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Sensory and Motor Mechanisms
Chapter 49
Sensory and motor mechanisms
• Sensory receptors in general - transduction
• Sound receptors - the cochlea and pitch• Chemoreceptors - insect pheromones• Electromagnetic receptors - migration
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
Sensory reception: crayfish stretch receptors - Fig. 99.2a
LE 49-2a
MuscleWeakmuscle stretch
Receptor potential
Action potentials
Mem
bra
ne
po
ten
tial
(m
V)
Time (sec)0 1 2 3 4 5 6 7
–70
–70
–50
0
Stretchreceptor
Dendrites
Axon
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
in the axon of the stretch receptor. A stronger stretch produces a larger receptor potential and higher frequency of action potentials.
Strongmuscle stretch
Time (sec)0 1 2 3 4 5 6 7
–70
–70
–50
0
Sensory reception: vertebrate hair cells - Fig. 99.2b
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.
No fluidmovement
Fluid moving inone direction
Receptor potentialAxon
“Hairs” ofhair cell
Neuro-trans-mitter atsynapse
Fluid moving inother direction
Moreneuro-trans-mitter
Lessneuro-trans-mitter
Time (sec)0 1 2 3 4 5 6 7
–70
–70
–50
0
Action potentials
Mem
bra
ne
po
ten
tial
(m
V)
Time (sec)0 1 2 3 4 5 6 7
–70
–70
–50
0
Mem
bra
ne
po
ten
tial
(m
V)
Time (sec)0 1 2 3 4 5 6 7
–70
–70
–50
0
Mem
bra
ne
po
ten
tial
(m
V)
Sensory and motor mechanisms
• Sensory receptors in general - transduction• Sound receptors - the cochlea and pitch• Chemoreceptors - insect pheromones• Electromagnetic receptors - migration
Transduct-ion in the cochlea -- Fig. 49.8
Transduct-ion in the cochlea -- Fig. 49.8
Transduct-ion in the cochlea -- Fig. 49.8
Transduct-ion in the cochlea -- Fig. 49.8
Transduct-ion in the cochlea -- Fig. 49.8
Transduction in the cochlea -- Fig. 49.9
Ovalwindow
Cochlea
Tympaniccanal
Basilarmembrane
Vestibularcanal
Perilymph
Stapes Axons ofsensoryneurons
Apex
Base
Roundwindow
Sensing pitch in the cochlea -- Fig. 49.10
Cochlea(uncoiled) Basilar
membrane Apex(wide andflexible)
Frequencyproducingmaximum vibrationBase
(narrow and stiff)
16 kHz(high pitch)
8 kHz4 kHz
2 kHz1 kHz
500 Hz (low pitch)
Sensory and motor mechanisms
• Sensory receptors in general - transduction
• Sound receptors - the cochlea and pitch• Chemoreceptors - insect
pheromones• Electromagnetic receptors - migration
text
Chemoreceptors in a silkworm moth - Fig. 49.4
The pheromones and the protein that binds them are known
text
Sensory and motor mechanisms
• Sensory receptors in general - transduction• Chemoreceptors - insect pheromones• Sound receptors - the cochlea and pitch• Electromagnetic receptors - migration
Electromagnetic receptors - beluga whales migrating
a molecular profile for the baluga whale…
Trout have magnets in their noses.
magnet
response of individual particles
Magnetotactic bacteria synthesize magentite in membrane-bound vesicles – the vesicles align to make a compass.
One cell
One string of vesicles
Sensory and motor mechanisms
• Sensory receptors in general - transduction• Chemoreceptors - insect pheromones• Sound receptors - the cochlea and pitch• Electromagnetic receptors - migration