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Home , Illusion, Mechanoreceptor, Proprioception

Somatosensory Reception Professor Martha Flanders fland001 @ umn.edu 3-125 Jackson Hall

Proprioception, Tactile sensation, ( and )

All respond to stretch

Classified by adaptation speed and conduction velocity

Somatosensory cortex combines various inputs

Homunculus and Molunculus…

Concepts

Somatosensory Reception

stretch

action potentials measure stretch

measure Proprioception stretch •Muscle Spindles Measures muscle length •Golgi Organs Measures muscle tension • Receptors Measures limb position/joint movement

3D of self Critical for coordination of complex movements

Conduction Velocity of Mechanoreceptors

Faster > Slower Tactile Mechanoreceptors Fast Conducting: AE A > B > C D > E > G Proprioception Mechanoreceptors Fast Conducting: Ia, Ib, II I > II > III (a > b > c) Conduction velocity determined by 1. diameter 2. myelination Cross Section of

Dorsal Dorsal Root (sensory) Horn

Ventral Ventral Root (motor) Horn

Classification (by conduction velocity) of in peripheral Dorsal Roots: Ia (AD) 70-120 m/s Primary Afferents - Rapidly adapting Ib (AD) 60-100 m/s Afferents - Slowly adapting II (AE) 35-70 m/s Secondary Muscle Spindle Afferents - Slowly adapting II (AE) 35-70 m/s Cutaneous and Joint Receptors -Rapidly & Slowly Ventral Roots: D 70-120 m/s D motoneuron efferents to extrafusal muscle fibers J 15-40 m/s J motoneuron efferents to intrafusal muscle fibers

Tactile Mechanoreceptors measure stretch

Rapidly adapting

Rapidly adapting Slowly adapting Slowly adapting Group C: Pain and Temperature Classification

Edin, B. B. Quantitative analysis of static strain sensitivity in mechanoreceptors from hairy . J Neurphysiol 1992; 67:1105-1113.

Directional Tuning

Edin, B. B. Quantitative analysis of static strain sensitivity in human mechanoreceptors from hairy skin. J Neurphysiol 1992; 67:1105-1113. Somatosensory Pathways I Primary somatic

Synapse in

The Dorsal Column- pathway (red)

Dorsal column nuclei

Mechanoreceptor inputs . Fibers cross.

Somatosensory Pathways II

Primary somatosensory cortex Synapse in Thalamus

Facial (Trigeminal Somatic Sensory system) Pons Fibers enter, synapse and cross Combined input from spindle, tendon, joint and cutaneous afferents leads to the conscious perception of limb and body position

Perceptual :

Tendon vibration at 80-100 Hz is an excellent 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 :

= biceps spindle input + tactile input from fingertip and nose

Cortical Mapping of Somatosensory Information

Homunculus (“little man”)

SS Cortex 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 . Curr Opin Neurobiol. 2006; 16(4):467-73.

Star-nosed mole

Marasco, P. D. et al. Response properties of primary afferents supplying Eimer’s organ J Exp Biol 2007;210:765-780. 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…