NB9-3 - Ocular Reflexes 2, Chemical Senses, and DLAs

Question 1

In reference to the chair experiment

Answer 1

E

Question 2

In reference to the chair experiment

Answer 2

C

Question 3

In reference to the chair experiment

Answer 3

D

Question 4

Describe the pupillary light reflex pathway. Use light shined into the right eye as an example.

Answer 4

• When light is shined into the right eye, the right optic nerve carries the signal to and synpases on both (right and left) pretectal nucei. This portion of the optic nerve DOES NOT synapse in the thalamus first
• The pretectal nuclei axons then synapse on the Edinger-Westphal nucleus
• The EW nucleus then activates both oculomotor nerves
• The oculomotor nerves will then synapse onto the short ciliary nerves which will cause the sphincter pupillae muscles to constrict

Question 5

How would a lesion of the right optical nerve affect pupillary responses?

Answer 5

No effect when light is shined into the left eye. Direct and consensual response present.

Absence of direct and consensual response when light if shined into the right eye

Question 6

How would a lesion of the right oculomotor nerve affect pupillary responses?

Answer 6

If light is shined into the right eye, you will see no direct response but an intact consensual response

If light is shined into the left eye, you will see an intact direct response but no consensual response

Question 7

Answer 7

A

Question 8

What is the corneal reflex? What is it aka? What can an abnormal corneal reflex indicate?

Answer 8

The corneal reflex, aka blink/lid reflex, is a reflexive closure (blinking) of the eye lids of both eyes when one eye is touched. An abnormal corneal reflex could indicate:

• Brain stem lesion
• Trigeminal neuropathy
• Weakness/paralysis of facial muscles
• Facial nerve palsy

Question 9

Describe the corneal reflex pathway.

Answer 9

1. Pain receptros in cornea are stimulated and signal travels in the trigeminal nerve (CN V) which will synapse onto the spinal trigeminal nucleus in the medulla
2. Via a trifid interneuron, the spinal trigeminal nucleus activates both the right and left facial nerve and conveys the pain signal to the VPM for conscious sensation
3. This will stimulate the orbicularis occuli muscles which will cause the eyes to close quickly

Question 10

What is Bell’s Palsy? What are its clinical signs? What causes it and what is its prognosis?

Answer 10

Bell’s Palsy is an idiopathic facial paralysis due to some kind of lesion to the facial nerve. The main clinical signs are a dropped angle of mouth, loss of brow furrowing, and weak eye closure. Causes is unknown but likely contributors are trauma, swelling, and nerve inflammation/infection. It usually only lasts about 2-3 weeks before resolving itself

Question 11

Answer 11

B

Question 12

List the five basic taste qualities and the chemical components that activate them.

Answer 12

Sweet - sugar

Sour - acid

Salty - NaCl

Bitter - wide range of molecules, many toxic

Umami - monosodium glutamate

Question 13

On which parts of the tongue are each of the five taste qualities sensed?

Answer 13

Question 14

Describe the gustatory pathway

Answer 14

• The facial nerve (CN VII), via its chorda tympani branch, carries taste information from the anterior 2/3 of the tongue. It synapses in the ipsilateral geniculate ganglion.
• The glossopharyngeal nerve (CN IX) carries taste information from the posterior 1/3 of the tongue. it synapses in the ipsilateral petrosal ganglion.
• The vagus nerve (CN X) carries taste information from the upper pharynx and epiglottis. It synapses in the ipsilateral nodose ganglion.

From their respective ganglia, each then synapse on the ipsilateral solitary nucleus in the medulla. Secondary neurons then synapse at the ipsilateral VPM. Tertiary neurons then synapse at the ipsilateral gustatory cortex in the anterior insula-frontal operculum. NO DECUSSATION ANYWHERE IN THE PATHWAY

Question 15

Answer 15

Right Half

Question 16

Briefly describe how signal tranduction occurs for the 5 taste qualities.

Answer 16

• Salty - Na+ ions enter taste bud via amiloride sensitive Na+ channels causing membrane depolarization which opens v-gated Ca++ channels and NT release
• Sour - H+ enters through amiloride sensitive Na+ channels causing closure of acid sensitive K+ channels leading to membrane depolarization. This opens v-gated Ca++ channels and NT release
• Sweet - sugar binds to a GPCR causing an increase in [cAMP] which causes K+ channel closure. This causes membrane depolarization, opening of v-gated Ca++ channels, and NT release
• Bitter - a bitter molecule binds to a receptor that activates PLC and the inositol tris-phosphate pathway, leading to an increase in [Ca++] and NT release
• Umami - don’t need to know this one

Question 17

Label image and say what structure this is an image of

Answer 17

Medulla Oblongata

Question 18

What artery supplies the majority of the medulla oblongata?

Answer 18

Posterior inferior cerebellar artery

Question 19

What is Wallenberg Syndrome and what causes it?

Answer 19

Wallenberg syndrome is causes by a lesion to the dorsolateral branch of the posterior inferior cerebellar artery. It presents with:

• Loss of ipsilateral taste (solitary nucleus)
• Loss of ipsilateral pain from face (spinal trigeminal nucleus)
• Loss of contralateral pain from the body (antero-lateral system)

Question 20

Why is smell so important to taste?

Answer 20

When you eat, vapors from the food rise retronasally to the olfactory receptors. Therefore, olfaction is occurring simultaneously with gustation. Because of this our minds are trained that these two sensations go hand in hand and something appears to be off when one is missing.

Question 21

Answer 21

Question 22

Briefly describe olfactory signal transduction.

Answer 22

An odorant binds to a GPCR in the cilia of the olfactory receptor neuron. This leads to an increase in [cAMP] which results in the opening of cation channels and calcium sensitive chloride channels. This leads to a membrane depolarization which migrates to the soma to help initiate an AP.

Question 23

Describe the olfactory pathway

Answer 23

1. Signal originates in olfactory bulb and is carried through the olfactory tract where it synapses in the olfactory cortex which consists of the piriform cortex, peri-amygdaloid cortex, and entorhinal cortex, all located around the uncus.
2. All will go on to synapse in the prefrontal cortex
3. Entorhinal cortex fibers will also synapse in the hippocampus via the perforant pathway which is why smell is often closely associated with memory.

Question 24

What are the technical names for the loss of taste and smell.

Answer 24

Hypogeusea/Ageusea - are decreased and complete loss of taste, respectively.

Hyposmia/Anosmia - are decreased and complete loss of smell, respectively.

Question 25

Answer 25

A

Question 26

Answer 26

C

Question 27

Answer 27

G

That’s the olfactory cortex