Test 146  (Ocular physiology)

1. The following are true about the lens:

a. it has a higher concentration of sodium than potassium

b. it has the highest concentration of protein than other 
    organs in the body

c. 90% of proteins in the lens are water-soluble

d. gluthatione is reduced in cataract

e. gluthatione in the lens is 10 times than of the aqueous
 

Answer
a.F   b.T   c.T   d.T   e.F
The potassium concentration is higher than sodium 
within the lens. Gluthatione in the lens is 1000 times that of the aqueous.

2. The felderstrukter fibres of the extraocular muscles:

a. form the bulk of the orbital part of the muscle

b. have poorly developed sarcoplasmic reticulum

c. are singly innervated

d. are more richly supplied by blood than the 
    fibrillenstrukter fibres

e. respond to succinylcholine with a prolonged tonic
    contraction

Answer
a.F   b.T   c.F  d.F  e.T
Felderstrukter fibres form globe and core of 
the extraocular muscles. They are innervated 
by multiple nerve endings. They are less blood supply compared with fibrillenstrukter fibres. 

3. The following are true about rods in darkness:

a. there is tonic release of neurotransmitters

b. the sodium ion channels are open

c. the potassium ion channels are shut

d. there is a net influx of sodium ions

e. the cyclic GMP level is low in the rods

Answera.T  b.T  c.F  d.T  e.F
Both sodium and potassium ion channels are open. There is a net influx of sodium to maintain the resting membrane at -40mV. The cyclic GMP is high in rods in the dark.

4. When a photon strikes the rhodopsin:

a. bleaching occurs

b. retinal molecules are bound to rhodopsin

c. the intracellular cGMP is increased

d. the sodium ion channels are closed

e. neurotransmitter release by rods decreases.

Answer
a.T   b.F  c.F  d.T  e.T
When a photo strikes the rhodopsin, the retinal molecules become unbound from the rhodopsin a process known as bleaching. The resultant opsin activates the second messenger and causes a decrease in the intracellular cGMP. The sodium ion channels are closed leading to hyperpolarization and neurotransmitter decreases.

5. A lesion in the right medial longitudinal fasciculus:

a. causes left abduction nystagmus

b. impairs right adduction

c. impairs left adduction

d. causes problem with upgaze

e. causes problem with convergence

 
Answer
a.T   b.T  c.F   d.F  e.F
A right medial longitudinal fasciculus lesion causes 
right adduction deficit and left abduction nystagmus. Convergence is intact.

 

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