Somatosensory Reception. Somatosensory Reception

Transcription

1 Somatosensory Reception Professor Martha Flanders umn.edu Jackson Hall Proprioception, Tactile sensation, (pain and temperature) All mechanoreceptors respond to stretch Classified by adaptation speed and conduction velocity Somatosensory cortex combines various inputs Homunculus and Molunculus Concepts Somatosensory Reception stretch action potentials

2 Proprioception measure stretch Proprioception Muscle Spindles Golgi Tendon Organs Joint Receptors measure stretch Measures muscle length Measures muscle tension Measures limb position/joint movement 3D perception of self Critical for coordination of complex movements Conduction Velocity of Mechanoreceptors Tactile Mechanoreceptors Fast Conducting: A Proprioception Mechanoreceptors Fast Conducting: Ia, Ib, II Conduction velocity determined by 1. axon diameter 2. myelination Faster > Slower A > B > C > > I > II > III (a > b > c)

3 Cross Section of Spinal Cord Dorsal Root (sensory) Dorsal Horn Ventral Root (motor) Ventral Horn Classification (by conduction velocity) of axons in peripheral nerves Dorsal Roots: Ia (A ) m/s Ib (A ) m/s II (A ) m/s II (A ) m/s Primary Muscle Spindle Afferents - Rapidly adapting Golgi Tendon Organ Afferents - Slowly adapting Secondary Muscle Spindle Afferents - Slowly adapting Cutaneous and Joint Receptors -Rapidly& Slowly Ventral Roots: m/s motoneuron efferents to extrafusal muscle fibers m/s motoneuron efferents to intrafusal muscle fibers Tactile Mechanoreceptors measure stretch Rapidly adapting Rapidly adapting Slowly adapting Slowly adapting Group C: Pain and Temperature

4 Classification Edin, B. B. Quantitative analysis of static strain sensitivity in human mechanoreceptors from hairy skin. J Neurphysiol 1992; 67: Directional Tuning Edin, B. B. Quantitative analysis of static strain sensitivity in human mechanoreceptors from hairy skin. J Neurphysiol 1992; 67:

5 Somatosensory Pathways I Primary somatic sensory cortex Synapse in Thalamus The Dorsal Column-Medial Lemniscus pathway (red) Dorsal column nuclei Mechanoreceptor inputs synapse. Fibers cross. Somatosensory Pathways II Primary somatosensory cortex Synapse in Thalamus Facial information (Trigeminal Somatic Sensory system) Pons Fibers enter, synapse and cross

6 Combined input from spindle, tendon, joint and cutaneous afferents leads to the conscious perception of limb and body position Perceptual illusions: Tendon vibration at Hz is an excellent stimulus for muscle spindle afferents - gives rise to the perception that the muscle is stretched, i.e., that the muscle containing the stimulated spindles is longer than it really is - > the Pinocchio illusion: = biceps spindle input + tactile input from fingertip and nose Cortical Mapping of Somatosensory Information Homunculus ( little man ) SS Cortex

7 Star-nosed mole Moleunculus ( little mole ) (a) The 22 fleshy appendages of the star surround the mole's nostrils. (b) The moleunculus illustrating how the animal's body would look if each body part were based on their cortical proportions. (c) body proportions in the superior colliculus. The star has a greatly magnified representation and takes up approximately half of the somatosensory map. (d) The right half of the nose. Scale bar = 1 mm. (e) Representation of the star in S1. Each nasal appendage is represented by a cytochrome oxidase-dense stripe of cortex. Somatosensory fovea (appendage 11). Scale bar = 0.5 mm. (f) A section of flattened cortex. Catania KC, Henry EC. Touching on somatosensory specializations in mammals. Curr Opin Neurobiol. 2006; 16(4): Star-nosed mole Marasco, P. D. et al. Response properties of primary afferents supplying Eimer s organ J Exp Biol 2007;210:

8 Somatosensory Reception Key Concepts Mechanoreceptors respond to various types of stretch Directional tuning Somatosensory cortex combines multiple input types More neural tissues devoted to more behaviorally important areas (fovea) One behavioral strategy: take snapshot of receptor array and move quickly on to next