Sensory physiology- basics and chemosensation Flashcards
What are the 4 steps of chemosensation?
Reception
Transduction
Transmission
Perception
What are the 7 types of receptors?
Chemoreceptors Mechanoreceptors Photoreceptors Thermoreceptors Electroreceptors Magnetoreceptors Nociceptors
What do chemoreceptors detect?
Chemical stimuli- smell and taste
What do mechanoreceptors detect?
Mechanical stimuli- touch and sound
What do photoreceptors detect?
Electromagnetic stimuli- vision
What do thermoreceptors detect?
Temperature related stimuli
What do electroreceptors detect?
Electrical stimuli
What do magnetoreceptors detect?
Magnetic stimuli
What do nociceptors detect?
Chemical stimuli-pain
Describe the reception step of chemosensation
The reception of the stimulus by a receptor
Describe the transduction step of chemosensation
The conversion of the stimulus into a change in the membrane potential
Describe the transmission step of chemosensation
The signal is sent to an integration centre
Describe the perception step of chemosensation
The stimulus is perceived at the integration centre
What is lateral inhibition?
A relatively weak stimulus across multiple receptors will produce a response in each afferent neuron
A strong stimulus in the middle of these receptors will trigger the horizontal interneurons to inhibit signals at the outer receptors
Why is lateral inhibition important?
Allows sharper discrimination of the boundaries of a stimulus
What is dynamic range?
The range of stimuli intensities a sensory receptor is able to encode stimuli
What is the threshold intensity?
The weakest stimulus that produces a response in a receptor 50% of the time
What is range fractionation?
Groups of receptors that are each sensitive to a different range of stimulus that work together to cover the whole range of stimulus intensity
What does encoding signals logarithmically do?
It allows a receptor to have a constant response to a given percentage change in stimulus intensity
Prevents the saturation of receptors
What are tonic receptors?
They fire action potentials as long as the stimulus occurs and can provide information about how long a stimulus lasts
What are phasic receptors?
They adapt very quickly and depolarise at the beginning of a stimulus and allow the tuning out factors in the environment that aren’t changing
Give an example of a stimulus that is controlled by tonic receptors
A paper cut
Give an example of a stimulus that is controlled by phasic receptors
A hot/cold bath
What is the sense of smell called?
Olfaction
What are the chemicals that are detected by the olfactory system called?
Odorants
What is the name of the receptors that detect odorants?
Odorant receptors
What is the sense of taste called?
Gustation
What are the chemicals that are detected by the gustatory system called?
Tastants
Where are taste receptors located?
The taste buds
Describe signal transduction in vertebrate olfactory receptor cells
Thee binding of odorant chemicals to the receptor causes a conformational change
The activated Golf protein moves through the membrane and activates adenylate cyclase
The adenylate cyclase converts ATP to cAMP
cAMP opens cAMP gated ion channels
Ca2+ and Na+ enter the cell and cause a generator potential
Ca2+ opens Ca2+ activated Cl- channels causing Cl- to leave the cell increasing the depolarisation
The generator potential opens voltage-gated Na+ channels triggering action potentials
What is the vomeronasal organ?
A small paired tubular structure embedded in the nasal epithelium of amphibians, reptiles, and many mammals
Where is the vomeronasal organ located in mammals?
In the septum and has a pore that opens into the nasal cavity
What does the vomeronasal organ do in rodents?
Detects pheromones that signal the sex, strain, identity, and sexual receptivity of another individual
What is the vomeronasal organ called in snakes?
Jacobson’s organ
Where is the Jacobson’s organ located in snakes?
In the oral cavity
How do snakes use their Jacobson’s organ?
They use their tongues to transfer pheromones to it by flicking their tongue in their mouth
How are pheromones released and detected in insects?
The female releases a pheromone from a gland at the tip of her abdomen and it can travel thousands of meters in the air
The male detects it by air passing over their antennae
What are the hairs that cover an insect’s antennae called?
Chemosensitive sensilla
Describe how insects use their sensilla
Olfactory sensilla have a small pore at the tip to allow odorants to enter and sensory neurons express odorant receptors to detect those molecules
How do we taste salty things?
Na+ from salty food enters through Na+ channel
Resulting depolarisation opens voltage-gated Ca2+ channels
Influx of Ca2+ causes neurotransmitter to be released
How do we taste sweet things?
The sweet substance binds to its receptor causing a conformational change
The activated G protein gustducin activated adenylate cyclase
Adenylate cyclase catalyses the conversion of ATP to cAMP
cAMP activates a protein kinase that phosphorylates and closes a K+ channel
Resulting depolarisation opens voltage-gated Ca2+ channels
Influx of Ca2+ causes neurotransmitter release
How do we taste sour things?
H+ ions from sour foods block the K+ channel
This prevents the K+ from leaving
Resulting depolarisation opens voltage-gated Ca2+ channels
Influx of Ca2+ causes neurotransmitter release
How do we taste bitter things?
Bitter substance binds to its receptor causing a conformational change
The activated G protein transducin activated PLC
PLC catalyses the conversion of PIP2 into the second messenger IP3
IP3 causes the release of Ca2+ from intracellular stores
Influx of Ca2+ causes neurotransmitter release
