Lecture 20: Olfaction and Taste

sensory receptors:

interpret environmental stimuli to create electrical signals

mechanoreceptors

• sensory cells that respond to the compression, bending, or stretching of cells, usually through mechanically gated ion channels

• involved in sensing touch, pressure, proprioception, hearing, and balance.

chemoreceptors: (3)

• chemicals attach to receptors on the membrane

• can bind to ligand gated ion channels or set off signaling cascade

• involved in smell and taste

Thermoreceptors:

• Detect temperature changes

• temperature causes proteins in the plasma membrane to change shape, opening ion channels.

Photoreceptors:

Respond to light and enable vision

Nociceptors:

Receptors that detect extreme mechanical, chemical, or thermal stimuli, causing pain.

Nose Anatomy

The nose is made up of

made up of bones and cartilage 

Nose Anatomy

ethmoid bone:

frontal bone:

hard palate:

ethmoid bone: roof of nasal cavity

frontal bone: covers forehead and frontal region of brain

hard palate: inferior; separates nasal and oral cavities

Nose Anatomy

cribriform plate:

thin region of ethmoid bone with foramina, which allows nervous signals to move from nasal to cranial cavity 

Nose Anatomy

nostrils:

also known as nares; separated by the septum

Olfactory Region

olfactory nerve fibers:

run through cribriform plate 

Olfactory Region

olfactory bulb:

olfactory nerve fibers synapse with the second neuron

Olfactory Region

Olfactory tract:

Axons from the olfactory bulb bundle together and travel to the brain ; in the PNS

Olfactory Region

olfactory epithelium:

layer of epithelial cells with specialized receptor cells embedded within 

Olfactory Epithelium

olfactory neuron:

specialized bipolar receptor cells, whose dendrites extend towards the nasal cavity

Olfactory Epithelium

olfactory vesicle:

enlarged region of olfactory neuron dendrite

Olfactory Epithelium

olfactory hairs:

cilia on the end of the olfactory vesicles; where the chemoreceptors are located 

Olfactory Epithelium

mucus layer (2)

• Covers vesicles and hairs, allowing odorants to dissolve and bind to receptors

• mucus-producing glands are located in the connective tissue layer.

Olfactory Epithelium

epithelial cells:

supporting cells; help hold neurons in place

Olfactory Epithelium

basal cells: (2)

• involved in regenerating the epithelium and neurons

• all cells are replaced about every 2 months 

Olfactory Function

Pathway

1) an odorant entering the air through the nostril

2) passing through the nasal cavity where the conchae filter and direct it

3) then reaching mucus and hairs that activate chemoreceptors, triggering electrical signals that travel through the cribriform plate to the olfactory bulb and tract,

4) finally reaching the brain's olfactory areas for processing.

Olfactory Function

primary olfactory area:

located in the olfactory cortex of the frontal and temporal lobes and is responsible for the conscious perception of smell.

Olfactory Function

secondary olfactory area (3):

• deep region near corpus callosum

• visceral and emotional reactions to smell

• connected to the habenula 

Olfactory Function

thalamus:

smell is the only sense that bypasses the thalamus

Olfactory Function

odor classes:

• based on chemicals with similar shapes and structures, which therefore activate a specific pattern of receptors

• up to 50 classes

Olfactory Function

Smell Definitions:

camphoraceous:

musky:

floral

pepperminty:

ethereal:

pungent:

putrid:

camphoraceous: mothball (camphor tree)

musky: animal mating (colognes) 

floral: ...flowers 

pepperminty: ...peppermint (candy canes ! ) ethereal: fruity (sweet) 

pungent: strong stink 

putrid: rotting smell

Olfactory Function

receptors: (2)

• there are ~1000 types of olfactory chemoreceptors

• the pattern of activated chemoreceptors is what makes a certain scent 

Olfactory Function

adaptation:

When there are too many odorants, the receptors become fully saturated, and the brain can signal to stop processing the smell if it becomes overwhelming.

Oral Anatomy

gustatory receptors location:

located mostly on tongue, but also the roof of the mouth, throat, and the lips

Oral Anatomy

epiglottis: (2)

• posterior portion of tongue, deep within throat

• structure that covers the windpipe when swallowing

Oral Anatomy

papillae:

small epithelial projections covering the tongue

Oral Anatomy

vallate:

Vallate are the largest papillae, forming a V shape at the back of the tongue, with 8-12 large bumps, each containing 100-300 taste buds.

Oral Anatomy

Foliate (3):

• Foliate taste buds are leaf-shaped, on the side of the tongue,

• smaller and more numerous than vallate buds,

• become less common with age, being the most sensitive taste buds.

Oral Anatomy

Fungiform:

Fungiform papillae are mushroom-shaped structures on the surface of the tongue that contain most of the taste buds, with about five taste buds on each.

Oral Anatomy

Filiform

Filiform papillae are flame-shaped structures on the surface of the tongue that don't have taste buds but create a rough texture to help manipulate food.

Oral Anatomy

taste buds:

• about 10,000 receptors found inside the pocket formed by papillae

Oral Anatomy

oral cavity:

• covered in stratified squamous epithelium, with taste buds embedded within

Taste Buds

gustatory cells:

create nervous system signal 

Taste Buds

gustatory hairs (2):

• microvilli which extend through an opening in the epithelium, towards the oral cavity

• about 50 per taste bud

Taste Buds

cell body:

• there is NO AXON

  • they're so short they don't need it, since the graded potential reaches right to the end of the cell and releases Neurotransmitters through the synaptic vesicles 

Taste Buds

basal cells (2):

• help regenerate

• taste cells are regenerated about every 10 days

Gustatory Function

Pathway

tastant > saliva > receptors > depolarization > NT > EPSP created > CN VII (anterior tongue), IX (posterior tongue), and X (throat and epiglottis) > medulla oblongata > thalamus > taste area of insula 

Gustatory Function

5 tastes:

salt, sour, bitter, sweet, and umami; each has its own receptor type

Gustatory Function

ion channels: (2)

• salt has sodium and sour has hydrogen

• these ions go through channels and cause depolarization 

Gustatory Function:

G-protein signaling pathways:

• for bitter, sweet, and umami

• activating these pathways opens relevant ion channels

Gustatory Function

chemoreceptor variety:

each taste cell has one type of chemoreceptor, but each taste bud can have multiple types (usually with one favorite)