Extraocular muscles and control of eye movements

Extraocular muscles and control of eye movements
Extraocular muscles and control of eye movements
1 Which of the following statements are true?
A The fascia of the orbit acts as a fluid brake
B The eyeball has a fixed centre of rotation
C Movement can be analysed with Fick’s axes
D Each extraocular muscle has two layers of fibres with the
larger fibres orbital
E The perimesium has a large number of elastic fibres
2 Regarding Fick’s axes
A The X axis passes through the pupil
B Depression occurs around the Z axis
C Incycloduction occurs around the Y axis
D Adduction occurs around the X axis
E Accommodation involves the Z axis
3 Of the extraocular muscles
A The secondary function of the superior oblique is intorsion
B The primary function of the inferior oblique is extorsion
C The medial rectus has minimal secondary function
D The superior rectus will not elevate an adducted eye
E The vertical recti together can apply significant adduction
4 In extraocular muscle
A The thick filaments comprise myosin and tropomyosin
B The thin filaments contain actin alone
C The size of the A band is consistent in contraction
D The H band is between A bands
E The Z line is at the centre of the I band
5 At the neuromuscular junction
A There is always a large single motor end plate
B An action potential is always conducted through the muscle
C The motor nerve terminals are unmyelinated
D The synaptic cleft measures 1.0-5.0 nm
E A single nerve action potential is able to generate an action
potential in the muscle
6 Regarding calcium
A Calcium concentration below ΙΟ” 7
Μ inhibits muscle
contraction
Spread of excitation down the t-tubule leads to calcium
release from the sarcoplasmic reticulum
C Calcium uptake involves secondary active transport
D Calcium binds tropomyosin to trigger contraction
Calcium is protein bound within the terminal cisternae
7 Muscle ATP
A Provides energy for cross-bridge movement
Provides energy for calcium release
C Production can be by oxidative phosphorylation in the
mitochondria
D Binds myosin to allow dissociation of actin and myosin
Can be formed by substrate phosphorylation in glycolysis
8 Muscle tension
A Has active and passive components
Always increases as muscle length increases
C Is maximal at normal muscle length during contraction
D Isometric contraction involves a change in muscle length
Always involves ATP hydrolysis
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