1 dr w kolbinger, sensory systems (2009) sensory systems picture: rene descartes (1596-1650)

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  • 1 Dr W Kolbinger, Sensory Systems (2009) Sensory Systems Picture: Rene Descartes (1596-1650)
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  • 2 Lecture Outline Common Plan of Sensory Systems Four Sensory Receptor Classes Three Basic Processes in a Sensory Receptor Encoding of Four Stimulus Attributes Convergence, Divergence and Lateral Inhibition
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  • 3 Common Plan of Sensory Systems Perception Behavior Picture: Rene Descartes (15961650) Pathway Stimulus Receptor
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  • Sensory receptors First-order sensory afferent neurons Second-order sensory afferent neurons Third-order sensory afferent neurons Fourth-order sensory afferent neurons
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  • 5 Sensory Systems and their Receptors Sensory SystemSensory Receptor Class Somatosensory System (touch, vibration, proprioception, pain and temperature) Nociceptors Visual System Vestibular System Auditory System Olfactory System Gustatory System Mechanoreceptors Thermoreceptors Chemoreceptors Photoreceptors Mechanoreceptors Chemoreceptors Chemoreceptors
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  • 6 Examples of Sensory Receptors Sensory receptor neuron( somatosensory and olfactory systems Sensory receptor cell( visual, taste, and auditory systems
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  • 1. Sensory receptors A: Free nerve endings (pain, temperature) B: Pacinian corpuscle (pressure) C: Meissner s corpuscle (touch) D: Muscle spindle (stretch) A B C D
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  • 8 Three Basic Processes Cell body transduction site synaptic Terminal graded potentials 1) Receptor potential 2) Action potentials 3) Transmitter release in Different Components of a Sensory Receptor
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  • 9 Encoding of Four Stimulus Attributes AttributesEncoding Modality labeled lines IntensityAmplitude of graded receptor potentials Frequency code of action potentials DurationMechanisms depending on receptor adaptation LocationConcept of receptive fields and other mechanisms
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  • Sensory Transduction and Receptor Potentials 1. The environmental stimulus interacts with the sensory receptor and causes a change in its properties 2. receptor potential or generator potential. 3.receptor potentials are graded in amplitude Encoding of Stimulus Intensity
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  • 12 Encoding of Duration: Different Strategies Slowly adapting receptors remain active for the duration of a stimulus Rapidly adapting receptors are active only during times of changes (on/off) slowly adapting receptors are better in constantly monitoring levels of stimulation, whereas rapidly adapting receptors are most sensitive to changes, not to constant stimulation.
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  • 13 A receptive field defines an area of the body that when stimulated results in a change in firing rate of a sensory neuron Encoding of Location: Receptive Field of a Sensory Receptor 1 2 1 2 StimulationRecordings
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  • 14 ConvergenceDivergence Convergence and Divergence convergence answers the question Where does the information come from? divergence answers the question Where does the information go to?
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  • Receptive fields can be excitatory or inhibitory. The areas of inhibition contribute to a phenomenon called lateral inhibition, and aid in the precise localization of the stimulus by defining its boundaries and providing a contrasting border lateral inhibition
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  • 16 Lecture Outline Five Modalities and their Receptors Different Fibers for Different Receptors Segmental Spinal Nerves and Dermatomes Pathways for Different Modalities Clinical Correlations Somatosensory System
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  • 17 Modalities of the Somatosensory System Touch (discriminative touch) Vibration Proprioception Pain (nociception) Temperature most of the somatic sensory modalities refer to sensations of the skin, proprioception refers to sensory receptors originating in the skeleto-muscular system. All receptors of the somatic sensory system are pseudo-unipolar neurons. Their sensory endings can be found in skin, or in (or close to) the muscle. Their fibers run in peripheral nerves and their cell bodies are located in ganglia (dorsal root ganglia in case the fibers run in spinal nerves or in cranial nerve ganglia).
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  • Touch is transduced by Merkels disks (discriminative touch) and Ruffinis endings (skin stretch). Vibration is transduced by Meissners corpuscles (for lower frequencies of about 50 Hz) and Pacinian corpuscles (for higher frequencies of about 300 Hz). Pain (pricking pain by rapidly adapting mechano-sensitive or thermo-sensitive receptors, burning pain by slowly adapting polymodal receptors) and Temperature (cold receptors and warm receptors) are transduced by free nerve endings.
