Sensing the World flashcards

How many olfactory receptors do humans have?

approximately 400 expressed on cilia

Bowmans gland

gland in the olfactory system which contains enzymes involved in mucus production

lamina propria

part of mucous membrane - connective fibroblast tissue in the olfactory system

GTP to GDP

causes dissociation

Describe the neurones found in the olfactory system

Exposed, highly ciliated, and express only 1 receptor type

Why do olfactory neurones only express 1 olfactory receptor type?

Random gene exchange on chromosomal level

G_olf

• stimulates adenylyl cyclase

• cAMP opens cation channels → depolarisation

• action potential propagated → brain olfactory bulb

olfactory code

Different smells/ligands are recognised by specific groups/ receptor ensembles so similar ligand structures can elicit very different smell responses

hOR 17-4

• floral odorant receptor

• guides sperm to egg

gustation

senses components in food to trigger response to brain

umami

savoury taste from some L-amino acids eg MSG

hedonic and homeostatic eating

pleasure and good for you interacts with taste and hunger state

soft palate

muscle fibres and connective tissue covered by membrane. Contains secondary salivary glands

gust cortex

distinguishes taste

taste receptors

mainly GPCRs. work as dimers for umami, sweet and bitter

ENaC

epithelial sodium channel for sodium taste

TRPM5

• calcium activated non selective channel

• induces depolarisation when intracellular calcium increases

• important for sweet taste

What is taste response dependent on?

taste cell type, not receptor

Receptor activated solely by a synthetic ligand and spiradoline

Spiradoline normally tasteless. Artificially expressed RASSL caused different reactions depending on what taste cells they were expressed in in mice

hypogeusia

reduced sense of taste

dysosmia

altered perception of smell

What causes diseases affecting taste and smell?

aging, coronavirus, mineral deficiency, Parkinson’s and some psychiatric conditions

rhodopsin

GPCR associated with photon ligands. Contains chromophore retinal located in the transmembrane domain

How does light affect retinal?

• cis → trans retinal

• cascade of conformational changes in rhodopsin alpha and beta

• heterotrimeric G protein signal transduction cascade

What happens to trans retinal after G protein cascade?

dissociates from rhodopsin and undergoes enzymatic recycling to its cis form

hyperpolarisation in sight

inhibits neighbouring bipolar cells so that glutamate isn’t released from photoreceptors

different types of cone cell

L(ong) = red, M(edium) = green and S(hort) = blue

What does vitamin A deficiency cause?

night blindness as vit A is precursor for retinal

dry macular degeneration

age related, due to thinning of macular and deposits of Drusen material

wet macular degeneration

vasculature leakage problem

diabetic retinopathy

common form of vision loss caused by retinal microvasculature damage

melanopsin

• expressed in retinal ganglion cells

• senses light for body clock

• signals to SCN in brain