Special SensesSpecial Senses

Chapter 15Chapter 15

Olfactory:Olfactory:Small patch of olfactory epithelium Small patch of olfactory epithelium

located on the superior nasal concha located on the superior nasal concha that contains three types of tissue:that contains three types of tissue:

- Olfactory receptorsOlfactory receptors- Supporting cells (sustentacular)Supporting cells (sustentacular)- Basal cellsBasal cells

1- Olfactory receptors: bipolar neurons1- Olfactory receptors: bipolar neuronsDendrites have olfactory hairs (cilium) Dendrites have olfactory hairs (cilium)

hanging from the dendriteshanging from the dendrites

2- Supporting cells: mucous membrane 2- Supporting cells: mucous membrane lining the nose containing columnar lining the nose containing columnar epitheliumepithelium

3- Basal cells continually produce new 3- Basal cells continually produce new olfactory receptors (neurons). They olfactory receptors (neurons). They regenerate every month. Exception to the regenerate every month. Exception to the rule that mature neurons are not replaced.rule that mature neurons are not replaced.

Olfactory bulb and tract.Olfactory bulb and tract.

Taste and smell centers lie very close Taste and smell centers lie very close together in the brain (primary olfactory together in the brain (primary olfactory cortex)cortex)

Physiology of olfaction.Physiology of olfaction.

Odors are made up of multiple odorant Odors are made up of multiple odorant molecules and each odorant molecule will molecules and each odorant molecule will activate several olfactory receptors. This activate several olfactory receptors. This system can allow us to recognize and system can allow us to recognize and remember some 10,000 odors.remember some 10,000 odors.

Odor molecule dissolves on the mucous Odor molecule dissolves on the mucous membrane. The molecules will bind to G-membrane. The molecules will bind to G-proteins located on the plasma membrane of proteins located on the plasma membrane of the receptor cells. This will activate the the receptor cells. This will activate the enzyme cAMP (adenylate cylase or cyclic enzyme cAMP (adenylate cylase or cyclic AMP) and cause AMP) and cause

the opening of sodium channels, the opening of sodium channels, depolarization and nerve impulse.depolarization and nerve impulse.

From the olfactory tracts impulse will From the olfactory tracts impulse will travel to two main destinations.travel to two main destinations.

1- thalamus to the pyriform (pear shaped) 1- thalamus to the pyriform (pear shaped) areaarea

- uncus- uncus

- entorhinal area- entorhinal area

- limen insula (junction between the - limen insula (junction between the cortex of the frontal and insula lobes)cortex of the frontal and insula lobes)

- frontal lobe above the orbits - frontal lobe above the orbits where smell is interpreted and where smell is interpreted and identifiedidentified

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

Olfactory terms:Olfactory terms:

Anosmia: loss of smellAnosmia: loss of smell

Hyposmia: decr. smellHyposmia: decr. smell

Hyperosmia: incr. smellHyperosmia: incr. smell

Dysosmia: distorted smellDysosmia: distorted smell

Gustation:Gustation:Gustatory receptor cells are located in Gustatory receptor cells are located in

the taste budsthe taste buds- papillae (elevations scattered on - papillae (elevations scattered on tongue, roof of mouth and walls of tongue, roof of mouth and walls of pharynx)pharynx)

Primary taste sensations: sour, bitter, Primary taste sensations: sour, bitter, salty and sweet.salty and sweet.

Recently discovered is umami. Sensed Recently discovered is umami. Sensed in response to a salt (monosodium in response to a salt (monosodium glutamate) found in the amino acid glutamate) found in the amino acid glutamate.glutamate.

Sour, salty and sweet are carried via Sour, salty and sweet are carried via CN VII (facial nerve) and bitter CN VII (facial nerve) and bitter carried via CN IX (glossopharyngeal). carried via CN IX (glossopharyngeal).

All taste sensations are relayed to the All taste sensations are relayed to the ventral posterior (vp) medial ventral posterior (vp) medial nuclei of the thalamus from the nuclei of the thalamus from the solitary nucleus (gustatory nucleus) solitary nucleus (gustatory nucleus) then on to the primary gustatory then on to the primary gustatory cortical area of the inferior post-cortical area of the inferior post-central gyri of the parietal lobes. central gyri of the parietal lobes.

