physiology

Question 1

what produces cerebrospinal fluid?

Answer 1

the secretory epithelium of the choroid plexus

Question 2

describe the path of cerebrospinal fluid

Answer 2

formed in the ventricles and then circulates in the subarachnoid space then absorbed into venous circulation

Question 3

what are the 3 major functions of cerebrospinal fluid?

Answer 3

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

Question 4

describe CSF secretion

Answer 4

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

Question 5

how are the ventricles connected?

Answer 5

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

Question 6

what are the components of the blood brain barrier?

Answer 6

the capillary endothelium, its basal membrane and perivascular astrocytes

Question 7

what tumours can you get in the ventricles, choroid plexus and CSF?

Answer 7

• Colloid cyst (often found at the interventricular foramen)
• Ependymomas (arising from the ependymal cells lining the ventricles)
• Choroid plexus tumours

Question 8

what are the types of ventricular haemorrhage?

Answer 8

• Epidural hematoma, arterial bleed between skull and dura
• Subdural hematoma, venous bleed between dura and arachnoid
• Subarachnoid hemorrhage

Question 9

describe hydrocephalus

Answer 9

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

Question 10

describe idiopathic intracranial hypertension

Answer 10

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

Question 11

what is papilloedema?

Answer 11

optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve

Question 12

what are the symptoms of papilloedema?

Answer 12

enlarged blind spot, blurring of vision, visual obscurations and loss of vision

Question 13

describe aqueous humor

Answer 13

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

Question 14

what is the direct (vertical) pathway for signal transmission?

Answer 14

photoreceptors –> bipolar cells –> ganglion cells

Question 15

what lateral connections influence signal processing?

Answer 15

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

Question 16

what are the 4 regions of photoreceptors?

Answer 16

Outer segment
Inner segment
Cell body
Synaptic terminal

Question 17

what do photoreceptors do?

Answer 17

Converts electromagnetic radiation to neural signals (transduction!)

Question 18

what are the 2 types of photoreceptors?

Answer 18

rods and cones

Question 19

describe the basis of phototransduction

Answer 19

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

Question 20

what are the components of rhodopsin?

Answer 20

Retinal (Vitamin A derivative) + Opsin (G-protein coupled receptor)

Question 21

what is visual acuity?

Answer 21

the ability to distinguish two nearby points

Question 22

what determines high visual acuity?

Answer 22

photoreceptor spacing and refractive power
(more dense higher acuity)

Question 23

what are rods for?

Answer 23

seeing in dim light

Question 24

what are cones for?

Answer 24

seeing in daylight

Question 25

what is the result or more convergence in the rod system?

Answer 25

increasing sensitivity with decreasing acuity
(can see in the dark but vision is blurry)

Question 26

rods vs cones

Answer 26

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

Question 27

in which half of the retina do the nerve fibres cross over at the optic chiasm?

Answer 27

nasal half

Question 28

how much does each eye see?

Answer 28

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°).

Question 29

what is amblyopia?

Answer 29

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

Question 30

what can cause amblyopia?

Answer 30

strabismus (wandering eye)
seen in babies and children, treated with patch over good eye and/ or surgery when they’re old enough