physiology Flashcards
what is ICP
pressure within the cranial cavity
pathophysiology of raised ICP
increased pressure in fluid surrounding the brain or an increase in the pressure within the brain itself
name some causes of raised ICP
brain tumours
head injuries
hydrocephalus
meningitis
stroke
main complication of raised ICP
can cause damage to the brain or spinal chord by compressing them
what makes infants less affected by raised ICP
fontanelles and open suture lines means that they have potential for change in cranial size
what is the monro-kellie hypothesis
blood, brain and CSF are in equilibrium
if volume of one of the components increases, the volume of a different component must decrease to maintain equilibrium
what happens in brain herniation
the brain becomes displaced
name some visual problems caused by raised ICP
double vision, blurred vision, loss of vision, pupillary changes, papilledema
describe the optic nerves
CNS tracts - paired anterior extensions of the forebrain
what are optic nerves formed by
the axons of the retinal ganglion cells
complication of raised ICP on the optic nerve
compression of the nerve, as well as the central artery and vein of the retina causes papilledema
name 5 possible visual symptoms of papilledema
- Transient visual obscurations (greying-out of vision)
- Transient flickering
- Blurring of vision
- Constriction of the visual field
- Decreased colour perception
what are dural septae
folds of dura mata creates divisions in the cranial cavity
what is the role of dural septae
divide the cranial cavity into falx cerebri and tentorium cerebelli
impact of raised ICP on the dural septae
brain can herniate through openings (tentorial notch, foramen magnum)
when will raised ICP affect the oculomotor nerve
if medial temporal lobe herniates through tentorial notch
result of raised ICP on the oculomotor nerve (2)
- paralysis of somatic motor innervation - 4 extra-ocular muscles and eyelid
- paralysis of parasympathetic innervation of sphincter of pupil
clinical sign of damage to the oculomotor nerve due to raised ICP
lose/slowness of pupillary light reflex, dilated pupil, ptosis, eye turned inferolaterally (‘down and out’)
why is the trochlear nerve susceptible to damage
small diameter with a long intracranial course
result of damage to the trochlear nerve due to raised ICP
paralysis of superior oblique muscles
clinical presentation of damage to the trochlear nerve due to raised ICP
eye cannot move inferiomedially, resulting in diplopia when looking down
result of damage to the abducent nerve due to raised ICP
paralysis of lateral rectus muscle
clinical presentation of damage to the abducent nerve due to raised ICP
eye cannot move laterally in horizontal plane, resulting in medial deviation of the eye
what creates the blood-ocular barrier
endothelium of capillaries in the iris, ciliary body and retina
what creates the blood-aqueous barrier
capillaries of the iris and ciliary body
what creates the blood-retinal barrier
non-fenestrated capillaries of the retinal circulation andtight junctions between retinal epithelial cells
what is the aqueous humour
clear fluid that flows through the anterior segment of the eye
name some ways we can overcome the blood-ocular barrier when administrating drugs (3)
- alcohol or acetate makes steroid more hydrophobic
- phosphate makes it more hydrophilic
- various additives may be added to topical eye drops such as viscosity enhancers, permeation enhancers
what is CSF
a clear, colourless fluid that surrounds the brain and the spinal cord
what is the main component of CSF
water
where is the CSF contained
within the subarachnoid space and the central canal of the spinal cord
what are the 3 main roles of CSF
mechanical protection
homeostatic function
circulation
role of CSF in mechanical protection
shock-absorbing medium that protects brain tissue; brain ‘floats’ inside the cranial cavity
role of CSF in homeostatic function
pH of CSF affects pulmonary ventilation and cerebral blood flow, transports hormones
role of CSF in circulation
medium for minor exchange of nutrients and waste products between blood and brain tissue
what produces CSF
secretory epithelium of the choroid plexus
where is the choroid plexus located
in the two lateral ventricles, and in the roof of the third and fourth ventricles
what is the usual total volume of CSF
150ml
what is the choroid plexus
network of capillaries in the walls of the ventricles
name the ions involved in CSF secretion (3)
Na+, Cl- and HCO3-
state the flow of CSF (4)
- choroid plexus of each lateral ventricle
- third ventricle via narrow openings in interventricular foramina (more added)
- flows through the aqueduct of the midbrain into 4th ventricle (more added)
- enters subarachnoid space + circulates in the central canal of the spinal chord
name the 4 main foramina of the ventricles of the brain
- intraventricular Foramina (of Monroe)
- cerebral Aqueduct (of Sylvius)
- foramen of Magendie
- foramina of Luschka
what do the Interventricular foramen (Foramen of Monro) connect
the lateral ventricles to third ventricle
how many foramina in the lateral ventricles of the brain
3
what is another name for the foramen of megendie
median aperture
what is another name for the foramina of luschka
