The Genetic Basis of Development

1
Sensory and Motor Mechanisms

Chapter 49
2
Sensory and motor mechanisms

• Sensory receptors in general - transduction
• Sound receptors - the cochlea and pitch
• Chemoreceptors - insect pheromones
• Electromagnetic receptors - migration

3
Functions Performed by Sensory Receptors

• All stimuli represent forms of energy
• Sensation involves converting energy into change
  in the membrane potential of sensory receptors
• Functions of sensory receptors sensory
  transduction, amplification, transmission, and
  integration

4
Sensory reception crayfish stretch receptors -
Fig. 99.2a
LE 49-2a
Weak muscle stretch
Strong muscle stretch
Muscle
Dendrites
Receptor potential
50
50
70
70
Stretch receptor
Membrane potential (mV)
Action potentials
0
0
Axon
70
70
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
Time (sec)
Time (sec)
in the axon of the stretch receptor. A stronger
stretch produces a larger receptor potential and
higher frequency of action potentials.
Crayfish stretch receptors have dendrites
embedded in abdominal muscles. When the abdomen
bends,
muscles and dendrites stretch, producing a
receptor potential in the stretch receptor. The
receptor potential triggers action potentials
5
Sensory reception vertebrate hair cells - Fig.
99.2b
No fluid movement
Fluid moving in one direction
Fluid moving in other direction
Hairs of hair cell
More neuro- trans- mitter
Neuro- trans- mitter at synapse
Less neuro- trans- mitter
Axon
50
50
50
Receptor potential
70
70
70
Membrane potential (mV)
Membrane potential (mV)
Membrane potential (mV)
Action potentials
0
0
0
70
70
70
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
Time (sec)
Time (sec)
Time (sec)
Vertebrate hair cells have specialized cilia or
microvilli (hairs) that bend when surrounding
fluid moves. Each hair cell releases an
excitatory neurotransmitter
at a synapse with a sensory neuron, which
conducts action potentials to the CNS. Bending in
one direction depolarizes the hair cell, causing
it to release more
neurotransmitter and increasing frequency of
action potentials in the sensory neuron. Bending
in the other direction has the opposite effects.
Thus, hair cells respond to the direction of
motion as well as to its strength and speed.
6
Sensory and motor mechanisms

• Sensory receptors in general - transduction
• Sound receptors - the cochlea and pitch
• Chemoreceptors - insect pheromones
• Electromagnetic receptors - migration

7
Transduct-ion in the cochlea -- Fig. 49.8
8
Transduct-ion in the cochlea -- Fig. 49.8
9
Transduct-ion in the cochlea -- Fig. 49.8
10
Transduct-ion in the cochlea -- Fig. 49.8
11
Transduct-ion in the cochlea -- Fig. 49.8
12
Transduction in the cochlea -- Fig. 49.9
Cochlea
Stapes
Axons of sensory neurons
Vestibular canal
Perilymph
Oval window
Apex
Base
Tympanic canal
Basilar membrane
Round window
13
Sensing pitch in the cochlea -- Fig. 49.10
Cochlea (uncoiled)
Basilar membrane
Apex (wide and flexible)
500 Hz (low pitch)
1 kHz
2 kHz
4 kHz
8 kHz
16 kHz (high pitch)
Frequency producing maximum vibration
Base (narrow and stiff)
14
Sensory and motor mechanisms

• Sensory receptors in general - transduction
• Sound receptors - the cochlea and pitch
• Chemoreceptors - insect pheromones
• Electromagnetic receptors - migration

15
text
16
Chemoreceptors in a silkworm moth - Fig. 49.4
17
The pheromones and the protein that binds them
are known
18
text
19
Sensory and motor mechanisms

• Sensory receptors in general - transduction
• Chemoreceptors - insect pheromones
• Sound receptors - the cochlea and pitch
• Electromagnetic receptors - migration

20
Electromagnetic receptors - beluga whales
migrating
21
a molecular profile for the baluga whale
22
Trout have magnets in their noses.
magnet
response of individual particles
23
Magnetotactic bacteria synthesize magentite in
membrane-bound vesicles the vesicles align to
make a compass.
One cell
One string of vesicles
24
Sensory and motor mechanisms

• Sensory receptors in general - transduction
• Chemoreceptors - insect pheromones
• Sound receptors - the cochlea and pitch
• Electromagnetic receptors - migration