Sensory Physiology (6/26/15) Flashcards
Where does the “sensory experience” begin?
At the receptor
What is Transduction?
The initial interaction of the stimulus with the receptor which is the transfer of physical energy into a neural signal.
Define Adequate Stimulus….
The type of energy that a given receptor is most sensitive to.
What is Sensory specificity?
Receptors have a range they are tuned to respond to.
What is the “Law of specific nerve energies?”
The fact that the receptor does not determine what you “hear, see or feel”. The CENTRAL CONNECTIONS (CNS) do! (we know this because you can bypass a receptor and stimulate a central connection and still experience something.)
Which sensory systems have receptors directly on AFFERENT nerves?
Somatosensory and olfaction
Which sensory systems have Separate RECEPTOR CELL from afferent nerve with a synapse between them?
Vision
Balance
Taste
Audition
What are the two major classes of Transduction? (Method of intimal interaction of stimulus with receptor)
- Physical (direct) interaction of stimulus with membrane protein protein that opens ion channel. (Somatosensory, vestibular, auditory) Ex. Na+ enters through epitheial sodium channels, Action potential leads to Ca++ entry, Release of ATP as neurotransmitter.
- Molecular interaction of stimulus with membrane protein (such as G protein) (Vision, taste and olfaction)
Ex. Sugars bind to receptor coupled G-protein, Release of intracellular Ca++ activates TRPm5 channel (TRP), depolarization leads to action potentials and release of neurotransmitter ATP.
What are TRP (Transient Receptor Potential) channels?
They are a family of (Cation) ion channels that are composed of 6 membrane domains with channels between the 5th and 6th domain.
* Can pass Ca++ through channel.
What type of stimuli can open TRP channels?
Intracellular Ca++ Temperature Chemicals Sound Light pH Osmolarity Mechanical stimuli
What does Sensory Coding tell us?
Intensity ( How much?)
Location (Where?)
Time/Duration (How long?)
True or false, When it comes to Intensity, there is no set value for the threshold?
True, Threshold is not a specific value. Many factors can influence the Threshold level such as physiological, neurological or pharmacological factors.
In regards to Location coding, what is “Receptive Field”?
Area a receptor is sensitive to
What is “Confounding”?
A confusion as to the location of the stimuli that can occur if there is only one neuron. Ex. a mild stimuli in center of receptive field can feel the same as a larger stimuli on the periphery of the receptive field.
Describe “Across Neuron Coding”…
Basically its the opposite of “Confounding”. You have multiple neurons that can kind of triangulate the location of a stimuli based on the level of stimulus they are each receiving.
What is Lateral Inhibition?
Lateral Inhibition is a way to combat “Confounding”. It basically inhibits the signal on adjacent neurons and enhances the signal at the true point of stimulus to better pinpoint it.
How does Time coding work?
Well, there are two types Neurons:
- Rapidly adapting Neurons = AP’s occur only at the very beginning of the stimulus and then at the when the stimulus ceases (Because the get used to the stimulus rapidly)
- Slowly adapting = AP’s are frequent at beginning of stimulus, yet they do continue through stimulus although they may lessen. (because they never quite get used to it)
What are the 2 types of CNS modulation of Peripheral Input?
- Presynaptic Inhibition
2. Postsynaptic Inhibition
What is Presynaptic Inhibition and how does it work?
So basically you have a axon with a AP barreling down it towards several branches leading to several target cells….then you have an inhibitory axon attached to one (Or several) of the axon terminals that hyperpolrizes the axon terminal which leads to less Ca++ entry and less neurotransmitter release. (This is common with the pain and auditory systems)
EX. Auditory: Efferents (inhibitory) from the Superior olive synapse on hair cells to “set gain” or receptor neuron.
What is Postsynaptic Inhibition and how does it work?
So here you have a Excitatory Presynaptic axon and a Inhibitory Presynaptic axon both ending on a postsynaptic neuron. These Excitatory and Inhibitory signals balance out so that threshold is not reach and not AP potential will result and thus no neurotransmitters are released to target cells downstream.
What is a somatotopic map?
Body representation laid out on brain.
What is a Tonotopic map?
Auditory pitch representation
What is a Retinotopic map?
Visual field representation
What is Central Sprouting?
If part of a digit is lost, uninjured digit will send a collateral “Sprout” to rest of injured digit.
