BMC L11 Flashcards
State the role of chemoreceptors
Detect
-smell
-taste
-chemicals in blood
why?
-Food
-Sexual mates
-Predators
-Harmful substances
-Hypoxia
State the 2 classes of chemoreceptors
- Taste GUSTATORY RECEPTORS
- Smell OLFACTORY RECEPTORS
Anatomy of nose
Olfactory bulb
Cribriform plate of ETHMOID BONE
Olfactory epithelium
State the role of the nasal conchae
Aids in humidifying air
Air must be humidified as it is inhaled as you can only smell a subsance in solution
Air also humidified to prevent drying of oral mucosa
conchae also called turbinates
What are the 3 nasal conchae?
Superior
Middle
Inferior
NASAL CONCHAE ALSO KNOWN AS TURBINATES - WARM + MOISTEN AIR
Describe the location of the olfactory epithelium
- Located on roof of nasal cavity
-Along nasal septum
Describe the locartion of the Ethmoid bone
- Located in skull - separates nasal cavity from brain
-Cribriform plate is part of ethmoid bone
-Has lots of holes in it, which allows olfactory nerve endinvs to pass from skull cavity to olfactory epithelium
Describe the location of the olfactory mucosa
Made up of olfactory epithelium,
contains
Bowman’s glands
Sate examples of Odorants
Chemicals, have odor, bind to + stimulate olfactory receptors
- ESTERS
-LACTONES
-KETONES
-ALDEHYDES
State the site of of olfaction
Olfactory epithelium
State what type of epithelium is present in olfactory epithelium
Pseudostratifed epithelium
Explain why humans “sniff”
Olfactory epithelium - ill poisitioned
Needs moevement to stimulate receptors
this movement is “sniffing”
Describe the structure of the olfactory epithelium
-contains olfactory neurones, surrounded by epithelial cells
-epithelial cells are yellow - due to lipofuscin
-consists of 3 types of cells:
1. Olfactory receptors
2. Basal cells - at base of olfactory epitelium, also known as olfactory stem cells
3. Supporting cells / SUSTENTACULAR CELLS
State the output cells of the olfactory bulb
Mitral cells
State the spherical structures where mitral cells and olfactory cells synapse
Glomeruli
State which nerve penetrates the cibriform plate
Cranial nerve 1 - Olfactory nerve
Describe the location and function of Bowman’s glands
- Situated in olfactory mucosa
-Beneath olfactory epithelium
-In the lamina propria
-Secrete gel forming mucin
mucin moistures surface of the olfactory epithelium which allows odourants to dissolve in it and transduction to occur
-Secrete proteins: lysozyme. amylase, IgA
Describe the structure of olfactory neurones
bipolar neurones
dendrites have many cillia
Cillia extend from olfactory receptor into mucus
surface of cillia covered with olfactory receptors
olfactory receptors are G protein coupled receptors
Describe the structure of olfactory neurones
bipolar neurones
dendrites have many cillia
Cillia extend from olfactory receptor into mucus
surface of cillia covered with olfactory receptors
olfactory receptors are G protein coupled receptors
Describe the structure of olfactory receptors
- Each receptor binds to a variety of odour molecules
- Olfactory receptors have varying affinity
-Affinity differences causes differences in activation patterns resulting unique odorant profiles
Describe olfactory transduction
- An odorant molecule binds to an olfactory receptor protein which simulates it (which is G protein)
- When G protein is activated, it activates adenylate cyclase, to produce cAMP
- cAMP opens ion channels in the cell membrane (Ca2+ Na+ ion channels)
- Influx of Na+ Ca2+ but eflux Cl- ions
- Ca2+ binds calmodulin to form CaM
- CaM binds to cAMP activated channels + closes them
- Therefore, no Ca2+ Na+ influx
- CaM binding to the cAMP activated channels activates CaM kinase II
- CaM kinase phosphorylates adenylyl cyclase III, reduces cAMP production
- CaM kinase II activates PDE hydrolyses cAMP
- Seizes signal - inhibits neurone from further activation
Describe the olfactory pathway
odours which activate same receptors, have the same glomeruli
Axons of olfactory receptors synapse in olfactory bulb
Synapse with mitral cells in glomeruli in olfactory bulb
Each odour activates a certain set of glomeruli
Once you are at the olfactory bulb, the signal travels through olfactory tract (AXONS OF MITRAL CELLS) to olfactory cortex, frontal lobe (awareness of smell) (conscious interpretation of smell, COMPLEX), AMYGDALA, HYPOTHALAMUS (limbic system) (emotional response)
IMAGINING ODOUR ACTIVATES PRIMARY OLFACTORY CORTEX
Does the olfactory bulb contain amacrine cells?
