SPECIAL SENSES AND CLINICAL NEUROLOGY

ASPECT

Anwar Wardy W

SpS (K), DFM

FKK UMJ

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4 CLASSIFICATIONS OF CRANIAL NERVES

1. Sensory nerves: carry somatic sensory information:

touch, pressure, vibration, temperature, and pain

2. Special sensory nerves: carry sensations:

smell, sight, hearing, balance

3. Motor nerves: axons of somatic motor neurons

4. Mixed nerves: mixture of motor and sensory fibers

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THE SENSORY SYSTEM IS DIVIDED INTO 2 SECTIONS:

The somatic sensory system is the system responding to information from the skin, muscles and viscera (organs).

The special senses are taste, smell, vision and hearing.

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RECEPTORS Receptor

Specialized cell or multicellular structureCollects information about the

environmentSends information via afferent pathways to

spinal cord and brain. Cerebral cortex then processes

information.

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RECEPTORSTypes of receptors

ChemoreceptorsSense changes in chemical concentration.

Ex: smell and tastePain receptors (nociceptors)

Sense tissue damage from excess stress on tissue.

ThermoreceptorsSense temperature change

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RECEPTORS Types of receptors (cont)

Mechanoreceptors Sense changes that deform the receptor

Proprioceptors Sense change in tensions of muscles and

tendons. Baroreceptors

Sense changes in blood pressure in blood vessels.

Stretch receptors Sense changes in tissue length (found in lungs).

Photoreceptors Sense changes in light intensity.

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SENSORY IMPULSES

Stimulasi reseptor menyebabkan perubahan potensial membran yang menghasilkan aksi potensial dalam serabut sensorik.

Jadi semua reseptor pada dasarnya melakukan hal yang sama; ……..mereka menerima informasi tentang lingkungan dan perubahan menjadi informasi elektrokimia sehingga dapat diproses oleh sistem saraf

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SENSATIONKetika impuls sensorik diproses

oleh otak dan menghasilkan sensasi.

Otak menginterpretasikan sensasi yang berasal dari daerah impuls proyeksi.

So from the person’s perspective, the sensation is occurring in one area of the body, but the processing of the actual “feeling” of the sensation is occurring in the brain.

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SENSATION

When receptors are continually stimulated they become less responsive to the stimulus—sensory adaptation.

Example: hot and cold

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SPECIAL SENSESThis concludes the review of the somatic

sensory system. We will now investigate the special senses…

Smell

Taste

Hearing

Vision

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Feel

SeNsE and PerCepTiOn

Lihat

Cium

Dengar

RasaRaba

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SPECIAL SENSESSmell

Sensed via olfactory receptors in olfactory organsChemoreceptorsSmell and taste work together75-80% of flavor comes from sense of smell.

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SPECIAL SENSESSmell (pathway)

Olfactory receptors stimulated by substance.

Nerve impulse travels via fibers running through cribriform plate of ethmoid bone.

Fibers synapse with neurons located in olfactory bulbs (crista galli of ethmoid bone).

Impulses are analyzed and travel along olfactory tracts to limbic system (smell may be linked to memory).

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SPECIAL SENSES

TasteTaste buds located on surface of

tongue (papillae) (also on roof of mouth, linings of cheeks and walls of pharynx.

Chemoreceptors (taste cells) pick up dissolved substances.

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SPECIAL SENSES

TasteThere are 4 primary taste

sensations. So all tastes are combinations of these 4 primary tastes.

1. Sweet2. Sour3. Salty 4. Bitter

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SPECIAL SENSES

Taste is carried by cranial nerves and is processed in the parietal lobe. Sensory impulses on anterior 2/3 of

tongue travel via CN VII. Posterior 1/3 of tongue = CN IXBase of tongue = CN XImpulses travel to medulla

oblongata—thalamus—parietal lobe.

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Smell

SPECIAL SENSESHearing is processed by the ear.

The ear is divided into 3 main divisions:

External—middle—inner ear

We’ll first look at the external ear…

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HEARINGExternal Ear

Auricle (pinna) (outer portion you see) External auditory meatus (passes into temporal

bone) EAM lined with skin that contains ceruminous

glands that secrete cerumen (wax).

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Middle earTympanic membrane marks boundary

between external and middle ear. Has thin layer of skin on outside and mucous

membrane on inside. Proximal to tympanic membrane is the tympanic

cavity.

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TYMPANIC MEMBRANE

Contains 3 small bones (auditory ossicles)Incus MalleusStapes

The stapes or “stirrup” is connected to the inner ear at the oval window. The oval window marks the start of the inner ear.

