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SOMATIC SENSORY SYSTEM D. C. MIKULECKY PROFESSOR OF PHYSIOLOGY AND FACULTY MENTORING PROGRAM FUNCTIONS OF THE SOMATIC SENSORY SYSTEM TACTILE RECEPTORS THERMAL RECEPTORS NOCIOCEPTORS PROPRIOCEPTORS TACTILE RECEPTORS SENSE MECHANICAL STIMULATION ON BODY’S SURFACE TOUCH, PRESSURE, AND VIBRATION RAPIDLY ADAPTING (PACINIAN CORPUSCLE, HAIR RECEPTOR) OR SLOWLY ADAPTING (RUFFINI ENDING) TYPES OF SENSORY RECEPTORS IN THE SKIN EPIDERMIS DERMIS RUFFINI ENDING FREE NERVE ENDING HAIR RECEPTOR PACINIAN CORPUSCLE STATIC PROPRIOCEPTORS LIMB POSITION I LIMB POSITION I I LIMB POSITION II I DYNAMIC PROPRIOCEPTORS CHANGE IN LIMB POSITION CHANGE IN LIMB POSITION CHANGE IN LIMB POSITION THERMAL RECEPTORS SENSE CHANGES IN TEMPERATURE ON THE BODY’S SURFACE COLD RECEPTORS: BELOW 30° C WARM RECEPTORS: ABOVE 30° C NOCIOCEPTORS PAIN RECEPTORS ACTIVATED BY HARMFUL STIMULI MECHANICAL HEAT PROPRIOCEPTORS REPORT POSITION AND MOVEMENTS STATIONARY OR STATIC (TONIC-JOINT CAPSULE AND CUTANEOUS MECHANORECEPTORS, MUSCLE SPINDLE RECEPTOR) DYNAMIC: ACTIVATED BY LIMB MOVEMENTS ORGANIZATION OF SOMATIC SENSORY SYSTEM GENERAL PRINCIPLES ANATOMICAL CONSIDERATIONS GENERAL PRINCIPLES OF SOMATIC SENSORY ORGANIZATION LABELED LINE MOST PATHWAYS CROSS RELATIVE POSITIONS IN BODY ARE PRESERVED ALL THE WAY UP ANATOMICAL CONSIDERATIONS TYPE DIAMETER (m) CONDUCTION VELOCITY (m/s) Ia(A) 22 120 PRIMARY MUSCLE SPINDLE Ib(A) 22 120 PRIMARY TOUCH AND PRESSURE II(A) 13 70 III(A) 5 15 SECONDARY MUSCLE SPINDLE, TOUCH, AND PRESSURE LIGHTLY MYELINATED: TOUCH, PRESSURE, AND PAIN IV(C) 1 2 SENSORY INFORMATION UNMYELINATED: PAIN AND TEMPERATURE FURTHER ANATOMICAL CONSIDERATIONS CELL BODIES OF SOMATIC SENSORY NERVES ARE IN THE DORSAL ROOT GANGLION TWO MAJOR PATHWAYS: DORSAL COLUMN AND ANTEROLATERAL ANATOMICAL CONSIDERATIONS: TERMINOLOGY ROSTRAL-CAUDAL: NOSE TO TAIL DORSO-VENTRAL: BACK TO BELLY MEDIAL: TOWARDS THE MIDLINE LATERAL: TOWARDS THE SIDE ANTERIOR: TOWARDS THE FRONT POSTERIOR: TOWARDS THE BACK TERMINOLOGY ILLUSTRATED ROSTRAL (SUPERIOR) DORSAL VENTRAL CAUDAL (INFERIOR) THE SPINAL CORD IN SOMATIC SENSORY FUNCTION WHITE AND GREY MATTER SEGMENTAL ORGANIZATION SEGMENTAL STRUCTURE OF SPINAL NERVES DERMATOMES SPINAL CORD DORSAL HORN DORSAL DORSAL ROOT GANGLION SPINAL NERVE GREY MATTER LATERAL WHITE MATTER VENTRAL HORN VENTRAL TOUCH AND PRESSURE DORSAL COLUMN PATHWAY INCOMONG SENSORY NERVE TRAVELS UPWARD IN THE DORSAL COLUMN AND SYNAPSES IN THE DORSAL COLUMN NUCLEUS PAIN AND TEMPERATURE ANTEROLATERAL PATHWAY LESION ON RIGHT HALF OF SPINAL CORD LOSS OF PAIN SENSATION ON LEFT SIDE BELOW LESION LOSS OF TOUCH AND VIBRATION ON RIGHT SIDE BELOW LESION LOSS OF BOTH ON RIGHT SIDE AT SAME LEVEL NO LOSS ABOVE LESION THE CRANIAL NERVES TRIGEMINAL GLOSSOPHARYNGEAL PLAY SAME ROLE AS SPINAL NERVES THE THALAMUS IN SOMATIC SENSATION MAJOR SITE FOR RECEIVING SENSORY INFORMATION VENTRAL POSTERIOR LATERAL NUCLEUS (VPL) SENDS SENSORY INFORMATION TO THE CORTEX THE THALAMUS IN SOMATIC SENSATION SENSORY NEOCORTEX MEDIAL LEMNISCUS DORSAL COLUMN NUCLEI DORSAL COLUMN MEDULLA SOMATOSENSORY CORTEX NEOCORTEX: REGION OF CORTEX WHICH EVOLVED MOST RECENTLY PRIMARY: POST CENTRAL GYRUS SOMATOTOPIC ORGANIZATION THE SOMATOSENSORY CORTEX SOMATOTOPIC ORGANIZATION OF THE SENSORY CORTEX GENETALS TOES FOOT LEG HIP . . . LIPS TONGUE SOMATOTOPIC ORGANIZATION OF THE SENSORY CORTEX