Explain the neural transduction process

1. Adequate Stimulus

Stimulus that best activates a receptor

-Inadequate stimulus is pressure on eye causing flash of light.  Light is adequate stimulus.

2. Membrane conductance effect

 -Sodium channel opening up (depolarization)

3. Generator Potential

 Dependent on strength of stimuli

4. Initiator of Action Potential

All or none process

-Generator potential needs to be sufficient!

It is a mechanoreceptor

-senses pressure

-connective tissue fluid filled ending

The generator potential!

(not action potential)

With repect to action potentials, what happens when there is a sustained generator potential that is above threshold?  What happens to the APs when the GP is increased in intensity?

A train of action potentials is formed (multiple spikes)

When intensity of GP is increased, frequency of AP increases

How does a Pacinian corpuscle cause a signal transduction?

PCs, or any mechanoreceptor, has stretch sensitive channels.

When this receptor senses pressure, the cell membrane is deformed, which deforms the channels, allowing the flow of sodium into the interior of the nerve ending.

Sufficient deformation, enough sodium comes in, causes depolarization, ACTION POTENTIAL!

Pain Reception 

It is a 'noxious' stimuli receptor

-measure harmful or potentially harmful signals

Travels up the spinothalamic pathway (anterolateral)

Presynatic Inhibition

A brain stem neuron synapses with an inhibitory interneuron.  This inhibtory interneuron releases enkephalin onto the presynaptic terminal of the pain fiber.

It is an inhibitory neurotransmitter, released from an inhibitory interneuron, that closes cation channels on the presynaptic terminal of pain fibers.

Associated with Runner's High

-enkephalin endorphin issue

-diminished pain sensation 

Taste buds are tastes cells...they are located on taste papillae (Circumvallate, Foliate, Fungiform).

What you see are NOT taste buds, they are papillae.  You can't see the taste buds (cells)!

Filliform are the only taste papillae that don't have taste bud.

1.  Salt- sodium ions move through channel

2.  Sour- Hydrogen protons move through channel

Each causes depolarization-->Ca influx-->transmitter release-->increase firing of afferent nerve.

3. Sweet, 4. Bitter, 5. Umami

TRPM5-->G-Protein-->Activates DAG and IP3-->calcium release-->transmitter release-->increased firing of afferent nerve.

What are the two ways that nerve cells report the intensity of a stimulus?

1.  Frequency Coding (single cell)

-Light pressure=low frequency

-Higher Pressure=high frequency

(has to do with membrane & Na+ pore deformation)

2.  Population Coding (Multiple cells)

Light pressure=few PC activated

Heavy pressure=MANY PCs activated

What are the two types of proprioception receptors.

1.  Static

-Only measures position (i.e. Jaw)

-more impulses/sec when jaw opens more

2.  Dynamic

-deals with rate of jaw opening

-fast opening=fast firing rate

-slow opening=slow firing rate

How do nerve cells report the Quality of a stimulus?

Label-line coding

pain and somatic senses travel different pathways

-Pain (spinothalamic/antereolateral)

-Somatic (Dorsal Column)

This ensures fidelity and clarity of stimulus

All nociceptor signals travel the ______ pathway

All proprioceptive signals travel the _____ pathway.

Light touch signals travel _______

Anterolateral aka spinothalamic

Dorsal column

Both pathways

How do nerve cells adjust to repetitive or chronic stimuli?

What are the three components?

Sensory Adaptation

Types:

No adaptation, Slow Adaptation, Rapid Adaptation 

3 Components: 

1.  Mechanical

-PC remains deformed but nerve ending returns to original shape (signal at initiation and termination)

 -Parcinian Corpuscle are Rapid Adaptor

2.  Chemical

-Photochemical adaptation of photoreceptor

-Dark environment-->Increase sensitivity to light (more rhodopsin)

-Bright environment-->less rhodopsin

3.  Cellular

Continuous exposure to an odor

-results in internalization of cellular receptors for odor.

It is a Neural Adaptation Response 

Taste and smell are such powerful stimuli and they are hooked into the limbic system (survival sense). When we have a favorable taste/smell at the same time as nausea caused by chemo, that favorable food becomes associated with the bad experience.