Neuro Exam 3: Olfactory And Gustatory Systems

Front 1

What is the olfactory epithelium?

Back 1

located in roof of each nasal cavity

Front 2

What are the olfactory glands?

Back 2

secrete a layer of mucous fluid in which odor-producing substances dissolve

Front 3

What are the olfactory neurosensory cells?

Back 3

bipolar neurons. A short peripheral process extends to surface where it is stimulated by dissolved odor-producing molecules and a long central process projects to CNS.
-These cells and their unmyelinated axons constitute the first cranial nerves (CV I)
-They pass superiorly through the foramina of teh cribriform plate of the ethmoid bone to terminate in the paired olfactory bulbs

Front 4

What is the olfactory bulb?

Back 4

An ovoid flattened mass of gray and white matter that is part of the cerebral hemisphere

Front 5

What is the olfactory tract?

Back 5

Extends caudally from the olfactory bulb to the olfactory trigone at the rostral margin of the anterior perforated substance
-Most axons of the olfactory tract pass into the lateral olfactory stria, other axons constitute the intermediate olfactory stria (No media olfactory stria in humans)

Front 6

Describe the lateral olfactory area

Back 6

-Also called the primary olfactory area
-Receives afferents through the lateral olfactory stria
Contains:
-pyriform cortex (entorhinal area, uncus, limen insulae -- inferior portion of insula)
-corticomedial nuclei of the amygdala
-May be the region of conscious awareness of olfactory stimuli

Front 7

Describe the anterior perforated substance

Back 7

-Comprises the intermediate olfactory area
-Penetrated by small blood vessels that supply the hypothalamus
-Situated caudal to olfactory trigone

Front 8

Where do the projections from the lateral and intermediate olfactory areas go?

Back 8

-Join the medial forebrain bundle which projects to hypothalamic nuclei as it passes through the lateral hypothalamus
-Hypothalamus projects to brain stem and spinal cord autonomic nuclei
-Medial forebrain bundle terminates more caudally in dorsal motor nucleus of the vagus and others in the nucleus of the tractus solitarius
-Each olfactory bulb projects to ipsilateral subcortical and cortical structures

Front 9

How many odors can the olfactory neurosensory cells distinguish?

Back 9

Between 2000-4000

Front 10

What fibers are also in the nasal cavity and stimulated by irritating substances?

Back 10

Trigeminal pain fibers. This pain is perceived falsely as part of "odor."

Front 11

What's a simple depiction of the olfactory system pathway?

Back 11

-olfactory neurosensory cells
-olfactory bulb
-primary olfactory area in/around uncus and amygdala
*nerves project through foramina of cribriform plate ipsilaterally (e.g., right nostril to right cerebral hemisphere)

Front 12

What is anosmia?

Back 12

-Loss of smell
-Compains of loss of "taste"
-Causes: allergic rhinitis, chronic upper respiratory infections, tumor compressing one olfactory bulb or tract, head trauma that damages olfactory nerves as they pass through cribriform plate

Front 13

What often cause olfactory hallucinations?

Back 13

Epileptic seizure that arises in anterior part of medial temporal lobe near olfactory cortex

Front 14

How do olfactory thresholds change with age?

Back 14

They often increase with advancing age

Front 15

Where are taste buds located?

Back 15

Primarily on the tongue, but also in the mucosa of the soft palate, pharynx, and epiglottis

Front 16

Describe the taste information pathway

Back 16

-Nerve fibers from taste buds of anterior 2/3 of tongue and soft palate go through facial nerve to peripheral ganglion
-central processes join the nervus intermedius, enter the brain stem, join the solitary tract to the solitary tract nucleus
-to medial portion of VPm in thalamus
-to gustatory area of cortex located posterior to mouth somatosensory area and to a second gustatory area in the insular cortex
*Most taste sensation from one side of tongue likely projects to ipsilateral subcortical and cortical structures

Front 17

What are the four types of taste receptors in taste buds?

Back 17

Bitter (quinine, related alkaloids), salty (NaCl), sour (acids), sweet (sugars)
-There may be a 5th taste, umami, the taste of protein as produced by MSG
-The brain detects these tastes by decoding "modified labeled lines" (info for a given taste contained partly in output of nerve fibers specific for that taste and partly in comparison of fiber activity with the activities in the other nerve fibers)
-The ability to detect the 4 basic tastes varies within the oral cavity

Front 18

How does taste aversion learning work?

Back 18

Mediated by the gustatory to limbic/autonomic connections
-important for individual survival

Front 19

What are ageusia, hypogeusia, and dysgeusia?

Back 19

Aguesia: absence of sense of test
Hypogeusia: diminished taste sensitivity
Dysgeusia: disturbed sense of taste

Front 20

When do gustatory hallucinations occur?

Back 20

May accompany epileptic seizures

Front 21

How do medications sometimes influence taste?

Back 21

1) Have an upleasant smell or taste that persists after med is taken
2) Interferes with any step of biological processes of smell or taste
3) Secondary effects that can lead to disordered smell or taste

Front 22

What are the three groups of smell/taste disorders?

Back 22

1) Decrease/loss of sensation
-due to blockage of access, loss/dysfunction of peripheral or central structure in neural pathway
2) Abnormal quality of sensation
-due to peripheral or central lesion
3) Perception of sensation that is not there
-due to peripheral or central lesion
-"release" hallucinations (decrease or loss of the sensation) or epileptic hallucination (abnormal involuntary activation of the primary sensory cortex as part of a seizure)

Front 23

Treatment of smell/taste disorders

Back 23

-Treat underlying disorder
-Anosmia safety
-medications, saline drops, topical local anesthetics, surgical removal of olfactory epithelium
-routine dental evaluations
-maintenance of good nutrition