Taste & Smell

Papillae which have taste buds

- Fungiform - Circumvallate/Vallate - Foliate (few in adults)

Dendrites of Olfactory Receptor Cells

- extend to the surface of the olfactory epithelium and terminate with rounded knoblike-region from which non-motile cilia project - cilia extend into mucus layer of nasal cavity and possess receptors for odorant molecules

Structure of Taste Recptor Cells

- microvilli located at apical end and extend through small taste pore where they are exposed to chemical stimuli - associated with NT afferents on basal side - replaced every 7-10 days - contain internal Ca2+ stores - voltage gated Ca2+ channels in membrane

Structure of Olfactory Epithelium

- pseudostratified columnar epithelium - comprised of olfactory receptor cells/neurons, basal cells, and support cells - Bowman's Glands (produce mucous) also present - Olfactory receptor cells are neurons (unlike taste receptor cells!)

Axons of Olfactory Receptor Cells

- unmyelinated - pass through lamina propria and group together in bundles (olfactory filia) - Olfactory Filia collectively form olfactory Nerve - travel through cribriform plate (ethmoid bone) and terminate in olfactory bulb

Only sensory system with no precoritcal relay to the thalamus

CN I (Olfactory Nerve)

Cranial Nerves that carry somatic & visceral sensory info from oral cavity to CNS

CN V: anterior 2/3 tongue, hard & soft palate (GSA) CN IX: posterior 1/3 tongue, palatine tonsils, and pharynx (GVA) CN X: epiglottis (GVA) CN VII: sensory from glands (GVA)

Cranial Nerves that carry Taste Info (SA) from oral cavity to CNS

CN VII: anterior 2/3 of tongue & palate CN IX: Posterior 1/3 of tongue (including vallate papillae) CN X: Epiglottis

What would happen if an animal had bilateral lesions in the ventral medial hypothalamus

animal would develop a voracious appetite and become obese

Location of Gustatory Cortex

insula & the medial surface of the frontal operculum

Hippocampus and olfaction

learning associated with feeding

Operculum

- (plural, opercula) - region of frontal, parieta, and temporal lobes located adjacent to the lateral sulcus and covering the insula - latin for "little lid"

Cribriform Plate

- Ethmoid bone - bone through which olfactory Nerves (collection of olfactory filia, which are bundles of CN I AXONS) must penetrate in order to synapse onto olfactory bulb

CN I

- Olfactory Nerve - comprised of SA fibers - involved in sense of smell (olfaction) - only sensory system with NO PRECORTICAL relay to the thalamus, BUT will EVENTUALLY be processed through the thalamus

Gustatory Nucleus

- Superior aspect of nucleus soliatrius - location on solitary nucleus where SA fibers of CN VII, IX, and XI synapse

Taste Pathway

- Taste buds of tongue/palate/epiglottis activate CN VII, IX, X SA Fibers --> Ganglia (Geniculate/Inferior Glossopharyngeal Ganglion/Inferior Vagal Ganglion) --> Gustatory Nucleus (superior aspect of Solitary Nucleus) --> Central Tegmental Tract --> Ipsilateral VPM, reticular formation, and brainstem nuclei that influence salivation and swallowing --> (from VPM) --> Ipsilateral Gustatory Cortex (insula &medial surface of the frontal operculum) **NOTE: Taste Pathway follows an IPSILATERAL course.

Locations of Taste Receptors

- clustered in taste buds (assoc with fungiform & circumvallate/vallate papillae; foliate papillae have few taste buds in adults) - also located on palate & epiglottis (extralingual taste buds that are not located within papillae but rather in epithelium) - many located on soft palate but ones located on hard palate are only present on most posterior aspect near junction between hard & soft palate

Primary Olfactory Cortex

- located in uncus of temporal lobe - Composed of: Piriform Cortex, Periamygdaloid Cortex, and Anterior Parap=hippocampal Gyrus - important in ability to discriminate and identify odors -

Foliate Papillae

- papillae located on the sides of the tongue on both the anterior 2/3 and posterior 1/3 of tongue - contain few taste buds in adults - ones within anterior 2/3 region of tongue are innervated by CN VII (SA) - ones within posterior 1/3 region of tongue are innervated by CN IX (SA)

Fungiform Papillae

- papillae located toward tip of tongue - contain taste buds - innervated by CN VII (SA)

Vallate Papillae

- papillae on most posterior aspect of tongue - contain taste buds - innervated by CN IX (SA)

Organization of olfactory nerves as they enter the olfactory bulb

- receptors responsive to different odorant molecules are intermingled in the olfactory epithelium - At level of the glomeruli (of the olfactory bulb), the axons of olfactory neurons carrying similar olfactory info separate from ones carrying different olfactory info -- similar neurons synapse on same glomerulus - glomeruli respond selectively to one or two molecules that characterize complex odor - info is carried along the olfactory tract (axons of mitral & tufted cells) to several areas

What would happen if an animal had bilateral lesions in the ventral lateral hypothalamus?

animal would lack appetite, fail to feed, and ultimately waste away due to anorexia

