Class Notes (835,866)
Canada (509,453)
Kinesiology (1,408)
Lecture

special senses.docx

7 Pages
112 Views
Unlock Document

Department
Kinesiology
Course
KINESIOL 1Y03
Professor
Krista Howarth
Semester
Fall

Description
Chapter 15- The Special Senses Olfaction - Sense of smell occurs in response to odours that stimulate receptors located In the extreme superior region of the nasal cavity. - Only a small superior part of the nasal cavity is dedicated to olfaction. - Olfactory epithelium is the nasal epithelium in the olfactory region. Olfactory Epithelium and Bulb - 10 million olfactory neurons are present within the olfactory epithelium. - Axons of these bipolar neurons project to the olfactory bulbs where they synapse with secondary neurons. - Olfactory tracts project from the bulbs to the cerebral cortex. - Dendrites of olfactory neurons extend to the epithelial surface of the nasal cavity, and their ends are modified into bulbous enlargements called olfactory vesicles. - These vesicles possess cilia called olfactory hairs . - Airborne molecules enter the nasal cavity and are dissolved in the fluid covering the olfactory epithelium. - Some of these odorants bind to transmembrane odorant receptor molecules of the olfactory hair membranes. - A G protein, associate with each odorant receptor, is activated by the binding of the odorant. - The a subunit of the activated G protein binds to and activates adenylate cyclase, which in turn catalyzes the formation of cyclic AMP from ATP, Camp in these cells causes na+ and ca2+ channels to open. - The influx of ions into the olfactory hairs results in depolarization ad the production of action potentials in the olfactory neurons. - Odor receptors are composed of seven transmembrane polypeptide subunits produced by a large family of genes. - Combinations of subunits from approximately 1000 different odorant receptors can be produced. - These receptors can react to odorants of different sizes, shapes and functional groups. - These capabilities, together with multiple intracellular pathways involving G proteins, adenylate cyclase and ion channels allow for a wide variety of detectable smells, which is about 4000 for the avg. person. - Seven primary classes have been proposed: camphoraceous(eg. Moth balls), musky, floral, pepperminty, ethereal (eg. Fresh pears), pungent and putrid. - Threshold for the detection of odors is very low, so very few odorant molecules are required to trigger the response. - Low specificity- a given receptor may react to more than one type of odorant. - Odorant receptors may become saturated with odorants and no longer respond to odorant molecules. - Makes people less sensitive to as odor after beong exposed to it for a short time. - The primary olfactory neurons have the most exposed nerve ending of any neurons, and they are constantly being replaced. - The entire olfactory epithelium, including the neurosensory cells, is lost about every 2 months as the olfactory epithelium degenerates and is lost from the surface. - Basal cells in the olfactory epithelium replace lost olfactory cells. - Unique among neurons. Neuronal Pathways for Olfaction - Axons from the olfactory neurons form the olfactory nerves, which enter the olfactory bulbs where they synapse with mitral cells or tufted cells. - These cells relay olfactory info to the brain through the olfactory tracts and synapse with granule cells in the olfactory bulb. - Olfactory bulb neurons also receive input from nerve cell processes entering the olfactory bulb from the brain. - As a result of input from both mitral cells and the brain, olfactory bulb neurons can modify olfactory info before it leaves the olfactory bulb. - This enhances the accommodation occurring in the odorant receptors. - Olfaction is the only major sensation that is relayed directly to the cerebral cortex without first passing through the thalamus. - Each olfactory tract terminates in an area of the brain called the olfactory cortex. - The olfactory cortex is in the frontal and temporal lobes, within the lateral fissure of the cerebrum, and it can be divied structurally and functionally into three areas: lateral, medial and intermediate. - The lateral area is involved in the conscious perception of smell. - The medial olfactory area is responsible for visceral and emotional reactions to odors and has connections to the limbic system, through which it connects to the hypothalamus. - Axons extend from the intermediate olfactory area along the olfactory tract to the bulb and synapse with the olfactory bulb neurons, thus constituting a major mechanism by which sensory information is modulated within the olfactory bulb. - The feedback from