Olfaction: Sense of Smell (Nursing)

00:01 Welcome.

00:02 In this lecture, we will be learning about the special senses.

00:07 The special senses include the sense of smell, taste. vision, hearing, and also your sense of equilibrium.

00:19 Starting with our sense of smell, also referred to as olfaction, smell is considered a chemical sense.

00:28 The human nose contains 10 to 100 million receptors for smell in the olfactory epithelium which is located in the superior part of the nasal cavity.

00:42 The olfactory epithelium covers the inferior surface of the cribriform plate of the ethmoid bone at the skull and extends along the superior nasal concha.

00:57 pDepicted in the figure, we see the path of inhaled air comes through the nasal cavity The olfactory epithelium that contains ciliated olfactory cells and mucus-producing olfactory gland cells and also other cells and connect the nasal cavity to the olfactory cranial nerves.

01:22 There are three types of cells that are responsible for olfaction.

01:27 We have the olfactory receptor cells which are first order bipolar neurons with an exposed knob-shaped dendrite and an axon that travels through the cribriform plate of the ethmoid bone and end at the olfactory bulb.

01:45 We also have supporting cells which are going to support and nourish our olfactory receptor cells.

01:53 And finally we have basal cells which are stem cells that are used to generate new olfactory cells.

02:01 The supporting cells are going to be located in the mucous membrane lining of the nose.

02:08 Again, these are used for the physical support, nourishment and as well the electrical insulation for our olfactory receptor cells.

02:20 Our basal stem cells are able to undergo mitosis and are there to replace old and dead olfactory receptor cells.

02:32 Also, along with the three cell types that are responsible for olfaction, the olfactory epithelium also contains olfactory glands that are known as the olfactory glands or Bowman's glands.

02:46 These are gonna produce mucus that is used to dissolve odor molecules also called odorants so that they may be transduced.

02:58 Olfactory transduction is the binding of an odorant molecule to an olfactory receptor proteins Olfactory transduciton begins when an odorant binds to the olfactory receptor cells.

03:14 This leads to a chemical reaction involving cyclic AMP and causes depolarization The binding of an odorant molecule to the G protein-coupled receptor found in the membrane activates the G protein which then binds to the adenylyl cyclase enzyme.

03:38 The adenylyl cyclase is a membrane protein that catalyzes the reaction converting ATP to cyclic AMP.

03:48 From there, cyclic AMP binds to and opens cation channels in the olfactory receptor cell.

03:58 This causes an influx of sodium and calcium which leads to the depolarization of the receptor cell.

04:05 This causes an action potential to propagate to the primary olfactory area of the cerebral cortex.

04:15 All of this is going to happen by way of the olfactory nerve.

04:21 The human nose has about 10 million olfactory receptors.

04:27 There are approximately 400 functional types of olfactory receptors.

04:35 Each type can only react to a select group of odorants and only one type is found in each of our receptor cells.

04:46 The receptors and the nasal mucosa are going to send impulses along the branches of the olfactory nerve through the cribriform plate where they synapse with the axons and converge into mitral cells.

05:06 Axons on the mitral cells form the olfactory tract and impulses travel along this olfactory tract And some of the axons are also gonna travel to the primary olfactory area of the temporal lobe of the cerebral cortex for interpretation.

05:25 From the primary olfactory area, a pathway is going to extend by way of the thalamus to the orbitofrontal cortex in the frontal lobe where odor identification and discrimination is going to occur.

05:40 Other axons of the olfactory tract go to the limbic system.

05:45 This is going to be responsible for our emotional response to certain odors such as feeling happy when you have the smell of brownies or cookies.