physiology Flashcards
what produces cerebrospinal fluid?
the secretory epithelium of the choroid plexus
describe the path of cerebrospinal fluid
formed in the ventricles and then circulates in the subarachnoid space then absorbed into venous circulation
what are the 3 major functions of cerebrospinal fluid?
Mechanical protection: shock-absorbing medium that protects brain tissue. Brain “floats” inside the cranial cavity
Homeostatic function: pH of CSF affects pulmonary ventilation and cerebral blood flow. Transports hormones.
Circulation: medium for minor exchange of nutrients and waste products between blood and brain tissue
describe CSF secretion
involves the transport of ions ( Na+, Cl¯ and HCO3¯) across the epithelium from blood to CSF
can occur because of the polarized distribution of specific ion transporters in the apical or basolateral membrane of the epithelial cells
how are the ventricles connected?
Intraventricular Foramina (of Monroe): Lateral Ventricles to Third Ventricle
Cerebral Aqueduct (of Sylvius): Third Ventricle to Fourth
Foramen of Magendie: Median aperture – Fourth ventricle to subarachnoid space
Foramina of Luschka: Lateral apertures – Fourth ventricle to subarachnoid space
what are the components of the blood brain barrier?
the capillary endothelium, its basal membrane and perivascular astrocytes
what tumours can you get in the ventricles, choroid plexus and CSF?
- Colloid cyst (often found at the interventricular foramen)
- Ependymomas (arising from the ependymal cells lining the ventricles)
- Choroid plexus tumours
what are the types of ventricular haemorrhage?
- Epidural hematoma, arterial bleed between skull and dura
- Subdural hematoma, venous bleed between dura and arachnoid
- Subarachnoid hemorrhage
describe hydrocephalus
accumulation of CSF in the ventricular system or around the brain (either due to obstruction or overproduction)
subsequent enlargement of one or more ventricles and increase in CSF pressure
describe idiopathic intracranial hypertension
Enigmatic condition
Symptoms include headache and visual disturbances (visual field disturbances to blindness) due to papilloaedema
Despite increased CSF pressure no imaging features of hydrocephalus
what is papilloedema?
optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve
what are the symptoms of papilloedema?
enlarged blind spot, blurring of vision, visual obscurations and loss of vision
describe aqueous humor
a specialized fluid that bathes the structures within the eye.
It provides oxygen and metabolites and contains bicarbonate (HCO3).
Bicarbonate buffers the the H+ produced in the cornea and lens by anaerobic glycolysis.
Ascorbate is a powerful antioxidant
what is the direct (vertical) pathway for signal transmission?
photoreceptors –> bipolar cells –> ganglion cells
what lateral connections influence signal processing?
Horizontal cells, Receive input from photoreceptors and project to other photoreceptors and bipolar cells
Amacrine cells, Receive input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells
what are the 4 regions of photoreceptors?
Outer segment
Inner segment
Cell body
Synaptic terminal
what do photoreceptors do?
Converts electromagnetic radiation to neural signals (transduction!)
what are the 2 types of photoreceptors?
rods and cones
describe the basis of phototransduction
In the dark,
PNa PK (Na channels in the outer segment)
Vm therefore between ENa and EK
In response to light,
PNa is reduced (outer segment channels close), PK > PNa
therefore, Vm –> EK, hyperpolarizes
Change is local and graded
what are the components of rhodopsin?
Retinal (Vitamin A derivative) + Opsin (G-protein coupled receptor)
what is visual acuity?
the ability to distinguish two nearby points
what determines high visual acuity?
photoreceptor spacing and refractive power
(more dense higher acuity)
what are rods for?
seeing in dim light
what are cones for?
seeing in daylight
what is the result or more convergence in the rod system?
increasing sensitivity with decreasing acuity
(can see in the dark but vision is blurry)
rods vs cones
rods:
- achromatic
- peripheral retina
- high convergence
- high light sensitivity
- low visual activity
cones:
- chromatic
- central retina (fovea)
- low convergence
- low light sensitivity
- high visual activity
in which half of the retina do the nerve fibres cross over at the optic chiasm?
nasal half
how much does each eye see?
Each eye sees a part of the visual space,
monocular visual field (±45°) but their
visual fields overlap extensively to create a binocular visual field (±45°).
what is amblyopia?
a variety of visual disorders when there is no problem with the eye (the optics and retina are fine), but one eye has better vision than the other
what can cause amblyopia?
strabismus (wandering eye)
seen in babies and children, treated with patch over good eye and/ or surgery when they’re old enough
