Suzanne D'Anna1 Sense of Smell

Suzanne D'Anna2 Olfactory Organs n lie in nasal epithelium mucous membrane n total area of olfactory epithelium is less than 1 square inch n located in superior portion of nasal cavity - superior nasal conchae - part of nasal septum

Suzanne D'Anna3 Olfactory Epithelium n Consists of three types of cells: - olfactory receptors - supporting cells - basal cells

Suzanne D'Anna4 Olfactory Receptors n million n lifespan about 30 days

Suzanne D'Anna5 Olfactory Receptors (cont.) n bipolar neurons with knob-shaped dendrite at distal end - cilia called olfactory hairs protrude from dendrite - cilia are sites of olfactory transduction n respond to chemical stimulation of an odorant molecule n single axon projects into olfactory bulb at proximal end

Suzanne D'Anna6 Supporting Cells n columnar epithelial cells of mucous membrane lining the nose n surround and support olfactory receptors

Suzanne D'Anna7 Basal Cells n located around supporting cells n stem cells that produce new olfactory receptors (neurons)

Suzanne D'Anna8 Olfactory Glands also called Bowman’s glands n within connective tissue that supports epithelium n produce mucus - moistens surface of olfactory epithelium - dissolves odorant gasses - continued production clears surface area and prevents continued stimulation by same odor

Suzanne D'Anna9 Physiology of the Sense of Smell

Suzanne D'Anna10 Olfactory Stimulation n Primary scents: - floral - pungent - musky - minty - putrid - camphoraceous - etheral

Suzanne D'Anna11 Olfactory Stimulation (cont.) n irritating odors also stimulate lacrimal and nasal receptors producing tears and sniffles n Example: - onions

Suzanne D'Anna12 Olfaction or Transduction n chemical interaction with receptor sites - sodium channels open leading to depolarization which causes action potential in axon leading to olfactory bulb n low threshhold - only a few molecules of a substance in the air are necessary to stimulate olfactory receptors

Suzanne D'Anna13 Adaptation n decreasing sensitivity to odors n occurs rapidly; about 50% in the first second after stimulation and very slowly thereafter n even though adaptation to one odor has occurred, sensitivity to other odors remains unchanged

Suzanne D'Anna14 Olfactory Pathway n olfactory receptors n olfactory nerves n olfactory bulbs n olfactory tract n prepyriform cortex and limbic system n frontal lobes

Suzanne D'Anna15 Taste

Suzanne D'Anna16 Taste Buds n about 10,000 are located on surface of tongue, throat, and epiglottis n Oval body consisting of three kinds of epithelial cells: - supporting cells - gustatory receptor cells - basal cells

Suzanne D'Anna17 Supporting Cells n form capsule supporting gustatory receptor cells n inside capsule - gustatory receptor cells Gustatory Receptor Cells n single hair-like gustatory hair projects from each bud to external surface through taste pore - hairs make contact with stimuli

Suzanne D'Anna18 Basal Cells n found at periphery of taste bud near connective tissue layer n produce supporting cells which develop into receptor cells whose life-span is about 10 days

Suzanne D'Anna19 Papillae n elevations on tongue n contain taste buds n give tongue rough appearance n Types of papillae: - circumvallate - fungiform - filiform

Suzanne D'Anna20 Circumvallate n largest n form v-shaped row on posterior surface of tongue Fungiform n mushroom-shaped n found on tip and sides of tongue

Suzanne D'Anna21 Filiform n thread-like n cover anterior 2/3 of tongue n contain no taste buds

Suzanne D'Anna22 Taste Sensations n Four basic: n sour - lateral edges of tongue n salty - anterior portions of tongue n bitter - posterior portions of tongue n sweet - anterior portions of tongue

Suzanne D'Anna23 Gustatory Pathway (once a chemical is dissolved in saliva) n contact is made with plasma membrane of gustatory hairs (site of transduction) n gustatory receptors - release neurotransmitter n nerve impulses arise in neurons that synapse with gustatory receptors n sensory fibers become part of three cranial nerves

Suzanne D'Anna24 Gustatory Pathway n Three cranial nerves: - facial (VII) - glossopharyngeal (IX) - vagus (X) taste impulses conduct from taste buds along cranial nerves to medulla oblongata

