Topic 4 - NERVOUS SYSTEM II - Sensory "Input

Question 1

afferent nervous system: interpretation of sensory stimuli

stimuli are detected by what?

Answer 1

receptors

stimuli are detected by receptors (only respond to a specific stimulus e.g. temperature)

Question 2

afferent nervous system: interpretation of sensory stimuli

receptors can be:

Answer 2

1. dendrites on a unipolar neuron
2. an individual cell that synapses to a neuron
   
   • e.g. hair cell (internal ear)

Question 3

afferent nervous system: interpretation of sensory stimuli

what happens when a receptor is stimulated?

Answer 3

• stimulus causes opening of gated channels (usually Na⁺) on receptor membrane
• GP on receptor membrane (stim becomes electrical) IF:
  
  • receptor = dendrite of unipolar neuron and GP (depolarization) directly generates an AP = generator potential
  • receptor = individual cell e.g. hair cell (no axon) = receptor potential ⇒nt onto associated neuron ⇒ PSP on neuron ⇒ generates an AP

Question 4

what are the 2 types of receptors?

Answer 4

1. phasic receptors
2. tonic receptors

Question 5

phasic receptors

Answer 5

• receptors respond to stimulus change
• in the presence of a constant stimulus, show adaptation (usually decrease in sensitivity)

e. g. put a hat on → bursts of APs (feel it) → then get decrease in AP frequency to CNS (can’t feel it) even though stim maintained at constant strength
- take hat off - bursts of APs - feel it again

Question 6

tonic receptors

Answer 6

• frequency of APs remains constant - NO adaptation
• give continuous info e.g. posture, condition, pain ⇒ protective
• monitor presence + intensity of stimulus

Question 7

How does brain perceive different types of stimuli?

• mainly by what?
• axon activated by ______ ⇒ ______ connections to part of ___ concerned with that _____. (______ from receptor to brain - always knows “who” is calling (__________) and from where (_____)

Answer 7

• mainly by type of receptor stimulated
• axon activated by receptor ⇒ synaptic connections to part of CNS concerned with that sense (hardwired from receptor to brain - always knows “who” is calling (type of receptor) and from where (location)

Question 8

How does brain perceive different types of stimuli?

axon ___________ ⇒ synaptic connections to ___________ - (hardwired from _____ to ______ - always knows ______ (type of receptor) and ______ (location)

Answer 8

axon activated by receptor ⇒ synaptic connections to part of CNS​ concerned with that sense

(hardwired from receptor to brain - always knows “who” is calling (type of receptor) and from where (location)

Question 9

How does brain perceive different types of stimuli?

2 examples

Answer 9

1. stimulate meissners corpuscle (touch receptor) in right index finger ⇒ impulses to post central gyrus region for right index finger
2. mechanical pressure on eyeball ⇒ “seen” as light - ALL signals received from retina perceived as light

Question 10

How does brain perceive stimuli of different strengths?

Answer 10

• e.g. determining if feather or brick on foot
• mainly by frequency of AP (#/time) going to CNS
  
  • e.g. increased stimulus = increased AP frequency
• stronger stimulus also activates more receptors (e.g. pressure +touch)

Question 11

sensory (ascending) pathways

name an example and draw diagram

Answer 11

e.g. posterior (dorsal) column pathways for touch

3 neurons in succession - 1st, 2nd, or 3rd order

Question 12

vision

steps

1. lighter enters where and image focuses on what?
2. light stimulates what on where? which produces what?

Answer 12

1. light enters pupil & image focused on retina (reduced + inverted)
2. light stimulates chemical reaction on rods and/or cones - produces a receptor potential (GP)

Question 13

vision

diagram

Answer 13

Question 14

hearing

Answer 14

draw diagram

Question 15

equilibrium

Answer 15

draw diagram