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