COGS 17 Fall 2009 The Other Senses Mary ET Boyle, Ph.D. Department of Cognitive Science UCSD Peripheral Vestibular Structure: • Inner ear miniaturized accelerometers inertial guidance devices Continually reporting information about: motions and position of head and body Information goes to: brainstem cerebellum somatic sensory cortices 1 Central Vestibular Structure: • Vestibular Nuclei Directly controls motor neurons controlling: extraocular cervical postural Important for: stabilization of gaze head orientation posture during movements The Vestibular Labyrinth: • Main peripheral component Connected with cochlea Uses same specialized hair cells Transduce physical motion into neural impulses head movements inertial effects due to gravity ground-borne vibrations Vestibular endolymph (like cochlear endolymph) high in K+ and low in Na+ 2 Vestibular navigation • Translational movements are in terms of x, y, z Saccule Utricle Rotational movements roll, pitch, yaw • Roll – tumbling left or right -- move your head from your left to your right shoulder • Pitch – nod your head “yes” • Yaw – shake your head “no” Semicircular canals 3 The Vestibular Labyrinth – otolith organs • Two otolith organs - (vestibular sacs) Utricle – hair cells are located on the floor- horizontal plane Saccule – hair cells are located on the wall – vertical motion •Respond to: Information about the position of the head relative to the body utricle cochlea Vestibulocochlear nerve VIII saccule The Vestibular Labyrinth – semicircular canals • Three semicircular canals- (vestibular sacs) Oriented in three planes Ampullae – located at the base of each of the semicircular canals. •Respond to: Rotational accelerations of the head ampullae cochlea Vestibulocochlear nerve VIII 4 The Vestibular Hair cells Similar to auditory hair cells Mechanically gated transduction Channels located at the tips of the stereocilia Otolithic hair cells Scanning EM of calcium carbonate crystals (otoconia) in the utricular macula of the cat. Each crystal is about 50mm long. Lindeman, 1973 5 Otolithic neurons sense linear accelerations of the head 6 Semicircular neurons sense angular acceleration of the head 7 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 -head movements -head rotation •Vestibular sacs -position of head relative to the body 8 Vestibular Pathways • Vestibular hair cells convert 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: vestibular ganglia (receive input from vestibular hair cells) axons of the vestibular ganglia become the vestibu lar ne rve (combin e wi th cochle ar ner ve fibers to form the auditory nerve) 9 Most vestibular nerve fibers synapse with vestibular nuclilei in the mmdlledulla. 10 When vestibu lar nucle i projec t to the spina l cord and cerebe llum, they influence the coordination of balance, changes in body position, and body movement. Vestibulo-Cervical Reflex & Vestibulo-Spinal Reflex • Postural adjustments of the head & body • Descending projections 11 When they project to other areas of the medulla and to the pons, they coordinate head and eye movements (movement of the eyes to compen stsate for hdhead mmmovements) . VOR – Vestibulo-occular Reflex 12 Thalamocortical Pathways Motion Sickness • Feelings of dizziness and nausea; occur when the body is moved passively without motor activity and corresponding feedback to the brain. 13 • The vestibular system detects movements, but motor actions that could have produced the movement have not occurred (e.g., riding in a car, plane, or boat). Inconsistent information • 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). 14 The Somatosenses • Somatosense—The skin sensations of touch, pain, temperature, and proprioception. • Proprioception—The somatosense that monitors body position and movement, acts to maintain bodyyp position, and ensures the 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; • 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. 15 The Somatosenses: 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 skin Approximately 0.5 mm wide by 1.0 mm long Have quite large receptive fields Sensitive to touch stimulation, especially to high-frequency vibrations (200 to 300 Hz) 16 • Free nerve endings—Located just below the surface in both hairy and hairless skin detects temperature change and pain stimuli (both fast pain and slow pain) • Meissner’s corpuscle—A type of skin receptor in hairy skin located in the elevations of the dermis into the epidermis responds to pressure and low- frequency vibrations; small receptive fields 17 • Merkel’s disk—A type of skin receptor in the base of the epidermis near the sweat ducts sensitive to pressure, but not to vibrations small receptive fields • Ruffini’s corpuscle—A type of skin receptor just below the surface detects low-frequency vibrations, but not pressure large receptive fields 18 Somatosensory Pathways • Once information from the skin reaches the CNS, the neural message travels through one of three somatosensory systems: The dorsal column-medial lemniscal system The anterolateral system The spinocerebellar system • Dorsal column-medial lillemniscal system—A somatosensory pathway that begins in the spinal cord and transmits information about touch and proprioception to the primary somatosensory cortex. 19 • Anterolateral system— The stsssomatosensory pathway that begins in the spinal cord and transmits information about temperature and pain to the brain stem, reticular formation, and the primary and secondary somatosensory cortices. • Spinocerebellar system—The somatosensory pathway that begins in the spinal cord and transmits proprioceptive information to the cerebellum. 20 Locating Input on the Somatosensory System • The somatosensory system is topographically organized – adjacent places on the skin activate adjacent neurons in the primary somatosensory cortex, though the cortical organization is upside down. • Not all body parts are equall y represented. The greatest representation is for areas such as the hands, lips, and tongue, which are involved in fine tactile discrimination. 21.