Anatomy: Eye

Question 1

What are the outermost layers of the eye? Describe them

Answer 1

There are three layers to the eye inc:
sclera: thick protective outermost layer
choroid: vascular layer
retina: contains retinal pigment epithelium and photoreceptors. Photoreceptors carry impulses via the nerve ganglion–>optic nerve–>brain.

Question 2

Which part of the eye contains the most amount of cones? Label it on this diagram

Answer 2

Fovea centralis, light from the cornea is also refracted onto this structure

Question 3

Label and describe the remainder of this diagram

Answer 3

The eye is filled with vitreous humour in the vitreous body- this is for structural support
Cornea refracts light into the eye

Question 4

The eyes lie in the bony orbits. Describe these

Answer 4

Each orbit has a square base, superolateral to the piriform aperture (‘nose hole’)
The orbital margins v strong superiorly and laterally to protect the eyes. But the medial wall= thin and delicate

The orbit has 4 walls: superior, inf., medial, lateral
7 bones of the skull contribute to these walls (the 6 in the diagram + nasal bone)

Question 5

Label this

Answer 5

Question 6

What is this v shaped structure?

Answer 6

This V shaped structure is the orbital fissure it has a superior part (highlighted) and inferior part.
there are two distinct parts because different structures pass through the superior and inferior part of the orbital fissure.

Question 7

What is the origin of the extra occular muscles?

Answer 7

The Annulus of Zinn: ring of fibrous tissue surrounding the entrance of the optic nerve
It encloses part of the sup.orbital fissure
The extraocular muscles originate from the annulus of zinn (in green) except for the inf + sup. oblique.

Question 8

Which nerves pass through the annulus?

Answer 8

Question 9

Six extraocular muscles move the eye. What are they?

Answer 9

Question 10

Label this

Answer 10

Question 11

There is also an eyelid elevator. What is this and explain why sometimes the eyelid can droop in a stroke

Answer 11

There is also an eyelid elevator, levator palpabrae superioris – this is mainly voluntary striated muscle.
Innervated by cranial nerve III (oculomotor nerve). In 3rd cranial nerve lesions you can have a ptosis where the eyelid droops.

Question 12

Describe the extraoccular muscles

Answer 12

The sup. rectus originates from the annulus of Zinn. elevate, adduct and intorts eyeball
Inf. rectus extort, depress and adducts eyeball
Medial rectus: eye adduction
Lateral rectus: eye abduction
Sup.oblique runs through a pulley (trochlea) structure on the medial orbit. Depresses, abducts, intorts the eye.
Inf. oblique originates from maxilla surface. Elevate, extort and abduct eyeball

Question 13

What is the innervation for the extraoccular muscles?

Answer 13

ALL cranial nerve III, except:
Superior oblique: 4th cranial nerve (trochlear)
Lateral rectus: 6th cranial nerve (abducens).

Question 14

Describe the retinal layers

Answer 14

Layers 1-9, 9 being most deep
Rod cells are throughout the retina, whereas cones are found closer to the fovea
The output is via the nerve fibre layer, and this means that it can be easily damaged in high intraocular pressure states such as glaucoma.

Question 15

What is the Uveoscleral outflow pathway? What happens if this pathway gets blocked?

Answer 15

Aqueous humor produced by the ciliary body passes out of the anterior chamber via the trabecular meshwork and schlemm canal.

If this is blocked it can lead to glaucoma and raised intraocular pressure.

Question 16

Describe the fovea

Answer 16

On the temporal side optic disc, opposite the pupil is a yellow area called the macula lutea. At the middle of the macula is the fovea centralis/fovea.

Fovea= many cones and accounts for the majority of the visual afferent stimuli that is transmitted to the brain.

Question 17

Describe the optic nerve pathway

Answer 17

The ganglionic cells aggregate at the optic nerve which passes out of the orbit via the optic canal, encased in dura.
The nasal fibers then cross at the optic chiasm, temporal fibres remain on the same side.

Question 18

What is the role of nasal fibres?

Answer 18

Nasal fibres carry info about the temporal aspect of your visual field.
This is why lesions at the optic chiasm mostly affect these nasal fibres and give rise to bitemporal hemianopia

Question 19

Describe pretectal synapses in the light reflex

Answer 19

If light has shone into one eye, the impulse is transmitted by the optic nerve.
Impulse passes into the midbrain–>pretectal nucleus–> Edinger-westphal nucleus (a parasymp nucleus for CNIII)
Fibres from E.westphal innervate the ciliary body and the iris to cause pupil constriction.

Question 20

What is the consensual reflex?

Answer 20

When you shine light into one eye, the other eye will also constrict
This is a consensual light reflex. And this is because the pretectal nucleus on one side synapses w the e.westphal nucleus on both sides= bilateral efferent reaction

Question 21

Describe the accomodation reflex

Answer 21

Question 22

What is the Lateral geniculate nucleus?

