CNS/Sensory III

Question 1

What is sensation?

Answer 1

Awareness of sensory stimulation

Question 2

What is perception?

Answer 2

The understanding of a sensation’s meaning

Question 3

What is the law of specific nerve energies?

Answer 3

Regardless of how a sensory receptor is activated, the sensation felt corresponds to that of which the receptor is specialized.

Question 4

Give an example of the law of specific nerve energies.

Answer 4

Rub your eyes hard and you will see light.

Question 5

What is the law of projection?

Answer 5

Regardless of where in the brain you stimulate a sensory pathway, the sensation is always felt at the sensory receptor’s location.

Question 6

The phenomenon of phantom limb pain corresponds to which law of perception? Explain why.

Answer 6

Law of projection. The axons from the original limb try to innervate something else, so they get activated by the wrong thing, creating the sense of phantom pain where the limb used to be

Question 7

What is labeled-line code?

Answer 7

It is the notion that the brain knows the modality (class of stimulus) and location of every sensory afferent.

Question 8

What is an exception to labeled-line code?

Answer 8

In certain instances dealing with pain - this is referred pain.

Question 9

Name the 5 steps of sensory receptor functioning.

Answer 9

1. Stimulus energy is received.
2. The corresponding receptor membrane reacts with the stimulus energy
3. The energy is used for transduction of ion channels
4. The ion channels activate
5. The signal is sent to the CNS via afferent neurons.

Question 10

Stimulus energy gets converted into […]

Answer 10

Afferent activity

Question 11

Name and explain the steps involved in the conversion of stimulus energy into afferent activity.

Answer 11

1. Start with stimulus energy
2. Membrane depolarization takes place, affecting receptor potential.
3. If the threshold is met, action potentials are produced.
4. Action potentials are propagated along the body to the brain.
5. Neurotransmitters are released.

Question 12

What happens if the membrane depolarization caused by stimulus energy doesn’t meet the threshold for an action potential?

Answer 12

No action potential will be fired. So even though something is touching you, for example, you won’t feel it.

Question 13

What are the 3 levels of stimulus intensity?

Answer 13

Subthreshold, weak, strong

Question 14

Describe how a subthreshold stimulus intensity will affect…
a) The magnitude of receptor potential
b) The frequency of action potentials
c) The magnitude of neurotransmitters release

Answer 14

a) The magnitude of the receptor potential will be small
b) No action potentials will be sent out
c) No neurotransmitter release

Question 15

Describe how a weak stimulus intensity will affect…
a) The magnitude of receptor potential
b) The frequency of action potentials
c) The magnitude of neurotransmitters release

Answer 15

a) Medium receptor potential
b) A few action potentials released
c) Some neurotransmitter released

Question 16

Describe how a strong stimulus intensity will affect…
a) The magnitude of receptor potential
b) The frequency of action potentials
c) The magnitude of neurotransmitters release

Answer 16

a) High magnitude of receptor potential
b) High frequency of action potential
c) High magnitude of neurotransmitters released

Question 17

Explain the purpose of adaptation of afferent response.

Answer 17

The majority of afferents show adaptation, which allows us to be sensitive to changes in the sensory input.

Question 18

How does adaptation of afferent response work? Compare non-adapting, slowly adapting, and rapidly adapting

Answer 18

In non-adapting afferents, the action potential frequency is constant and is slow to respond to change. In slowly adaptive afferents, there are moderate stimulus changes and some stimulus intensity. In rapidly adaptive afferents, it sends action potentials when there are fast stimulus changes. ??

Question 19

What is a receptive field?

Answer 19

The region in space that activates a sensory receptor or neuron (afferent).

Question 20

The response across a receptor field can be described as […]. Explain why.

Answer 20

Graded, because the location of the stimulus will be strongest at the direct area of contact, but the receptors around that one will got a smaller afferent response will less spikes.

Question 21

Overlapping receptive fields produce […]

Answer 21

A population code

Question 22

What is a population code?

Answer 22

It is when the body realizes that there’s a stimulus across several afferents. This allows the body to tell which receptive fields have been activated and how much.

Question 23

What is stimulus acuity?

Answer 23

The ability to differentiate one stimulus from another on a given site.

Question 24

Compare the relationship between acuity and location based on acuity for lips vs back.

Answer 24

For lips, since the receptor field size is smaller, acuity is higher. For back, since the receptor field size is larger, acuity is lower.

Question 25

What is the relationship between lateral inhibition and sensory acuity?

Answer 25

Lateral inhibition sharpens sensory acuity.

Question 26

Lateral inhibition occurs at the […] level of processing

Answer 26

Second order (neurons)

Question 27

Explain how lateral inhibition works (using the example of three afferents A, B, and C where the stimulus affects B).

Answer 27

If there is a stimulus at location B, a population code is generated for A, B, and C. Further up the afferents, there are inhibitory neurons running between them. Since B is the most active afferent, its inhibitory neurons will be the strongest. This supresses the response of A and C and sharpens sensory acuity to focus on B.

Question 28

Lateral inhibition is a […] process

Answer 28

Bottom-up

Question 29

Descending pathways is a […] process

Answer 29

Top-down

Question 30

Explain how descending pathways works.

Answer 30

They inhibit certain signals (such as pain). Inhibition signals are sent down from the CNS towards the receptor, and provide presynaptic inhibition to prevent the travel of a pain signal.

Question 31

Describe the general structure of touch receptors.

Answer 31

They are mechanoreceptors wrapped in specialized end organs.

Question 32

Name 2 superficial touch receptors.

Answer 32

Meissner’s corpuscle and merkel disk

Question 33

Describe the structure and function of the Meissner’s corpuscle.

Answer 33

It is a fluid-filled structure enclosing the nerve terminal. It is rapidly adapting and responds to light stroking and fluttering.

Question 34

Describe the structure and function of the Merkel disk.

Answer 34

It consists of small epithelial cells surrounding the nerve terminal. It is slowly adapting and responds to surface pressure and texture.

Question 35

Name 2 deep touch receptors.

Answer 35

Pacinian corpuscle and Ruffini endings

Question 36

Describe the structure and function of the Pacinian corpuscle

Answer 36

It consists of large concentric capsules of connective tissue surrounding the nerve terminal. It is rapidly adapting and responds to strong vibrations.

Question 37

Describe the structure and function of the Ruffini endings.

Answer 37

Nerve endings wrapping around a spindle-like structure. It is slowly adapting and responds to the stretch and bending of the skin (shape of an object).

Question 38

What is proprioception?

Answer 38

Muscle spindles provide a sense of static position and movement of limbs and body.

Question 39

What is the role of the end organs in tranduction?

Answer 39

They determine what kind of mechanical deformation gets through to activate the ion channels in the receptor.

Question 40

Explain how the mechanoreceptors in the somatosensory system get activated.

Answer 40

Every time you touch something, it deforms your skin. The membrane of the afferents also gets deformed. These membranes have cytoskeletal strands that line the membrane and attach to ion channels. So, when you touch something, it pulls open the ion channels, which changes the membrane potentials and allows the action potentials to travel up through the CNS.

Question 41

What type of ion channels are involved in the somatosensory system?

Answer 41

Mechanically-gated channels and thermally-gated channels.

Question 42

Explain how the somatosensory systems deals with temperature.

Answer 42

Thermoreceptors, which are free nerve endings, contain ion channels that respond to different temperatures ranges.

Question 43

What are the 2 main types of thermoreceptors? State their range and the chemicals that can activate them.

Answer 43

Cold afferents: 0-35ºC, activated by menthol)
Warm afferents: 30-50ºC, activated by capasaicin and ethanol