Chemical Senses Flashcards
Taste (27 cards)
Describe the role of chemoreceptors in the senses of smell and taste.
Chemoreceptors are specialized cells that detect chemicals in the environment. In smell (olfaction) and taste (gustation), they allow us to identify whether a substance should be savored or avoided by responding to chemicals dissolved in aqueous solutions.
Explain how smell receptors are activated.
Smell receptors are activated by chemicals that are dissolved in nasal fluids, which then bind to olfactory sensory neurons located in the olfactory epithelium.
Define the structure and function of the olfactory epithelium.
The olfactory epithelium is the organ of smell located in the roof of the nasal cavity. It contains olfactory sensory neurons, supporting cells, and olfactory stem cells, and is responsible for detecting odorants.
How do olfactory neurons differ from other types of neurons?
Olfactory neurons are unusual bipolar neurons that have thin apical dendrites terminating in a knob with long, nonmotile olfactory cilia. They also possess stem cells that allow for the regeneration of new neurons every 30–60 days.
Explain the significance of the mucus covering olfactory cilia.
The mucus covering olfactory cilia serves as a solvent for odorants, allowing them to dissolve and bind to the receptors on the cilia, which is essential for the detection of smells.
Describe the organization of olfactory receptor cells in the olfactory epithelium.
Olfactory receptor cells are organized such that neurons with different receptors are interspersed, while those with the same receptor type are confined to specific zones but scattered within those zones.
How do olfactory receptors contribute to the perception of different smells?
Humans have approximately 400 active ‘smell’ genes, each encoding a unique receptor protein that responds to one or more odors. A single odorant can bind to multiple receptors, and each receptor cell has only one type of receptor protein.
Explain the concept of glomeruli in the olfactory system.
Each glomerulus in the olfactory system is dedicated to one type of receptor. When a single odorant is detected, it activates multiple glomeruli, with input from different receptors, allowing for a complex perception of smells.
Describe the regeneration process of olfactory neurons.
Olfactory neurons have the ability to regenerate through olfactory stem cells located at the base of the olfactory epithelium, allowing for the replacement of old neurons every 30–60 days.
How do the axons of sensory neurons converge in the olfactory system?
The axons of sensory neurons that express the same type of odorant receptor converge in two specific glomeruli, facilitating the processing of olfactory information.
Describe the state of a substance necessary for it to be smelled.
A substance must be volatile and in a gaseous state to be smelled.
Explain the role of olfactory epithelium fluid in the process of smelling.
The odorant must be able to dissolve in the olfactory epithelium fluid to activate olfactory sensory neurons.
How do dissolved odorants initiate a response in olfactory sensory neurons?
Dissolved odorants bind to receptor proteins in olfactory cilium membranes, opening cation channels and generating a receptor potential.
Define olfactory adaptation.
Olfactory adaptation is the decreased response to a sustained stimulus, causing people to be unable to smell a certain odor after prolonged exposure.
What is the role of G protein in the smell transduction process?
G protein activation leads to the synthesis of cAMP, which opens Na+ and Ca2+ channels, causing depolarization.
Explain the process of smell transduction starting from odorant binding.
The odorant binds to its receptor, activating a G protein (Golf), which then activates adenylate cyclase to convert ATP to cAMP, leading to depolarization.
Describe the function of mitral cells in the olfactory system.
Mitral cells are second-order neurons that amplify, refine, and relay signals from olfactory nerves to the olfactory cortex.
How do impulses from activated mitral cells travel in the brain?
Impulses travel via olfactory tracts to the piriform lobe of the olfactory cortex and some information is sent to the hypothalamus and amygdala.
What are glomeruli in the context of the olfactory system?
Glomeruli are structures where synapses occur between filaments of olfactory nerves and mitral cells, with axons from neurons of the same receptor type converging.
Explain the emotional responses related to smell.
Emotional responses to odours are elicited through connections to the hypothalamus, amygdala, and other regions of the limbic system.
Define anosmias.
Anosmias are disorders related to the sense of smell.
Describe the common causes of olfactory hallucinations.
Olfactory hallucinations commonly result from head injuries that tear olfactory nerves, aftereffects of nasal cavity inflammation, neurological disorders such as Parkinson’s disease, and temporal lobe epilepsy that involves the olfactory cortex.
Explain the relationship between temporal lobe epilepsy and olfactory hallucinations.
Temporal lobe epilepsy can cause olfactory hallucinations, also known as phantosmia, and some individuals may experience olfactory auras prior to experiencing epileptic seizures.
Define phantosmia and its potential causes.
Phantosmia is a type of olfactory hallucination where a person perceives smells that are not present. It can be caused by head injuries, nasal cavity inflammation, neurological disorders, and temporal lobe epilepsy.