Answer 22

Laterally and inferiorly on either side of the diencephalon are the lateral geniculate bodies.
There are two types of cells - magnocellular and parvocellular found in the geniculate nucleus where the optic tracts synapse.
This generates neurons which project directly to the primary visual cortex.

Question 23

Complete this diagram to show the visual pathways

Answer 23

Question 24

Describe the anatomy of the cerebellum, using this posterior diagram to distingish between the different lobes

Answer 24

Question 25

In the anatomy of the cerebellum from an anterior view, describe the retrotonsillar fissure and the tonsils. What is a pathological example to do with one of these structures?

Answer 25

Retrotonsillar fissure- separates the tonsils from the rest of the cerebellum
Tonsils (green) can pathologically descend thru the f.magnum= Chiari malformation

Question 26

On the anterior cerebellum, point out the following structures:
Biventral lobe, flocculondular lobe, flocculus, sup. Peduncle, middle and inferior peduncle

Answer 26

they attach the cerebellum to the brainstem and give rise to various pathways

Question 27

How is the cerebellum related to the fourth ventricle?

Answer 27

The cerebellum covers the brainstem and creates the cavity that is the fourth ventricle. Remember CSF drains via the aqueduct of sylvius which drains into the fourth ventricle

Question 28

Describe the layers of the cerebral cortex, in particular the purkinje cells

Answer 28

Split into 4 layers: molecular, purkinje, granule, white matter
Sole and main output of the cc is via the purkinje cells
These are v large cells within the cc and dendrites They extend into the molecular layer to form synapses w other neural cells -mainly granule cells
- P cells are inhibitory in nature (release GABA)
- various targets (primarily the cerebellar nuclei)
- efferent cell of cerebellum and main one of the cc

Question 29

Describe cerebellar neural connections

Answer 29

Question 30

What are the principle cell types of the cerebellum?

Answer 30

Purkinje cells - travel into the deep cerebellar nuclei. These cells utilize GABA (inhibitory effect).
Mossy fibers - arise from pontine nuclei, as well as vestibular nuclei and from the spinal cord. These fibers form excitatory connections with the deep cerebellar nuclei.
Climbing fibers - arise from the inf. olivary nucleus and send collaterals to the deep nuclei before entering the cerebellar cortex.

Question 31

One of the functional aspects of the cerebellum is the dentate. What is the dentate nuclei?

Answer 31

Receives input from the lateral cerebellar hemisphere via mossy and climbing fibers.
The nuclei receive GABA (inhibit) input from Purkinje cells.
Most output from the cerebellum arises from these dentate cerebellar nuclei.
Output passes through the superior cerebellar peduncle and decussates in the midbrain

targets: red nucleus - the thalamus en route to the cortex modulates cs tract and rubrospinal tract

Question 32

What is the second functional division of the cerebellum?

Answer 32

Question 33

What is the third functional division of the cerebellum?

Answer 33

Question 34

What is the function of the globose nuclei?

Answer 34

fine tune coordination and help coordinate movement
fibres are sent from the spinocerebellar tract, by the inf peduncle - mossy fibres will then synapse on the two nuclei and the granular cells
Granular cells excite the purkinje, and modulate their inhibitory effect on these 2 nuclei
From these fibres, you get your efferent fibres, which pass by the superior cerebellar peduncle to the end targets

Question 35

There are 3 functional divisions of the cerebluum. Describe the spinocerebellum

Answer 35

Spinocerebellum/paleocerebellum.
Consists of the lobes near the midline.
Monitor and fine-tunes limb movements. This is achieved by proprioceptive input from the dorsal column pathway, the cranial trigeminal nerve, the visual and auditory systems, and spinocerebellar tract.
Output–>deep cerebellar nuclei. These then project to the cerebral cortex, and brainstem. This enables the region to monitor and modify the activity of the descending motor pathways.

Question 36

There are 3 functional divisions of the cerebluum. Describe the cerebrocerebellum

Answer 36

Cerebrocerebellum/neocerebellum.
It consists of the lateral cerebellar lobes.
Receives info from the parietal lobe, the primary sensory lobe of the brain), with pontine nuclei in between
Output–>ventrolateral thalamus–>premotor cortex and primary motor area.

Question 37

There are 3 functional divisions of the cerebluum. Describe the vestibulocerebellum

Answer 37

Vestibulocerebellum/archicerebellum
Spatial awareness and balance.
Input from the vestibular nuclei, auditory and visual systems
If a patient has damaged this region=disturbed balance and gait.

Question 38

Describe the inferior cerebellar peduncles

Answer 38

Question 39

Describe the middle cerebellar peduncle

Answer 39

Question 40

Describe the Superior cerebellar peduncle

Answer 40

Question 41

Describe cerebellar lesions

Answer 41

Question 42

Differentiate between dyssynergy and dysmetria

Answer 42

dyssenergy → decompensation of movement (a complex movement is broken down into its own individual components)

dysmetria → mainfested when you ask a patient to touch an object in front of them, they overshoot the mark due to lack of coordination