somatosensation
DESCRIPTION
Somatosensation. Lesson 17. Somatosensation. Sensory info from body Cutaneous senses exteroceptors touch / pain Kinesthesia interoceptors body position & movement ~. The Cutaneous Senses. Physical events next to organism info about stimuli in direct contact surfaces, objects, energy - PowerPoint PPT PresentationTRANSCRIPT
Somatosensation
Lesson 17
Somatosensation
Sensory info from body Cutaneous senses
exteroceptors touch / pain
Kinesthesia interoceptors body position & movement ~
The Cutaneous Senses Physical events next to organism
info about stimuli in direct contact surfaces, objects, energy body position
Feedback critical for skilled movements walking after foot falls asleep talking after a shot of novocaine no feedback from touch ~
The Cutaneous Senses
Primarily mechanical stimulation Several types of receptors
Several submodalities Touch & pressure Kinesthesis Haptic System Temperature Pain ~
Somatosensory Receptors
Several types mechanoreceptors nociceptors thermoreceptors chemoreceptors proprioceptors
Transduction of environmental energy ~
Mechanoreceptors Unmyelinated axon branches Free nerve ending
glabrous & hair regions pain sensation
Basket cells Hairy regions ~
Mechanoreceptors Encapsulated end organs
Glabrous (hairless) skin Non-neural tissue Merkel’s Disks Meissner’s corpuscle Pacinian corpuscles Ruffini endings ~
~
Receptor Adaptation
Different rates of adaptation response to continued stimulation
Slowly adapting (SA) steady pattern of firing
Rapidly adapting (RA) fire only at onset of stimulus ~
Somatosensory Pathways
Touch & Proprioception Dorsal column-medial lemniscal
pathway Pain and Temperature
Spinothalamic system Trigeminal pathway
face & neck cranial nerve V, also others ~
Dorsal
Ventral
dorsal columns
Spinal Cord
lateral columns
Somatosensory cortex
S1 - Postcentral Gyrus Somatotopic Organization
topographic representation of body Distorted Homunculus
disproportionate amount of cortex for body parts
high sensitivity: large cortical area ~
M1S1PPC
Somatosensory Cortex
Topographic representation Body Image – S1 Space around us – PPC Coordinates for movement
Phantom limbs & pain after amputation
Contralateral neglect PPC damage ~
Kinesthesia
Body Position & Movement proprioception
Joint information Pacinian corpuscles & Ruffini endings
Muscle & tendon information changes in tension
Golgi tendon organ
muscle spindle fibers ~
Cutaneous Receptors
Stretching of the skin Limited role in proprioception Knee: anesthesia no affect Mouth, hands, & feet proprioception
significantly reduced by anesthesia Ruffini Endings
slow adapting population of neurons responding
simultaneously ~
Muscle Receptors
Major role in proprioception Stretch receptors
detect changes in tension 2 types of receptors
Muscle spindles & Golgi tendon organs differences in threshold & location ~
Muscle length detectors Parallel with extrafusal fibers Low threshold
Monosynaptic stretch reflex Postural adjustments Muscle tonus
Sensory neuron alpha motor neurons monosynaptic excitation disynaptic inhibition ~
Muscle-Spindle Receptors
Innervated by gamma motor neurons active concurrently with alpha
motor neurons Control tension on muscle spindles
Not force for movement “Load the Spindles” ~
Intrafusal Muscle Fibers
Dorsal
Ventral
+
MS
GammaMotoneuron
+
Golgi Tendon Organ
Gauges muscle tension high threshold
Stretch receptor safety mechanism controlled muscle contraction ~
Dorsal
Ventral
-+
GTO
+Inhibits alphamotor neuron
GTO: Function
Inhibits muscle contraction Control of motor acts
slow contraction as force increases e.g., holding an egg
Autogenic inhibition safety mechanism too much tension damage ~