Test 170  (MRCS Questions, 2003)

1. True statements about Bruch's membrane:

 a. it has five well defined layers

 b. it is penetrated by the choriocapillaries

 c. it is 2-4 mm thick

 d. it is secreted by the RPE

 e. it is absent at the fovea
 

Answera.T  b.F  c.F   d.T  e.F
Bruch's membrane consists of five layers: the basement membrane of the retinal pigment epithelium, the inner collagenous layer, the elastic layer, the outer collagenous layer, and the basement membrane of the choriocapillaris. All five layers of Bruch's membrane are permeable to fluorescein under normal conditions. Bruch 's membrane is thickest at the posterior pole (2 to 4 µm) and tapers in the periphery (1 to 2 µm)..
 

2. The trochlear nerve:

a. is vulnerable to head injury

b. passes between the posterior cerebral and the superior 
    cerebellar arteries

c. crosses within the anterior medullary vellum

d. lies in the lateral wall of the cavernous sinus

e. innervates the superior oblique muscle on its inferior 
    surface
 

Answera.T  b.T  c.T  d.T  e.F
The trochlear nerve provides innervation to the superior oblique muscle only. Its nucleus is located in the
midbrain, just beneath the cerebral aqueduct, caudal to the oculomotor nuclear complex. The axons exit dorsally and cross within the anterior medullary velum that lies just caudal to the inferior colliculi. Thus, innervation to the superior oblique muscles is strictly contralateral. After decussating, the nerve runs forward in the subarachnoid space around the mesencephalon and cerebral peduncles, along the free edge of the tentorium, between the posterior cerebral and superior cerebellar arteries. It enters the cavernous sinus just below the oculomotor nerve . Although the trochlear nerve passes through the superior orbital fissure, it enters the orbit outside the annulus of Zinn (a position unique for the ocular motor nerves) and crosses above the superior rectus muscle en route to innervate the superior oblique muscle. It innervates the muscle on its undersurface.
The trochlear nerve innervates the superior oblique muscle on its superior surface.
.
 

3. The following arteries make up the Circle of Willis:

a. the anterior communicating artery 

b. the internal carotid artery

c. the posterior cerebral artery 

d. the basilar artery

e. anterior cerebral artery
 

Answer
a.T   b.T  c.T  d.F  e.T
The circle of Willis provides the major arterial anastomosis between the carotid and vertebrobasilar circulations. Surrounding the ventral thalamus, this arterial polygon consists of the internal carotid arteries, anterior cerebral arteries, anterior communicating artery, posterior communicating arteries, posterior cerebral arteries, and basilar tip (Note: not the artery).. 

4. The following structure arise from surface ectoderm:

a. conjunctival epithelium

b. lens

c. meninges

d. lacrimal gland

e. sclera
 

Answer
a.T  b.T  c.F  d.T  e.F
The meninges are derived from the cranial neural crest. Sclera is derived from mesenchyme.

.

5. The lens zonules:

 a. comprises of collagen type II and to a lesser extent 
     type IV

 b. are attached to the lens 2 mm anterior to the equator

c. are attached to the valley areas of the ciliary processes

d. contain a high amount of the protein cystein

e. are produced by the pars plicata of the ciliary epithelium

Answer
a.F   b.T  c.T  d.T  e.F
The zonules are made up of non-collagenous 
carbohydrate-protein mucopolysaccharide and 
glycoprotein complexes secreted by the ciliary epithelium. The zonules arise from its posterior insertion at posterior pars plana region of ciliary 
body near ora serrata and extend longitudinally 
toward pars plicata of ciliary body as a mat or flat meshwork of interlacing fibres. The zonule
fibres pass from pars plana zonule through the valley between the ciliary processes and on to
the anterior zonules and attach to the lens capsule anterior and posterior to the equator.

 

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