Sensory Physiology (6/26/15)

Question 1

Where does the “sensory experience” begin?

Answer 1

At the receptor

Question 2

What is Transduction?

Answer 2

The initial interaction of the stimulus with the receptor which is the transfer of physical energy into a neural signal.

Question 3

Define Adequate Stimulus….

Answer 3

The type of energy that a given receptor is most sensitive to.

Question 4

What is Sensory specificity?

Answer 4

Receptors have a range they are tuned to respond to.

Question 5

What is the “Law of specific nerve energies?”

Answer 5

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.)

Question 6

Which sensory systems have receptors directly on AFFERENT nerves?

Answer 6

Somatosensory and olfaction

Question 7

Which sensory systems have Separate RECEPTOR CELL from afferent nerve with a synapse between them?

Answer 7

Vision
Balance
Taste
Audition

Question 8

What are the two major classes of Transduction? (Method of intimal interaction of stimulus with receptor)

Answer 8

1. 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.
2. 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.

Question 9

What are TRP (Transient Receptor Potential) channels?

Answer 9

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.

Question 10

What type of stimuli can open TRP channels?

Answer 10

Intracellular Ca++
Temperature 
Chemicals
Sound
Light
pH
Osmolarity 
Mechanical stimuli

Question 11

What does Sensory Coding tell us?

Answer 11

Intensity ( How much?)
Location (Where?)
Time/Duration (How long?)

Question 12

True or false, When it comes to Intensity, there is no set value for the threshold?

Answer 12

True, Threshold is not a specific value. Many factors can influence the Threshold level such as physiological, neurological or pharmacological factors.

Question 13

In regards to Location coding, what is “Receptive Field”?

Answer 13

Area a receptor is sensitive to

Question 14

What is “Confounding”?

Answer 14

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.

Question 15

Describe “Across Neuron Coding”…

Answer 15

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.

Question 16

What is Lateral Inhibition?

Answer 16

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.

Question 17

How does Time coding work?

Answer 17

Well, there are two types Neurons:

1. 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)
2. 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)

Question 18

What are the 2 types of CNS modulation of Peripheral Input?

Answer 18

1. Presynaptic Inhibition

2. Postsynaptic Inhibition

Question 19

What is Presynaptic Inhibition and how does it work?

Answer 19

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.

Question 20

What is Postsynaptic Inhibition and how does it work?

Answer 20

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.

Question 21

What is a somatotopic map?

Answer 21

Body representation laid out on brain.

Question 22

What is a Tonotopic map?

Answer 22

Auditory pitch representation

Question 23

What is a Retinotopic map?

Answer 23

Visual field representation

Question 24

What is Central Sprouting?

Answer 24

If part of a digit is lost, uninjured digit will send a collateral “Sprout” to rest of injured digit.