Monday, November 26, 2007

PSC 129 Chapter 13 Olfaction

I. Olfactory Physiology
1. Odors and Odorants
- Odors are chemical compounds; must be volatile, small, and hydrophobic
2. The human olfactory apparatus
- The primary function of nose is to filer, warm and humidify the air that we breathe
- Air pass through a narrow space called olfactory cleft and settle on a yellowish patch of mucous membrane called the olfactory epithelium
- Epithelium contains three types of cells: supporting cells, basal cells, and olfactory sensory neurons
a. OSN are small neurons that have cilia protruding into the mucus covering the olfactory epithelium
b. The cilia have olfactory receptors on their tips.
c. The interaction between an odorant and OR stimulates a cascade events that will produce an action potential that is transmitted along the axon of the OSN to the olfactory bulb.
d. In order to fire action potential, 7 or 8 odor molecules must bind to receptor, and takes 40 of these nerve impulses for a smell sensation to be reported.
e. The axons on the ends of OSN opposite the cilia pass through the tiny holes of the cribriform plate
f. Anosmia: smell blindness
g. Stem cells in the olfactory epithelium can form new OSN
h. The OSN axons pass through the cribriform plate and bundle together to form the olfactory nerve (CN I) and enter a blueberry-sized extension of the brain just above the nose, called the olfactory bulb.
i. Olfactory is ipsilateral: the right olfactory bulb gets information from the right nostril and the left olfactory bulb gets information from the left nostril.
j. Inside the olfactory bulb are glomeruli where OSN axons synapse with dendrites of two other types of neurons: mitral cells and tufted cells.
k. Each glomerulus may receive axons from different receptor types.
-Brain structures: olfactory bulb, olfactory cortex, amygdala-hippocampal complex, and entorhinal cortex --> network called limbic system which is involved in emotion and memory

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