Taste is 80% smellTaste is 80% smell

Gustatory terms:Gustatory terms:

Ageusia: loss of tasteAgeusia: loss of taste

Hypogeusia: decr. tasteHypogeusia: decr. taste

Hypergeusia: incr. tasteHypergeusia: incr. taste

Dysgeusia: distorted tasteDysgeusia: distorted taste

Hearing:Hearing:

External, middle and inner earExternal, middle and inner ear

External ear:External ear:

Outer auricle or pinna will funnel sound Outer auricle or pinna will funnel sound towards the ear drum. Remember external towards the ear drum. Remember external auditory meatus (EAM) through the auditory meatus (EAM) through the temporal bonetemporal bone

Sound waves are transmitted through the Sound waves are transmitted through the EAM until they reach the tympanic EAM until they reach the tympanic membrane (ear drum)membrane (ear drum)

- semitransparent membrane covered - semitransparent membrane covered by skin on the outside and mucous by skin on the outside and mucous membranes on the inside.membranes on the inside.

Middle ear: Petrous portion of temporal boneMiddle ear: Petrous portion of temporal bone The ear drum magnifies the vibrations of The ear drum magnifies the vibrations of

sound waves mechanically. One of the main sound waves mechanically. One of the main purposes of the ear is to transform these air purposes of the ear is to transform these air pressure waves to an electrical nerve signal pressure waves to an electrical nerve signal that the brain can understand that the brain can understand

The ossicles areThe ossicles are

- hammer (malleus) attaches to drum- hammer (malleus) attaches to drum

- short and long handle (processes)- short and long handle (processes)

-manubrium-manubrium

- anvil (incus)- anvil (incus)

- stirrup (stapes).  The stirrup attaches to the - stirrup (stapes).  The stirrup attaches to the oval window of the inner ear or cochlea oval window of the inner ear or cochlea

Otitis mediaOtitis media

Tympanostomy tubesTympanostomy tubes

Inner ear: labyrinthInner ear: labyrinth

Vibration of the stapes on the oval Vibration of the stapes on the oval windowwindow

moves fluid (perilymph) within the moves fluid (perilymph) within the inner ear. Vibrations will stimulate inner ear. Vibrations will stimulate the hearing receptors.the hearing receptors.

Pressure on the oval window is 22x Pressure on the oval window is 22x greater than the wave pressure greater than the wave pressure exerted on the ear drum.exerted on the ear drum.

Pressure waves are transmitted from the Pressure waves are transmitted from the scala vestibuli to the scala tympani and scala vestibuli to the scala tympani and then into the round window then into the round window

Pressure waves deform walls of scala Pressure waves deform walls of scala vestibuli and scala tympani, collectively vestibuli and scala tympani, collectively causing the vestibular membrane to move causing the vestibular membrane to move (pressure in endolymph increases & (pressure in endolymph increases & decreases) decreases)

Pressure fluctuations in endolymph move Pressure fluctuations in endolymph move the basilar membrane the basilar membrane

Hairs of the organ of Corti, connected to Hairs of the organ of Corti, connected to the basilar membrane, move against the the basilar membrane, move against the tectorial membrane and cause the tectorial membrane and cause the generation of nerve impulses generation of nerve impulses

Decibels (dB) measures sound intensity.Decibels (dB) measures sound intensity.0 dB is least perceived by the human 0 dB is least perceived by the human earear10 dB is 10x louder than 0 dB10 dB is 10x louder than 0 dB20 dB is 100X as loud as 0 dB etc..20 dB is 100X as loud as 0 dB etc..

Whisper: 40 dBWhisper: 40 dBNormal speech: 60-70 dBNormal speech: 60-70 dBRock concert: 120 dBRock concert: 120 dBJet plane: 140 dB (nociception)Jet plane: 140 dB (nociception)Prolonged periods of 90 dB will cause Prolonged periods of 90 dB will cause

permanent hearing losspermanent hearing loss

Hearing nerve fibers are located in the Hearing nerve fibers are located in the cochlear branch of the cochlear branch of the vestibulocochlear nerve (VIII).vestibulocochlear nerve (VIII).

Auditory pathway for hearing:Auditory pathway for hearing:

- cochlear branch enters b/w the - cochlear branch enters b/w the medulla oblongata and the pons to medulla oblongata and the pons to end in the cochlear nuclei both dorsal end in the cochlear nuclei both dorsal and ventral.and ventral.

- fibers cross and ascend into - fibers cross and ascend into thalamus (medial geniculate body) to thalamus (medial geniculate body) to terminate in the primary auditory terminate in the primary auditory cortex of the temporal lobecortex of the temporal lobe

Equilibrium: feeling of the position of the Equilibrium: feeling of the position of the head at rest and movementhead at rest and movement

Static (rest): organ is located in the Static (rest): organ is located in the vestibule between the semicircular canals vestibule between the semicircular canals and the cochlea. Specifically, the utricle and the cochlea. Specifically, the utricle and saccule. Helps keep head still and and saccule. Helps keep head still and balanced.balanced.