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  • Muscle spindles are embedded in extrafusal fibers of the working musculature of the muscle. The primary receptor of a muscle spindle is a rapidly adapting receptor with a Ia ("one a") afferent fiber. It carries sensory information of muscle stretch. This receptor forms the afferent limb of the myotatic reflex (deep tendon reflex), The secondary receptor of a muscle spindle is a slowly adapting receptor carrying sensory information of muscle length. It uses a class II ("two") afferent fiber. Golgi tendon organs are positioned close to the border between muscle and tendon. Their Ib afferent fibers form the afferent limb of the reverse myotatic reflex (inverse myotatic reflex).
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  • 20 Afferent Fiber Classification A alpha A beta A delta C I II III IV 72-120 m/sec 36-72 m/sec 4-36 m/sec 0.4-2 m/sec 12-20 m 6-12 m 1-6 m 0.2-1 m
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  • 21 Afferent Fiber Classification and Somatosensory Modalities 12-20 m 6-12 m 1-6 m 0.2-1 m Touch, Vibration Pain, Temperature Proprioception From skin: From muscle:
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  • Segmental Organization of Spinal Nerves and Dermatomes - segmental organization of the sensory innervation of the skin
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  • 23 Pathway for Touch, Vibration, Proprioception: Dorsal Column / Medial Lemniscus System Touch, vibration and proprioception are carried in a pathway called the dorsalcolumn / medial lemniscus system
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  • 24 Topographical Organization of the Spinal Cord Dorsal column Midline From leg From trunk From arm
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  • Spatial Orientation of Signals from Different Parts of the Body in Somatosensory Area Somatosensory area has a high degree of localization of the different parts of the body
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  • Sensory Neurons: Two-Point Discrimination
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  • 27 Pathway for Pain and Temperature: Anterolateral System
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  • 28 Topographical Organization of the Spinal Cord ALS Midline From leg From trunk From arm
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  • 29 Topographical Organization of the Spinal Cord L T A RightLeft L T A Touch, vibration, proprioception from left side of body Pain, temperature from right side of body
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  • 30 Lissauers Tract and the Anterolateral System RightLeft
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  • Chief Complaint: Left Leg Paralysis, Right Leg Numbness History: A 75 year old retired pastry maker was in good health until about one year ago, when he started to develop gait difficulties and numbness of his right leg. Recently, he also experienced urinary urgency with occasional incontinence. Though he started taking laxatives, he experienced problems with bowel movements. His wife reported that he also had stiffness in the legs bilaterally. At times, the left leg has unexpectedly not been able to support his body weight for a brief period, causing him to stumble to maintain balance. He also reported that in addition to the numbness in the right leg, he also has a constant tingling feeling in the same limb, which he describes as intolerable. General Examination: Normal vital signs. Patient has no significant cardiovascular history. Abdomen was soft and non-tender. No palpable abdominal masses. Digital rectal examination showed significantly reduced muscle tone in the external sphincter and weakness of voluntary contraction. Prostate was felt to be enlarged with a highly nodular, irregular surface. Neurological examination: Patient was fully alert and oriented x 3. Cranial nerve exam was unremarkable. Upon motor examination, the upper extremities had normal strength, bulk, and tone, and the reflexes were 2+ throughout the C5 to C8 spinal level. In the lower extremities, however, the muscle tone was increased in left leg and the left iliopsoas muscle was weaker than the right (4/5). The muscle bulk in both legs was normal. Reflexes in the right leg were 2+, knee jerk on the left leg was 3+, and ankle jerk was 4+. Plantar response was extensor the left and flexor on the right. Finger to nose and heel to shin testing was normal. Pinprick testing and temperature sensation showed decreased sensitivity on the right side of the trunk below the umbilicus. Vibration and joint position sense was significantly reduced in the left leg and foot.
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  • 32 Brown Sequard Syndrome X X X X
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  • 33 Dr W Kolbinger, Visual System (2009) Visual System 33 Lecture Outline Structures of the Eye Refraction and Image Formation Visual Acuity Autonomic Control of Pupil Diameter Clinical Correlations
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