second process the axon along with many others enters the olfactory bulb of the

Second process the axon along with many others enters

This preview shows page 3 - 5 out of 9 pages.

second process (the axon), along with many others, enters the olfactory bulb of the brain as olfactory nerve fiber (cranial nerve I) o supporting cells - insulating the olfactory receptor cells and producing mucus o basal cells which differentiate into olfactory epithelium Steps of the Olfactory Pathway Olfactory cilia/hair – terminals of the fused dendrites of the bipolar neurons in the nasal mucosa Axons of the bipolar neurons form the fibers of the olfactory nerve (cranial nerve I) that leaves the nasal cavity and enters the cranial cavity through the openings in the ethmoid bone (cribriform plate) Olfactory bulb – axons of the bipolar neurons synapse here with the second-order neurons (olfactory bulb is the location of cell bodies of second order neurons - mitral cells) Axons of the second-order neurons leave the olfactory bulb and enter the olfactory cortex in the temporal lobe (via the olfactory tracts ); olfactory pathway is the only sensory pathway reaching the sensory cortex directly (without synapsing in thalamus) Dysfunctions of Taste and Smell Taste dysfunctions – damage or inflammation (e.g., dental surgery, viral infections) of facial nerve (VII) or glossopharyngeal nerve (IX) which involve the taste pathways are rare Smell dysfunctions – more common than the taste dysfunction o fracture of ethmoid bone or lesion of olfactory fibers resulting from head injuries o inflammation of nasal cavity – cold, allergy, smoking o physical obstruction – polyps o zinc deficiency (one-third of all cases) THE SENSE OF SIGHT/VISION - THE EYE Vision – dominant sense o 70% of all sensory receptors in the body are in the eyes o almost half of cerebral cortex is involved in some aspects of processing of visual information 3
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Accessory Structures of the Eye (Accessory structures of the eye either protect the eye or enable eye movement) Figure 17-4 Bony orbit - made up of portions of several of the bones of the skull and lined with fat tissue that insulates and cushions the eye Eyebrows - help to prevent perspiration and airborne particles from entering the eye Eyelids (palpebrae) - cover and protect the eyes from desiccation (drying out), foreign matter (act like windshield wipers), and sunlight; eyelashes protect the eye from airborne particles o the gap that separates the upper and lower eye lids = palpebral fissure o connection between the upper and lower eye lids = medial and lateral canthus o small modified sebaceous glands associated with eyelashes = tarsal glands also called Meibomian glands (their secretion keeps the eyelids from sticking together ( chalazion = inflammation/blockage of a tarsal gland; also described as sty) o soft tissue located at the medial canthus = lacrimal caruncle ; it contains glands (sebaceous and sweat glands) producing the whitish, oily secretion ("Sandman's eye sand") o the mucus membrane (specialized stratified squamous epithelium) covering the inner surface of the eyelids and the outer surface of the eye = conjunctiva - palpebral and ocular
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