Auditory and Visual Pathways

Question 1

Give a brief overview of the auditory pathway

Answer 1

Organ of Corti > spiral ganglion > ventral or dorsal cochlear ganglion > either straight to a lateral lemniscus (may or may not cross) or to lateral lemnisus via superior olivary nuclei > inferior colliculus > medial geniculate body > primary auditory cortex

Question 2

The spiral ganglion houses ______

Answer 2

cell bodies of 1st order neurons which receive info from hair cells in the organ of corti, the central axons form the main component of the cochlear nerve

Question 3

The cochlear fibres bifurcate and info is sent to _______

Answer 3

cochlear nuclei on both sides of the brain stem (dorsal and ventral left and right)

Question 4

Describe where fibres can go from the ventral cochlear nuclei?

Answer 4

Some fibres ascend ipsilaterally in the lateral lemniscus but most cross to the contralateral superior olivary nucleus in a region known as the trapezoid body, it also projects up through the lateral lemniscus.

Question 5

Define the lateral lemniscus?

Answer 5

The lateral lemniscus is a tract of axons in the brainstem that carries information about sound from the cochlear nucleus to various brainstem nuclei and ultimately the contralateral inferior colliculus of the midbrain.

Question 6

Describe where fibres can go from the dorsal cochlear nuclei?

Answer 6

Most fibres cross the midline and ascend in the contralateral lateral lemniscus

Question 7

Fibres ascending through the lateral lemniscus from both cochlear nuclei and from the superior olivary nuclei arrive at the ___________ where all these fibres carrying auditory info converge

Answer 7

inferior colliculus

Question 8

Define the inferior colliculus?

Answer 8

The inferior colliculus is a part of the midbrain that serves as a main auditory (sound) center for the body. It acts as the channel for almost all auditory signals in the human body.

Question 9

The fibres from the inferior colliculus project to the ______________

Answer 9

ipsilateral medial geniculate body in the thalamus

Question 10

The medial geniculate ganglion has reciprocal connections with the _________

Answer 10

auditory cortex and mediates refinement of the incoming info

Question 11

Projections from the medial geniculate ganglion proceed to the ____________

Answer 11

primary auditory cortex

Question 12

Where is the primary auditory cortex located?

Answer 12

superior temporal gyrus, right under the lateral fissure

Question 13

Why are hearing problems rarely central?

Answer 13

Both the dorsal and ventral nuclei, some fibers decussate while others don’t. For that reason, information from both ears travels bilaterally in each lateral lemniscus. This means that lesions above the level of the cochlear nuclei is unlikely to lead to serious hearing impairment because the information is coming from both sides on both sides from different places.

Question 14

The projection of vestibular information onto the cerebral cortex is bilateral and is less _______________

Answer 14

well defined than for other senses, there is no agreed upon “primary vestibular cortex”

Question 15

Within the ____1_____ cranial fossa, the optic nerves from each eye unite to form the _____2_____. At the chiasm, fibres from the ____3____ half of each retina cross over to the contralateral optic tract, while fibres from the ____4____halves remain ipsilatera

Answer 15

1) middle
2) optic chiasm
3) nasal
4) temporal

Question 16

Explain how all information from the left visual field is processed on the right side of the brain and vice versa?

Answer 16

In the left eye:
The right visual field hits the left temporal retina so doesn’t cross and is processed in the left.
The left visual field hits the left nasal retina so crosses at the optic chiasm and is processed in the right.

In the right eye:
The left visual field this the right temporal retina so doesn’t cross and is processed in the right.
The right visual field hits the nasal retina so doesn’t cross and is processed in the left.

Question 17

Give a brief overview of the visual pathway

Answer 17

optic nerve > optic chiasm (nasal decussate temporal don’t) > optic tracts > lateral geniculate nucleus > optic radiations (inferior visual field/upper retina through parietal lobe in upper tract, superior visual field/ lower retina through temporal lobe in lower tract) > visual cortex

Question 18

Each optic tract travels to corresponding _______1________ located in the ___2_____ where the fibres ____3______

Answer 18

1) lateral geniculate nucleus
2) thalamus
3) synapse

Question 19

Good way to remember which geniculate ganglion is auditory and which is visual?

Answer 19

You see light and visual is Lateral

You hear music and auditory is Medial

Question 20

Axons from the lateral geniculate nucleus then carry visual information via pathway called _______

Answer 20

optic radiations

Question 21

The upper optic radiations carry fibres from the __1____ retinal quadrants which corresponds to the _____2_____ it travels though the ____3_____ to reach the visual cortex

Answer 21

1) superior retinal quadrants
2) inferior visual fields
3) parietal lobe

Question 22

The lower optic radiations carry fibres from the ____1____ retinal quadrants which corresponds to the ____2_____ it travels through the ___3_____ via pathway known as ____4_____to reach the visual cortex

Answer 22

1) inferior retinal quadrants
2) superior visual fields
3) temporal lobe
4) Meyer’s loop

Question 23

Optic radiations are also known as the _______

Answer 23

geniculocalcarine tract

Question 24

What is the location of the primary visual cortex?

Answer 24

The posterior occipital lobe

Question 25

Both the _____ and ______ have roles in eye movement

Answer 25

visual cortex and frontal eye fields

Question 26

In general the visual cortex provides for movements ___________

Answer 26

in response to visual stimuli e.g. tracking moving objects

Question 27

The frontal eye fields controls movements of ________

Answer 27

command- movements that are independent of moving visual stimuli

Question 28

Tracking movements tends to be ____1__ while movements of command tend to be __2_____

Answer 28

1) smooth

2) jumpy/ saccadic

Question 29

The pupillary light reflex is a _______ neuron chain

Answer 29

4

Question 30

Give a brief overview of the pupillary light reflex pathway?

Answer 30

1st neurones:
retinal ganglion cells
pass via ipsilateral optic nerve
decussate in optic chiasm
synapse in pretectal nucleus in midbrain

2nd neurones (bilateral):
located entirely within midbrain & connect pretectal nucleus to next synapse in Edinger-Westphal nucleus  (location of cell bodies of parasympathetic axons of CN III)

3rd neurones (bilateral):
pass from EW nucleus, via CN III then its inferior division, to synapse in ciliary ganglion

4th neurones (bilateral):
course in short ciliary nerves to sphincter pupillae muscles

Question 31

Eye reflexes that aren’t the pupillary light reflex require input to __________

Answer 31

oculomotor and Edinger Westphal nucleus from the visual cortex

Question 32

What sort of lesion would cause unilateral visual loss?

Answer 32

optic nerve lesion

Question 33

What sort of lesion would cause a bitemporal hemianopia?

Answer 33

optic chiasm lesion

Question 34

What sort of lesion would cause a homonymous hemianopia?

Answer 34

optic tract lesion

Question 35

What sort of lesion would cause a homonymous hemianopia with macular sparing?

Answer 35

occipital cortex

Question 36

What sort of lesion would cause a homonymous inferior quadrantopia?

Answer 36

parietal lesion

Question 37

What sort of lesion would cause a homonymous superior quadrantopia?

Answer 37

temporal lesion