Chapter 17 Smell

The human nose contains 10-100 million receptor cells

Olfactory receptor cell- Bipolar neuron with a knob shaped dendrite

Extending from the dendrite are several nonmotile olfactory cells

Sites of olfactory transduction conversion of stimulus energy into a graded potential in a sensory receptor

Supporting cells- Columnar epitheal cells of the mucous membrane

lining the nose

Function- provide physical support, nourishment, electrical insulation for the olfaction reeption cells and detoxify chemicals

Basal cells- stem cells located between bases of supporting cells

Function- undergo cell division to produce new olfactory receptor cells

Olfactory receptor cells live for about 2 months

Olfactory glands = Bowman’s glans- produce mucus that is used to dissolve odor molecules so that transduction may occur

Steps of transduction of olfaction…

  1. Binding of an odorant to an olfactory receptor protein in a olfactory cillium stimulates a membrane protein called a G protein

  1. G protein activates an enzyme that produces cAMP, a type of second meassenger molecule

  1. cAMP opens cation channels that allows Na+ and Ca+ to enter cystol

  1. Depolarizing potential forms in the membrane of the receptor cell, and action potential generates along its axon

After the odor impulse is generated…

  1. Bundles of axon form the right and left olfactory nerves

  1. Olfactory nerves pass through the olfactory foramina of the ethmoid bone and extends to the olfactory bulbs. These bulbs contain ball like arrangements called glomeruli

  1. Within each glomeruli axons of the OR cells converge to mitral cells, second order neurons of the olfactory pathway

  1. Axons of the mitral cells form the olfactory tract

  1. Some axons project to the temporal lobe, where concious awareness of smell occurs

  1. Some axons project to the limbic system to emotional response to odors

  1. From temporal lobe primary olfactory area, pathway exists to orbifrontal cortex where odor identification occurs