Physiology

Question 1

what is CSF

Answer 1

clear, colourless liquid that supplies water, amino acids and ions while removing metabolites

Question 2

three major functions of CSF

Answer 2

1. mechanical protection= shock absorbing
2. Homeostatic= pH of CSF affects pulmonary ventilation and cerebral blood flow. Hormone transport.
3. circulation

Question 3

how is clinical analysis of CSF obtained?

Answer 3

lumbar puncture

Question 4

define the choroid plexus

Answer 4

network of capillaries in the walls of ventricles that produces CSF

Question 5

what does the secretion of CSF by the choroid plexus depend on?

Answer 5

active transport of Na+ across the cells into CSF as the electrical gradient pulls along Cl- and both ions drag water by osmosis

Question 6

is the concentration of K+, glucose and protein lower in CSF than blood?

Answer 6

yes

Question 7

is the concentration of Na+ and Cl- higher in CSF than the blood?

Answer 7

yes

Question 8

structure of the BBB

Answer 8

• consists of capillary endothelium, basal membrane and perivascular astrocytes
• tight junctions prevent paracellular movement of molecules

Question 9

what parts of the brain lack the BBB?

Answer 9

circumventricular organs

pineal gland

Question 10

tumour pathologies of the ventricles, choroid plexus and CSF

Answer 10

colloid cyst
ependymomas
choroid plexus tumours

Question 11

examples of ventricular haemorrhage

Answer 11

• epidural haematoma
• subdural haematoma
• subarachnoid haemorrhage

Question 12

describe an epidural haematoma

Answer 12

arterial bleed between skull and dura

Question 13

describe a subdural haematoma

Answer 13

venous bleed between dura and arachnoid

Question 14

describe hydrocephalus

Answer 14

accumulation of CSF in the ventricle system or around the brain
subsequent enlargement of one or more ventricles and increase in CSF pressure

Question 15

what causes hydrocephalus

Answer 15

obstruction

overproduction

Question 16

symptoms of idiopathic intracranial hypertension/pseudotumour cerebri

Answer 16

headache
visual disturbance (fields > blindness, due to papilloedema)

Question 17

what ion does aqueous humour contain?

Answer 17

bicarbonate HCO3-

Question 18

what is the role of bicarbonate HCO3- in the aqueous humour?

Answer 18

it buffers H+ produced by the cornea and lens in anaerobic glycolysis

Question 19

what are the two layers that cover the ciliary body and posterior surface of the iris

Answer 19

pigmented retinal layer (RPE)

non-pigmented epithelial layer (NPE)

Question 20

how are HCO3- and H+ produced?

Answer 20

hydration of CO2 catalysed by carbonic anhydrase

Question 21

where are HCO3- and H+ transported?

Answer 21

across the basolateral membranes of the pigmented epithelial cells into interstitial fluid in exchange for Cl- and Na+

Question 22

how do Cl- and Na+ reach the aqueous humour?

Answer 22

they diffuse through gap junctions between PE and NPE and are transported into the aqueous humour via Na+/K+/Cl- co-transporter

Question 23

what is the net movement of Cl- and Na+ to the aqueous humour accompanied by?

Answer 23

water moving through ciliary epithelial aquaporins and paracellular pathway

Question 24

define glaucoma

Answer 24

raised intra-ocular pressure due to imbalance in secretion and removal of aqueous humour

Question 25

management of glaucoma

Answer 25

CA inhibitors reduce production of aqueous humour e.g. dorzolamide and acetazolamide

Question 26

side effects of acetazolamide

Answer 26

acidosis in kidneys

Question 27

retinal structure

Answer 27

epithelial layer contains pigment first neural layer is photoreceptors which release glutamate which attaches to bipolar cells which release neurotransmitters to ganglion cells lateral connections- horizontal cells and amacrine cells

Question 28

what is the photoreceptors resting membrane potential?

Answer 28

more positive -20mV than other neurones

Question 29

what happens to the photoreceptors resting membrane potential with light exposure?

Answer 29

hyperpolarises

Question 30

describe the dark currant

Answer 30

the positive resting membrane potential is due to a cGMP-gated Na+ channel being open in the dark causing a constant release of glutamate

Question 31

what happens to the cGMP-gated Na+ channel when exposed to light

Answer 31

it closes

Question 32

Na+/K+ in the dark

Answer 32

pump is equally permeable to both ions | Vm is therefore between ENa and EK

Question 33

Na+/K+ in response to light

Answer 33

PNa is reduced (outer segments close), therefore Vm becomes closer to ion potential of K+ (-90mV)

Question 34

what is the visual pigment in rods called?

Answer 34

rhodopsin= retinal (vitamin A) and opsin (GPCR)

Question 35

describe how hyperpolarisation happens?

Answer 35

all-trans-retinal activates transducing (GPCR) activates PDE which hydrolyses cGMP closing Na+ channels

Question 36

what is high visual acuity facilitated by?

Answer 36

photoreceptor spacing

Question 37

what lighting do rods see best in?

Answer 37

dim light

Question 38

how are rods distributed on the retina?

Answer 38

all across the retina with large spaces (low density= high convergence)

Question 39

what lighting do cones see best in?

Answer 39

daylight

Question 40

where are cones distributed on the retina?

Answer 40

concentrated at the fovea

Question 41

three types of cone cells

Answer 41

1. short-wave cones= blue 2. medium-wave cones= green 3. long-wave cones= red

Question 42

properties of rod cells

Answer 42

``` achromatic peripheral retina high convergence high light sensitivity low visual acuity ```

Question 43

properties of cones

Answer 43

``` chromatic central retina (fovea) low convergence low light sensitivity high visual acuity ```

Question 44

visual fields on the retina

Answer 44

- each eye sees monocular visual field +/- 45 degrees - they overlap to create a binocular visual field +/- 45 degrees - retina is divided in half relative to the fovea into nasal and temporal hemiretina - nasal cross at the optic chiasm, temporal do not

Question 45

what do people with congenital cataracts struggle with?

Answer 45

perceiving shape and form as they cannot be removed until 10-20 years

Question 46

define amblyopia (cortical blindness)

Answer 46

variety of visual disorders where there is no problem with the eye but one eye has better vision than the other

Question 47

causes of amblyopia

Answer 47

strabismus (wandering eye) if not corrected in infancy

Question 48

management of strabismus in childhood

Answer 48

cover good eye for some hours each day so weak eye still grows connections until it can be surgically corrected

Question 49

define Hebb's postulate

Answer 49

cells that fire together wire together (if not working, invades space)