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COGS 17 Fall 2009

The Other Senses

Mary ET Boyle, Ph.D.Department of Cognitive ScienceDepartment of Cognitive Science

UCSD

Peripheral Vestibular Structure:

• Inner ear• Inner earminiaturized accelerometers inertial guidance devices

Continually reporting information about:motions and position of head and body

Information goes to:Information goes tobrainstemcerebellumsomatic sensory cortices

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Central Vestibular Structure:

• Vestibular Nuclei• Vestibular NucleiDirectly controls motor neurons controlling:

extraocularcervicalpostural

Important for:stabilization of gazestabilization of gazehead orientationposture during movements

The Vestibular Labyrinth:

• Main peripheral component• Main peripheral componentConnected with cochleaUses same specialized hair cellsTransduce physical motion into neural

impulseshead movementsinertial effects due to gravityground-borne vibrations

Vestibular endolymph(like cochlear endolymph)

high in K+ and low in Na+

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Vestibular navigation

• Translational • Translational movements are in terms of x, y, z

SacculeUtricle

roll, pitch, yawRotational movements

• Roll – tumbling left or right -- move your head from your left to your right shoulder

• Pitch – nod your

Semicircular canals

Pitch nod your head “yes”

• Yaw – shake your head “no”

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The Vestibular Labyrinth – otolith organs

• Two otolith organs (vestibular sacs)• Two otolith organs - (vestibular sacs)Utricle – hair cells are located on the floor- horizontal planeSaccule – hair cells are located on the wall – vertical motion

• Respond to:Information about the position of the head relative

to the body

utricle

saccule

utriclecochlea

Vestibulocochlear nerveVIII

The Vestibular Labyrinth – semicircular canals

• Three semicircular canals (vestibular sacs)• Three semicircular canals- (vestibular sacs)Oriented in three planesAmpullae – located at the base of each of thesemicircular canals.

• Respond to:Rotational accelerations of the head

ampullaecochlea

Vestibulocochlear nerveVIII

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The Vestibular Hair cells

Similar to auditory hair cellsSimilar to auditory hair cells

Mechanically gated transduction

Channels located at the tips of the stereocilia

Otolithichair cells

Scanning EM of calcium carbonate Scanning EM of calcium carbonate crystals (otoconia) in the utricularmacula of the cat.

Each crystal is about 50mm long.Lindeman, 1973

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Otolithic neurons sense linear accelerations of the head

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Semicircular neurons sense angular acceleration of the head

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Adaptation

Adaptation is explained in the gating spring model by adjustment of the insertion point of tips links. Movement of the insertion point up or down the shank of the stereocilium, perhaps driven by a Ca2+-dependent protein motor, can continually adjust the resting tension of the tip link. (Hudspeth and Gillespie, 1994.)

components• Semicircular canals• Semicircular canals

-head movements-head rotation

• Vestibular sacs-position of head position of head

relative to the body

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Vestibular Pathways

• Vestibular hair cellsconvert information about passive head movement and

active head rotation into an increase or decrease in neurotransmitter release

synapse with bipolar neurons

Vestibular Pathways• Cell bodies of bipolar neurons form:• Cell bodies of bipolar neurons form:

vestibular ganglia (receive input from vestibular hair cells)

axons of the vestibular ganglia become the vestibular nerve (combine with cochlear nerve st u ar n r (com n w th coch ar n r fibers to form the auditory nerve)

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Most vestibular nerve fibers synapse with vestibular l i i th m d ll nuclei in the medulla.

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Wh tib l l i j t t th i l d d b ll When vestibular nuclei project to the spinal cord and cerebellum, they influence the coordination of balance, changes in body position, and body movement.

Vestibulo-Cervical Reflex &

Vestibulo-Spinal Reflex

• Postural adjustments of • Postural adjustments of the head & body

• Descending projections

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When they project to other areas of the medulla and to the pons, they coordinate head and eye movements (movement of the eyes t m s t f h d m m ts)to compensate for head movements).

VOR – Vestibulo-occular Reflex

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Thalamocortical Pathways

Motion Sickness• Feelings of dizziness and nausea; occur when the body

is moved passively without motor activity and is moved passively without motor activity and corresponding feedback to the brain.

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• The vestibular system • The vestibular system detects movements, but motor actions that could have produced the movement have not occurred (e.g., riding in a car plane riding in a car, plane, or boat).

Inconsistent information

• The vestibular system senses movement • The vestibular system senses movement inconsistent with the information about movement sensed by the eyes (e.g., spinning around with eyes closed and then stopping and opening eyes).

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The Somatosenses• Somatosense The skin sensations of • Somatosense—The skin sensations of

touch, pain, temperature, and proprioception.

• Proprioception—The somatosense that monitors body position and movement, acts to maintain body position, and ensures the y p ,accuracy of intended movements; located in the muscles, tendons, and joints; essential to the control of movement.

Skin Receptors• The functions of the skin include protecting the

internal organs from injury; internal organs from injury; • helping regulate body temperature by producing

sweat, which cools the body when it becomes too hot;

• and providing a first line of defense against invading microorganisms.

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The Somatosenses: Receptors

• Skin receptors• Skin receptors• Pacinian corpuscles• Free nerve endings• Meissner’s corpuscles• Merkel’s disks• Ruffini’s corpuscles

• Pacinian corpuscles—The largest of the somatosensory receptors of the somatosensory receptors of the skinApproximately 0.5 mm wide by 1.0 mm

longHave quite large receptive fieldsSensitive to touch stimulation, especially

to high-frequency vibrations (200 to to high frequency vibrations (200 to 300 Hz)

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• Free nerve endings—Located just below the surface in both hairy and hairless skinthe surface in both hairy and hairless skindetects temperature change and pain stimuli

(both fast pain and slow pain)

• Meissner’s corpuscle—A type of skin receptor in hairy skinof skin receptor in hairy skinlocated in the elevations of the

dermis into the epidermisresponds to pressure and low-

frequency vibrations; small receptive fields

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• Merkel’s disk—A type of skin receptor in the base of skin receptor in the base of the epidermis near the sweat ductssensitive to pressure, but not

to vibrations

small receptive fields

• Ruffini’s corpuscle—A type of skin receptor just below of skin receptor just below the surfacedetects low-frequency

vibrations, but not pressurelarge receptive fields

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Somatosensory Pathways• Once information from the skin reaches the CNS,

the neural message travels through one of three the neural message travels through one of three somatosensory systems:

The dorsal column-medial lemniscal systemThe anterolateral systemThe spinocerebellar system

• Dorsal column-medial l i l t A lemniscal system—A somatosensory pathway that begins in the spinal cord and transmits information about touch and proprioception to the primary somatosensory cortex.

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• Anterolateral system—Th s t s sThe somatosensorypathway that begins in the spinal cord and transmits information about temperature and pain to the brain stem, reticular formation, and th i d the primary and secondary somatosensorycortices.

• Spinocerebellart Th system—The

somatosensory pathway that begins in the spinal cord and transmits proprioceptiveinformation to the cerebellum.

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Locating Input on the Somatosensory System

• The • The somatosensorysystem is topographically organized –adjacent places on the skin activate adjacent neurons adjacent neurons in the primary somatosensorycortex, though the cortical organization is upside down.

• Not all body parts are equally Not a o y parts ar qua y represented. The greatest representation is for areas such as the hands, lips, and tongue, which are involved in fine tactile discrimination.