Olfactory Tubercle

area where the olfactory tract attaches to the brain; very small in humans

Hypothalamus and olfaction

concerned with feeding behaviors -- appetite control - bilateral lesions in ventral medial hypothalamus produced animals with voracious appetitie and resulting in obesity - bilateral lesions in ventral lateral hypothalamus produced aimals failing to feed and wasting due to starvation

Locations where olfactory tract fibers terminate

1. Anterior Olfactory Nucleus (**Neurons in the anterior olfactory nucleus cross via the anterior commissure to the contralateral olfactory bulb) 2. Olfactory Tubercle 3. Amygdala 4. Primary Olfactory Cortex (Piriform Cortex, periamygdaloid cortex, and anterior parahippocampal gyrus)

Major Anatomical Structures associated with Olfaction

1. Olfactory Epithelium 2. Dendrites of olfactory receptor cells 3. Cribriform Plate 4. Axons of Olfactory Receptor Cells 5. Olfactory Bulb

Mechanism of Taste Cell activation

1. Taste molecule activates taste receptor cell 2. Depolarizing receptor potential (inside of the taste receptor cell become more positive through several different mechanisms) 3. Increased intracellular Ca2+ through voltage gated Ca2+ channels and release from internal stores. 4. release of NT on peripheral nerve (primary afferent) 5. Transduction of signal to CNS (nucleus solitarius/soliatary nucleus in brainstem)

Where does the Primary Olfactory Cortex Project to?

1. Thalamus (dorsomedial Nucleus) --> Association Cortex (orbitofrontal Cortex) 2. Hippocampus (learning assoc with feeding) 3. Hypothalamus (feeding behaviors)

Pathway of Odorant info starting in nose

Cilia detect odorant molecules --> info sent to cell body (within olfactory epithelium) --> axons of olfactory receptor cell --> cross cribriform plate --> similar odorant info fibers synapse on same glomeruli within olfactory bulb --> info carried along olfactory tract (axons of mitral & tufted cells) --> Olfactory Tract fibers terminate in: Anterior Olfactory Nucleus, Olfactory Tubercle, Amygdala, and primary olfactory cortex (piriform cortex, periamygdaloid cortex, and anterior parahippocampal gyrus) -- (From primary Olfactory Cortex) --> Thalamus (dorsomedial nucleus), Hippocampus (learning & memory), and Hypothalamus (feeding behaviors) --(from Thalamus) --> Association Cortex (orbitofrontal cortex)

What is responsible for the perception of flavor?

Convergence in the orbitofrontal cortex (association cortex) --> receives input from gustatory cortex, somatosensory cortex, amygdala, olfactory cortex, and visual cortex. **NOTE: Olfactory info is is processed in thalamus before being relayed to orbitofrontal cortex.

Where do CN I fibers emerge?

EMerge into anterior cranial fossa via foramina of cribriform plate (ethmoid bone)

True/False: In order to send olfactory info to the olfactory bulb, olfactory receptor cell dendrites must penetrate the lamina propria and travel through the cribriform plate

FALSE - Axons pass through the cribriform plate to synapse onto the olfactory bulb - Dendrites travel in the opposite direction, traveling to the surface of olfactory epilthelium and exposing cilia to the mucosal side of nasal cavity

TRUE/FALSE: Flavor is solely dependent on having a wide variety of taste buds that can detect different odor molecules

FALSE - several factors contribute to perception of flavor - Determined by integration of gustatory, olfactory and somatosensory info at the orbitofrontal cortex

TRUE/FALSE: Olfactory receptor cells are like taste receptor cells in that: 1. Both are comprised of receptor cells, basal cells, and support cells; 2. Both are replaced throughout life; and 3. Both types of receptor cells are neurons that relay info to the CNS

FALSE -- - 1st 2 statements are true - Only the olfactory receptor cells are actual neurons, themselves - taste receptor cells are ASSOCIATED with primary afferent neurons -- activated when receptor cells release NT onto peripheral afferent

TRUE/FALSE: All taste buds are found within papillae

FALSE -- Extralingual taste buds (on palate & epiglottis) are located within epithelium, not papillae

TRUE/FALSE: Olfaction is the only sensory system that has no processing through the thalamus

FALSE -- It is the only sensory system with no PRECORTICAL relay to the thalamus, BUT it is EVENTUALLY processed through the thalamus

TRUE/FALSE: Taste buds are found within soft palate but not within hard palate

FALSE -- while many taste buds exist within soft palate, few extralingual taste buds also reside within hard palate. Those hard palate taste buds are only present on the most posterior aspect near the junction between hard and soft palate

Location of cell bodies of CN VII SA fibers

Geniculate Ganglion

Location of cell bodies of CN IX SA fibers

Inferior Ganglion of CN IX (Inferior Glossopharyngeal Ganglion)

Location of cell bodies of CN X SA fibers

Inferior Ganglion of CN X (inferior vagal ganglion)

TRUE/FALSE : Taste buds are not exclusive to the tongue

TRUE -- Extralingual taste buds exist within the hard & soft palates, as well as the epiglottis. These taste buds are within epithelium instead of within papillae.