Sensory System

Question 1

What is the most common neurotransmitter utilized by sensory receptors?

Answer 1

Glutamate

Question 2

Must sensory neurons use action potentials to propagate?

Answer 2

Sometimes.. only if the neuron is > 0.1mm in length. Shorter neurons simply use passive electronic transmission.

Question 3

How are hyperpolarizing receptors (rod photoreceptor for example) hyperpolarized when activated? (what channel is responsible for the hyperpolarization?)

Answer 3

Due to closing of cation channels

Question 4

Describe the transduction of a rod photoreceptor that leads to hyperpolarization.

Answer 4

Light enters the photoreceptor and activates rhodopsin. When a molecule of l-cis-retinal bound to rhodopsin absorbs light retinal changes in conformation to l-trans-retinal. Rhodopsin undergoes a conformational change to metarhodopsin, which stimulates the G-protein transducin. Transducin activates a cGMP phosphodiesterase enzyme which breaks down cGMP to guanosine. The cation channel then closes leading to hyperpolarization.

Question 5

Describe how stretch depolarizes mechanoreceptors.

Answer 5

Mechanosensitive cation channels open in response to stretch –> depolarization of cell.

Question 6

How is the depolarized resting potential of a rod photoreceptor maintained?

Answer 6

Maintained by the opening of cGMP-gated cation channels in the presence of high cGMP concentrations under resting conditions.

Question 7

How does a short receptor encode stimulus intensity?

Answer 7

Short receptors encode stimulus intensity by altering the amount of time their channels stay open (or closed)

Question 8

How does a long receptor encode stimulus intensity?

Answer 8

As an increase in action potential firing

Question 9

What type of information does an A-alpha axon carry?

Answer 9

Muscle spindle afferents & tendon organ afferents

Question 10

What type of information does an A-beta axon carry?

Answer 10

Mechanoreception of skin and secondary muscle spindle afferents

Question 11

What type of information does an A-delta axon carry?

Answer 11

Sharp pain and cold temperature

Question 12

What type of information does a C axon carry?

Answer 12

Burning pain, warm temperature, itch, and crude touch

Question 13

What is the relationship between axon size and conduction velocity?

Answer 13

The bigger the diameter, the higher the velocity

Question 14

What is the relationship between axon myelination and conduction velocity?

Answer 14

The more the myelination, the higher the velocity

Question 15

Which axon type is unmyelinated?

Answer 15

C fibers

Question 16

Which axon type is poorly myelinated?

Answer 16

A-delta fibers

Question 17

What fiber type are somatosensory mechanoreceptors of the Lemniscal system?

Answer 17

A-beta fibers

Question 18

(Of Merkel’s disc, Meissner’s corpuscle, Pacinian corpuscle, & Ruffini’s ending) Which receptor has a small receptive field size and slow adaptation?

Answer 18

Merkel’s disk

Question 19

What does the word “corpuscle” indicate?

Answer 19

Fast adaptation - responds to vibration

Question 20

(Of Merkel’s disc, Meissner’s corpuscle, Pacinian corpuscle, & Ruffini’s ending) Which receptor has a small receptive field size and fast adaptation?

Answer 20

Meissner’s corpuscle

Question 21

(Of Merkel’s disc, Meissner’s corpuscle, Pacinian corpuscle, & Ruffini’s ending) Which receptor has a large receptive field size and slow adaptation?

Answer 21

Ruffini’s ending

Question 22

(Of Merkel’s disc, Meissner’s corpuscle, Pacinian corpuscle, & Ruffini’s ending) Which receptor has a large receptive field size and fast adaptation?

Answer 22

Pacinian corpuscle

Question 23

The cell bodies of Lemniscal system receptor neurons are located where?

Answer 23

Dorsal root ganglia

Question 24

What fiber type are proprioreceptors of skeletal muscle?

Answer 24

A-alpha

Question 25

Which cortical layer receives input from the thalamus?

Answer 25

Layer IV

Question 26

Which cortical layer projects to the thalamus?

Answer 26

Layer VI

Question 27

Which cortical layers project to other areas of the sensory cortex?

Answer 27

Layers II & III

Question 28

Which cortical layer projects to other subcortical structures?

Answer 28

Layer V

Question 29

Where are the somas of the skin mechanoreceptors of the trigeminal nerve?

Answer 29

Trigeminal ganglion