Receptor Physiology and the Somatosensory System

Question 1

Define receptor.

Answer 1

Transducers that can convert various forms of energy to an action potential.

Question 2

How do we classify sensory receptors?

Answer 2

Adequate stimulus
Location
Duration of adaptations

Question 3

Describe how free/specialized nerve endings work.

Answer 3

Stimulus applied on afferent
opens Na+ channels
local current flow depolarized and adjacent regions.
Opens voltage-gated Na+ channels
Reaches graded potential threshold
initiates an AP in afferent nerve self propagates to CNS

Question 4

Describe how a separate receptor cell works.

Answer 4

Stimulus on cell
influx of Na+
local depolarizing
Opens Voltage-gated Ca2+ channels
influx of Ca2+
causes exocytosis of neurotransmitters.
binds to the afferent end on chemically gated receptors
permitting influx of Na+
Depolarizes adjacent region
voltage-gated Na channels open
self propagates AP

Question 5

List the different tactile receptors and their functions.

Answer 5

Hair receptor- hair movement, gentle touch
Merkel- light sustained touch
Pacinian corpuscle- vibrations and deep pressure
Ruffini endings- deep pressure
Meissner’s corpuscle, light fluttering touch

Question 6

Describe the modality.

Answer 6

an adequate stimulus is a partial form of energy to which a receptor is most sensitive.
receptors respond to other forms of energy or stimuli, but the thresholds for these are higher

Question 7

Define the sensory unit and how it relates to the receptive field.

Answer 7

it refers to a single sensory axon and all its peripheral branches. it determines the spatial distribution in which a stimulus can produce a response.

Question 8

Explain the lateral inhibition phenomenon.

Answer 8

info from neurons whose receptors are at the peripheral edge of the stimulus is inhibited, compared to information from the sensory neurons at the center of a stimulus

Question 9

Describe the doctrine of specific energies.

Answer 9

When the nerve pathways from a particular sense organ are stimulated, the sensation evoked is that for which the receptor is specialized no matter how or where along the pathway the activity is initiated.

Question 10

Describe the law of projection

Answer 10

If we stimulate a sensory pathway along its course to the sensory cortex, the conscious sensation produced is perceived to be from the location of receptors

Question 11

Describe Weber-Frechner Law.

Answer 11

The amount of change needed for sensory detection to occur increases with the initial intensity of the stimulus, and is proportional to it.

Question 12

Describe rapidly adapting receptors.

Answer 12

When RARs are stimulated, they quickly respond with a burst of electrical activity, but then rapidly decrease their firing rate, even if the stimulus remains constant.

This rapid adaptation allows RARs to be particularly sensitive to changes in stimuli, such as a sudden change in pressure, but less sensitive to constant pressure or vibration.

M and P Corpuscles

Question 13

Describe Slow adapting receptors.

Answer 13

When SARs are stimulated, they respond with a sustained burst of electrical activity that persists as long as the stimulus is present. This slow adaptation allows SARs to be particularly sensitive to the magnitude and duration of a stimulus.

Merkels disk and ruffini endnig

Question 14

Compare axon firing in large vs small receptive field size.

Answer 14

small- faster

Question 15

What is sensory coding?

Answer 15

conversion of a receptor stimulus to a recognizable sensation

Question 16

Describe perception.

Answer 16

refers to the process by which our brain interprets and organizes sensory information to give it meaning. Perception involves the integration of sensory information with our prior knowledge, expectations, and memories to create a coherent and meaningful experience. Perception is a cognitive process that involves higher-level processing and interpretation of sensory information.

Question 17

Describe sensation.

Answer 17

refers to the process by which our sensory receptors (such as our eyes, ears, nose, tongue, and skin) detect and respond to stimuli from the environment. This process involves the initial gathering of information through our senses and the transmission of that information to the brain. The sensation is a physical process that occurs when sensory information is detected by our sensory organs.

Question 18

Describe Pacinian Corpuscles.

Answer 18

1.Unmyelinated dendrite
endings of a sensory nerve
fibre
2. Encapsulated by
concentric lamella of
connective tissue
3. Responds to deep pressure
and fast vibrations
4. Ab axon

Question 19

Describe the Transduction of the Pacinian corpuscle.

Answer 19

1. Pressure applied
2. Receptor potential
   generated
3. Action potential generated
4. Increased stimulus results
   in increased frequency of
   APs