the intermediate olfactory is mostly inhibitory, further enhancing the rapid accommodation of the olfactory system. - Accommodation is what makes the olfactory system insensitive to an odorant after a brief exposure. Taste - Sensory system that detect gustatory or taste stimuli are the taste buds. - Associated with specialized portions of the tongue called papillae. - Also located on other areas of the tongue, the palate and even the lips and throat, especially in children. - The four major types of papillae according to their shape are: vallate, fungiform, foliate, and filiform. - Taste buds are associated with vallate, fungiform and foliate papillae. - Filiform are the most numerous but have no taste buds. - They provide a rough surface on the tongue. - Vallate are the largest but least numerous. - 8-12 of these form a v-shaped row along the border between the anterior and posterior parts of the tongue. - Fungiform are scattered irregularly over the entire superior surface of the tongue, appearing as small, red dots interspersed among the far more numerous filiform papillae. - Foliate papillae are distributed in folds on the sides of the tongue and contain the most sensitive of the taste buds. - They are most numerous in young children and decrease with age. - They are located mostly posteriorly in adults. Histology of Taste Byds - Taste buds are oval structures embedded in the epithelium of the tongue and mouth. - Each of the 10 000 taste buds on a person’s tongue consists of three major types of specialized epithelial cells. - The sensory cells of each taste bud consist of about 50 taste or gustatory cells. - The remaining two cell types which are nonsensory, are basal cells and supporting cells. - The cells are replaced continuously. - Having a lifespan of about 10 days. - Each taste cell has several microvilli called gustatory hairs, extending from its apex into a tiny opening in the epithelium called the taste or gustatory, pore. Function of Taste - Substances called tastants dissolved in saliva, enter the taste pores and by various mechanisms, cause the taste cells to depolarize. - These cells do not have classic axons but have short connections with secondary sensory neurons. - These connections have some characteristics of chemical synapses. - Neurotransmitters( including ATP) are released from the taste cells and stimulate action potentials in the axons of sensory neurons associated with them. - The taste of salt results when na+ diffuse through na+ channels of the gustatory hairs or other cell surfaces of taste cells, resulting in depolarization of the cells. - Hydrogen ions of acids, which result in sour taste can cause depolarization of taste cells by one of three mechanisms: they can enter the cell through h+ channels, they can bind to ligand-gated k+ channels and block the exit of k+ from the cell, or they can open ligand-gated channels for other positive ions and allow them to diffuse into the cell. - Sweet and bitter tastants bind to receptors on the gustatory hairs of taste cells and cause depolarization through a G protein mechanism. - A taste called umami results when amino acids such as glutamate bind the receptors on gustatory hairs of taste cells and cause depolarization through a G protein mechanism. - Texture of food also affects the perception of taste - Hot or cold food may interfere with the ability of the taste buds to function in tasting food. - If a cold fluid is held in the mouth, the body warms the fluid and the taste becomes enhanced. - Adaptation is very rapid for taste. - Adaptation occurs at the level of the taste bud and within the CNS. - Adaptation may occur 1 or 2 sec after a taste sensation is perceived, and complete adaptation may occur within 5 minutes. - Humans can perceive a fairly large number of different tastes - Many of the sensations thought of as being taste are strongly influenced by olfactory sensations. - Thresholds vary for the five primary tastes. - Sensitivity for bitter substances is the highest. - Sweet and salty is the lowest. - Many alkaloids are poisonous, thus the high sensitivity for bitter tastes may be protective. - On the other hand, humans tend to crave sweet, salty and umami tastes, perhaps in response the the body’s need for sugars, carbs, proteins and minerals. Neuronal Pathways for Taste - Taste from the anterior two thirds of the tongue except from the circumvallate papillae is carried by the means of the facial nerve called the chorda tympani. - It crosses over the surface of the tympanic membrane of the middle ear. - Taste from the posterior one thi
More Less

Related notes for KINESIOL 1Y03

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit