Sensory Physiology

Question 1

What makes up the Sensory System?

3

Answer 1

Sensory receptor +
neural pathway to brain/spinal cord +
area of the brain that process this information

Question 2

What is Sensation?

Answer 2

sensory information brought to our conscious awareness

Question 3

What is Perception?

Answer 3

understanding of sensation

Question 4

What is Sensory Processing?
What does it lead to?

Answer 4

• Transduction of stimulus energy (i.e., pressure, sound, light, smell, temperature, etc.) into graded potentials and then action potentials
• Processing in the CNS may lead to efferent reflexes, perception, storage, comparison to memories and assignment of emotional significance to the sensory information

Question 5

What are Sensory Receptors?
(2 classes)

Answer 5

Specialized endings of primary afferent neurons

Receptor Cell: (release NT’s)

Question 6

What are the Classes of Sensory Receptors?

5

Answer 6

Mechanoreceptor: mechanical stimuli (pressure and stretch)
Thermoreceptor: changes in temperature
Photoreceptors: light wavelengths
Chemoreceptors: binding of chemicals to receptor membrane
Nociceptors: threatening/painful stimuli

Question 7

Classes of Sensory Receptors

What are Exteroreceptors?

Answer 7

monitor the external environment

Question 8

Classes of Sensory Receptors

What are Interoreceptors?

Answer 8

monitor visceral organs

Question 9

Classes of Sensory Receptors

What are Proprioreceptors?

Answer 9

monitor position of skeletal muscles and joints
(posture)

Question 10

What are General Senses?

4

Answer 10

• Pain
• Temperature
• Touch
• Proprioception

Question 11

What are Special Senses?

5

Answer 11

• Smell
• Sight
• Hearing
• Taste
• Balance

Tend to be more complex, and found in specific sense organs

Question 12

What is the The Receptor Potential?
What is Sensory Transduction?

Answer 12

• graded potential that can initiate an action potential
• Sensory transduction: process by which a sensory stimulus is transformed into an electrical response (graded or action potential)

Question 13

How does Transduction of the stimulus into a receptor (graded) potential of an afferent neuron work?
Where does the AP Initiate?

Answer 13

• The stimulus causes ion channels to open -> change in the receptor potential due to influx of positive ions
• If threshold potential is achieved, an action potential will be initiated
• The first node of Ranvier is usually the site of action potential initiation, due to the presence of voltage-gated ion channels

Question 14

What does a greater frequency of action potential lead to?

Answer 14

If threshold potential is reached

greater frequency of action potential leads to greater frequency of neurtransmitter release

Graded potentials – can increase in size in response to the size of the stimulus

Action potentials increase in frequency in response to the size of the stimulus

Question 15

What is an Adaptation?

Answer 15

• A reduction in receptor sensitivity which leads to reduced action potential firing frequency (despite continuous signaling)
• Receptors can be slow or fast adapting

Question 16

What are Slow Adapting Receptors (Tonic)?

Answer 16

• Persistent/slow decaying receptor potential
• Found where sensory information is needed to be constantly monitored (i.e., muscles that control posture)

Question 17

What are Rapid Adapting Receptors (Phasic)?

Answer 17

• Quickly cease responding in response to continued stimuli
• Monitor sensory information that persists but does not need to be monitored closely (i.e., the pressure of a chair when you first sit down)

Question 18

What is Primary Sensory Coding?

Answer 18

Conversion of stimulus energy into a signal that can be interpreted by the CNS.

Question 19

Primary Sensory Coding

What is a Sensory unit?

Answer 19

single afferent neuron with all its receptor endings… sound familiar?

Question 20

Primary Sensory Coding

What is a Receptive Field?

Answer 20

area of the body that, when stimulated, leads to activity in an afferent neuron. Receptive fields of neighboring afferent neurons usually overlap, allowing one area to stimulate several sensory units.

Question 21

How is Primary Sensory Coding Achieved?

3

Answer 21

Achieved by:
1. Stimulus type (modality)
2. Stimulus strength
3. Stimulus location

Question 22

How is Primary Sensory Coding Achieved?

What are Stimulus Types/Modalities?

3

Answer 22

• A given receptor is particularly sensitive to one modality – the adequate stimulus
• All receptors of a single afferent neuron are preferentially sensitive to the same modality
• Adjacent neurons do not always have the same adequate stimulus

Question 23

Same Adequate Stimulus: Inside
Different Adequate Stimulus: Outside

Answer 23

Question 24

How is Primary Sensory Coding Achieved?

What is Stimulus Intensity?

Answer 24

• As adjacent receptors of the same neuron are activated (due to an increase in pressure), their local signals are summated, resulting in greater action potential firing frequency.
• Perceived stimulus intensity can also increase if additional afferent neurons are recruited.

Question 25

How is Primary Sensory Coding Achieved?

What are Stimulus Location?

Answer 25

• APs travel along unique pathways to a specific region of the CNS associated with only that modality and body location

Question 26

Acuity in which we can discriminate stimulus location depends on what?

3

Answer 26

• Convergence of neuronal input
• Size of receptive field covered by a single sensory unit
• Density of sensory units