Physiology Flashcards
Where is CSF produced
The secretory epithelium of the choroid plexus
This is found in the ventricles of the brain (spaces)
Describe the appearance of the CSF
Clear, colourless liquid
Mostly water
Roughly how much CSF is produced daily
150ml is present at any time and is replaced 3-4x per day
What does CSF give to tissues
Water
Amino acids
Ions
Removes metabolites
Describe how CSF ‘circulates’
Produced from lateral ventricles
Passes through interventricular foramen to 3rd and then through the cerebral aqueduct to 4th ventricle
They add to CSF as it drains through
Passes through the median and lateral apertures to subarachnoid space
Then absorbed back into venous circulation by passing through arachnoid villi into the SSS
What are the main functions of CSF
Mechanical protection - shock absorber that protects brain
Homeostasis - pH affects pulmonary system and cerebral blood flow
Some hormones are transported in it
Provides nutrients
How do you analyse CSF clinically
Lumbar puncture
Should be completely clear
Presence of blood or pus indicates a problem
What is the choroid plexus
Network of capillaries are lined by the ependymal cells of the ventricles
Good connection between blood and brain
The apical surface if the ependymal cells faces the circulation - true or false
FALSE
basolateral surface faces capillary
CSF is secreted through the apical membrane
Which ions are transported in the production of CSF
Na, Cl and HCO3
Water also moves across due to ion movement
What drives the ion movement needed for CSF production
The distribution of ion channels
NOT arterial blood pressure
Are the ventricles in the brain connected to each other?
YES
There are 4 - 2x lateral and the third + fourth
How many ventricles are in the brain
4
2x lateral
The third
The fourth
How does CSF pass from the ventricles to the subarachnoid space
There are 3 holes in the roof of the 4th ventricles
The median aperture
2x lateral apertures
How does CSF return to the venous system
Passes into the superior sagittal sinus via
Gets there by entering arachnoid villi - areas of arachnoid layer that push up into dura to be nearer blood
What forms the blood brain barrier
Tight junctions between endothelial cells in the brain capillaries- prevent molecules passing through
What are the pros and cons of the BBB
Pro = protects brain from many bacterial infections and toxins
Con - barrier to drug delivery into the CNS
What is the aqueous humour
Specialized fluid that bathes the structures within the eye.
It provides oxygen and metabolites and contains bicarbonate
Where is aqueous humour produced
Epithelial layer of the ciliary body
Describe the path of aqueous humour
Produced in ciliary body
Flows into anterior chamber
Drains into the scleral venous sinus
Continuous process of secretion and reabsorption
How do you block the production of aqueous humour
Block carbonic anhydrase (involved in its production)
Can be used to reduce pressure in glaucoma
Which ions are involves in the production of aqueous humour
carbonic anhydrase in the cells generates HCO3
The bicarb is used to drive Na and Cl movement in the cell
What 4 things must happen for us to see an object
Pattern of object must fall on the visual receptors in the retina
Amount of light entering must be regulated
The energy from light must be transduced to electrical signals
The brain must receive these signals
Describe the layers of the retina
Photoreceptors are the furthest back
Bipolar cells sit in front and Ganglion cells in front of those
Light passes to back of eye and signal passes forward again
What are the 2 types of photoreceptors
Rods and cones
3 different types of cones
What is the function of photoreceptors
Converts electromagnetic radiation to neural signals
Describe the changes in membrane potential in photoreceptors
When exposed to light the photoreceptor becomes hyperpolarised
Doesn’t quite trigger a AP
Releases less glutamate
How is an AP triggered in the eye
Hyperpolarisation of photoreceptor then bipolar cells causes AP generation in ganglion cells
Caused by light
What is the dark current in the eye
A cGMP-gated Na+ channel that is open in the dark and closes in the light
More glutamate is released in the dark so more sodium moves in
What is rhodopsin
A visual pigment molecule
Made of retinal and opsin
Undergoes a conformational change when exposed to light
When active it triggers a cascade involving G proteins which closes the Na channel
Causes AP
What is visual acuity and what determines it
Ability to distinguish two nearby points. Determined largely by photoreceptor spacing and refractive power
What cells allow us to see colour
Cones cells
Different types absorb different wavelengths of light
List features of cone cells
See colour Found in central retina - fovea Low convergence Low light sensitivity - work in well lit High visual acuity
List features of rod cells
Achromatic - no colour vision Peripheral retina High convergence High light sensitivity - used in dark places Low visual acuity
Why is the left visual field perceived by the right side of the brain
The nerves cross over at the optic chiasm
Where is visual information processed
Visual cortex in the brain
What are the meninges
3 layers of tissue surrounding the entire brain
Dura mater - tough, fibrous layer
Arachnoid mater - thinner, spidery layer
Pia mater - single cell layer
CSF is found between which layer of the meninges
Deep to the arachnoid layer (subarachnoid space)
Between arachnoid and pia
What passes through the tentorial notch in the dura mater
The brain stem and some cranial nerves
The optic nerves are covered by meninges - true or false
TRUE
therefore some consider optic nerves as extensions of the brain/CNS
Which type of fibres are contained in the oculomotor nerves
Motor
Parasympathetic
Describe the trochlear nerve
Long intracranial course
Very thin as only supplies 1 muscle - superior oblique
Describe the abducent nerve
Also has a long intracranial course
Innervates the lateral rectus in eye
What do the parasympathetic fibres of the oculomotor nerve supply
Constrictor papillae
Responsible for constricting the pupil
If damaged the eye will dilate
What are the 3 components of the accommodation reflex
Fattening of the lens
Constriction of the pupil
Convergence of the eyes
What is the purpose of the accommodation reflex
It is used to focus on near objects
