Topic 4: Nervous System II

Question 1

Interpretation of Sensory Stimuli

Answer 1

Stimuli are detected by receptors

Question 2

Receptors can be

Answer 2

• dendrites on unipolar neurons

- individual cells which synapse to neurons

Question 3

What happens when a receptor (R) is stimulated?

Answer 3

• stimulus causes opening of gated channels (usually Na+) on receptor membrane
• GP on receptor membrane (stimulus becomes electrical)

Question 4

GP on receptor membrane (stimulus becomes electrical) if:

Answer 4

• receptor = dendrite of unipolar nueron and GP (depol.) directly generates an AP = a generator potential
• receptor = individual cell e.g. hair cell (no axon) = receptor potential ⇒ nt onto associated neuron ⇒ EPSP on neuron ⇒ generates an AP

Question 5

Types of Receptors

Answer 5

• Phasic Receptors

- Tonic Receptors

Question 6

Phasic Receptors

Answer 6

• receptors respond to stimulus change
• in the presence of a constant stimulus show adaptation (usually ⇓ in sensitivity)
  e. g. 1: put a hat on ⇒ bursts of APs (feel it) ⇒ then get ⇓ in AP frequency to CNS (can’t feel it) even though stim. maintained at constant strength
  e. g. 2: take hat off - bursts of APs – feel it again

Question 7

Tonic Receptors

Answer 7

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

Question 8

How does brain perceive different types of stimuli?

Answer 8

• mainly by type of receptor stimulated
• axon activated by receptor ⇒ synaptic connections to part of CNS concerned with that sense 9hardwired from receptor to brain - always knows ‘who’ is calling (type of receptor) and from where (location))
  e. g.1: stimulate Meissner’s corpuscle (touch receptor) in right index finger ⇒ impulses to postcentral gyrus region for right index finger
  e. g.2: mechanical pressure on eyeball ⇒ “seen” as light - ALL signals received from retina perceived as light

Question 9

How does brain perceive stimuli of different strengths?

Answer 9

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

Question 10

Sensory (ascending) Pathways

Answer 10

Posterior (Dorsal) Column Pathways for touch:

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

Question 11

See diagrams in notes for

Answer 11

special senses and sensory pathways