chapter 10 biopysch

chemical senses

chemical senses

• smell and taste are both chemical senses

• flavor combines with smell, taste and other sensations in the mouth

• molecules in the environment activate receptors and sends signals to the brain

olfactory epithelium

olfactory epithelium

• located high inside the nasal cavity

• contains olfactory receptor neurons

• these neurons have tiny hair like structure called cilia which is covered in mucus

• olfactory molecule binds to receptors on the cilia

odorant, olfactory receptor, olfactory receptor neurons

odorant: a chemical molecule that causes smell

olfactory receptor: a protein that detects odorant

olfactory receptor neuron: an entire nerve cell that detects and sends smell information

how smell works

how smell works

• olfactory receptor are GPCR

• odorant binds to receptors and activate signaling processes

• neurons depolarize and fire action potentials that travel towards brain

nose to the brain

1. odorant enters the nose and binds to receptors on the cilia

2. olfactory receptor neurons depolarize and fire action potentials

3. axons pass through cribriform plate

4. signals reach glomeruli in olfactory bulb

5. mitral cells carry information to olfactory brain regions

Cribriform plate, olfactory bulb, glomeruli, mitral cells, piriform plate, amygdala, orbitofrontal cortex

Cribriform plate: bone that olfactory axons pass through 

Olfactory bulb: processes incoming smell information 

Glomeruli: organizes incoming signals from receptor neurons

Mitral cells: carries smell information onward 

Piriform plate: primary processing and representation of odor 

Amygdala: emotional responses to smells 

Orbitofrontal cortex: furthering processing of smell and flavor 

How brain identifies smell

How brain identifies smell

• Different odors create different patterns of activity across receptors and glomeruli

• Brain identifies smell using population code: multiple receptors work together to identify odor 

• One glomerulus does not represent one entire smell

What make smell different, Smell and brain injury 

What make smell different 

• Smell reaches primary olfactory cortex without passing through thalamus first 

• Other sensory pathways use thalamus as relay. Smell is an exception

Smell and brain injury 

• Trauma can damage axons passing through cribriform plate

• This can cause loss or impairment of smell 

• Olfactory receptor neurons can regenerate but recovery is not guaranteed 

congestion and smell, retronasal olfaction

congestion: blocks odorant molecules from reaching olfactory epithelium. this is why food tastes less flavorful when you have a cold.

retronasal olfaction: food odors travel from the mouth through the back of throat into the nasal cavity. this helps us experience flavor. pinching your nose reduces the odors from reaching nasal cavity making food less flavorful

Taste, Pheromones

Taste: The five basic qualities detected by taste receptor cells

Pheromones: Chemical signals between members of the same species.

• Many animals have a vomeronasal organ (VNO) detects certain chemical signals 

• Humans do not have a functional VNO comparable to rodents

• Claims about pheromones causing menstrual cycle synchronization are not established facts

Papillae, Taste buds, Taste receptor cells, tongue map is misleading, Supertasters

Papillae: Structures on the tongue that can contain taste buds

Taste buds: Groups of taste receptor cells.

Taste receptor cells: detects chemicals in food.

• specialized epithelial cells, NOT sensory neuron

• communicate with sensory nerve endings

• do not have long axons 

• can still generate action potentials

tongue map is misleading

• traditional tongue map shows separate areas for tastes. Incorrect. 

• Different taste qualities can be detected across multiple regions of the tongue

• There are no exclusive taste zones

Supertasters

• People differ in how sensitive they are to tastes

• Genetics and the number and distribution of papillae can contribute

heterodimerization, ATP signaling, Sweet, umami, and bitter use GPCR signaling

heterodimerization: when 2 different receptor subunit work together to form 1 receptor. this is important for sweet and umami receptors. different pairings allow receptors to detect different tastants

ATP signaling

• chemical signal released by taste cells. Communicates taste info to sensory nerves. 

• Not all taste cells release glutamate through synaptic vesicles

Sweet, umami, and bitter use GPCR signaling

• Tastant binds to GPCR. G protein/second messengers activate. 

• Calcium is released from internal stores and membrane conductance changes

• Taste cell becomes electrically active. Chemical signal activates the sensory nerve

Depolarization,Calcium and neurotransmitter release

Depolarization: inside the cell becomes less negative. Positive ions enter cell (such as Na⁺). Less positive potassium (K⁺) leaves the cell. 

Calcium and neurotransmitter release

• Depolarization opens voltage-gated calcium channels. Calcium enters cell

• Calcium helps trigger chemical signaling to sensory nerves

• Bitter taste can also increase calcium by releasing it from internal storage inside the cell