Special senses

• Taste buds


  • Located on the tongue, some are located within other areas of the mouth
  • Papillae: small elevated projections on the tongue
  • Fungiform (sweet), circumvallate (bitter), and foliate (sour) contain taste buds (all taste salty)
  • Filiform are sensitive to touch
• Gustatory cells


  Specialized receptors located on each taste bud (50-125 per taste bud); have special hair like projections (sensitive to various chemicals - acts as stimuli for various taste sensations)
• Gustation


  Gustatory nerves - connected by the cranial nerves to the medulla oblongata → relays the message to the thalamus → to the gustatory center of the brain where the stimulus is interpreted
• Gustation and olfaction


  Closely associated to produce the sensation of taste
• Olfactory sensory cells


  • Located in the epithelial lining of the mucous membrane of the nose
  • Olfactory neural chemoreceptors - have specialized cilia which detect the presence of specific chemicals within the air we breath
• Olfaction


  The neurons connected to the olfactory bulb when stimulated sends a message to the olfactory center of the brain where the smell is interpreted
• Auditory (Hearing) and Balance

  The ear is a dual organ, not only is responsible for the sense of hearing but also it functions as the organ of balance
• Regions of the ear

  • External: Pinna or auricle and auditory canal
  • Middle: Tympanic membrane (eardrum) and auditory ossicles (malleus (hammer), incus (anvil) and stapes (stirrup)
  • Inner: Semicircular canals and vestibular nerve (balance) and the cochlea and round or oval window and the cochlear nerve (sound)
• Outer ear


  • Pinna – ear flap, collects and directs sound waves into the ear
  • Auditory canal – channels waves to the ear drum; houses ceruminous glands
  • Ceruminous glands - secrete ear wax (cerumin) to keep ear drum moist
  • Tympanic membrane – ear drum, catches vibrations and sends them to the bones of the inner ear; separates the outer and middle ear
• Middle ear


  • Eustachian tube – connects the ear to the throat and equalizes pressure
  • Ossicles: Hammer (malleus) – outermost bones, receives vibrations from tympanic membrane, Anvil (incus) – middle bone, Stirrup (stapes) – innermost bone, transfers vibrations to the cochlea
• Inner ear


  • Vestibule – space between the cochlea and semicircular canals
  • Cochlea – snail shaped structure; fluid filled with endolymph and perilymph; contains the organ of corti
  • Organ of Corti – tiny hair-like cells that pick up vibrations and transfer them to the auditory nerve
  • Semicircular canals – contain liquid (perilymph) and tiny hair-like cells that blend with motion to help maintain equilibrium
  • Auditory nerve – carries information from the ear to the temporal lobe of the brain
• Perilymph


  Thin liquid in spaces of the inner ear
• Endolymph


  Thick liquid found in the cochlear ducts of the inner ear
• Hearing pathway


  Pinna → auditory canal → tympanic membrane → malleus → incus → stapes → cochlea → Organ of Corti → auditory nerve → temporal lobe of brain
• Hearing disorders


  • Presbyscusis – deafness with aging, caused by bones fusing; fusion makes them unable to transfer vibrations; hearing aids can help
  • Vertigo – dizziness, variety of causes
  • Meniere's disease – condition of they labyrinth (semicircular canals) which causes marked vertigo and fullness of the ear; may require bed rest
  • Otitis media – middle ear infection; build up of fluid caused by bacteria
  • Otosclerosis – bones of the ear become immovable; causes deafness because the stapes fuses with the bone of the ear and does not allow sound vibrations to transfer to the cochlea
  • Tinnitus – ringing in the ear; caused by wax build up, infection, exposure to loud sounds
• Balance


  The ear functions as the organ of balance
• The special senses include gustation, olfaction, vision, and audition
• The semicircular canals detect rotational movements of the head and send information about angular acceleration to the cerebellum.
• The cochlea contains the organ of Corti, which converts sound waves into electrical signals that are transmitted to the brain via the auditory nerve.
• The vestibular system is responsible for balance, equilibrium, and spatial orientation.
• The inner ear consists of two main structures: the cochlea and the vestibule.
• The vestibule contains two organs that are sensitive to linear movement or changes in position relative to gravity.
• The utricle is responsible for sensing vertical displacement, while the saccule is responsible for sensing horizontal displacement.
• The vestibular apparatus includes three semicircular canals oriented at right angles to one another, which respond to changes in rotation or movement of the head.
• The vestibular apparatus includes three semicircular canals oriented at right angles to one another and filled with endolymph.
• The cochlea is involved in hearing, while the vestibule is part of the vestibulocochlear nerve and plays a role in maintaining balance and posture.
• The otolith organs contain hair cells embedded within jelly-like material called otoconia.
• The cochlea is involved in hearing, while the vestibule is part of the vestibulocochlear nerve and plays a role in maintaining posture and balance.
• The vestibule houses three semi-circular canals (anterior, posterior, lateral) and two otolith organs (utricle and saccule).
• The inner ear consists of two main structures: the cochlea and the vestibule.
• The utricle and saccule contain maculae with hair cells embedded in gelatinous masses called otoconia or statoconia.
• The utricle and saccule contain sensory receptors called maculae that respond to changes in position relative to gravity.
• The maculae consist of hair cells embedded in gelatinous masses (otolithic membranes) containing calcium carbonate crystals (otoconia).
• When there is a change in position relative to gravity, the otoconia move on the otolithic membrane, causing deflection of the stereocilia on the hair cells.
• When there is no stimulus, the tip links between adjacent stereocilia are open, allowing potassium channels to be activated and depolarize the cell.