Special Senses

1. Special Senses Chapter 15

2. Olfactory: Small patch of olfactory epithelium located on the superior nasal concha that contains three types of tissue: • Olfactory receptors • Supporting cells (sustentacular) • Basal cells 1- Olfactory receptors: bipolar neurons Dendrites have olfactory hairs (cilium) hanging from the dendrites

4. 2- Supporting cells: mucous membrane lining the nose containing columnar epithelium 3- Basal cells continually produce new olfactory receptors (neurons). They regenerate every month. Exception to the rule that mature neurons are not replaced. Olfactory bulb and tract. Taste and smell centers lie very close together in the brain (primary olfactory cortex)

6. Physiology of olfaction. Odors are made up of multiple odorant molecules and each odorant molecule will activate several olfactory receptors. This system can allow us to recognize and remember some 10,000 odors. Odor molecule dissolves on the mucous membrane. The molecules will bind to G-proteins located on the plasma membrane of the receptor cells. This will activate the enzyme cAMP (adenylate cylase or cyclic AMP) and cause the opening of sodium channels, depolarization and nerve impulse.

7. From the olfactory tracts impulse will travel to two main destinations. 1- thalamus to the pyriform (pear shaped) area - uncus - entorhinal area - limen insula (junction between the cortex of the frontal and insula lobes) - frontal lobe above the orbits where smell is interpreted and identified

8. 2- Subcortical pathway to the amygdala, hypothalamus and other regions of the limbic system. Here is where smells are associated with danger and other emotional responses. i.e. smoke, natural gas, skunk. Sympathetic responses are initiated.

10. Olfactory terms: Anosmia: loss of smell Hyposmia: decr. smell Hyperosmia: incr. smell Dysosmia: distorted smell

11. Gustation: Gustatory receptor cells are located in the taste buds - papillae (elevations scattered on tongue, roof of mouth and walls of pharynx) Primary taste sensations: sour, bitter, salty and sweet. Discovered in Japan is umami. Sensed in response to a salt (monosodium glutamate) found in the amino acid glutamate.

13. Sour, salty and sweet are carried via CN VII (facial nerve) and bitter carried via CN IX (glossopharyngeal). All taste sensations are relayed to the ventral posterior (vp) medial nuclei of the thalamus from the solitary nucleus (gustatory nucleus) then on to the primary gustatory cortical area of the inferior post-central gyri of the parietal lobes. Taste is 80% smell

14. Gustatory terms: Ageusia: loss of taste Hypogeusia: decr. taste Hypergeusia: incr. taste Dysgeusia: distorted taste

16. Hearing: External, middle and inner ear External ear: Outer auricle or pinna will funnel sound towards the ear drum. Remember external auditory meatus (EAM) through the temporal bone Sound waves are transmitted through the EAM until they reach the tympanic membrane (ear drum) - semitransparent membrane covered by skin on the outside and mucous membranes on the inside.

19. Middle ear: Petrous portion of temporal bone • The ear drum magnifies the vibrations of sound waves mechanically. One of the main purposes of the ear is to transform these air pressure waves to an electrical nerve signal that the brain can understand • The ossicles are - hammer (malleus) attaches to drum - short and long handle (processes) -manubrium - anvil (incus) - stirrup (stapes).  The stirrup attaches to the oval window of the inner ear or cochlea

22. Otitis media

23. Tympanostomytubes

24. Inner ear: labyrinth Vibration of the stapes on the oval window moves fluid (perilymph) within the inner ear. Vibrations will stimulate the hearing receptors. Pressure on the oval window is 22x greater than the wave pressure exerted on the ear drum.

26. Pressure waves are transmitted from the scala vestibuli to the scala tympani and then into the round window • Pressure waves deform walls of scala vestibuli and scala tympani, collectively causing the vestibular membrane to move (pressure in endolymph increases & decreases) • Pressure fluctuations in endolymph move the basilar membrane • Hairs of the organ of Corti, connected to the basilar membrane, move against the tectorial membrane and cause the generation of nerve impulses

28. Decibels (dB) measures sound intensity. 0 dB is least perceived by the human ear 10 dB is 10x louder than 0 dB 20 dB is 100X as loud as 0 dB etc.. Whisper: 40 dB Normal speech: 60-70 dB Rock concert: 120 dB Jet plane: 140 dB (nociception) Prolonged periods of 90 dB will cause permanent hearing loss

29. Hearing nerve fibers are located in the cochlear branch of the vestibulocochlear nerve (VIII). • Auditory pathway for hearing: - cochlear branch enters b/w the medulla oblongata and the pons to end in the cochlear nuclei both dorsal and ventral. - fibers cross and ascend into thalamus (medial geniculate body) to terminate in the primary auditory cortex of the temporal lobe

32. Equilibrium: feeling of the position of the head at rest and movement Static (rest): organ is located in the vestibule between the semicircular canals and the cochlea. Specifically, the utricle and saccule. Helps keep head still and balanced. Dynamic (motion): organ located in the ampullae of the semicircular canals. - anterior - posterior - lateral

34. The semicircular canals contain fluid and are responsible for detecting changes in motion. The three semicircular canals (all at different angles), are responsible for detecting motion on a different plane. Within the canals are nerve hairs which sense changes in the movement of the perilymph fluid and depolarize, thus sending a message to the brain. Ex: spinning in a circle- (remember the sit and spin toy)

35. Vestibular portion of CN VIII enters b/w the medulla oblongata and the pons and ends in the vestibular nuclear complex. • Works closely with the cerebellum to signal appropriate skeletal muscles in response to changes in equilibrium.

36. Vision: Eyeball has three layers: Outer: Fibrous tunic Middle: Vascular tunic Inner: Nervous tunic Fibrous tunic: Anterior portion contains the clear avascular cornea which helps focus light rays. Very pain sensitive It is continuous with the white sclera that surrounds the eyeball and is the attachment site for the extrinsic ocular muscles. Dura mater is continuous with the sclera at the site of the optic nerve that exits the back of the eyeball.

39. Vascular tunic (uveal layer) includes the iris, ciliary body and choroid coat. • Choroid coat contains blood vessels that nourish the eye and is loosely joined to the sclera. • Ciliary body located in the anterior part of the eye has ciliary muscles that are attached to suspensory ligaments that hold the lens (transparent structure located behind the iris) in place. When the muscles contract these ligaments are able to change the shape of the lens (ligaments relax causing lens to thicken) aiding in focusing close objects. (accommodation- remember parasympathetic division: CN III)

44. iris: - colored smooth muscles portion of eye - thin diaphragm allowing light to enter. - lies b/w the cornea and the lens - separates the eyeball in an anterior (b/w the iris and cornea) and posterior chamber (b/w the iris and vitreous humor) ant.: aqueous humor post.: vitreous humor

46. - Pupil - hole in the iris - pupil size is controlled by smooth muscles in the iris called circular and radial sets. - circular set acts as sphincter to constrict pupil in the presence of bright light. (parasympathetic) - radial set increases diameter of pupil causes it to dilate. (sympathetic.)

47. Nervous tunic: The retina is a thin, delicate structure that contains specialized photoreceptor cells and is continuous with the optic nerve. Five types of neuron located in the retina • Receptor cells (rods and cones) • Bipolar neurons • Ganglion cells • Horizontal cells • Amacrine cells

50. In the center of the retina is yellowish spot called the macula lutea. A depression in the center called the fovea centralis is the region where the sharpest vision is produced. Medial to the fovea is the optic disc. The optic disc is where the optic nerve exits the eyeball. No receptors are present for vision so it is also called the blind spot.