Sensory receptors and the PNS (Chapter 9)

Question 1

What are the different types of sensory receptors?

Answer 1

Chemoreceptors, photoreceptors, thermoreceptors, mechanoreceptors, nociceptors

Question 2

What is the difference between sensory modality and quality?

Answer 2

Modality: what type of receptor is stimulated.
Quality: Experience of that modality, generally associated with the presence of multiple sensory receptor types whose separate outputs are combined in the CNS for richer sensations.

Question 3

Receptive fields encode…

Answer 3

Stimulus intensity and duration

Question 4

More intense stimuli produce…

Answer 4

Larger receptor potentials

Question 5

Longer stimuli produce…

Answer 5

Longer receptor potentials

Question 6

What are the general organizational characteristics of sensory systems?

Answer 6

3 general parts: receptive area, area rich in mitochondria (supply energy for transduction), synaptic area (message passed to CNS).

Question 7

How do sensory receptors transduce a stimulus into an electrical signal?

Answer 7

Sensory receptors use ionotropic and metabotropic mechanisms to produce receptor potentials by opening/closing ion channels. Ion channels’ conductance can be affected directly by a stimulus (transmitted-gated channels) or indirectly (via G-protein coupling).

Question 8

What are the eight general principles of sensory systems?

Answer 8

1) Transduction
2) Receptive fields
3) Multiple coding
4) Recoding
5a) Redundant pathways
5b) Feedback (cortical feedback alters primary sensory experience)
6) Redundant representations
7) Integration at cortical level (mix modalities to produce integrated experience, e.g., flavor = taste + olfaction)
8) Behavior is always dependent on integration of both sensory AND motor functioning

Question 9

When would a sensory receptor produce an action potential as well as a receptor potential?

Answer 9

When the receptor is too far from the site of transduction for the receptor potential, which dies out in a few mm, to travel (e.g., big toe –> spinal cord)

Question 10

What do Pacinian corpuscles code for and what is their adaptation?

Answer 10

Vibration; rapid

Question 11

What do Meissner corpuscles code for and what is their adaptation?

Answer 11

Touch; rapid

Question 12

What do Ruffini endings code for and what is their adaptation?

Answer 12

Pressure; slow

Question 13

What do Merkel endings code for and what is their adaptation?

Answer 13

Touch; slow

Question 14

What do free nerve endings code for and what is their adaptation?

Answer 14

Pain, temperature, itch, touch; varies

Question 15

What do endings around hairs code for and what is their adaptation?

Answer 15

Touch; rapid

Question 16

Why do fingertips have finer tactile discrimination than the palm of the hand?

Answer 16

Because the fingertips contain Meissner corpuscles and Merkel endings at a much higher concentration (units per cm^2), resulting in higher spatial resolution in those areas.

Question 17

What are the two stages of pain and their associated fibers?

Answer 17

Initial sharp pain or “delta pain” (A-delta fibers)

Aching pain or “slow pain” (unmyelinated C fibers)

Question 18

What is the role of the axon reflex in pain?

Answer 18

The axon reflex produces the redness and edema around the site of injury. APs at the nociceptor trigger zone travel in both directions (backward to periphery and forward to spinal cord/brainstem). It is the only reflex that does not involve any synapse(s) in the CNS.

Question 19

How is sensitivity to pain chemically modulated?

Answer 19

Neurotransmitters are released from damaged tissue and sensitize nociceptors in that region (e.g., serotonin upregulates nociceptors).

Question 20

Muscle spindles detect _______ and contribute to _______.

Answer 20

Muscle length/stretch; proprioception.

Question 21

Golgi tendon organs detect _______.

Answer 21

Muscle tension (code for tension along tendon as proxy for muscle contraction).

Question 22

What is the role of alpha motor neurons in muscle spindles?

Answer 22

Alpha motor neurons create large, voluntary muscle movements. They do not register small changes in muscle length because the muscle is contracted.

Question 23

What is the role of gamma motor neurons in muscle spindles?

Answer 23

Gamma motor neurons “pre-stretch” the central receptive spindle region in a contracted muscle, thereby increasing sensitivity to stretch (i.e., -1 to 0).

Question 24

How do Golgi tendon organs and muscle spindles work together to monitor muscle tension and length simultaneously?

Answer 24

Muscle spindles - stop firing when muscle contracts (and shortens), and bursts as muscle relaxes and lengthens.
GTOs - burst as muscle contracts (tension on tendon increases), then go silent as muscle relaxes (tendon tension decreases).

Question 25

What are the extensions of the meninges that envelop peripheral nerves?

Answer 25

(outside -> inside): Epineurium, perineurium, endoneurium.

Question 26

The receptors/afferent functions with the widest axon diameter and myelin sheath are…

Answer 26

Alpha motor neurons, Golgi tendon organs, muscle spindle primary endings.

Question 27

Thin, unmyelinated axon fibers are involved in…

Answer 27

Slow pain, heat, itch, touch (some); postganglionic autonomic.