Sensory Physiology

Question 1

Sensory physiology is the study of ___________________

Answer 1

Sensation and sensory systems

Question 2

3 primary components of a sensory system

Answer 2

One or more sensory receptors
- can be responsive to stimuli in either the external or internal environment

Regions of the PNS responsible for processing the info from the sensory receptors
- info can be sent to more than one region, can be concious or unconcious

Neural pathways that connect the receptors to the regions above

Question 3

Where does the first step of sensory processing occur? What happens?

Answer 3

At the level of the sensory receptors

Transduction of the stimulus into a receptor (graded) potential of an afferent neuron, which may turn into an AP if the stimulus reaches threshold

Question 4

What happens after the signal from the stimulus is transduced into a receptor potential?

Answer 4

Causes a change in receptor potential

If it reaches threshold, an AP is initiated

Question 5

Where is the first site of AP initiation? Why?

Answer 5

The first node of Ranvier

Due to presence of voltage gated ion channels

Question 6

What happens if the stimulus acting on a sensory receptor is sufficient?

Answer 6

It will cause a change in the membrane’s permeability

Opening of ion channels on the receptor membrane

Change in receptor potential

Question 7

If the stimulus is strong enough, _____________ of the receptor potentials will lead to _______________

Answer 7

Summation

Initiation of an AP

Question 8

What is Transduction

Answer 8

The process of translating a stimulus into an AP

Question 9

What does the magnitude of the receptor potential determine? What does it not determine?

Answer 9

Determines the frequency of APs in the afferent neuron

Does not determine the amplitude of the APs

Question 10

What is the frequency of sensory transduction

Answer 10

AP firing rate

Question 11

Factors that control the magnitude of the receptor potential (4)

Answer 11

STAR

Stimulus strength - i.e. amt of pressure

Rate of change of stimulus strength - i.e. gradual vs sudden inc in pressure

Temporal summation of successive receptor potentials - more succesive RPs = greater cumulative RP

Adaptation - decrease in receptor sensitivity
(over time, AP frequency will decrease despite continuing the presence of the stimulus - slow or fast adapting)

Question 12

Phasic receptors
Frequency generation? AP output? When does it stop responding?

Answer 12

Generates a high frequency burst of AP right at the onset of the stimulus

The receptor quickly stops responding to stimulus, even if it is still present

Generates more APs with stimulus removed

Not always active - only when stimulated

Question 13

Tonic receptors
Frequency generation? AP output? When does it stop responding?

Answer 13

Quite responsive immediately at the onset of stimulus

Maintain a persistant (slowly decaying) AP output while stimulus is present (background level of stimulus)

The receptor stops AP output when stimulus is removed

Question 14

How long will tonic receptors fire for?

Answer 14

Fire for the duration of the stimulus; often are tonically active

i.e. nocicdeptors fire if a painful stimulus is present - if it is less severe, AP firing frequency is lower but still constant, as the stimulus must be removed completely to stop AP firing

Question 15

Phasic receptors adapt _______________ and generally only fire APs in response to a _________________________________

Answer 15

Very rapidly

Change in the stimulus

Question 16

Peripheral adaptation

Answer 16

Differences in adaptation at the level of the sensory receptors

Phasic sensory receptors become less responsive to a stimulus

i.e. becoming used to background noise, clothing, etc.

Question 17

Central adaptation

Answer 17

Adaptation at the level of the CNS

Sensory receptors are still responsive to the stimulus, but adaptation occurs at the CNS due to inhibition of various nuceli

Sensory info may still be present, but there is no concious perception of that info

i.e. getting used to the smell of places you frequently visit

Question 18

Adaptation

Answer 18

Reduction in sensitivity of the nervous system in the presence of a constant stimulus

Question 19

Sensory receptors monitor changes in specific variables in either the _________ or _______________ environment

Answer 19

External

Internal

Question 20

Where are sensory receptors are usually present? What does the stimulus do?

Answer 20

At the peripheral (dendritic) end of an afferent neuron

Stimulus directly activates the afferent neuron

Question 21

Specialized neuron

Answer 21

A separate receptor cell that sends a signal to the afferent neuron via a chemical messeger (NT)

Stimulus indirectly activates the afferent neuron

Question 22

What does it mean when sensory receptors exhibit specificity?

Answer 22

Within one tissue, we may have several types of receptors that are sensitive to different stimuli. Receptors are only responsive to a specific type of stimuli

Question 23

Adequate stimulus

Answer 23

The stimulus that a sensory receptor is responsive to in normal functioning
- reaches threshold