Lesson 2 Special Senses An Introduction to the Special Senses Five Special Senses olfaction gustation vision equilibrium hearing Which one s depend upon mechanoreceptors Vision equilibrium hearing Which one s depend upon chemoreceptors Olfaction and gustation 17 1 Smell olfaction Olfactory Organs Provide sense of smell Located in nasal cavity on either side of nasal septum Made up of two layers o 1 Olfactory epithelium o 2 Lamina propria Layers of Olfactory Organs Olfactory epithelium contains o 1 Olfactory receptor cells o 2 Supporting cells o 3 Basal stem cells regenerates olfactory receptor cells Lamina propria contains o 1 Areolar tissue o 2 Blood vessels o 3 Nerves o 4 Olfactory glands form mucus Olfactory Glands Secretions coat surfaces of olfactory organs Olfactory receptors Highly modified neurons Olfactory Reception membrane of olfactory receptor cell Olfactory Pathways o Involves detecting dissolved chemicals as they interact with odorant binding proteins on cell Axons leaving olfactory epithelium axons collected into 20 or more bundles o Penetrate cribriform plate of ethmoid o Reach olfactory bulbs of cerebrum where first synapse occurs Axons leaving olfactory bulb o Travel along olfactory tract to reach olfactory cortex hypothalamus portions of limbic system Arriving information reaches information centers without first synapsing in thalamus Olfactory Discrimination Can distinguish thousands of chemical stimuli CNS interprets smells by the pattern of receptor activity Olfactory Receptor Population Considerable turnover receptor cells replenished by basal cells Number of olfactory receptors and resulting sense of smell declines with age 17 2 Taste Gustation Gustation Provides information about the foods and liquids consumed Taste Receptors gustatory receptors Distributed on tongue and portions of pharynx and larynx Clustered into taste buds o Associated with epithelial projections lingual papillae on superior surface of tongue Three Types of Lingual Papillae 1 Filiform papillae o Do not contain taste buds o Provide friction 2 Fungiform papillae o Contain 5 taste buds each 3 Circumvallate papillae o Contain 100 taste buds each Taste buds Contain 1 Basal cells 2 Gustatory cells Gustatory Discrimination Four Primary Taste Sensations o 1 Sweet o 2 Salty o 3 Sour o 4 Bitter Additional human taste sensations o Extend taste hairs through taste pore o Survive only 10 days before replacement Monitored by cranial nerves that synapse within the medulla oblongata o Then on to thalamus and primary sensory cortex o CN medulla thalamus PSC o 1 Umami o 2 Water Receptors sensitive to amino acids small peptides and nucleotides Detects characteristic of beef chicken broths and Parmesan cheese Detected by water receptors in the pharynx Dissolved chemicals contact taste hairs Bind to receptor proteins of gustatory cell Salt and sour receptors o Chemically gated ion channels o Stimulation produces depolarization of cell Sweet bitter and umami stimuli o Binds to membrane receptor protein to activate G proteins End Result of Taste Receptor Stimulation Release of neurotransmitters by receptor ell o Neurotransmitters generate action potentials in afferent fiber Taste Sensitivity Exhibits significant individual differences o 1000x more sensitive to acids sour taste than sweet salty 100x more sensitive to bitter than acids Some conditions are inherited o Why Because a lot of poisonous things are bitter so it is a defense mechanism by the body o For example phenylthiocarbamide PTC 70 of Caucasians taste it but 30 do not Number of taste buds begins declining rapidly by age 50 17 3 Accessory Structures of the Eye Accessory Structures of the Eye Provide protection lubrication and support Include o 1 The palpebrae eyelids continuation of skin Blinking keeps surface of eye lubricated free of dust and debris Tarsal glands secrete lipid rich product that helps keep eyelids from sticking together o 2 The superficial epithelium of eye includes Lacrimal caruncle contains glands producing thick secretions Contributes to gritty deposits that appear after good night s sleep Conjunctiva Epithelium covering inner surfaces of eyelids palpebral conjunctiva and outer surface of eye ocular conjunctiva Inflammation of the conjunctiva conjunctivitis pinkeye redness caused by infection allergy chemical irritation o 3 Lacrimal apparatus produces distributes and removes tears Lacrimal gland tear gland secretions contain lysozyome an antibacterial enzyme Tears Collect in the lacrimal lake at the medial canthus Pass through o Lacrimal puncta o Lacrimal canaliculi o Lacrimal sac o Nasolacrimal duct To reach inferior meatus of nose 17 3 The Eye Eyeball Hollow Divided into 2 cavities o 1 Large posterior cavity Filled with vitreous humor o 2 Smaller anterior cavity Filled with aqueous humor Consists of the anterior before the iris and posterior after the iris chambers Three Layers of the Eye 1 Outer Fibrous Layer 2 Intermediate Vascular Layer 3 Deep Inner Layer 1 The Outer Fibrous Layer Cornea transparent anterior region Sclera white of the eye Corneal limbus border between cornea and sclera 2 The Intermediate Vascular Layer Uvea Functions o 1 Provides route for blood vessels and lymphatics that supply tissues of eye o 2 Regulates amount of light entering eye o 3 Secretes and reabsorbs aqueous humor that circulates within chambers of eye o 4 Controls shape of lens which is essential to focusing Components o Iris Contains papillary muscles Sympathetic and parasympathetic innervations change the diameter of pupil by stimulating the pupillary dilator or constrictor respectively o Ciliary Body Contains ciliary processes and ciliary muscle that attaches to suspensory ligaments of lens Controls lens position and shape o Choroid Delivers oxygen and nutrients to retina 3 The Deep Inner Layer Outer layer called pigmented part absorbs light that passes through neural part prevents rebounding of light Inner called neural part retina o Contains visual receptors and associated neurons o Rods and cones are types of photoreceptors Rods Cones Do not discriminate light colors Highly sensitive to light used in low light night time Provide color vision Densely clustered in fovea at center of macula Inner Neural Part Bipolar cells o Neurons that allow rods and cones to synapse with ganglion cells Horizontal cells Amacrine cells o Extend across outer portion of retina o Comparable to horizontal cell layer o Where bipolar cells synapse with
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