General and Special Senses Notes PDF

ZA I T U NNATA K HIN ZA M L I  OVERVIEW At the end of this lecture, the student should be able to: Differentiate between general and special senses. Describe the structural and functional characteristics of receptors in the general and special senses. Describe the stru...

ZA I T U NNATA K HIN ZA M L I  OVERVIEW At the end of this lecture, the student should be able to: Differentiate between general and special senses. Describe the structural and functional characteristics of receptors in the general and special senses. Describe the structures of the special sense organs.  INTRODUCTION TYPES OF SENSATION: 1. General senses / Somatosensory Receptors for those sensations are distributed throughout the body Types: - Somatic senses: tactile (touch, pressure, and vibration), thermal (warm and cold), pain, proprioceptive (joint, muscle) sensations. - Visceral senses: pressure, stretch, chemical, nausea, hunger and temperature. 2. Special senses Specialized cells are located in sense organs. e.g. gustation, olfaction, vision, equilibrium and hearing.  RECEPTORS GENERAL FEATURES: Receptors are structures that detect stimuli. Receptor field is an area where the sensitive ends of a receptor are distributed. CLASSIFICATION OF RECEPTORS: Distribution – general and special senses Stimulus origin – exteroceptor, interoceptor & proprioceptor Stimulus modality – chemoreceptor, thermoreceptor, photoreceptor, mechanoreceptor, baroreceptor & nociceptor. GENERAL SENSES NOCICEPTORS REFERRED PAIN  THERMORECEPTORS & CHEMORECEPTORS THERMORECEPTOR Temperature receptor Free nerve endings located in the dermis, skeletal muscle, liver and hypothalamus. CHEMORECEPTOR Respond to water- and lipid-soluble substances (e.g. pH, CO2, O2, etc)  MECHANORECEPTORS Classes of mechanoreceptors: i. Tactile receptors - touch (shape and texture), pressure and vibration - types – uncapsulated and capsulated tactile receptors ii. Baroreceptor PRESSURE CHANGE - pressure changes in the wall of blood vessel, and in some parts of digestive, urinary and reproductive tracts. iii. Proprioreceptor - position of joints and muscles. SPECIAL SENSES  GUSTATION Taste buds - oval-shaped, ~ 40-60 cells / taste buds - locations – tongue, soft palate, pharynx, and epiglottis - each taste bud consists of: i. Taste cells  are epithelial cells  √ taste hair, which project into the taste pore  synapse with sensory nerve fibres (i.e. C VII, IX, X) ii. Supporting cells  similar to taste cells without taste hair iii. Basal cells  replace dead taste cells (t1/2= 7-10days) Taste hairs (microvilli) Taste cell  GUSTATION Tongue 1. Filiform papillae - tiny spike, most abundant - no taste buds! 2. Foliate papillae - parallel ridges on both sides of the tongue - degenerate by age of 2/3 years 3. Fungiform papillae - mushroom-like - concentrated at tip and sides of the tongue - ~3 taste buds/papillae, located at its apex 4. Vallate / Circumvallate papillae - large papillae, only ~7-10 papillae - ~250 taste buds/papillae, located at its wall  OLFACTION Olfactory mucosa - location - on the roof of nasal cavity - comprises of: i. Olfactory cells are olfactory sensory neurons not moving √ olfactory hair; covers by mucosa, immobilise and act as binding site for odour molecules the axons/olfactory nerve/ C (I) passes through the ethmoid bone via olfactory foramina, and synapse with mitral cells at the glomerulus which located in the olfactory bulb. ii. Supporting cells iii. Basal cells differentiate into new olfactory cells (t1/2= 60days) Mitral cell Glomerulus EQUILIBRIUM & HEARING EXTERNAL EAR mostly on the outside of the body consists: i. Auricle - cartilage, funnel-shaped ii. External acoustic meatus - canal - submucosa: √ hair follicles, sebaceous glands and ceruminous glands iii. Tympanic membrane / eardrum - delicate, funnel-shaped - lined by epithelium - func.: transmit sound wave to middle ear MIDDLE EAR in temporal bone air-filled cavity communicates with nasopharynx via auditory / eustachian tube consists : i. Auditory ossicles  Malleus Func.: amplifying sound wave and  Incus transmit into inner ear  Stapes ii. Middle ear muscles  Stapedius Func.: restrict ossicles movement  Tensor tympani medially: √ oval and round windows INNER EAR in temporal bone system of canals + cavities + tubes + sacs 2 parts: 1. Bony labyrinth - canals and cavities in temporal bone - contains perilymph  extracellular fluid 2. Membranous labyrinth - membrane-lined, fluid-filled tube in bony labyrinth - contains endolymph   Na  K &  proteins INNER EAR…cont.. 