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Middle ear

THE MIDDLE EAR Other structures of the middle ear include: Tensor tympani muscle Stapedius muscle Eustachian tube (auditory tube)

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Eustachian (auditory) tubeConnect middle ear to throat.Equalizes air pressure on both

sides of eardrum.

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EUSTACHIAN (auditory) tube

CochleaFunctions in hearing

Semicircular canals (3)Equilibrium, balance

VestibuleBetween cochlea and semicircular canals

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INNER EAR

VESTIBULEThe vestibule contains the utricle and

saccule which are both important structures in sensing equilibrium.

The cochlea senses hearing.

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Looks like a snail’s shell wound around a bony core (modiolus).

Upper and lower compartmentsUpper = scala vestibuliLower = scala tympani –extends to round window.

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COCHLEA

AUDITORY PATHWAY

Spinal organ

Bipolar neuron of cochlear ganglion

Cochlear nerve

Cochlear nuclei

Trapezoid body

Lateral lemniscus

Medial geniculate body

Acoustic radiation

Transverse temporal gyrus

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HEARINGSound is transmitted through the air as waves.

The sound waves then enter the external auditory meatus and travel to typmpanic membrane (eardrum). The tympanic membrane moves in response to the sound waves.

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HEARINGIn the middle ear, sound travels from

tympanic membrane to malleus (connected to membrane) then to the incus and stapes. The stapes is connected to oval window. The stapes acts as piston to move fluid in inner ear.

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HEARINGThe ossicles also act as lever to

amplify sound (from tympanic membrane to oval window). Small muscles attach to ossicles called the tensor tympani and stapedius. These muscles are important in what is called the tympanic reflex.

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HEARINGThe tympanic Reflex is a protective

mechanism: Muscles contract with loud sound and

restrict movement of ossicles (and amplification of sound to inner ear).

Also muffles lower frequency sounds during speech (for better understanding)

Tensor tympani muscle maintains some tension on tympanic membrane for efficient transmission of sound.

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PERILYMPHInside the inner ear are chambers

filled with fluid. The scala vestibuli and scala

tympani are filled with a fluid called perilymph.

The cochlear duct is filled with a fluid of a different density called endolymph.

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THE ORGAN OF CORTI

The organ of corti contains 2 membranes called the tectorial and basilar membranes.

There are special sensory cells called hair cells between them.

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THE SOUND WAVES

The sound waves are transferred to the fluid filled chambers (scala) by the movement at the oval window caused by the movement of the ossicles.

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The vibrations in the fluid cause the tectorial membrane to move in relation to the basilar membrane.

The movement is picked up by the hair cells that relay an impulse to the nervous system via cranial nerve 8 (vestibulocochlear nerve).

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Some impulses cross to contralateral side of cortex. So damage to one side of temporal region does not cause complete hearing loss.

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FUNCTIONS OF THE EAR

Now that we have seen how sound is processed, let’s look at the other functions of the ear…

Static equilibrium

Dynamic equilibrium

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BALANCE AND EQUILIBRIUM

Static equilibrium is sensed in small organs located in vestibule called the utricle and saccule. Each contains an area called a macula.

Inside the utricle and saccule is a macula.

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BALANCE AND EQUILIBRIUMStatic equilibrium is sensed:

When head is upright hairs of macula in utricle project vertically and hairs in saccule project horizontally.

Hairs contact calcium carbonate crystals (otoliths).

Hairs bend in response to gravity changing position of otoliths. This causes impulses to be sent to central nervous system via vestibulocochlear nerve.

Brain responds by sending motor impulses to skeletal muscles to correct and maintain balance.

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BENIGN POSITIONAL VERTIGO.

Sometimes the otoliths can get out of position. This can cause a condition called benign positional vertigo.

The otoliths can be repositioned by a relatively easy maneuver.

The next slide contains a link to see this maneuver.

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DYNAMIC EQUILIBRIUM Dynamic equilibrium is sensed by the

semicircular canals. There are 3 semicircular canals because we

live in 3-dimensional space.

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FLUID MOVESWhen a person moves, fluid inside the

semicircular canals moves the cupula. The movement of the cupula bends the hair

cells. The hair cells then send impulses to the

vestibular portion of cranial nerve 8.

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Figure 14–20

THE OPTIC NERVES (II)

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OPTIC NERVES (II) Primary function:

special sensory (vision) Origin:

retina of eye Pathway:

optic canals of sphenoid Destination:

diencephalon via optic chiasm

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OPTIC NERVE STRUCTURES Optic chiasm:

where sensory fibers converge and cross to opposite side of brain

Optic tracts: reorganized axons leading to lateral geniculate nuclei

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EYE—NEURO CASE Conjunctiva

Mucous membrane lining inner surface of eyelids and folds back to cover surface of eyeball.

