Exam 2 Study GuideChemical Senses1. Olfactory Receptors-Bipolar neurons-thin dendrite that ends with knob giving way to olfactory cilia-Olfactory cilia- serve to increase receptive surface area and lay flat on the epithelium and are covered by mucous produced by supporting cells.-Filaments of the olfactory nerve run superior to inferior through the cribriform plate-Olfactory Receptor cells are replaced every 30-60 days by differentiation of basal cells-These cells can distinguish about 10,000 different colors and their receptors are stimulated by at least 1,000 “smell genes”. Each cell has only 1 TYPE of receptor protein and these unique receptor proteins respond to some odorants more than others-Olfactory epithelium is a pseudostratified epithelium (meaning 1 layer of cells giving the impression of multi-layers) located on the roof of the nasal cavity. The olfactory epithelium has three types of cells:-olfactory receptor cells: millions on each side of the nasal septum- supporting cells: surround olfactory receptor cells- basal cells: base of epithelium2. Transduction of smell begins when an odor binds to a receptor and activate G protein (signaling molecule) which activates the enzyme adenylate cyclase to synthesize cAMP (secondary messanger). cAMP allows a cation membrane channel to open from extracellular to intracellular space. The inflow of Na+ and Ca2+ causes depolarization.At the circuit level, olfactory receptors send an action potential to second order neurons (mitral cells which are inside glomeruli); different glomeruli respond to different odors. Mitral cells send information down the olfactory tract to the Thalamus or Hypothalamus, amygadala, or limbic system.Olfaction has a low threshold meaning only a few molecules need to be present. Adaptation occurs rapidly adapting 50% in the first second then more slowly afterwards. Complete adaptation to strong odors occurs in 1 minute.3. Taste buds are our sensory receptors for taste. They are located on our tongue, cheeks, soft palate, pharynx, and epiglottis. Taste buds are primarily on the tongue housed in papillae. The three main types include: fungiform (top), foliate (lateral), and circumvallate papillae (back; largest/least) there are 8-12 circumvallate papillae.4. Each bud has 50-100 cells which are either gustatory or basal cells (are replaced 7-10 days).Basal cells are the most dynamic cell and acts like a stem cell. Gustatory cells have gustatory hairs that project through a taste pore into saliva. Dendrites in each cell take signal from receptor cells to the brain.There are two types of gustatory cells, one release its neurotransmitter serotonin and the other uses ATP.5. The major types of taste stimuli are sour (acids), sweet (organics), salty (inorganic salts), bitter (alkaloids), and umami (AAs). The locations of these receptors respectively are: sides of tongue (sour and salty), tip of tongue, back, and pharynx.6. Physiology of GustationChemicals dissolved in saliva contact gustatory hairs. Binding of chemicals to the gustatory cell induces depolarization. At the highest change of membrane voltage, neurotransmitter is released from the synapse and binds to the associated afferent fiber (dendrite) and moves information to the 1st motor neurons. Afferent fibers involved include the Facial Nerve (VII) the covers the anterior 2/3 of tongue, the Glossopharyngeal Nerve (IX) the covers the posterior 1/3 of the tongue, and the Vagus Nerve (X) covering the throat region. 2nd order neuron: solitary nucleus of the Medulla and elicits digestive reflexes through the Parasympathetic Nervous System on the way3rd order neuron: Thalamus7. Disorders of Chemical Senses:o Anosmias- absence of smello Hyposmia- impaired sense of smello Dysosmia- distorted sense of smello Ageusia- absence of tasteo Hypogeusia- decreased sensitivityo Hypergeusia- increased sensitivityo Dysgeusia- distorted sense of tasteVision: The EyePart 1:1. The accessory structures of the eye include:- Eyebrows: overlie supra-orbital margins of the skull. They shade the eyes from sunlight and prevent perspiration from reaching the eyes; contraction of oculi not oris(mouth)- Eyelids: (palpebrae) separated by the palprbral fissure; meet at the medial and lateral commissures of the eye. Protect the eyes, blink every 3-7 seconds, prevent drying through blinking- Lacrimal caruncle- in medial commissure; fleshy elevation that contains sweat glands- Tarsal Plates- connective tissue sheets that support the eyelid- Eyelashes- projecting follicles of which a touch prevents reflex blinking. Has tarsal glands in the tarsal plates to secrete oily lubrication- Conjunctiva- transparent mucous membrane covering the eyelidThe lacrimal apparatus includes lacrimal glands and ducts that drain secretions. The lacrimal gland is in orbit above the lateral end of the eye. It releases lacrimal secretion as a saline solution.As you blink, tears spread downward through the lacrimal pathway: through lacrimal puncta, enter lacrimal canaluculi and drain into the lacrimal sac then fall into lacrimal duct and finally tears enter the nasal cavity at inferior meatus.Simplified: glandpunctumcanalsacductnasal cavity2. Extrinsic Eye Muscles:- Rectus Muscles: originate from annular ring which surrounds the optic canal- Oblique Muscles: move eyeball in vertical plane when eye is already looking medially- Superior/Inferior Oblique: rotate eye opposite to their name and laterally- Superior/Inferior Rectus: naturally turn eye medially when they depress and elevate it; pull eye laterally(this table helps!!)Name Action Controlling Cranial NervesLateral Rectus Moves eye laterally VI (abduncens)Medial Rectus Moves eye medially III (oculomotor)Superior Rectus Elevates eye III (oculomotor)Inferior Rectus Depresses eye III (oculomotor)Inferior Oblique Depresses eye & turns III (oculomotor)laterallySuperior Oblique Elevates eye & turns laterallyIV (trochlear)3. Layers of the Eyeball-Fibrous Layer is the outermost coat of the eye containing the sclera and cornea; mostly connective tissue.o The sclera is the posterior portion of the eye or “white of eye”. This posterior portion articulates with dura mater of the brain through the optic nerve (blind spot).o The cornea is the anterior 1/6th of the fibrous layer covered by stratified squamous epithelium. It is the part of the eye most susceptible to damage and has pain receptors.- Vascular Layer is the middle coat of the eyeball with 3
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