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 Muscle Weak muscle stretch Receptor potential Action potentials Membrane potential (mV) Time (sec) –70 –50 0 Stretch receptor 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. Strong muscle stretch Time (sec) –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 fluid movement Fluid moving in one direction Receptor potential Axon “Hairs” of hair cell Neuro- trans- mitter at synapse Fluid moving in other direction More neuro- trans- mitter Less neuro- trans- mitter Time (sec) –70 –50 0 Action potentials Membrane potential (mV) Time (sec) –70 –50 0 Membrane potential (mV) Time (sec) –70 –50 0 Membrane potential (mV)

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

Transduc t-ion in the cochlea -- Fig. 49.8

Transduction in the cochlea -- Fig Oval window Cochlea Tympanic canal Basilar membrane Vestibular canal Perilymph Stapes Axons of sensory neurons Apex Base Round window

Sensing pitch in the cochlea -- Fig Cochlea (uncoiled) Basilar membrane Apex (wide and flexible) Frequency producing maximum vibration Base (narrow and stiff) 16 kHz (high pitch) 8 kHz 4 kHz 2 kHz 1 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

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Chemoreceptors in a silkworm moth - Fig. 49.4

The pheromones and the protein that binds them are known

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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