Lacrimal apparatusConsists of lacrimal gland and series of

ducts. Tears move from lacrimal gland –across eye

—superior and inferior canaliculi—lacrimal sac—nasolacrimal duct—nasal cavity.

Tears contain lysozyme (enzyme with antibacterial properties) to inhibit infections.

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VISUAL PATHWAY

Optic nerve

Optic chiasma

Optic radiation

Lateral geniculate body

Visual area

Optic tract

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EYE MUSCLES There are 6 different eye muscles that move the eye:Eye muscles

Superior rectusInferior rectusMedial rectusLateral rectusSuperior obliqueInferior oblique

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EYE MUSCLESDamage to any eye muscles causes double

vision. Eyes will normally track together to follow a moving object. This movement is called conjugate eye movement. If eye muscles or the cranial nerves controlling the eye muscle movements are damaged the eyes cannot track properly. This leads to double vision (diploplia).

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PUPILThe pupillary reflex occurs when

light enters the eye and pupil constricts. The reflex is carried by 2 cranial nerves:

Afferent pathway follows cranial nerve 2 (optic) frontal lobes

Efferent pathway—cranial nerve 3 (PS) light reaction

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PUPILLARY REFLEXES

Pretectal area

Accessory oculomotor nuclei

Occculomotor n.

Ciliary ganglia

Sphincter pupilCiliary muscle

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PUPILLARY REFLEXSo, if a light is shown into one eye and

the pupil on the same side constricts what cranial nerves are we testing?

CN II and III on same side (unilatareal) This is called the direct reflex.

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PUPILLARY REFLEXOr, if a light is shown into one eye and the

pupil constricts on the other side, what cranial nerves are we testing?

CN II on the same side of constriction and CN III on the opposite side.

This is called the consensual reflex.

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PUPILLARY REFLEXHow does the pupil constrict?

There is a small sphincter muscle around the pupil.

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PUPILSIf the sympathetic nervous system

is involved in producing the fight or flight response, would the pupil constrict or dilate when the SNS is active?

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Dilate—to let more light in (mydriasis)Opposite response for PNS stimulation.

2 TYPES OF RECEPTORS

The light coming into the eye is sensed by receptors in the retina.

There are 2 types of receptors:

RodsCones

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VISUAL RECEPTORSRods

Hundreds of times more sensitive to light than cones

Provide vision in poor light. Produce colorless (black and white)

vision. Nerve fibers converge so impulses

produce more general outlines.Concentration of rods increases in

areas away from fovea centralis.

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That means that your peripheral vision is better in the dark than your direct vision.

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VISUAL RECEPTORSCones

Provide sharp imagesNerve fibers do not converge as

much so impulses produce more detailed images.

Concentration of cones greatest in fovea centralis.

Concentration of cones decreases in areas away from fovea centralis.

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VISUAL PIGMENTSRods contain rhodopsin (visual

purple)Light causes rhodopsin to change

shape and release opsin which acts as an enzyme in further reactions.

Net result is hyperpolarization directly proportional to intensity of light stimulus.

Rhodopsin replenished in dim light. In dim light, a rhodopsin-replenished

eye is said to be dark-adapted (can see in dark).

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VISUAL PIGMENTSCones contain iodopsins

A group of pigments sensitive to light waves of different frequencies.

If all are stimulated = white light

If none are stimulated = black

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VISUAL NERVE PATHWAYSOptic nerveOptic chiasma

Medial fibers cross overLateral fibers do not cross overSo medial ½ of right eye and lateral

½ of left eye = left optic tract. Fibers continue through thalamus

via optic radiations to visual cortex of occipital lobes.

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VISUAL FIELD This means that the visual field in one

eye is actually processed on both sides of the brain;

• Monoculer field defect ant. Optic chiasm.

• Bitemporal field defectoptic chiasm.• Homonymous field defectBehind OC• Congruous homonymous fdBehind

the lateral geniculate bodies.

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SISTEM SOMATO SENSORIK

Eksteroseptif : superfisial, raba, nyeri, suhu

Propioseptif : gerak, sikap, otot dan sendi, getar, tekan dalam

Viseral : lapar, enek Sensasi khusus:

melihat, mendengar

Lesi di thalamus

Lesi traktus spino thalamikus

GANGGUAN SENSIBILITAS PADA POLINEUROPATI

Bentuk sarung tangan dan kaos kaki

POLA DERMATOM SISTEM SOMATO SENSORIK

Rostal = mulut Kaudal = anus Perhatikan :

Bahu C5 Tangan C6 – C8 Puting susu T4 Pusar T10

DISTRIBUSI DERMATOM CAUDAL + KAKI

DISTRIBUSI DERMATOM= Daerah kulit : dipersyarafi akar posterior dan ganglionnya.

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