Neuroanatomy of Gustation and Olfaction

Question 1

Why are olfactory receptors very sensitive to facial trauma?

Answer 1

bones of nasal cavity are very thin

Question 2

What can recognize a wider variety of sensations?

Answer 2

nose

Question 3

How are we able to recognize different tastes other than the 4 basic ones?

Answer 3

few taste receptors in different combos results in different taste sensations

Question 4

How are smell molecules transmitted into sensory information?

Answer 4

• smell molecules will contact the mucus layer that covers the olfactory epithelium where it will interact with the odorant binding proteins in the mucus
• act as a ligand and interact with the GPCR of an olfactory neuron receptor
• activates adenyl cyclase which results in an increase in cAMP
• leads to increases in Ca2+ and Na+ into the cell
• depolarization and action potential
• action potential travels up olfactory neuron receptor to where it synapses with the neurons in the olfactory bulb

Question 5

Layers of the Olfactory Bulb

Answer 5

Deep to superficial:

1) granule cell layer
2) mitral cell layer
3) external plexiform layer
4) glomerular layer
5) olfactory nerve layer
- cribriform plate
- olfactory epithelium

Question 6

What are the components of the olfactory tract?

Answer 6

• lateral olfactory tract
• cells of anterior olfactory nucleus
• fibers of the anterior limb of the anterior commissure

Question 7

What is the role of centrifugal fibers?

Answer 7

• reach the olfactory bulb via anterior commissure

- help regulate feedback loops

Question 8

Where do afferent projections from olfactory neuron receptors synapse?

Answer 8

mitral cells in the olfactory glomerulus

Question 9

Which cell types carry information from the olfactory bulb to the brain?

Answer 9

tufted and mitral cells

Question 10

Which cell type carries efferent information from the brain to the olfactory bulb?

Answer 10

centrifugal fibers (most directly reacts with granular cells to regulate mitral and tufted cells)

Question 11

What occurs after constant stimulation of mitral and tufted cells?

Answer 11

The mitral and tufted cells activate the granular cells which then feedback and inhibit the mitral and tufted cells from spreading on information to the olfactory cortex

Question 12

How does information get carried from the olfactory bulb to the olfactory cortex?

Answer 12

lateral olfactory tract by mitral and tufted cells

Question 13

What occurs if information from the olfactory cortex sent to the lateral hypothalamus?

Answer 13

body responds with appropriate feeding behavior

Question 14

If information from olfactory cortex sent to hippocampus?

Answer 14

input linked to learning and behavior

Question 15

How many neurons took part in the transmission of smell before the brain can react?

Answer 15

2

• first one is the olfactory receptor neuron
• second is mitral or tufted cell

Question 16

What is the orbitofrontal cortex responsible for?

Answer 16

integration of smell and taste

Question 17

Components of the olfactory cortex

Answer 17

• anterior olfactory nucleus: sends efferents to olfactory bulb
• olfactory tubercle
• piriform cortex
• anterior cortical amygdaloid nucleus: fear related smell
• periamygdaloid cortex
• lateral entorhinal cortex: memory associations with smell

Question 18

Where do taste buds take sensory information to?

Answer 18

Solitary Nucleus

Question 19

Steps of the central taste pathway

Answer 19

1) synapse in solitary nucleus
2) sensory info from taste buds travels through 2nd order neurons to ipsilateral central tegmental tract
3) neurons travel to parvicellular ventral posteromedial nucleus (VPMpc)
4) in the VPMpc, the 2nd order neurons synapse with the 3rd order neurons
5) gustatory sensory info is shuttled to frontal operculum and anterior insular cortex via IPSILATERAL posterior limb of internal capsule

Question 20

Anosmia

Answer 20

loss of smell

Question 21

Hyposomia

Answer 21

decreased sensitivity to odorants

Question 22

Ageusia

Answer 22

complete loss of taste (rare because many nerves carry gustatory sensory information)

Question 23

Hypogeusia

Answer 23

decreased sensitivity to taste

Question 24

Para/Dysgeusia

Answer 24

perception of taste altered; commonly due to drug use

Question 25

Lesions of CN VIII

Answer 25

• vestibular schwannoma
• loss of taste in anterior 2/3 of tongue on IPSILATERAL side
• IPSILATERAL facial paralysis
• hearing loss
• impaired secretion of nasal, lacrimal, submandibular, sublingual glands

Question 26

Damage to distal geniculate ganglion

Answer 26

• first ganglion where facial nerve fibers carrying taste info from tongue synapse
• taste may or may not be lost
• IPSILATERAL facial paralysis