

Through the ventricular system, into the subarachnoid space, and returns to blood via arachnoid villi

Front 21

How often is the CSF formed and absorbed?

Back 21

Every 8 hours

Front 22

What are the functions of the CSF?

Back 22

1) Mechanical protection (cushions brain during accel and decel)
2) Bichemical function: Eliminates metabolic degradation products from brain, maintains ionic equilibrium in brain interstitial space

Front 23

What are the main site of the blood-brain barrier?

Back 23

The brain capillary endothelial cells
-endothelial cell membranes in brain fused by tight junctions
-molecules can only cross barrier by diffusion or active transport

Front 24

The ease with which a compound can diffuse across the brain capillary endothelium is directly related to what?

Back 24

-Its lipid solubility
-Endogenous substances or drugs with high lipid solubility enter brain rapidly and compounds with water solubility enter brain slowly
-water, gases, psychoactive drugs, high lipid soluble substances

Front 25

What are carrier mediated transport systems?

Back 25

Bring into the brain some lipid insoluble substances that cannot readily diffuse across the brain capillary endothelial membranes

Front 26

How does the glucose transporter work?

Back 26

-Facilitated diffusion, does nto require energy
-Extremely rapid, stereospecific (transports D-glucose, not L-glucose)
-Glucose is primary energy substrate for brain and transport system can bring in 2-3 times amount of glucose required by brain under normal conditions
-transport of glucose does not limit the rate of brain metabolism

Front 27

What are the most important carrier mediated transport systems?

Back 27

-Glucose
-Monocarboxylic acid
-neutral amino acid
-choline

Front 28

What are the two important neutral amino acid transport systems?

Back 28

1) L system: transports large amino acids into the brain
2) A system: slower transport of small amino acids out of the brain into the plasma
-These two systems allow brain to locally control neurotransmitter concentrations by synthesis from precursors

Front 29

What does the choline transporter do?

Back 29

-Makes this precursor of Ach available to brain

Front 30

What is the importance of protein binding?

Back 30

Limits the entry of some substances into the brain
-large plasma proteins do not cross capillary endothelial cells by means of diffusion or carrier mediated transport
-some substances have lower concentrations than would be expected by their lipid solubility because they are protein bound

Front 31

What is the blood-CSF barrier?

Back 31

-The choroid plexus and the arachnoid villi
-similar to blood-brain barrier in that water, gases, and lipid-soluble components can move freely across and glucose and large amino acids are transported by carrier systems

Front 32

What are circumventricular organs?

Back 32

Small regions of the CNS that have no blood-brain barrier
-posterior pituitary, ventral part of median eminence of hypothalamus
-these are neurohemal organs where hormones produced in CNS cells must be able to enter the circulation

Front 33

What is the blood-nerve barrier?

Back 33

-Similar to blood-brain barrier
-composed of perineurium surrounding nerve fascicle nd tight junctions of endothelial cells at intrafascicular capillaries
-Not present at axon terminals or in region of dorsal root ganglia (some viruses penetrate nervous system here)

Front 34

What is the function of the blood-brain and blood-CSF barriers?

Back 34

-protect brain from rapid physio alterations in chemical environment, maintain ionic contancy
-protect brain from blood-borne toxins
-prevention of direct entry of neurotransmitters from blood to brain
-prevention of unwanted exit of neurotransmitters from brain to blood

Front 35

What is a lumbar puncture?

Back 35

-Needle inserted into two adjacent lumbar vertebra (usually L3/L4 or L4/L5), through the dura, and into the subarachnoid space surrounding the cauda equina
-to examine CSF for infections, pressure, red/white blood cell count, protein/glucose concentration, etc.
-done here because risk of damaging spinal cord is low
-common side effect: transient low pressure syndrome (10% of patients)
-can be hazardous in patients with elevated intracranial pressure (esp caused by intracerebral masses) because abrupt lowering of lumbar CSF pressure may lead to herniation of cerebellar tonsils through the foramen magnum (can be compression of medulla in foramen magnum and be life threatening)

Front 36

What imaging is available to examine CSF spaces?

Back 36

-MRI
-CT
-Myelography
-Cisternography

Front 37

What is hydrocephalus?

Back 37

Increase of CSF volume with dilation of some or all of cerebral ventricles

Front 38

What is obstructive hydrocephalus?

Back 38

Blockage of CSF flow before it reaches subarachnoid space (can obstruct any of the foramen)
-best treated by removing the source of blockage
-otherwise CSF can be "shunted" from the ventricles to another fluid space within the body, particularly the peritoneal cavity

Front 39

What is communicating hydrocephalus?

Back 39

Blockage of CSF flow occurs at level of superior sagittal sinus or subarachnoid space over the cerebral hemispheres

Front 40

What is hydrocephalus ex vacuo?

Back 40

Increase in CSF volume with normal CSF pressure that is compensatory for a loss of brain tissue
-Example: normal aging, AD

Front 41

What is meningitis?

Back 41

Inflammation of meninges, often due to an infection within the subarachnoid space

Front 42

What is low CSF pressure syndrome?

Back 42

Associated with a headache relieved by lying down
-may result from CSF leak

Front 43

What conditions may cause increased permeability of the blood-brain and plasma-CSF barriers?

Back 43

-Meningitis
-Brain tissue injury due to trauma or stroke
-CNS tumors
-Sudden, marked hypertension
-Hyperosmolality
-Premature babies/neonates
-Medication administered directly into spinal subarachnoid space or ventricles can reach CNS without crossing blood-brain barrier

Front 44

How long does it take for tight junctions to refer after brain injury?

Back 44

3-4 weeks

Front 45

What is a cerebral edema?

Back 45

State of increased water content of the brain with a resulting increased brain tissue volume
-may be focal or diffuse
-Types: vasogenic, cytotoxic, ischemic, interstitial

Front 46

What is a vasogenic edema?

Back 46

-Most common form
-due to breakdown of blood-brain barrier which leads to increased volume of interstitial fluid (increased water in interstitial fluid)
-white matter affected more than gray matter
-resolves by edema fluid flowing along perivascular spaces into CSF

Front 47

What is cytotoxic edema?

Back 47

Increased swelling due to pump failure
-Gray/white matter affected
-Resolved by clearing inhibiting toxins restoring pump

Front 48

What is ischemic edema?

Back 48

Begins intracelluarly and evolves over several hours into vasogenic edema

Front 49

What is interstitial edema?

Back 49

Hydrocephalus (increased CSF pressure in ventricles) pushes water into brain through ependyma

Front 50

Why is a breakdown of the blood-brain barrier a common/early pathological response to many forms of CNS injury?

Back 50

-Because the tight junctions are fragile and the active transport mechanisms are highly energy dependent
-breakdown of BBB during CNSN infections facilitates penetration of some drugs into CNS such as penicillin G