Sensory transduction Flashcards
All sensory systems convey which 4 basic types of information when stimulated?
Modality
Location
Intensity
Time course
What are the 2 superficial mechanoreceptors?
Meissner corpuscles
Merkel cells
What are the 2 deep mechanoreceptors?
Pacinian corpuscles
Ruffini endings
What are the 2 rapidly adapting mechanoreceptors?
Meissner corpuscles
Pacinian corpuscles
What are the 2 slowly adapting mechanoreceptors?
Merkel cells
Ruffini endings
Describe the 3 ways in which pressure opens ion channels on mechanoreceptors.
The force of the pressure causes the cell membrane to stretch and pull ion channels open:
- Change in tension in the lipid bilayer
- Changes in extracellular matrix
- Changes in intracellular cytoskeleton
Which specific mechano-sensitive ion channel is present on Merkel’s discs?
Piezo 2
Describe the process of sensory transduction in a Merkel’s disc.
Stretch opens Piezo 2, which causes receptor potential depolarization
This receptor potential depolarization opens voltage-gated Ca2+ channels, leading to the release of neurotransmitter
Action potentials are produced in SA1 neuron
What do slowly adapting mechanoreceptors detect?
Object pressure and form
What do rapidly adapting mechanoreceptors detect?
Object motion and vibration
When are nerve action potentials fired when receiving input from Pacinian corpuscles?
At the start and end of the stimulus
What is found in the layers of Pacinian corpuscles?
Viscous fluid
What is the peak sensitivity of Pacinian corpuscles?
200 to 300 Hz
Describe the receptive fields of superficial receptors.
Small
Describe the receptive fields of deep receptors.
Large
Distinguishing between two points of contact on the skin is termed what?
Tactile acuity
Where on the body is tactile acuity the best and why?
Fingertips - receptors are dense
When light passes through the retina, which cells does it first pass through?
Ganglion cells
What are the 4 common regions in rods and cones?
- Outer segment
- Inner segment
- Cell body
- Synaptic terminal
What type of receptors are rods and cones?
Photoreceptors
Which part of rods and cones contains photopigment?
Outer segment (contains light sensitive discs)
Which type of photoreceptor is more sensitive to light?
Rods
How many rods and cones are in the retina?
Rods - 100 million
Cones - 5 million
Which type of photoreceptor detects colour perception?
Cones
Which type of cell is concentrated in the fovea?
Cones
Why is resolution best in the fovea?
Due to 1:1 connections with bipolar and ganglion cells
In dark conditions, what is the resting potential of photoreceptors? What is this known as?
-30mV
‘Dark current’ - Na+
In dark conditions, what is the activity level of glutamate in photoreceptors?
Glutamate is released
Which molecule keeps Na+ channels open in the ‘dark current’?
cGMP
What affect does light have on the membrane potential of photoreceptors?
Hyperpolarises the cells
Describe how light causes hyperpolarization of photoreceptors.
Light causes a conformational change in the rhodopsin molecules
This causes the release of phosphodiesterase
Phosphodiesterase reduces the levels of cGMP, leading to the closure of Na+ channels, causing hyperpolarization
Which fluid is found in the scala vestibuli?
Perilymph
Which fluid is found in the scala tympani?
Perilymph
Which fluid is found in the scala media?
Endolymph
Describe the composition of perilymph in terms of Na+ and K+.
High Na+
Low K+
Describe the composition of endolymph in terms of Na+ and K+.
Low Na+
High K+
Which structure lies on the basilar membrane and contains the auditory receptor cells?
Organ of Corti
Which cells are found in the Organ of Corti?
Hair cells
Hair cells have which specialised feature?
Stereocilia
What are stereocilia on hair cells attached to?
Tectorial membrane
Hair cells synapse onto what?
Spiral ganglion cells
What do stereocilia contain and how does this affect their form?
Aligned actin filaments - they are rigid and bend only at the base
What connects the mechanosensitive ion channels to adjacent stereocilia?
Tip links
Describe the process of auditory transduction.
Displacement of the stereocilia increase tension on the tip links and cause ion channels to open - this allows the influx of K+ and depolarizes the hair cell
Receptor potentials stimulate neurotransmitter release which goes on to generate AP in neurons
In auditory transduction, why does K+ move into the hair cells?
Because the endolymph has a high concentration of K+
What structure divides the endolymph from the perilymph?
Reticular lamina
How does the base of the basilar membrane differ from the apex?
The base is stiff, the apex is soft
The base of the basilar membrane detect which kind of frequency?
High frequency
The apex of the basilar membrane detects which kind of frequency?
Low frequency
What is Piezo 2?
A mechano-sensitive ion channel present on Merkel’s discs