Dynamic (motion): organ located in the Dynamic (motion): organ located in the ampullae of the semicircular canals.ampullae of the semicircular canals.

- anterior- anterior

- posterior- posterior

- lateral- lateral

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

Vestibular portion of CN VIII enters Vestibular portion of CN VIII enters b/w the medulla oblongata and the b/w the medulla oblongata and the pons and ends in the vestibular pons and ends in the vestibular nuclear complex. The vestibular nuclear complex. The vestibular nuclei is located in the rostral m.o. nuclei is located in the rostral m.o. and caudal pons.and caudal pons.

Works closely with the cerebellum to Works closely with the cerebellum to signal appropriate skeletal muscles signal appropriate skeletal muscles in response to changes in in response to changes in equilibrium.equilibrium.

Vision:Vision:Eyeball has three layers:Eyeball has three layers:Outer: Fibrous tunicOuter: Fibrous tunicMiddle: Vascular tunicMiddle: Vascular tunicInner: Nervous tunicInner: Nervous tunic

Fibrous tunic:Fibrous tunic:Anterior portion contains the clear avascular Anterior portion contains the clear avascular

cornea which helps focus light rays. Very cornea which helps focus light rays. Very pain sensitive pain sensitive

It is continuous with the white sclera that It is continuous with the white sclera that surrounds the eyeball and is the surrounds the eyeball and is the attachment site for the extrinsic ocular attachment site for the extrinsic ocular muscles.muscles.

Dura mater is continuous with the sclera at Dura mater is continuous with the sclera at the site of the optic nerve that exits the the site of the optic nerve that exits the back of the eyeball.back of the eyeball.

Vascular tunic (uveal layer) includes the Vascular tunic (uveal layer) includes the iris, ciliary body and choroid coat.iris, ciliary body and choroid coat.

- Choroid coat contains blood vessels that Choroid coat contains blood vessels that nourish the eye and is loosely joined to the nourish the eye and is loosely joined to the sclera.sclera.

- Ciliary body located in the anterior part of Ciliary body located in the anterior part of the eye has ciliary muscles that are the eye has ciliary muscles that are attached to suspensory ligaments that attached to suspensory ligaments that hold the lens (transparent structure hold the lens (transparent structure located behind the iris) in place. When the located behind the iris) in place. When the muscles contract these ligaments are able muscles contract these ligaments are able to change the shape of the lens (ligaments to change the shape of the lens (ligaments relax causing lens to thicken) aiding in relax causing lens to thicken) aiding in focusing close objects. (accommodation- focusing close objects. (accommodation- remember parasympathetic division: CN remember parasympathetic division: CN III)III)

- iris:iris: - colored smooth muscles portion of - colored smooth muscles portion of

eyeeye- thin diaphragm allowing light to - thin diaphragm allowing light to

enter.enter.- lies b/w the cornea and the lens- lies b/w the cornea and the lens- separates the eyeball in an - separates the eyeball in an

anterior (b/w the iris and cornea) and anterior (b/w the iris and cornea) and posterior chamber (b/w the iris and posterior chamber (b/w the iris and vitreous humor)vitreous humor)

ant.: aqueous humorant.: aqueous humorpost.: vitreous humor post.: vitreous humor

- Pupil- Pupil

- hole in the iris- hole in the iris

- pupil size is controlled by smooth - pupil size is controlled by smooth muscles in the iris called circular and muscles in the iris called circular and radial sets.radial sets.

- circular set acts as sphincter to - circular set acts as sphincter to constrict pupil in the presence of constrict pupil in the presence of bright light. (parasympathetic) bright light. (parasympathetic)

- radial set increases diameter of - radial set increases diameter of pupil causes it to dilate. pupil causes it to dilate. (sympathetic.) (sympathetic.)

Nervous tunic:Nervous tunic:

The retina is a thin, delicate structure The retina is a thin, delicate structure that contains specialized photoreceptor that contains specialized photoreceptor cells and is continuous with the optic cells and is continuous with the optic nerve.nerve.

Five types of neuron located in the retinaFive types of neuron located in the retina- Receptor cells (rods and cones)Receptor cells (rods and cones)- Bipolar neuronsBipolar neurons- Ganglion cellsGanglion cells- Horizontal cellsHorizontal cells- Amacrine cells Amacrine cells

In the center of the retina is yellowish In the center of the retina is yellowish spotspot

called the macula lutea. A depression called the macula lutea. A depression in the center called the fovea in the center called the fovea centralis is the region where the centralis is the region where the sharpest vision is produced.sharpest vision is produced.