Yes
State the role of the fontal lobe, hypothalamus, and amygdala in olfaction
Frontal lobe - Conscious interpretation of smell (distinguishing and determining different smells)
Hypothalamus / Amygdala - emotional response / memory associated to different smells
Describe olfactory adaptation
Odour response desensitisation
Decrease in sensitivity to olfactory system over time
When continuous non-changing stimulus / rapid repeating stimulus applied
TAKES LONGER TO RECOVER - REFRACTORY PERIOD BECOMES LONGER
E.g. smelling perfume for too long
DIAGRAM L11 - overtime, signals become identical
Why does short-term olfactory adaptation occur?
Due to refractory period when calcium ion levels inside cell returned to normal (Calcium negative feedback)
What happens when we are perceiving complex odours?
In a mixture of complex odours (2-4) we can distinguish individual components of odourants. However, this ability is lost for vert complex odours
Explain the configurational hypothesis of olfaction
The component odour from a recognisable signature which is perceived as a single distinctive odour
HCN + benzaldehyde - very different structures, both smell of almonds, both produced by almond
What is the function of stem cells in the olfactory epithelium ?
- Olfactory cells have high turnover rate
-Due to lots of stem cells (BASILAR CELL) - the source, in olfactory epithelium
Explain Amoore’s theory and why it may be incorrect
Theory states that each odour molecule has a specific shape and a complementary receptor (enzyme, lock key model)
INCORRECT:
- humans have 350 different olfactory receptors, if each receptor was specific to only a few / responded to only a few odorants, we would only be able to smell 1000 odours, but we can we can smell, distinguish, detect 10,000 odours - we can also discriminate 3000 of these
- Does not take into account molecules of similar shapes which overlap in smell as they activate the same receptor e.g. HCN / benzaldehyde
Explain the labelled lined theory and why it may be incorrect
Each of 350 receptors sends labelled line to brain
enables the brain to determine the odour by determine which of the 350 receptors were stimulated
INCORRECT:
LIMITS US TO 1000 DETECTABLE SMELLS
Explain the Combinatorial odour code theory and why it may be incorrect
- Each receptor responds to a small range of odourants, brain can distinguish odours based on pattern of receptor activation
Allows infinite number of odours to be detected
INCORRECT:
we really only discriminate 3000 because we have 350 receptors
Explain intrinsic signal imaging to view the olfactory bulb
- View olfactory bulb under a red light
-To visualise flow of oxygenated blood in glomeruli in olfactory bulb
-Each odour gives a distinct pattern of glomeruli activation
-Only those glomeruli activated by an odour use a (burst of/lots of) oxygen
-INDIVIDUAL ODOUR CAN ACTIVATE MANY GLOMERULI (perfume can have many smells)
purpose of this: to view THE PATTERN OF GLOMERULI ACTIVATED CHARACTERISES THE ODORANT
State the role of the epiglottis
FLAP-LIKE Folds over windpipe when swallowing
Prevents you from breathing and speaking while chewing
However, humans can breath + speak while chewing, increasing risk of choking as food can enter windpipe
State the 3 devisions of the pharnyx and their functions
- Nasopharynx
- Oropharynx
- Laryngopharynx
State the role of the pharngotympanic tube
EUSTACIAN TUBE
CONNECT THROAT - INNER EAR to balance pressure on both sides of ear drum
State the role of the uvula
dangly part at back of throat
SPEECH / GAG REFLEX
State 5 taste sensations
Sweat -Sugars
Sour -Acids
Bitter - alkaloids
Salty - Salts, NaCl
Umami - amino acids
State the function and location of taste receptors
For sensation of taste
TASTE BUDS
NUMBER OF TASTE BUDS DECLINE WITH AGE
State locations where taste buds are found
Tongue
Soft palate
Eppiglottis
Pharynx
Describe the structure of the taste bud
Taste bud is oval / flask shaped structure, consists of 3 types of epithelial cells:
- Supporting cells
CONTAIN MICROVILLI, SURROUNDED BY GUSTATORY CELLS - Gustatory Receptor Cells - TASTE CELLS
CONTAIN MICROVILLI (GUSTATORY HAIRS) - PROJECT through taste pore to epithelium surface - Basal cells - DYNAMIC stem cells, produce supporting cells, which develop inti gustatory receptor cells
What type of epithelium is found in the tongue?
Stratified Squammous
State the exact location of taste buds in the tongue
Taste buds in tongue found in elevated structures known as papillae
INCREASE SA,
State the 4 types of papillae
- Circumvallate papillae , LARGEST, INVERTED V - contains lots of individual buds
- Fungiform papillae - mushroom shaped
- Folliate papillae - Laterally located, LOST EARLY
- Filliform palate
Which region of the tongue has no taste buds?
Filliform palate
