Session 7

Question 1

How does the inner ear develop?

Answer 1

Starts at otic placodes on the dorso-lateral surface of the embryonic head. They thicken and invaginate below the surface, then pinches off to form the otic vesicles. The surface ectoderm then closes over.
Otic vesicles then undergo morphological changes.

Question 2

What are the ossicles derived from?

Answer 2

Cartilage bars of the 1st and 2nd arches.

Malleus and incus from Meckel’s cartilage (1st arch), and stapes from Reichert’s cartilage (2nd arch).

Question 3

What are the tympanic cavity and auditory tube derived from?

Answer 3

1st pharyngeal pouch.

Question 4

Describe the development of the middle ear.

Answer 4

1st pharyngeal pouch expands distally, creating the tympanic cavity.
It remains narrow proximally - Eustachian tube.
The 3 ossicles become suspended in the tympanic cavity.

Question 5

Describe the development of the external ear.

Answer 5

Develop within the neck, then ascend as the mandible grows.

Question 6

Describe the innervation of the ear.

Answer 6

Vestibulocochlear nerve.
Tensor tympani = mandibular branch of trigeminal nerve.
Stapedius = facial nerve.

Question 7

Describe the development of the eye.

Answer 7

Begins as optic vesicles, which then grow and contact overlying ectoderm. This ectoderm becomes the lens placode.
The lens placode thickens, invaginates and pinches off. Sinks down into optic vesicle.
Optic vesicle stretches to grasp the lens placode for invagination.
Optic vesicle surrounds the lens placode.

Question 8

What three structures does the optic cup give rise to?

Answer 8

Retina, iris and ciliary body.

Question 9

What are the extraocular muscles derived from?

Answer 9

preotic myotomes.

Question 10

Describe the innervation of the eye.

Answer 10

Optic nerve for sensory function.

Oculomotor, trochlear and abducens move the eye.

Question 11

What are congenital cataracts?

Answer 11

Opacities of the lens and can be genetic or due to a teratogen.

Question 12

What are the classic triad of symptoms with congenital rubella syndrome?

Answer 12

1) sensineural deafness
2) cataracts or retinopathy
3) congenital heart disease

Question 13

What is a detached retina?

Answer 13

Separation of the two layers of the retina (sensory and pigmented layers).

Question 14

Describe the visual pathway.

Answer 14

Neurones leave the optic disc and exit in the optic nerve. They reach the brain and form the optic chiasm. Fibres from the nasal hemiretina cross over. After leaving the optic chiasm, the fibres become the optic tracts.

Question 15

What does the right optic tract contain?

Answer 15

Fibres of nasal hemiretina of the left eye and temporal fibres of the right eye. Hence visual information of the left hemifield.

Question 16

Where do the optic tracts project to?

Answer 16

The corresponding lateral geniculate nucleus.

Question 17

What happens to the fibres following the lateral geniculate nucleus?

Answer 17

They project through the optic radiation to the primary visual cortex.
Inferior retina through the temporal lobe. Superior retina fibres through the parietal lobe.

Question 18

Which extraocular muscles are supplied by which nerves?

Answer 18

LR6, SO4, R3.

Question 19

What are the clinical signs of an oculomotor nerve lesion?

Answer 19

Ptosis with a down and out, dilated pupil.

Question 20

What are the clinical signs of an trochlear nerve lesion?

Answer 20

The affected eye looks up and in. Can also have a subtle head tilt.

Question 21

What are the clinical signs of an abducens nerve lesion?

Answer 21

Inability to abduct the affected eye.

Question 22

Give two causes of an oculomotor nerve lesion?

Answer 22

Posterior communicating artery aneurysm.
Vasculopathies.
Idiopathic.

Question 23

Give two causes of a trochlear nerve lesion?

Answer 23

Head trauma
Tumour
Congenital
Vasculopathies

Question 24

Give two causes of an abducens nerve lesion?

Answer 24

Raised ICP
Pontine tumours
Idiopathic
Vasculopathies.

Question 25

What is monocular blindness?

Answer 25

Complete loss of vision in one eye due to damage on an optic nerve. Causes include optic nerve glioma or retinoblastoma.

Question 26

What is bitemporal hemianopia?

Answer 26

Damage to the optic chiasm compresses the nasal hemiretinae of both eyes, hence loss to both temporal fields.

Question 27

What is left homonymous hemianopia?

Answer 27

Damage to the right optic tract damages axons from the right temporal and left nasal hemiretinae. Hence there is loss of the left half of the visual fields in both eyes.

Question 28

What is macular sparing?

Answer 28

In a stroke affecting the posterior cerebral artery, most of the occipital lobe will be lost, except the occipital pole (macula) which is supplied by the middle cerebral artery.

Question 29

What is superior left homonymous quadrantanopia?

Answer 29

Damage to the right temporal lobe will cause vision to be lost in the superior quadrant of the left visual hemifield. Due to lesions in the inferior half of the temporal lobe.

Question 30

Describe the pupillary light reflex.

Answer 30

Axons from the retinal ganglion pass along the optic nerve to the midbrain.
These synapse with interneurones to the Edinger-Westphal nucleus, where they synapse with preganglionic parasympathetic neurones.
Then they run with CN3 and synapse with postganglionic parasympathetic neurones in the ciliary ganglion.
These then innervate the sphincter pupillae.

Question 31

What happens when the retinal ganglion are excited by light?

Answer 31

Increased parasympathetic activity, hence miosis (constriction) and reduced light entering the eye.

Question 32

How does the consensual light reflex work?

Answer 32

Due to bilateral projections to the Edinger-westphal nucleus.

Question 33

When is the accommodation reflex used?

Answer 33

When the eye must focus from a distant object to a near one.

Question 34

What three events are involved in the accommodation reflex?

Answer 34

1) Convergence
2) Pupillary constriction
3) Convexity of the lens to increase refractive power.