Suzanne D'Anna25 Gustatory Pathway n From medulla: - some taste fibers transmit impulses to hypothalamus and limbic system (emotional memory responses) - some taste fibers transmit impulses to primary gustatory area in parietal lobes of cerebral cortex (taste perception)

Suzanne D'Anna26 Somatic and Special Senses

Suzanne D'Anna27 Senses n constantly provide us with information about our surroundings n Grouped into two major categories: - general senses - special senses

Suzanne D'Anna28 Sensory Pathway n Includes: - receptors - sensory neurons - sensory tracts - sensory area

Suzanne D'Anna29 Receptors n detect stimuli n specific with respect to changes to which they respond Sensory Neurons n transmit impulses from receptors to central nervous system n found in both spinal and cranial nerves (each carries only one type of receptor)

Suzanne D'Anna30 Sensory Tracts n white matter in spinal cord or brain n transmit impulses to a specific part of brain Sensory Areas n most are in cerebral cortex n feel and interpret sensations n learning to interpret sensations begins in infancy without awareness and continues throughout life

Suzanne D'Anna31 General Senses n Somatic: - tactile - touch, pressure, vibration, itch, etc. - thermal - hot and cold - pain - acute and chronic - proprioceptive - muscle, tendon, joint n Visceral - distension of viscera - internal organs - chemical composition of extracellular fluid

Suzanne D'Anna32 Special Senses n Somatic: - visual - sight - auditory - hearing - equilibrium - static and dynamic equilibrium n Visceral: - olfactory - smell - gustatory - taste

Suzanne D'Anna33 Skin Receptors

Suzanne D'Anna34 Tactile Sensations n Touch receptors: - root hair plexuses - tactile discs - type II cutaneous mechanoreceptors - corpuscles of touch - (Meissner’s corpuscles)

Suzanne D'Anna35 Root Hair Plexuses n dendrites arranged around hair follicles n receptors that rapidly adapt to detect movements when hair is disturbed

Suzanne D'Anna36 Tactile Discs n expanded (flattened) nerve endings n slowly adapting touch receptors for discriminative touch

Suzanne D'Anna37 Type II Cutaneous Mechanorecptors n also called end organ for Ruffini n expanded nerve endings n embedded in dermis n receptors that adapt slowly to heavy and continuous touch

Suzanne D'Anna38 Corpuscles of Touch (Meissner’s Corpuscles) n small, oval, encapsulated nerve endings n rapidly adapting touch receptors n recognize exactly what point to which body is touched n abundant in hairless portions of skin

Suzanne D'Anna39 Corpuscles of Touch (cont.) n rapidly adapting receptors that respond to low frequency vibrations n also respond to pressure and touch stimuli

Suzanne D'Anna40 Tactile Sensations n Pressure and vibration receptors: - corpuscles of touch (Meissner’s) - lamellated corpuscles (Pacinian)

Suzanne D'Anna41 Lamellated Corpuscles (Pacinian) n oval structures n composed of connective tissue n layered like an onion n enclose a dendrite n rapidly adaptive receptors that respond to pressure and high frequency vibrations

Suzanne D'Anna42 Tactile Sensations (itch and tickle receptors) n free nerve endings are receptors for both tickle and itch sensations

Suzanne D'Anna43 Thermal Sensations (thermoreceptors) n heat receptors most sensitive to temperatures above 25 o C (77 o F) and become unresponsive at temperatures above 45 o C (113 o F) n cold receptors most sensitive to temperatures between 10 o C (50 o F) and 20 o C (68 o F)

Suzanne D'Anna44 Thermal Sensations (cont.) n intermediate temperature sensory input from combination of cold and heat receptors n both heat and cold receptors rapidly adapt to continuous stimulation

Suzanne D'Anna45 Pain Sensations (Nociceptors) n free, naked nerve endings n located between cells of epidermis n respond to all types of stimuli

Suzanne D'Anna46 Referred Pain n pain that feels as if it originated from a part other than site being stimulated n Example: - pain from heart attack (myocardial infarction) may be felt in left shoulder or inside of left arm - pain from gallstones may be felt in right shoulder