26. Muscles fibres:
a. have a plasma membrane also known as the sarcolemma
b. contains sarcoplasm which is rich in potassium, magnesium
and phosphate
c. have invaginations called T-tubules that run parallel to myofibrils
d. made up of functional units called the sarcomere which lies
between 2 successive M-lines
e. are subdivided into myofibrils that contain the filamentous proteins
actin and myosin, responsible for muscle contraction
27. Muscle fibres:
a. can be divided into fast-twitch and slow-twitch fibres dependent
on their duration of contraction
b. of the fast-twitch variety are found in the outer orbital layer
c. of the slow-twitch variety are found in the outer orbital layer
d. that are fast-twitch have a larger diameter than slow-twitch fibres
e. that are fast-twitch derive their energy from aerobic metabolism
in the Krebs cycle
f. that are slow-twitch maintain tonic states of contraction
g. that are slow twitch are innervated by multiple en grappe nerve
endings
28. The retina:
a. is divided into the outer pigmented layer and the inner
non-pigmented
b. is embryologically derived from neuroectoderm
c. forms the innermost layer of the of the eyeball
d. is thinnest at the posterior pole and thickens towards the
periphery
e. is related to Bruch’s membrane on its outermost surface
29. The neural retina:
a. extends from the optic disc periphery posteriorly to the
ora
serrata anteriorly
b. is derived from the inner layer of the optic cup
c. terminates more anteriorly on the temporal side
d. consists of 8 cellular layers and 2 membranes
e. is solely supplied with nutrients by the retinal vasculature
30. With respect to the posterior pole:
a. the macula lutea is 3 disc diameters lateral to the optic
disc
b. the macula lutea is yellow due to beta-carotene, a pigment found
in milk and some vegetables
c. the clivus is the sloping edge of the macula
d. the ganglion cell layer remains a constant thickness
e. the foveola is avascular and contains only cone photoreceptors
f. the fovea remains functional after a central retinal vein occlusion
due to its alternative blood supply