Medial to the fovea is the optic disc. Medial to the fovea is the optic disc. The optic disc is where the optic The optic disc is where the optic nerve exits the eyeball. No receptors nerve exits the eyeball. No receptors are present for vision so it is also are present for vision so it is also called the blind spot.called the blind spot.

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Refraction of light rays (bending of Refraction of light rays (bending of light) by the anterior and posterior light) by the anterior and posterior surfaces of the cornea as well as surfaces of the cornea as well as refraction by the lens cause light refraction by the lens cause light rays to come into exact focus on the rays to come into exact focus on the retina .retina .

Images focused on the retina are Images focused on the retina are invertedinverted

- Photoreceptors and visual pigmentsPhotoreceptors and visual pigments

- Rods and cones- Rods and cones

- stimulated when light reaches them- stimulated when light reaches them

- Rods are more sensitive to light than - Rods are more sensitive to light than cones and provide vision in dim light.cones and provide vision in dim light.

- Cones provide sharp images and color - Cones provide sharp images and color vision. Fovea centralis contains high vision. Fovea centralis contains high concentration of cones but no rods.concentration of cones but no rods.

- Light sensitive pigment in rods is called - Light sensitive pigment in rods is called rhodopsin (visual purple). Rhodopsin, in the rhodopsin (visual purple). Rhodopsin, in the presence of bright light, will break down presence of bright light, will break down into opsin and retinal (made from Vit. A).into opsin and retinal (made from Vit. A).

- With rhodopsin broken down, cones are With rhodopsin broken down, cones are activated and we see in color. activated and we see in color.

- In dim light, rhodopsin is made faster than In dim light, rhodopsin is made faster than it is broken down and cones remain it is broken down and cones remain unstimulated, therefore we see in shades unstimulated, therefore we see in shades of gray in dim light.of gray in dim light.

- Light sensitive pigment in cones is called Light sensitive pigment in cones is called iodopsin.iodopsin.

- Three sets of cones within retinaThree sets of cones within retina

1- erythrolabe- red light waves1- erythrolabe- red light waves

2- chlorlabe- green light waves2- chlorlabe- green light waves

3- cyanolabe – blue light waves3- cyanolabe – blue light waves

Extrinsic eye musclesExtrinsic eye muscles

1- Superior rectus: turns eye upward and 1- Superior rectus: turns eye upward and towards the midline (III)towards the midline (III)

2- Inferior rectus: turns eye downward and 2- Inferior rectus: turns eye downward and towards the midline (III)towards the midline (III)

3- Medial rectus: turns eye towards midline 3- Medial rectus: turns eye towards midline (III)(III)

4- Lateral rectus: turns eye away from 4- Lateral rectus: turns eye away from midline (VI)midline (VI)

5- Superior oblique: turns eye downward and 5- Superior oblique: turns eye downward and away from midline (IV)away from midline (IV)

6- Inferior oblique: turns eye upward and 6- Inferior oblique: turns eye upward and away from midline. (III)away from midline. (III)

Visual pathways:Visual pathways:

Axons of the ganglion cells in the retina Axons of the ganglion cells in the retina leave the eye by way of the optic nerveleave the eye by way of the optic nerve

Some fibers of the optic nerve will cross Some fibers of the optic nerve will cross just anterior to the pituitary gland at a just anterior to the pituitary gland at a junction called the optic chiasmajunction called the optic chiasma

- fibers coming from the medial - fibers coming from the medial (nasal) retina will cross while fibers (nasal) retina will cross while fibers coming from lateral (temporal) retina coming from lateral (temporal) retina will not.will not.

- Posterior to the optic chiasma is the optic Posterior to the optic chiasma is the optic tractstracts

- right optic tract is composed of - right optic tract is composed of

- right temporal and left nasal- right temporal and left nasal

- left optic tract is composed of- left optic tract is composed of

- left temporal and right nasal- left temporal and right nasal

Some fibers branch off to the superior colliculus Some fibers branch off to the superior colliculus (visual reflex)(visual reflex)

- Optic tracts synapse in the posterior portion - Optic tracts synapse in the posterior portion of thalamus at the lateral geniculate body.of thalamus at the lateral geniculate body.

- from the geniculate body the pathway - from the geniculate body the pathway travels through optic radiations into the visual travels through optic radiations into the visual cortex of the occipital lobe.cortex of the occipital lobe.