3 - Grover - Introduction to Sensory Systems

Question 1

Why do sensory systems exist?

Answer 1

Convert external and internal environments to chemical or electrical signals for monitoring

Make adaptive changes

Question 2

Transduction

Answer 2

Conversion of physical signal (energy) into neural signal (change in membrane potential)

Question 3

Encoding

Answer 3

Representation of qualitative and quantitative aspects of the stimulus

Question 4

Perception

Answer 4

Conscious awareness of stimulus

Question 5

Modality

Answer 5

Quality of the stimulus, determined by the nature of the energy transduced

Question 6

Modality for External: Skin? Type of receptor?

Answer 6

Touch, temperature, itch, pain

- -

Cutaneous, subcutaneous, nociceptors

Question 7

What are modalities of internal sensory system?

Receptors?

Answer 7

Joints, muscles, tendons, inner ear–proprioception, balance

- - -

muscle spindle, golgi tendon organ, vestibular hair cell

Question 8

Adequate Stimulus

Answer 8

Unique form of energy that activates a specific receptor at low energy level

Ex: Light is adequate stimulus for photoreceptors

Question 9

Intensity

Answer 9

Strength of stimulus, nervous system uses frequency coding to translate intensity

Question 10

Sensory Threshold

Answer 10

Lowest intensity which can reliably (50% of the time) be detected, inversely related to sensitivity

High Treshold = Low Sensitivity

Question 11

Duration

Why might receptor output not equal stimulus?

Answer 11

Length of the stimulus

• -

Adaptation

Question 12

Slow Adapting

vs

Rapid Adapting

Answer 12

Slow: Continue to fire as long as stimulus present, provide information about static properties, signal duration

Fast: Dynamic aspects of stimulus, fire in response to change in stimulus

Question 13

Receptive Field

Answer 13

Specific spatial location within sensory organ where stimulus energy is effective; for tactile this is a portion of the skin

Question 14

Mechanosensitive Ion Channel (stretch-gated ion channel)

Answer 14

Membrane deforms, opening cation (Na+, K+) channels

Cutaneous Tactile Receptors: Pacinian, Meissner, Ruffini, Merkel disks

Channels work same was a nACh, ionotropic glutamate receptors

Question 15

Transient Receptor Potentials (TRP) Channels

Answer 15

Can be cold (12-35) or warm (25-47)

Can also be stimulated by chemicals

Menthol (cold), Capaicin (warm)

Question 16

Thermal Pain Receptors (nociceptors)

Answer 16

Activated by extremes (<12, >47)

Question 17

Receptor Potential

Answer 17

Receptor potential creates capacitive current

Current must depolarize initial segment of axon to trigger action potential

Question 18

Encoding of Intensity (Frequency Coding)

Answer 18

Intensity coded by frequency of action potential firing

Direct–intensity = firing rate (neurotransmitter release)

Used by both rapidly and slowl adapting receptors

Question 19

What can a rapidly adapting receptor NOT encode?

Answer 19

Can not encode duration

Question 20

Adaptation

Answer 20

Reduced output despite constant stimulus

Two mechanisms:

Sensory (transduction)

Membran (ion conductance)

Question 21

Sensory Mechanism of Adaptation

Membrane Mechanism of Adaptation

Answer 21

Sensory - Physical changes to receptor

Membrane - Ion channel adaptation; intracellular Ca²⁺ K⁺-Channels open following gradual calcium accumulation from action potentials

Causes membrane to sag, or hyperpolarize toward E_K leading to reduced action pot. rate

Question 22

What are found in the integration (trigger) zone of all sensory receptors?

Answer 22

Voltage-gated Na+, K+, Ca2+, Ca2+-Activated K+ channels

Question 23

What are found in the conduction zone of all sensory receptors?

Answer 23

Voltage Gated Na+ and K+ channels

Question 24

What are found in the transmission zone of all sensory receptors?

Answer 24

Voltage-gated Ca2+ channels

neurotransmitter release