Lecture 6 - Chemical Senses Flashcards
What are two senses that tell us whether a substance should be savoured or avoided
Olfaction (Smell)
Gustation (Tases)
What type of receptors are used by olfaction and gustation?
Chemoreceptors
chemicals are dissolves in aqueous solution and then picked up by chemoreceptors
How are olfactory receptors excited?
the chemicals are dissolved in nasal fluids
How are taste receptors excited?
Respond to chemicals dissolved in saliva
Olfactory receptors send signals to:
The olfactory bulb in the olfactory nerve (I)
Describe olfactory epithelium
organ of smell that is located in the roof of the nasal cavity. Covering the superior nasal conchae and containing olfactory sensory neurons (bipolar neurons with radiating olfactory cilia)
Describe Olfactory Receptors
unusual bipolar neurons that are thin apical dendrites terminate in knob. they are long, largely nonmotile cilia that radiate from knob
Bundles of nonmyelinated axons of olfactory receptor cells gather in fasicles that make up filaments of olfactory nerve (I)
Olfactory neurons, unlike other neurons have stem cells that give rise to new neurons every 30-60 days
Unque to Olfactory Receptors
Smells may contain 100s of different odorants, and humans have about 400 smell genes active in the nose. Each encodes a receptor protein that responds to one or more odours. Each orr obdor to several different receptors and each receptor has one type of receptor protein
Olfactory Differences in Species
of OR genes: # of receptors
Human: 350. Humans: 6 million
Mouse: 1000. Mouse: 10 million
Dog: 1100. Dog: 250 million
What is necessary in order to smell a substance?
it must be volatile
it must be in a gaseous state
it must be able to dissolve in olfactory epithelium fluid
Describe activation of olfactory sensory neurons
dissolved odorants bind to receptor proteins in olfactory cilium membranes.
- open cation channels, generating receptor potential
- at threshold action potential is conducted to first relay station in olfactory bulb
Describe Smell transduction
Odorant binds to receptor, activating G protein
G protein activation causes cAMP (2nd messenger) synthesis
cAMP opens Na+ and Ca+ channels
NA influx causes depolarization and impulse transmission
Ca+ influx causes decreased response to a sustained stimulus - referred to as olfactory adaptationb
What is Olfactory Adaptation
Calcium influx cases decreased response to a sustained stimulus
- people cant smell a certain door after being exposed to it for a while
Describe the Olfactory Pathway
filaments of olfactory nerves synapse with mitral cells located in the overlying olfactory bulb
- mitral cells are second-order neurons that form olfactory tract
- Synapses occurs in structures called glomeruli
- axons from neurons with the same receptor type converge on the given type of glomeruli
- Mitral cells amplify, refine and relay signals
- impulses from activated mitral cells travel via olfactory tracts to piriform lobe of the olfactory cortex
- some information sent to the hypothalamus, amygdala and other regions of limbic system
- Emotional responses to odor are excited
Define Anosmias and how does it occur
olfactory disorders
- head injuries that tear olfactory nerves
- aftereffects of nasal cavity inflammation
- Neurological disorders, such as parkinon’s disease
Phantosmia
olfactory hallucinations
- usually caused by temporal lobe epilepsy that involves the olfactory cortex
Montreal Procedure for Epilepsy
The first surgical technique for treating focal epilepsy
- the cortex was mapped using direct electrical stimulation of the brain to preserve brain tissue and minimize functional loss during therapeutic resection
Wilder Penfield
Where and how is taste sensed
Gustatory Signals are detected by chemoreceptors in the taste buds
What are Taste Buds?
sensory organs for taste.
Most of the 10, 000 taste buds are located on tongue in papillae
Fungiform Papillae
Mushroom shaped structures house most taste buds; and are scattered across the tongue
Foliate Papillae
tastebuds found on the side walls of the tongue
Vallate Papille
Largest taste buds with 8-12 forming V at the back of the tongue
Gustatory epithelial Cells
Taste receptor cells have microvilli called gustatory hairs that project into taste pores, bathed in saliva
- sensory dendrites coiled around gustatory epithelial cells send taste signals to brain
Basal Epithelial Cells
Dynamic stem cells that divide every 7-10 days
