Chapter 8 (Sensory Systems)

Question 1

cephalization

Answer 1

• the development of a well defined region of sense organs and nervous integrating centres at the anterior end of the body
• occurs with complex nervous systems

Question 2

afferent neurons vs efferent neurons

Answer 2

• afferent neurons: internal/external stimuli sent to the brain and spinal cord
• efferent neurons: info. from CNS to the body (somatic motor division and autonomic division)

Question 3

Nerves are groups of axons from neurons organized in ___.

Answer 3

fascicles

Question 4

Describe the differences between the layers of connective tissue found in a nerve: endoneurium, perineurium, epineurium.

Answer 4

• endoneurium: surrounds axon + myelin sheath
• perineurium: surrounds each fascicle (bundle of axons)
• epineurium: surrounds each nerve (fascicles with blood vessels)

Question 5

Afferent sensory neurons enter the spinal cord on the ___ side whereas efferent sensory neurons exit the spinal cord on the ___ side.

Answer 5

dorsal; ventral

Question 6

Where are bipolar neurons found? What kind of potential occurs within these cells?

Answer 6

the olfactory system; the depolarization of olfactory receptor cells causes a generator potential

Question 7

Describe the depolarization of an olfactory receptor cell.

Answer 7

1. binding of odorant to odorant receptor causes conformational change
2. G protein (Golf) is activated and moves through membrane to activate adenylate cyclase
3. adenylate cyclase converts ATP to cAMP
4. cAMP opens cAMP-gated ion channels; Ca2+ and Na+ enter cell and cause generator potential
5. Ca2+ opens Ca2+ activated Cl- channels; Cl- leaves cell (increasing depolarization)
6. generator potential opens Na+ channels, triggering AP

Question 8

vomeronasal organ

Answer 8

detects pheromones released by an animal that can affect another animal’s behaviour

Question 9

Which type of animal may have taste buds on their external body?

Answer 9

aquatic vertebrates

Question 10

What are the 5 classes of tastes?

Answer 10

salty, sweet, bitter, sour, umami

Question 11

Describe the process of signal transduction for salty substances.

Answer 11

• Na+ enters taste receptor cell
• depolarization cases Ca2+ channels to open
• inflow of Ca2+ causes neurotransmitter release

Question 12

Describe the process of signal transduction for sour substances.

Answer 12

• H+ from sour food blocks K+ channels, preventing K+ to leave the cell (depolarization)
• depolarization opens Ca2+ channels
• inflow of Ca2+ causes neurotransmitter release

Question 13

Describe the process of signal transduction for sweet substances.

Answer 13

• sweet substance binds to receptor, causing conformational change that activates G protein gustducin
• activated gustducin activates adenylate cyclase, converting ATP to cAMP
• cAMP activates protein kinase that phosphorylates and closes K+ channels
• K+ cannot exit = depolarization, which opens Ca2+ and stimulates neurotransmitter release

Question 14

Describe the process of signal transduction for bitter substances.

Answer 14

• binding of bitter substance causes conformational change in G protein transducin
• transducin activates phospholipase C (PLC) which catalyzes conversion of PIP2 into second messenger IP3
• Ca2+ released from storage and triggers neurotransmitter release

Question 15

baroreceptors vs tactile receptors vs proprioceptors

Answer 15

• they are all types of mechanoreceptors
• baroreceptors are found in blood vessel walls
• tactile receptors are found on body surfaces
• proprioceptors monitor body position

Question 16

trichoid sensilla vs. campaniform sensilla

Answer 16

• a trichoid sensillum is associated with a hairlike projection of the cuticle
• a campaniform sensillum is associated with a dome-shaped projection of the cuticle
  [sensillum=sensory receptor]

Question 17

root hair plexus

Answer 17

• wraps around hair follicle
• stimulated when hair follicle is displaced
• phasic receptors: adapt rapidly to stimulus, response diminishes quickly)

Question 18

Ruffini corpuscle

Answer 18

• sensitive to skin stretch and joints

Question 19

Pacinian corpuscle

Answer 19

• composed of layers of lamellae (modified Schwann cells)
• rapidly adapting
• sensitive to both beginning and end of pressure stimulus

Question 20

free nerve endings

Answer 20

• embedded in surface epithelium

- associated with accessory structures

Question 21

Describe the process of signal transduction in a vertebrate hair cell.

Answer 21

1. at rest, hair cell is slightly depolarized; intermediate frequency of action potentials
2. if pressure signal causes stereocilia to pivot towards kinocilium: K+ channels open and K+ enters = depolarization = influx of Ca2+ = increased neurotransmitter released = increased frequency of AP
3. if pressure signal causes stereocilia to shift away from kinocilium, K+ channels close = hyperpolarization, Ca2+ gates close = less neurotransmitter release = reduced frequency of AP

Question 22

The K+ channels found on stereocilia are what kind of channels?

Answer 22

mechanically gated ion channels

Question 23

What kind of channels are the Ca2+ channels in hair cells?

Answer 23

voltage gated ion channels

Question 24

The pinna and auditory canal make up which part of the ear?

Answer 24

outer ear

Question 25

The tympanic membrane, auditory ossicles and ___ ear cavity make up which part of the ear?

Answer 25

middle ear

Question 26

The semicircular canals and cochlea make up which part of the ear?

Answer 26

inner ear

Question 27

The mechanoreceptors of the utricle and saccule are called ___.

Answer 27

maculae

Question 28

The mechanoreceptors of the semicircular canals are located in the ampulla and are found in structures called ___.

Answer 28

cristae

Question 29

How does the ampulla in a semicircular canal detect changes in equilibrium (angular acceleration)?

Answer 29

• when head is rotated in one direction, fluid in semicircular canal (endolymph) exerts pressure in opposite direction, causing shift in stereocilia of hair cells