Physiology Flashcards
Describe the appearance of CSF
Clear, colourless mostly composed of water
Where is CSF produced?
Secretory epithelium of the choroid plexus in the ventricles
What is the volume of CSF circulating in the CNS at any one time?
150ml
State three major function of CSF
- Mechanical protection (shock absorber of which the brain sits in)
- Homeostatic function (pH and transport of hormones)
- Circulation (exchange of nutrients/waste)
How obtained for analysis?
Lumbar puncture
How does the choroid fissure develop?
Arteries invaginate the roof of the ventricle to form the choroid tissue, this causes the ependymal cells and vessels to enlarge to villi and form the plexus
What causes hydrocephalus?
CSF outflow obstruction which can cause enlargement of the ventricular space
How are the ependymal cells held together?
Tight junctions
What ions are involved in the production of CSF from blood?
Na+
Cl-
HCO3-
How does fluid move across the membrane?
Active sodium transport, electrical gradient pull chloride and water moves by osmosis
How is CSF different to blood?
Lower potassium, glucose and protein
Higher sodium and chlorine
Is the production of CSF active or passive?
Active process does not depend on arterial BP
How many ventricles are there?
Two lateral, a third and a fourth
State the connections between the ventricles
Foramen of monroe - laterals to third
Aqueduct of sylvius - third to fourth
Foramen of magendie and foramen of luschka - fourth ventricle to subarachnoid space
Where does the CSF go from the subarachnoid space?
Drains into the arachnoid villi of dural venous sinuses
What does the blood brain barrier consist of?
Capillary endothelium, its basal membrane and perivascular astrocytes
In the BBB what type of junction are between the endothelial cells?
Tight junctions - prevent paracellular movement
Do all areas of the brain have a BBB?
No - circumventricular organs and the pineal gland do not
Name three types of tumour related to CSF
- colloid cyst (often in interventricular foramen)
- ependymonas
- choroid plexus tumour
What can ventricular haemorrhage result in?
- epidural haematoma
- subdural haematoma
- subarachnoid haematoma
What are the symptoms of idiopathic intracranial hypertension?
Headache and visual disturbance
What is papilloedema?
Optic disc swelling due to increased intracranial pressure as a result of excess CSF
What are the symptoms of papilloedema?
Enlarged blind spot, blurring of vision and visual obscurations
What is the serious complication of papilloedema?
Compression of optic nerve which can lead to loss of vision
Describe aqueous humour
Fluid that provides oxygen, metabolites and bicarbonate to the structures within the eye
What is the purpose of bicarbonate in aqueous humour?
Buffers hydrogen ions produced in the cornea and lens by anaerobic glycolysis
Describe the pathway of aqueous humour
- produced in ciliary body
- posterior chamber
- anterior chamber
- canal of schlem (iridocorneal angle)
- scleral venous sinus
Name the two types of epithelial cells in the ciliary body
pigmented and non-pigmented
What ion exchanges occur in the PE?
Bicarbonate and hydrogen ions are transported in exchange for Cl- and Na+
Where do the bicarbonate and hydrogen ions that go into the PE come from?
Hydration of carbon dioxide catalysed by carbonic anhydrase
What happens to the sodium and chloride ions?
Diffuse through the gap between PE and NPE cells and are transported by the Na+/K+/2Cl- co-transporter
What other transporters are also involved in the NPE?
Sodium potassium pump and chloride channels
Overall what ions move into the aqueous posterior chamber?
Sodium, chloride and water (due to osmosis)
What drug can be used in glaucoma and why?
Carbonic anhydrase inhibitors - decrease aqueous and reduce ocular pressure
Describe the retina structure
Photoreceptors
Bipolar cells
Ganglion cells
What is the purpose of horizontal cells?
Receive input from photoreceptors and project to other photoreceptors and bipolar cells
What is the purpose of amacrine cells?
Respond to glutamate produced by bipolar cells by projecting signals to ganglion cells, other bipolar cells and amacrine cells
Name two types of photoreceptors
Rods
Cones
Describe rods
Sensitive to light found on the periphery of the eye and responsible for night vision
Describe cones
Responsible for colour vision, found in the fovea. Three types - short, middle and long
Describe phototransduction in rods
- Light hits the photoreceptor
- Retinal and rhodopsin change shape
- Transducin alpha unit breaks away and binds to PDE thus activating it
- cGMP is converted to GMP
- cGMP no longer keeps the sodium channels open, they shut and hyper-polarisation occurs
What happens when hyper polarisation occurs?
Bipolar cells transmit the signal to ganglion cells and ultimately the brain
Define visual acuity
Ability to distinguish two nearby points determined by photoreceptor spacing and refractive power
Describe the visual acuity of rods
Large spacing between rods, high convergence as many rods contribute to one large ganglion but decreased acuity
Describe the visual acuity of cones
High density in fovea, low convergence lots of small ganglion cells
After cataract surgery what do people who have had congenital cataracts often struggle with?
Perceiving shape and form
What is amblyopia?
No pathology but one eye is better than the other
What can cause amblyopia if not corrected early?
Strabismus
How is amblyopia treated?
Eye patch over good eye to help brain process signals from bad eye but ultimately surgery
What conditions can increase intracranial pressure?
- tumours
- head injury
- hydrocephalus
- meningitis
- stroke
What is the Monro Kellie Hypothesis?
Intracranial volume is constant and the cranial cavity is inelastic so there is no room for expansion
What are the ocular symptoms for increased intracranial pressure?
Blurred vision Double vision Loss of vision Papilloedema Pupillary changes
What is special with the optic nerve?
They are tracts of the CNS covered by meninges
What happens to the optic nerve when ICP increases?
It gets compressed as well as the central artery and vein which leads to a bulging/swollen optic disc
What is a swollen optic disc known as?
papilloedema
If compression of the oculomotor nerve occurs what happens?
Only the superior oblique and lateral rectus still have innervation so the pupil will be turned down and out
How will oculomotor nerve compression present?
Dilated pupil, ptosis, down and out look
How can the oculomotor nerve be stretched or compressed?
The brain can herniate through folds created by the dura mater and if the medial temporal lobe herniates through the tectorial notch the oculomotor nerve can be affected
Why is the trochlear nerve susceptible to damage?
It has a long intracranial course
What is the effect of compression of the trochlear nerve?
Paralysis of the superior oblique which means the inferior oblique is unopposed
How will trochlear nerve compression present?
Eye cannot move inferomedially - diplopia when looking down
What will stretching of the abducent nerve cause?
Paralysis of the lateral rectus muscle
How will stretching of the abducens present?
Medial deviation of the eye