lateral apertures
how many foramina are found in the 4th ventricle of the brain
3
what does the cerebral aqueduct connect
3rd to 4th ventricle
what do the foramen of Magendie and Luschka connect
the 4th ventricle to the subarachnoid space
how does CSF return to venous blood
through arachnoid granulations into the superior sagittal sinus
what is the role of the blood brain barrier
protects the brain from neurotoxins and helps prevent infection from spreading to the brain
how do we obtain CSF
via lumbar puncture
what does normal CSF look like
clear and colourless, contains little protein, little immunoglobulins and only 1-5 cells/ml
what is an epidural haematoma
arterial bleed between skull and dura
what is a subdural haematoma
venous bleed between dura and arachnoid
what is hydrocephalus
accumulation of CSF in the ventricular system or around the brain causing ventricular enlargement and increased CSF pressure
what are the 2 main causes of hydrocephalus
obstruction of drainage or overproduction of CSF
what is papilledema
optic disk swelling due to increased intercranial pressure
how do we recognise raised intercranial pressure
transmitted to the subarachnoid space surrounding the optic nerve
name the 3 main roles of the aqueous humour
- provides oxygen and metabolites and contains bicarbonate
- bicarbonate buffers the H+ produced by the cornea and lens by anaerobic glycolysis
- very high in ascorbate, which is a powerful antioxidant
where is the aqueous humour produced
in the epithelial later of the ciliary body
describe the flow of the aqueous humour in the eye (2)
- from the ciliary body into the posterior chamber
- through the pupil into the anterior chamber
drainage of aqueous humour
- drains to the scleral venous sinus through a trabecular meshwork and the canal of Schlemm
- a small amount diffuses through the vitreous being absorbed across the retinal pigment epithelium
where is the canal of schlemm located
in the angle between the iris and cornea (iridocorneal angle)
what lines the ciliary body and the posterior surface of the iris
a forward continuation of the pigment epithelium of the retina (PE) overlain by an inner nonpigmented epithelial (NPE) layer
what drug can be used to reduce the production of aqueous humour
carbonic anhydrase inhibitors
name 2 carbonic anhydrase inhibitors and how they’re administered
dorzolamide (eye drops)
acetazolamide (oral)
name innate immune system components of the eye (3)
blink reflex
mucous layer
tears
role of the blink reflex in protecting the eye
tears flush the surface of the eye
how do tears act as a chemical barrier to protect the eye
antimicrobial agents e.g. lysozymes
name the immune cells found in tears (3)
neutrophils, macrophages and conjunctival mast cells
name the adaptive immune cell found in the eye
langerhans cells
role of langerhans cells in the eye
principle antigen presenting cell for the external eye
what is the only part of the eye with lymphatic drainage
conjunctiva
what is immune privilege
being able to tolerate the introduction of antigens without eliciting an inflammatory response
name some sites of the body that have immune privilege
brain/CNS, testes, placenta, eyes
name the 5 areas of the eyes which have immune privilege
cornea
anterior chamber
lens
vitreous cavity
subretinal space
what is sympathetic ophthalmia
rare, bilateral granulomatous uveitis
what is the most common cause of sympathetic ophthalmia
trauma
give an example of a type 1 hypersensitivity reaction in the eye
acute allergic conjunctivitis
give an example of a type 2 hypersensitivity reaction in the eye
ocular cicatricial pemphigoid
give an example of a type 3 hypersensitivity reaction in the eye
autoimmune corneal melting
give an example of a type 4 hypersensitivity reaction in the eye
corneal graft rejection
how is the retina divided
relative to the fovea into a nasal and temporal hemiretina
what is contained in the left optic tract
fibres from the left temporal (lateral) retina, and the right nasal (medial) retina
what is contained in the right optic tract
fibres from the right temporal retina, and the left nasal retina
upper optic radiation
carries fibres from the superior retinal quadrants through the parietal lobe to reach the visual cortex
lower optic radiation
carries fibres from the inferiorretinal quadrants through the temporal lobe to reach the visual cortex
describe the direct pathway for visual signal transmission
photoreceptors to bipolar cells to ganglion cells
axons of ganglion cells merge to form the optic nerve
role of horizontal cells in signal processing
receive input from photoreceptors and project to other photoreceptors and bipolar cells
role of amacrine cells in signal processing
receive input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells
role of photoreceptors
convert electromagnetic radiation to neural signals
what are the 2 main types of photoreceptors
rods and cones
resting membrane potential of photoreceptors
around 20 mV
what is rhodopsin
visual pigment molecule
what is visual acuity
the ability to distinguish 2 nearby points
name 2 factors that affect visual acuity
photoreceptor spacing and refractive power
role of cone receptors
colour receptors
role of rod receptors
night vision and seeing in black and white
