Topic 4: Nervous System 2: Sensory Input - Afferent NS

Question 1

What is the function of the afferent nervous system?

Answer 1

Interpretation of sensory stimuli

Question 2

How are stimuli detected?

Answer 2

• by receptors (only respond to a specific stimulus, ex temp)
• internal or external

Question 3

What are 2 types of receptors for stimulus?

Answer 3

• dendrites or unipolar neurons
• individual cells which can synapse to neurons (ex. hair cells in internal ear)

Question 4

What happens when a receptor (R) is stimulated? (2)

Answer 4

1. stimulus causes opening of gated channels (usually Na+) on receptor membrane
2. GP on receptor membrane (stimulus becomes electrical) (some exceptions)

Question 5

What are the exceptions to when a receptor is stimulated to cause a GP on receptor membrane for dendrites of unipolar neuron?

Answer 5

• 1. receptor = dendrite of unipolar neuron and GP (depolarization) directly generates an AP (GENERATOR POTENTIAL)

Question 6

What are the exceptions to when a receptor is stimulated to cause a GP on receptor membrane for receptors that are individual cells?

Answer 6

receptor = individual cell (ex. hair cell, no axon) = receptor potential to nt onto associated neuron to EPSP on neuron to generate an AP

Question 7

What are 2 types of receptors?

Answer 7

1. Phasic Receptors
2. Tonic Receptors

Question 8

What are phasic receptors?

Answer 8

• receptors respond to stimulus change
• in the presence of a constant stimulus, it shows adaptations (usually lower in sensitivity)
  note it allows us to not feel stimulus over time

Question 9

Give an example of a phasic receptor and the pathways it undergoes (3)

Answer 9

1. Put a hat on
2. bursts of AP (feel it)
3. then get lower in AP frequency to CNS (cannot feel it) even thought stimulus maintained at constant strength

Question 10

What are tonic receptors? (4)

Answer 10

• frequency of APs remain constant - NO adaptation
• gives continuous info ex. posture, pain
• protective
• monitor presence and intensity of stimulus

Question 11

How does the brain perceive different types of stimuli?

Answer 11

• mainly by type of receptor stimulated

Question 12

What is the mechanism by which the brain perceives different types of stimuli? (2 steps, 4 points)

Answer 12

1. Axon activated by receptor
2. synaptic connections to part of CNS concerned with that sense
   - hardwired from receptor to brain,
   - you always know “who” is calling (type of receptor) and from where (location)

Question 13

Give an example of how the brain perceives different types of stimuli using Meissner’s corpuscles (2)

Answer 13

1. stimulate Meissner’s corpuscles (touch receptor) in right index finer
2. Impulses to postcentral gyrus region for right index fingger

Question 14

Give an example of how the brain perceives different types of stimuli using mechanical pressure on eyeball

Answer 14

1. mechanical pressure on eyeball
2. “seen” as light
3. all signals received from retina perceived as light

Question 15

How does the brain perceive stimuli of different strengths? (3)

Answer 15

• mainly by frequency of APs (#/time) going to CNS
• greater stimulus is greater AP frequency
• stronger stimulus also activates more receptors (ex. pressure and touch)
  ex. determining if feather or brick on foot

Question 16

Diagram of Sensory (ascending) pathways

Answer 16

ex. posterior (dorsal) column pathway for touch
- 3 neurons in succession (1st, 2nd, 3rd order)