1. Bony labyrinth - 3 regions: i. Semicircular canals orientation: anterior, posterior and lateral dilated end open into vestibule ii. Vestibule ovoid space egg shaped communicates with middle ear via: - oval window - round window INNER EAR…cont.. iii. Cochlea bone canal; 2½ spiral turn into the bone coils around modiolus  √ nerves fibers, vessels and spiral ganglion laterally, modiolus form plates  osseous spiral lamina from spiral lamina extends the: 1. Basilar membrane 2. Vestibular membrane as a result, 3 subdivisions scala vestibuli, scala media/cochlear duct, scala tympani * Scala vestibuli and tympani communicate at helicotrema  Semicircular canal Membranous labyrinth Anterior Bony labyrinth Semicircular Lateral ducts Posterior Vestibule Cristae within ampullae Maculae Endolymphatic sac Utricle Saccule Vestibular duct Cochlear duct Tympanic Organ of Cochlea duct Corti INNER EAR…cont.. 2. Membranous labyrinth - tubes and sacs in bony labyrinth: i. Semicircular ducts and ampulla in semicircular canals ampulla: dilated parts open into utricle epi.: thicken part  crista ampullaris (covers by cupula) func.: to detect rotational movement of the head  Vestibular branch (N VIII) Anterior Ampulla Cochlea Semicircular Posterior ducts Lateral Endolymphatic sac Endolymphatic duct Utricle Right semicircular ducts, anterior view Saccule Maculae Displacement in Displacement in this direction this direction Ampulla stimulates hair cell inhibits hair cell filled with endolymph Cupula Kinocilium Stereocilia Hair cells Crista Supporting cells Hair cell Sensory nerve Cross section through the ampulla Direction of Direction of relative Direction of duct rotation endolymph movement duct rotation Sensory nerve ending Semicircular duct Ampulla Supporting At rest cell Endolymph movement and ampulla displacement Hair cell INNER EAR…cont.. ii. Utricle and Saccule sacs, interconnected with adjacent ducts/sacs epi.: thicken part  macula (covers by otolithic membrane: gelatinous layer + otoliths/calcium carbanate crystal) func.: to detect acceleration and deceleration  Gravity Otolith Otolithic membrane (Gelatinous Gravity Material) Hair cells Otolith moves Nerve Receptor “downhill,” fibers output distorting hair increases cell processes Structure of a macula Macular function iii. Cochlear duct triangular shape; roof: vestibular membrane; floor: basilar membrane √ spiral organ / organ of Corti - epi.: hair cells + supporting cells - epithelium sits on basilar membrane - √ tectorial membrane touches hair cells closes the spiral sulcus secretion of glycoproteins - hair cells  outer and inner hair cells - func.: hearing  Bony cochlear wall Vestibular duct Spiral ganglion Vestibular membrane Cochlear duct Tectorial membrane Basilar membrane Tympanic duct Organ of Corti Cochlear branch of N VIII Cochlear duct (scala media) Tectorial membrane Vestibular membrane Tectorial membrane Outer hair cell Basilar membrane Inner hair cell Nerve fibers Tympanic duct Basilar Hair cells Spiral ganglion (scala tympani) membrane of organ cells of of Corti cochlear nerve  VISION Comprises of: Eyeball Accessory visual structures: - conjunctiva - eyelids / palpebrae - lacrimal apparatus - extrinsic muscles - eyebrows EYEBALL spherical organ 2 cavities: i. Anterior cavity i. loc.: anterior to lens and post. to cornea. ii. 2 chambers: i. anterior chamber ii. posterior chamber iii. √ aqueous humor, produce by ciliary processes ii. Posterior cavity i. loc.: anterior to retina and post. to lens ii. √ vitreous humor, a transparent jelly-like substance. func.: to maintain the eye shape and support retina. EYEBALL…cont.. 3 main layers: i. Fibrous layer Cornea Sclera ii. Vascular layer Iris Ciliary body Choroid iii. Inner layer Retina - √ photoreceptors √ Lens  Limbus Ciliary muscle Suspensory ligaments Source: http://www.uptodateinc.com/ EYEBALL…cont.. Photoreceptor cells in the retina comprises of: i. Rods - thin, long, most numerous - 2 parts:  Outer segment - dendrite, cylindrical-shaped - membranous discs (not continuous with plasma membrane, √ rhodopsin pigments) - photosensitive area  Inner segment - nucleus, cytoplasm (>>mitochondria & glycogen granules) - func.: for night vision, cannot distinguish color EYEBALL…cont.. ii. Cones - least numerous, highly sensitive to light and color vision - 2 parts:  Outer segment - dendrite, cone-shaped - membranous discs (continuous with plasma membrane, √ photopsin pigments) - photosensitive area  Inner segment - nucleus, cytoplasm (>>mitochondria & glycogen granules) - func.: for day and color vision